Wind Power for Domestic and Small Business Applications FAQ

 

What is microgeneration?

Around the world the definition of microgeneration can vary. Microgeneration is classified by ESB Networks as grid connected electricity generation up to a maximum rating of 11kW when connected to the three phase grid (400V). The vast majority of domestic and agricultural customers are connected at single phase (230V) and for these customers to be classified as microgenerators the maximum rating permitted is 6kW. These ratings are in line with Irish conditions prescribed in European standard EN50438.

In Ireland customers with microgenerators can avail of a stream lined, one page connection process (using form NC6) which will be described elsewhere in these FAQs. Customers who exceed the classification must engage in a more demanding application and connection process. However ESB Networks intend to make the connection process for units up to 50kW less onerous than the process required for larger generators.

A microgenerator may use any one of the following technologies to generate electricity:

  • Wind turbine
  • Photovoltaic panels (also known as solar electric panels)
  • Micro-hydro (scaled down version of hydro-electricity station)
  • Micro-CHP (fuelled by bio or fossil fuels)

Two or more of the technologies may be combined to create a hybrid system. Domestic and small commercial wind microgeneration involves using a small-scale wind turbine system to harness energy from the wind. In general it is at its most competitive and cost effective in remote, exposed areas or for charging batteries on boats, caravans and holiday cabins i.e. where grid connection might be too expensive or impractical.

With the use of an electrical control panel and an inverter the electricity generated can be used to supply electricity to the home, the amount of which depends on the size of the turbine installed, the demand at any given time and of course the wind available. An inverter is necessary for a number of reasons. One of its functions is to convert direct current (DC) to alternating current (AC) which is the type of power utensils and appliances demand i.e. 'mains' electricity. Direct current is outputted by the controller which is in turn supplied with power from the turbine. The inverter is also necessary to synchronise the output of the turbine with the electricity being drawn from the grid to ensure the occupant sees no interruption in their supply.

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How are wind microgenerators used to capture energy?

Two main types of system can be utilised:

1. Stand-Alone Systems

Domestic turbines are often used in stand-alone power systems that are designed to charge a battery bank. The most common application for this set up is in cases where a grid connection is not an option due to a prohibitive cost or remote location.

2. Grid-connected Systems

In this type of system, the output of the wind turbine is connected to the existing mains electricity supply to the home via a controller and inverter. Excess electricity generated can be sent onto the grid while electricity can be drawn from the grid when the turbine is not producing enough electricity to meet your needs. ESB Customer Supply offers to domestic microgenerators a 9c/kWh payment for exported electricity. Electric Ireland is offering to all domestic electricity customers of all suppliers a further 10c/kWh for the first 3,000 kWh export in each year. This offer is open to the first 4,000 customers who qualify and is due to close in 2012.

A third arrangement employed by some users of small turbines is to heat water directly from the turbine and not connect the turbine to the electricity supply to the premises or to the grid. The energy can then be stored as heat to be used on demand if the storage capacity is sufficient and very well insulated. Heating applications for microgenerators will be discussed elsewhere in these FAQs.

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What kind of location is suitable for a small or micro-scale wind turbine?

Many residential areas are not suitable for wind turbines as buildings and trees shade the wind and create turbulence which can reduce the efficiency and lifespan of a turbine considerably. Generally speaking, the ideal location is on top of a high mast on a south westerly facing hill with gently sloping sides surrounded by clear countryside which is free from obstructions such as trees, houses or other buildings. Here the wind flows relatively smoothly and steadily enabling it to drive wind turbines with greater efficiency.

Wind turbines operate less efficiently in areas where obstacles interfere with wind flows. It is very important to understand and account for these reduced efficiencies when considering the use and economics of wind turbines in such areas.However, such areas, with less than ideal aspect and local conditions, may, with a good quality turbine system, have a sufficient wind resource to make an installation worthwhile. The predominant and most energetic winds in Ireland typically come from the southwest and west, so it is especially important that there are few or no obstacles to the turbine in these directions.

Ideally, the turbine should be 10m above any obstacle within 100m. As a rule of thumb, a wind generator should be installed no closer to an obstacle than at least ten times the object's height, and on the down wind side. The preferred distance is twenty times the height of the object. Turbine siting will be discussed in depth elsewhere in these FAQs.

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How can I find out if I live in an area which might be suitable for harnessing the wind?

Commercial wind farms use expensive calibrated wind measuring devices (anemometers) and data loggers to measure actual wind speeds for at least 12 months, combined with Met Éireann data over a number of years, before committing to developing a site. This type of wind study is not a viable option for small scale customers as it would increase the cost of the project disproportionately. But there are companies who will carry out a scaled down version of such a study for customers. These companies are often independent and provide a report to their customers which can be presented to suppliers of the turbines.

Opting to use a non-calibrated anemometer for such a study may not give you any more accurate information than might be gleaned by a trained and competent site assessor. The power in the wind is proportional to the cube of the wind speed so an inaccurate wind speed measuring device can lead to a large error in estimating power output. An error of 10% in the wind measurement leads to a 33% error in estimating power output.

If you have access to the internet the first port of call could be the wind atlas on the SEAI website. A CD-Rom of the wind atlas can be purchased from SEAI REIO's online bookshop. Using the CD and free trial GIS software from Pitney Bowes it is possible to estimate average wind speeds for your location by inputting GPS or grid co-ordinates. Wind speed and thus the power in the wind in your location is the single most important factor in the viability of a wind turbine. The wind atlas will only be able to show you if your area is windy or not when compared to other areas in Ireland. The lowest height currently available on the wind atlas is 50m above ground level and the speed at domestic and small commercial turbine heights of the range of 10-20m would be considerably less. The wind atlas will not give you an accurate estimate for the wind speed at small scale heights because local and ground conditions impact greatly on wind speed. A site assessor can use mathematics to estimate the wind speeds at the height of a turbine using the wind speed reading at 50m but the actual wind speeds could vary greatly due to obstructions and topography.

A site visit by a trained, competent site assessor should be part of the service provided by turbine suppliers and installers. It is not possible to assess a site fully by using the SEAI wind atlas alone or in combination with Google Earth or aerial pictures. Being on the ground is the only means by which a full appreciation of the site's suitability and viability for a micro wind turbine can be estimated. The turbine supplier may charge a fee for the site assessment to cover their travel expenses and time. This fee may be subtracted from the price of the turbine should the sale be completed.

It is impossible to predict exactly the average wind speed and thus the output of a wind turbine at a given site. However, with a thorough resource assessment, site assessment and independent test reports for the turbine it is possible to estimate a range within which the turbine should be expected to perform.

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Describe a typical good candidate site for this type of investment?

The ideal customer will have a large area site which is elevated, south westerly facing, in an exposed area on the west coast of Ireland where the owner has maximised their energy efficiency measures to the full but still has a steady demand for electricity throughout the day and night. This is an ideal site but the technology can still be viable in less than ideal conditions. The key considerations for assessing a site will be covered elsewhere in these FAQs.

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What are the planning requirements for a micro-scale wind installation?

Subject to certain conditions domestic wind turbines may be exempt from planning requirements up to a maximum hub height of 10m and total (tip) height of 13m. For commercial installations and the agricultural sector 2008 saw an increase in the exemption up to the maximum (blade tip) height of 20m. You should however consult with your local planners who can inform you if there are location specific conditions applicable to installations in your area which may mean the exemptions do not apply (see extract of SI No. 600 of 2001 below).

Your prospective turbine supplier should be able to provide you with the specifications of the turbine and the tower you are considering; In particular the height of the mast, the diameter of the blades and the sound emissions at different distances from the installation are important for planning purposes. The level of noise at your premises or the nearest neighbour's premises (whichever is closer) should not be above 43dB(A) (or 5dB(A) above the background noise). The European Standard in relation to noise levels is EN 61400-11:2003.

40dB(A) is comparable to the noise levels in a quiet rural area, quiet library or ¼ as loud as ordinary conversation. 50dB(A) can be approximated as equivalent to the noise levels in a quite suburban area, in an average home or with a dishwasher running in the next room. 50dB(A) is roughly ½ as loud as normal conversation. Conversational speech at 1m distance equates to noise levels of 60dB(A).

It is also a good idea to consult with your neighbours at an early stage to inform them of your plans.

Roof mounted or building mounted turbines are not exempt from planning requirements and planning must be applied for through the normal channels and on a case by case basis. Roof and building mounted turbines will be discussed elsewhere in these FAQs.

The following two Statutory Instruments (SI) describe situations where planning permission may not be required. SI No. 83 of 2007 refers to domestic settings while SI No. 235 of 2008 deals with commercial and agricultural installations. If the planned installation does not satisfy the appropriate conditions the planning process must be adhered to and permission sought. If the planned installation does not satisfy the pertinent conditions below, particularly with regard to height, it does not mean that the granting of planning permission through the normal planning process is not possible.

Paragraph (b) of SI 83 of 2007: the construction, erection or placing within the curtilage of a house of a wind turbine.

  1. The turbine shall not be erected on or attached to the house or any building or other structure within its curtilage.
  2. The total height of the turbine shall not exceed 13 metres.
  3. The rotor diameter shall not exceed 6 metres.
  4. The minimum clearance between the lower tip of the rotor and ground level shall not be less than 3 metres.
  5. The supporting tower shall be a distance of not less than the total structure height (including the blade of the turbine at the highest point of its arc) plus one metre from any party boundary.
  6. Noise levels must not exceed 43db(A) during normal operation, or in excess of 5db(A) above the background noise, whichever is greater, as measured from the nearest neighbouring inhabited dwelling.
  7. No more than one turbine shall be erected within the curtilage of a house.
  8. No such structure shall be constructed, erected or placed forward of the front wall of a house.
  9. All turbine components shall have a matt, non-reflective finish and the blade shall be made of material that does not deflect telecommunication signals.
  10. No sign, advertisement or object, not required for the functioning or safety of the turbine shall be attached to or exhibited on the wind turbine.

The full text can be viewed on the Department of Environment website or via this link: SI No. 83 of 2007

SI 235 of 2008: the construction, erection or placing within the curtilage of an industrial building or light industrial building, or business premises of a wind turbine:

  1. The turbine shall not be erected on or attached to the premises or building or any other structure within the curtilage of the building or premises.
  2. The total height of the turbine shall not exceed 20 metres.
  3. The rotor diameter shall not exceed 8 metres.
  4. The minimum clearance between the lower tip of the rotor and ground level shall not be less than 3 metres.
  5. The supporting tower shall be a distance of not less than the total structure height (including the blade of the turbine at the highest point of its arc) plus: (a) 5 metres from any party boundary, (b) 5 metres from any non-electrical overhead cables, (c) 20 metres from any 38kV electricity distribution line, (d) 30 metres from the centreline of any electricity transmission line of 110kV or more.
  6. The turbine shall not be located within 5 kilometres of the nearest airport or aerodrome, or any communication, navigation and surveillance facilities designated by the Irish Aviation Authority, save with the consent in writing of the Authority and compliance with any condition relating to the provision of aviation obstacle warning lighting.
  7. Noise levels must not exceed 43db(A) during normal operation, as measured from the nearest party boundary.
  8. Not more than one turbine shall be erected within the curtilage of the premises or building.
  9. All turbine components shall have a matt, non-reflective finish and the blade shall be made of material that does not deflect telecommunication signals.
  10. No sign, advertisement or object, not required for the functioning or safety of the turbine shall be attached to or exhibited on the wind turbine.
  11. The turbine shall not be located within an Architectural Conservation Area.

The full text can be viewed on the Department of Environment website or via this link: SI No. 235 of 2008

SI 235 of 2008: the construction, erection or placing within an agricultural holding of a wind turbine:

  1. The turbine shall not be erected on or attached to a building or other structure.
  2. The total height of the turbine shall not exceed 20 metres.
  3. The rotor diameter shall not exceed 8 metres.
  4. The minimum clearance between the lower tip of the rotor and ground level shall not be less than 3 metres.
  5. The supporting tower shall be a distance of not less than:
    • One and a half times the total structure height (including the blade of the turbine at the highest point of its arc) plus 1 metre from any party boundary.
    • The total structure height (including the blade of the turbine at the highest point of its arc) plus: (i) 5 metres from any non-electrical overhead cables, (ii) 20 metres from any 38kV electricity distribution line, (iii) 30 metres from the centreline of any electricity transmission line of 110kV or more.
  6. The turbine shall not be located within:
    • 100 metres of an existing wind turbine.
    • 5 kilometres of the nearest airport or aerodrome, or any communication, navigation and surveillance facilities designated by the Irish Aviation Authority, save with the consent in writing of the Authority and compliance with any condition relating to the provision of aviation obstacle warning lighting.
  7. Noise levels must not exceed 43db(A) during normal operation, as measured from the nearest habitable house.
  8. Not more than one turbine shall be erected within the agricultural holding.
  9. All turbine components shall have a matt, non-reflective finish and the blade shall be made of material that does not deflect telecommunication signals.
  10. No sign, advertisement or object, not required for the functioning or safety of the turbine shall be attached to or exhibited on the wind turbine.

The full text can be viewed on the Department of Environment website or via this link: SI No. 235 of 2008

Statutory Instrument No. 600 of 2001 outlines further conditions and situations where the exemptions do not apply. Microgenerators should contact their local authorities to receive guidance on their own site as they may not be fully aware of the classification of their locality. Each local authority has drawn up development plans which designate areas, for example, as areas of special conservation, natural amenity or development potential. Should you go ahead with an installation and adhere only to the exemptions as per SI No. 83 of 2007 and SI No. 235 of 2008 you may still be in contravention of planning laws as outlined in SI No. 600 of 2001.

Individuals can apply to their local authority to get a formal declaration on whether their planned installation is covered by the exemptions and not subject to the restrictions outlined in SI 600 of 2001. There is a small fee charged by the local authority for this facility but the local authority must reply within 4 weeks. If the local authority requires further information from the individual they may then avail of further 3 week period from receipt of the complete information required before issuing their declaration on the planned works. Details of this statutory process are contained in Planning and Development Actof 2000.

Extract from SI 600 of 2001: Restrictions on exemption

Article 9.(1)Development to which article 6 relates shall not be exempted development for the purposes of the Act -

  • if the carrying out of such development would -
    • (vi) interfere with the character of a landscape, or a view or prospect of special amenity value or special interest, the preservation of which is an objective of a development plan for the area in which the development is proposed or, pending the variation of a development plan or the making of a new development plan, in the draft variation of the development plan or the draft development plan,
    • (vii) consist of or comprise the excavation, alteration or demolition (other than peat extraction) of places, caves, sites, features or other objects of archaeological, geological, historical, scientific or ecological interest, the preservation of which is an objective of a development plan for the area in which the development is proposed or, pending the variation of a development plan or the making of a new development plan, in the draft variation of the development plan or the draft development plan, save any excavation, pursuant to and in accordance with a licence granted under section 26 of the National Monuments Act, 1930 ( No. 2 of 1930),
  • in an area to which a special amenity area order relates,

The full text can be viewed on the Department of Environment website or via this link: SI No. 600 of 2001.

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Can I put a small turbine on my roof or on a pole fixed to the building?

Current planning regulations state that roof or building mounted turbines are not exempt from the planning requirements. Therefore an application to your local authority through the normal planning mechanisms is required. Only mast mounted turbines of a certain size may be exempt from planning requirements under certain conditions.

Building mounted turbines have a history of poor performance. The building itself affects the flow of air around it. Even if the turbine is fitted in a position well above the uppermost part of the pitch or flat of the roof the airflow is still negatively impacted. Thus the output from the turbine is often very low and the return on the investment non-existent.

The ideal air flow over the blades of a turbine is smooth, constant and unidirectional over a period. In aerodynamics this kind of air flow is known as laminar flow. When air flow meets an obstruction currents, or 'eddies', are induced, creating turbulent flow. Visualise the wake caused by a rock in a fast flowing river or rapids.

Turbulent flow is not only undesirable for efficient electricity generation it is also undesirable from a mechanical point of view. The turbulent flow causes the turbine to yaw excessively in an attempt to always face into the wind. This excessive yawing causes cycling forces and premature wear on the unit and may significantly reduce its life span and increase maintenance costs.

If you choose to go ahead and apply for planning permission to mount a turbine on an inhabited building it should be remembered that there will be some vibration and noise transmitted into and through the fabric of the building. The transmitted vibrations and noise may not be fully counteracted by damping or sound proofing of the mounting. For that reason if you are choosing to mount a turbine on a structure it is advisable to seek planning to mount it on an adjacent non-inhabited building or solid separate structure.

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What permissions do I need before erecting or connecting a turbine?

Planning permission is required if the characteristics of the system to be installed are outside those described in Statutory Instrument No. 83 of 2007 or Statutory Instrument No. 235 of 2008. You should contact your local authority to ensure that the exemptions apply at your location and you are not subject to the restrictions on exemptions as outlined in SI No. 600 of 2001. (Refer also to the FAQ covering planning requirements).

ESB Networks operate an 'inform and consent' system of registering a grid connected system. The interface with the grid must be of a type compliant with EN 50438. ESB Networks maintains a list of 'type tests' for grid interfaces or inverters which comply with European standard EN50438.

The conditions governing the connection of a microgenerator, including the important points of EN 50438, can be viewed on the ESB Networks website.
The standard ensures quality of output if exporting or connected to the grid. The turbine must stop producing in times of grid outage. While it would be useful to have your own source of power during a network outage the automatic shutdown of a grid connected turbine is necessary to minimise the risk of injury to line technicians repairing or working on a line.

The Commission for Energy Regulation directed that individuals planning installations below 1 MW in capacity (includes all microgenerators) will no longer be required to apply for an Authorisation to Construct or a Licence to Generate. Each installation will stand duly authorised by order. All generators must comply with the requirements of the orders so it is each generator's interest to review the conditions of the authorisation and licence.

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What will a site assessor look for during an assessment?

Altitude

As distance above sea level increases the speed and the power of the wind also increases. Although affected by local conditions a general rule is that the higher the site is above sea level the more likely it is to have a good wind resource. Altitudes of 200m or more above sea level are most desirable. Furthermore the higher the site is above the immediate surrounding area the better the wind exposure is likely to be at that location.

Aspect

In Ireland the prevailing winds arrive from a south westerly direction. If there are obstructions in this direction the productivity of the turbine will be reduced. The obstructions, depending on their nature, will either slow down or cause turbulence in the air flow. If a large proportion of the wind during a year is coming from this direction it is clear that the turbine will not be exposed to ideal conditions. If there are similar obstructions in other directions (other than the prevailing wind direction) they would not have as great an impact on the output of the turbine. However it is preferable to have no obstructions close to the turbine in any direction.

The prevailing wind is categorised as a global wind. There may be conditions which create local winds such as sea/land breezes and mountain winds, which may be as important as the prevailing wind in terms of turbine output. Local winds are created by temperature differences between sea and land or highlands and lowlands at different times of the day and night.

Obstructions

It should be clear that the more exposed a site is to the wind the cleaner the air flow over the blades and the more productive the turbine will be. The turbine will also demand less maintenance if the air flow is less turbulent. The least desirable location for obstructions is close to the turbine in the direction of the prevailing wind.

Obstructions can be individual trees, houses, out-buildings, ditches, forests, or hills. It should of course be remembered that trees grow so obstructions can develop over time after the turbine is installed.

Obstructions affect the airflow in a number of ways. Firstly the airflow is disturbed leading up to the obstruction. This disturbed flow zone stretches outwards for twice the height of the obstruction before the obstruction. Imagine water flowing in a river and hitting a rock. The water is backed up and disturbed before it even hits the rock as the fluid (air is a fluid too) moves against, up and around or over the obstruction. For this reason it is undesirable to have a turbine within twice the height of an obstruction in any direction.

Downwind from an obstruction the zone of disturbed airflow stretches outward for up to 20 times the height of the obstruction before the wake settles.
The industry norm is to try to site the turbine at least 10m above any obstruction within 100m. However achieving this is quite difficult in reality.
Obstructions not only create disturbed flow before and after their position but also above. The disturbed airflow hits the obstruction and part of it is thrown up and over. This area of disturbed flow can stretch upwards to twice the height of the obstruction. One of the key reasons why roof mounted turbines perform poorly.

It is worth noting that when they are assessing a possible site for a wind farm, developers consider all obstructions and land use within 100's of metres of a development, even though they might be installing turbines with hub heights of 80m. Micro-scale turbines might only be 10m above ground level.

Space

The more space there is in a site the more options there are for constructing the turbine tower away from obstructions. Planning regulations state the distances the turbines must be from party boundaries and the noise levels allowable at premises. One of the requirements for a turbine in a domestic setting to be exempt from planning requirements is that it must be the total height of the turbine (uppermost point of blade tip) plus 1m from a boundary.

In order for a commercial application to be eligible for exemptions from planning requirements the turbine must be its total height plus 5m from the nearest party boundary.

In an agricultural setting the regulation states that the distance required is one and a half times the total height of the turbine plus 1m.

So a turbine which is 13m in total height must be 14m from the boundary in a domestic setting, 18m from the boundary in a commercial or industrial setting and 20.5m from a boundary in an agricultural application. You should contact your local authority to ensure that the exemptions apply in your situation.

Ample space is also required for the tower structure depending on the type recommended or supplied by the manufacturer. Guyed poles require a large area to accommodate the anchor points for the guy wires. Lattice towers and tubular steel poles can require considerable space in two directions in order to be hoisted up or tilted down either by a winch or crane. Guyed tower wires need to be protected from larger livestock and so may require a parcel of land which should be put to other safe use if currently used for grazing. Once free standing lattice towers or tubular steel towers are erected the land immediately around it can be used safely as normal.

During the site assessment it may be discovered by a competent trained assessor that the options for siting the wind turbine are limited by planning exemptions, safety considerations, obstructions and cost of cabling back to the premises. So a substantial parcel of land might just provide one or two small viable areas for construction.

Vegetation

Trees, shrubs and ditches can have an effect on small scale wind turbines. A field which one year is used for grazing, and so has short grass, and the next year grows maize, and so has tall planting, will affect airflow to varying degrees.

Vegetation can be used during a site assessment to point the direction of the prevailing winds as branches and even whole trees can be permanently deformed by the wind as it prevails in one direction. It is easier to see this effect during the winter when the leaves reveal the deformed limbs and branches.

Proximity to dwellings, neighbours, power lines, airports and other wind turbines

Careful consideration must be given to the location of the turbine for safety and planning reasons. The planning requirements outline the limitations with regard distances from dwellings, noise levels, siting near airports and power lines.

A balance must be found between siting the turbine as far away as possible from the house and minimising cabling costs and line losses in connecting to the house. The site assessment should encapsulate all of these considerations when choosing an optimal turbine location.

While the site might appear to have ample space for a turbine it may be discovered following the application of the various planning requirements that only a small area of the space remains eligible for an exemption from planning within reasonable distance from the property.

Demand profile

The assessment should also consider the dwelling or premises' consumption and the nature and timing of that consumption. Over-sizing a turbine may mean payback is affected in the long term and under-sizing a turbine may mean an opportunity is missed to maximize the potential of the site for reducing the customer's bill. Under-sizing a unit is preferable to over-sizing an installation however as it prevents an inefficient system being installed.

The installation should be looking to meet a steady demand for electricity throughout the day and night rather than peak demand for small periods. Ideally the site will have demand throughout the day and night so that the power generated has a use on-site, especially if it is not possible to avail of an export tariff equal to or greater than the import tariff. While 19c/kWh is currently available to ESB Customer Supply customers it is only for the first 3,000kWh exported per annum. The export value falls to 9c/kWh thereafter.

Refrigeration systems, heat pumps, existing storage heating, heat lamps and other appliances which require demand throughout the day and night improve the viability of the site with regard microgeneration. The demand should also be throughout the year and not just seasonal. Some sites may have demand for cooling in the summer and heating in the winter.

In their guided tour, www.windpower.org has free online tools which a site assessor or customer can use to try and put some numbers on the effect of various characteristics of the site.

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What are the main benefits of small scale wind power?

Environmental and Financial Benefits

A domestic or small business wind system should be viewed as a long-term environmentally beneficial investment, as it may be number of years into its life cycle before it gives payback in financial terms. The value of electricity produced will depend on the corresponding cost of mains electricity during the life of the turbine. While prices for electricity are currently decreasing, the cost of electricity to the consumer has risen substantially in the previous 5 years (by over 50%). While the price of oil has now fallen sharply, from its record highs during the summer of 2008, there are no guarantees about future prices. The price of electricity in Ireland is heavily dependent on the price of fossil fuels (more than 80% of electricity generated in 2007 was fossil fuel sourced) and it is expected that the long term trends in fuel prices will continue upward.

Why does the price of oil matter to an electricity customer? Because the cost of other fuels, such as natural gas, tracks the price of oil and as a result so too does the price of electricity in Ireland. In 2007, nearly 60% of our electricity was generated by burning natural gas. So a wind turbine can provide some stability to a portion of electricity costs and is likely to become more competitive if electricity prices increase again or if there is a carbon tax introduced which is applied to mains electricity.

Many users of small scale wind turbines are not motivated solely by financial concerns. Many are attracted by having an independent, local source for a portion of their energy needs. Others are concerned with the environmental impact of conventional electricity generation. Conventional thermal power generation inefficiently consumes valuable finite resources- for good. Other than carbon dioxide, by-products of the generation process, depending on the fuel used and mitigating measures employed, can include acid rain causing compounds, irritant particulate emissions, mercury emissions and ash. Wind generated electricity displaces energy from the grid when it is consumed on-site. Power generation is one of the biggest sources of greenhouse gas emissions in Ireland.

In 2007 Ireland produced more than 80% of its electricity by consuming fossil fuel resources, (gas 55%, oil 6%, CHP 4% and coal 18%) the vast majority of which had to be imported. On average in 2007, each unit (kWh) of grid electricity consumed had an associated carbon dioxide production of approximately 538g. The associated carbon production varies depending on the time of day and the suite of generation plant which is brought onto the system by the system operator. But in simplistic terms, for every 2 units of electricity produced by the domestic wind turbine over 1 kg of CO2 emissions could be avoided.

There are of course emissions associated with the manufacture, transportation and erection of a wind turbine but a correctly sited quality unit will be able to repay these in a reasonable time. Equally an ill-suited, badly sited, poor quality turbine may never produce the energy which has gone into its production, not to mention paying back in economical terms. For instance roof mounted turbines in built up areas can prove to be purely ornamental rather than productive or beneficial to the environment or the owner. They can in fact increase energy consumption as the occupant is misguided into thinking they are producing electricity at a rate which allows them to increase their own consumption without impact on the environment or on their bill.

A portion of the electricity produced by power stations is lost during transmission and distribution over long distances. The losses occur in transformers and in the wires. Energy generated closer to where it is consumed will reduce the total energy losses on the system.

Wind turbines are often the most cost effective energy option in remote off-grid areas where it may be very expensive to connect to the grid. Battery storage can be added to the off-grid system so that power may be available on demand.

Energy Security

Replacing electricity produced from imported fossil fuels with wind energy generated on site at your home or business could make a significant contribution to Ireland's energy security and reduce the carbon intensity of Ireland's electricity needs. As an island with very limited fossil fuel resources, Ireland is heavily dependent on imported energy supplies. Ireland currently imports over 90% of its consumed energy including petroleum products, coal and natural gas. While an individual installation will not improve security of energy supply or reduce emissions on a national level, the cumulative effect of a large number of installations will be positive.

Ireland has access to huge inexhaustible energy resources, such as wind, which happen to be renewable and clean. Wave energy devices are still in development and are expected to be useful only for commercial electricity production on a larger scale. Wind power is a mature technology and can be harnessed by the individual for personal or business use.

Following unprecedented prices for oil during 2008 the price has dropped significantly in the first quarter of 2009. OPEC have indicated that $70 to $80 may be a more realistic medium term price for production from ever more challenging reserves to be viable. The long term trend in oil prices is expected to continue upward. It is worth remembering that throughout the 1990's the price of a barrel of oil hovered around $20 and as recent as 2005 $70 was seen as a threat to fossil fuel dependent economies all over the world. Now that the price has returned to a seemingly low price in comparison with the record prices seen during 2008 we may have been desensitised to high prices. This should not discourage us from looking for energy supplies which are local, sustainable and not affected by global events far removed, geographically and politically, from Ireland.

Education and Awareness

The installation of a turbine or other renewable technology can be a focus for educational purposes and increase awareness of energy efficiency in a school and in student's homes. Many schools are involved in An Taisce's green schools initiative which includes energy as one of the main themes. As with any installation the load profile will need to be considered. Schools may have an unusual load profile due to the hours they are open during the day and due to the fact that they may be closed for longer than they are occupied i.e. evenings, weekends and during holidays. A thorough feasibility study by a competent supplier should examine the implications of each customer's demand profile and the payment available for exports.

The addition of microgeneration to a home can increase energy awareness and make an already efficient home even more so as the occupants modify their consumption behaviour as much as possible to minimise imports and consumption to maximise exports where payment is available.

'Green marketing'

A firm may wish to demonstrate to customers that they are aware of environmental issues and the environmental impact of the energy consumption of their business. An appropriately sited, well maintained and fully operational wind turbine is probably the most visible means by which this commitment can be demonstrated. As consumers become increasingly aware of environmental issues companies which are proactive in minimising the impact of their business on the environment may have the edge in a competitive marketplace.

Employment

Local jobs are supported by the microgeneration sector. As the industry grows from a small base it is hoped that more jobs will be created in site assessment, installation and maintenance. A number of Irish companies are also in advanced stages of developing of their own turbines which will be manufactured in Ireland.

SEAI will be over-seeing a comprehensive field study throughout 2009 and into 2010. Following this study we will be in a better position to detail the benefits of the technology to the domestic and small commercial user. The benefits of large scale wind are widely known.

The goals of the study include:

  • Monitor and assess turbine and equipment technical performance in Ireland;
  • Assess the reliability of a range of technologies and manufacturers;
  • Assess economic performance in the context of the Irish market;
  • Inform the design of intelligent tariffs for smart metering; and
  • Develop best practice guidelines for installers and suppliers.

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How much electricity can I expect a turbine to produce?

The output of the turbine depends on key factors such as:

  • Swept area of the blades;
  • Availability of wind at the site;
  • The characteristics of the available wind;
  • Availability and efficiency of the turbine; and
  • Real power curve of the turbine including cut-in/out wind speeds.

It should be a reasonably obvious assumption that turbines with longer blades have the potential to produce more electricity than turbines with smaller ones. However it can also be the case that two similar looking turbines with blades of the same length can produce different amounts of electricity due to variances such as generator efficiency. Furthermore, placing the same model turbine in different sites will produce different amounts of electricity. So it is impossible to predict exactly the output of a wind turbine. However, with a thorough resource assessment, site assessment and accurate turbine performance parameters it is possible to estimate a range within which the turbine should perform.

It is in your own interest to install a high quality turbine. A broken down turbine will not produce any electricity. The turbine should be maintained to keep producing as much electricity as it can for as long as it can. A turbine may be seen to be turning in light winds but the generator may not be producing electricity. A turbine which experiences turbulent flows of air will produce less power than one experiencing steady, laminar flows of air.

Swept area is an important indicator of the likely output of a turbine. The manufacturer's rating must be considered in conjunction with the swept area. It is possible to quickly use the swept area to check if the claims of a manufacturer or the rated power of a turbine is unrealistic or optimistic. If you compare two turbines of equal rating and one has a smaller swept area than the other, it is more likely that the one with the larger area will be closer to the rating. Swept area is discussed elsewhere in these FAQs.

All turbines have power curves which are graphical representations of key specifications such as:

  • The wind speed at which the turbine starts to generate ('cut-in');
  • The wind speed at which the turbine produces its rated output ('rated wind speed'); And
  • The wind speed at which the turbine shuts down for safety reasons ('cut-out').

The power curve will give an indication of the power production at a range of wind speeds. Manufacturers provide power curves but these are often somewhat optimistic or not based on real certified data. Only power curves drafted by an independent third party laboratory can be given any credence. It is best to use swept area in conjunction with the turbine rating as the specifications to help decide what size turbine you require.

Figure 1 below is a sample power curve. It shows that for this sample turbine the cut-in wind speed is between 2 metres per second (m/s) and 3 m/s, the rated wind speed is 10 m/s (22 mph) and the cut-out wind speed is 15 m/s. Between 10 m/s and 15 m/s control systems are used to prevent the turbine from over speeding while still availing of high energy winds to produce electricity. Once an upper limit is reached most turbines must deploy some means of avoiding excessive rotational speeds in high winds or storms. This is necessary to prevent damage and the control can include turning the turbine away from the wind (yawing), applying a brake to the rotating shaft or feathering/pitching the blades out of the wind.

Figure 1: Sample power curve for micro-scale wind turbine

Figure 1: Sample power curve for micro-scale wind turbine


The peak output of a turbine can exceed the rated power during times of high winds or gusts. This peak output must be known so that electronics such as the inverter can be sized correctly to prevent damage to their components. There may be a lag between the electrical spike occurring and the application of mechanical control mechanisms to prevent the damage so the system must be able to cope with such instances. Numerous inverters and controllers have been burned out in the past due to inadequate sizing for these events.

If you are making a decision between two turbines based on rated power compare two power curves of both turbines at 5 m/s and 10 m/s so that a direct comparison can be made (assuming both power curves are accurate and third party certified). 5 m/s and 10 m/s wind speeds occur more often than 15 m/s speeds.

A typical cut-in wind speed for a domestic or small scale turbine would be 3m/s. A low cut-in speed is desirable because the turbine will be producing electricity for longer periods and in periods of less energetic winds. Better to be producing something rather than nothing.

Typical rated wind speeds for small turbines are between 10 m/s and 15 m/s. As with cut-in speeds the lower a rated wind speed is the more often the turbine will be producing its rated output. This is one reason why turbines should not be selected on name plate rating alone. It may be the case that a turbine will only reach its rated output infrequently if the wind speed required occurs infrequently.

The key performance indicator for a turbine system is the amount of units it produces over a year or over its life-time, not the amount it produces during the 3 windiest nights or months of the year.

Table 1 below provides an indication of the possible output from a selection of sites. It is only an indication and all sites will be different. The suburban site might be a built up area including trees and houses. Descriptions of ideal sites and what factors are to be considered when rating a site are discussed elsewhere in these FAQs. The output figures were based on conservative capacity factors which could be experienced in the four types of locations. The capacity factor of a wind turbine is defined as the actual output of the turbine over a period, usually a year, versus the maximum output from the turbine had it operated at its nameplate rating for the entire period.

Table 1: Possible outputs from a selection of sites

It is clear that, with all other things being equal, location can greatly affect output.

The value of the energy produced is dependent on how much can be consumed on-site and what value can be placed on excess sent out to the grid. Every unit of electricity consumed on-site can be attributed the value of a unit if it was to be imported at that moment in time. A unit produced when it is not needed must be exported to the grid, stored in batteries, stored as heat in water or diverted to a dump load (often a heating element). In 2009 this unit of unwanted excess electricity can have a value of anywhere between zero and 19c/kWh for domestic customers. Its value to you is zero if it is dumped or exported to the grid for free. Its value to you is going to be 19c/kWh (for the first 3,000 kWh exported per annum for 5 years) if you are a domestic ESB Customer Supply account holder. Once you have exported 3,000 kWh the value per unit falls to 9c/kWh. All of the quoted prices will be subject to ongoing review.

Customers can modify their consumption behaviour to maximise the consumption of the turbines output as well as minimise their imports from the grid. Homes and businesses consume a portion of their energy in a discretionary manner. It is the discretionary portion which can most easily be targeted to reduce demand at certain times. For example immersion heaters and washing machines can be delayed or non-essential lighting can be switched off. Many washing machines now have a delay timer as standard (but it is not advisable to leave appliances to operate un-supervised).

Non discretionary consumption is more difficult to manipulate, for example a certain amount of lighting will be needed when it is dark. Cooking will be required at certain times determined by work, school and lifestyle (however it is possible to reduce energy costs for cooking and storing larger amounts for consumption at a later date). Non-discretionary demand for electricity will have to be met regardless of the availability of the wind for the turbine or daylight for the PV panel.

With payment for export being an option for domestic microgenerators in 2009, an exported unit will no longer have a value of zero. As mentioned previously, it will have a value up to 19c/kWh depending on your electricity supplier. This means that there could be a 36c/kWh swing between importing a unit of electricity and exporting it. This fact should be an incentive to households with microgeneration to be more energy efficient in how much power they use and at what time they use it.

The actual performance of turbines in Irish conditions will be better known following the completion of the field trials commencing in 2009.

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By how much will my electricity bill reduce if I install a wind turbine?

It is impossible for a manufacturer of a turbine to predict that installing one of their machines will reduce bills by, say, 30%. Every customer's total demand and profile is different. It is worth mentioning that generating your own electricity will reduce the energy payment portion of your bill (kWh or units) but it will not have an effect on the standing charges portion of your bill if you remain grid connected.

Depending on the quality of the turbine and the suitability of the site a 3kW turbine could produce, in excellent conditions, the average number of units a domestic customer consumes in a year (4,000 - 6,000 kWh). If the timing of the demand for power in the house exactly matches its generation then bills will be greatly reduced and only standing charges will remain outstanding. In fact if the demand matched the generation exactly (which is almost impossible with an intermittent energy source like wind) it would be possible to remove or disconnect the grid connection.

At the other extreme we could look at the example of a rugby club with electric showers and flood lights. The load factor of such an electricity customer would be very low. Load factor in this context refers to the ratio of average load to peak load over the year. Peak load might occur for 2 hours during each night of mid week winter training under lights on 2 nights per week totalling around 150 - 200 hours out of 8760 in a year. Matching the wind resource to this type of demand is impossible without significant battery storage. In the absence of storage the turbine might be producing 10 times the annual demand of the site but just not at the right time. By accessing an export tariff the economics can be improved in these types of situations but it should be remembered that only the first 3,000 kWh exported can avail of an 19c/kWh tariff. Each unit exported thereafter will receive 9c/kWh. And this only applies to domestic customers initially.

In reality the efficacy of a turbine in reducing bills can only be known with retrospective analysis. However, with a thorough resource assessment, site assessment and accurate, independently certified manufacturer performance parameters it is possible to estimate a range within which the turbine should perform. Consumers should research carefully the organisation providing the test reports. Only accredited test labs should be given credence as anyone can print a convincing certificate. You can check the accreditation of a test facility at http://db.european-accreditation.org/.

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Will I get paid for electricity exported to the grid?

Currently there are no export tariffs being offered  for micro- generated electricity.

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Can I sell any excess power I don't need to a neighbour or can we chip in for one turbine between us?

You must be licensed to supply electricity in Ireland. The requirements for such a licence would be sufficiently onerous and expensive to make it non-viable at the smaller scales. Furthermore, supplying electricity from a generator on one person's land to a second person's premises across a boundary is illegal under Irish legislation covering direct lines and private networks. Only ESB Networks and EirGrid are licensed to distribute or transmit electricity to customers in the State.

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What are the tax implications when buying a turbine and generating some of my own electricity?

There is currently no scheme of tax relief for individuals or domestic users who invest in their own on-site generation. Persons who conduct a trade can claim an annual tax allowance of 12.5% over 8 years on the actual cost of machinery or plant provided for the purposes of that trade. According to the Revenue Commissioners it is possible that on-site generating equipment could qualify as machinery and plant if used for the purpose of a trade i.e. no power is going to the home.

The relevant legislation is Section 284 of the Taxes Consolidation Act 1997.

The entitlement to the allowance is subject to the following conditions:

  • At the end of the year of assessment the machinery or plant continues to belong to the person carrying on the trade,
  • At the end of the year of assessment the machinery or plant is in use for the purpose of the persons trade,
  • The machinery or plant while being used for the purpose of the trade is wholly and exclusively so used.

Payment by electricity suppliers for excess electricity exported to the grid may have tax implications under current legislation. Persons resident in Ireland are liable to income tax on their income from all sources and should include such income in their annual tax return.

It is not possible to set out a generic position here as all the facts of a case need consideration. Depending on whether the generating of electricity is incidental to the main trade or whether it could be considered a separate activity/trade a different treatment applies. A person may be affected by the restrictions contained in section 409D of the Taxes Consolidation Act 1997 which limit the use of capital allowances by passive investors in certain trades, one of which is generation or supply of electricity.

The Revenue Commissioners recommend that any individual or business intending to invest in on-site generation technology seek professional tax guidance. The information provided here gives an indication of the tax implications but each individual or organisation's circumstances may be different.

Budget 2012 and VAT for Farmers

The 2012 Budget included an extension of the existing VAT Refund Order for flat-rate farmers to include a refund on the purchase of wind turbines.

“The existing VAT refund order, which provides for the refund of VAT paid by un-registered farmers on the construction of farm buildings, fencing, drainage and reclamation of farm land, will be amended to provide that such farmers may claim a refund on wind turbines purchased from 1 January 2012. This change is part of a series of measures aimed at assisting and promoting the farming community.”

In addition to retaining the VAT refund provided under the existing Order, with regard construction of farm buildings, fencing, drainage and reclamation of farmland, the new S.I. No. 201 of 2012 provides for a VAT refund to farmers who purchased from 1 January 2012, either a) a wind turbine system, b) a solar power system, or c) equipment ancillary to those systems required for storage of electricity or connection to the grid.  In order to qualify for a refund, the equipment must be designated as energy efficient by the Sustainable Energy Authority of Ireland and used only for farming purposes.

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How much do these systems cost?

Turbine systems costs vary depending on a number of factors. For a given suitable site the choice of turbine and supplier are the key factors which lead to a successful installation and a positive experience. It is possible to source seemingly inexpensive turbines on the internet from manufacturers in Asia but, without a local support network, if something does fail it could be very difficult to get the system up and running. If the turbine turns out to be of poor quality or not robust enough to cope with a high wind speed event it may be a wasted investment. Grid connected turbine systems generally range from approximately €20,000 to €30,000 for a 6kW unit and from €10,000 to €20,000 for a 3kW unit. A 1kW grid connected unit can cost from €3,000 to €7,000.

The cost per kW is usually inversely proportional to the size of the unit i.e. as the unit size increases the price per kW decreases. That is why a 5kW unit is not double the price of a 2.5kW unit from the same range for example. Suppliers will be able to provide you with indicative cost for the installation or cost of equipment alone prior to giving you an exact quote for your requirements and location.

The cost of the same system installed in two different locations may be slightly different due to the ground conditions, access, location, etc. Adding battery storage adds significant cost depending on the amount of energy which is required to be stored.

Once installed, the source of power - the wind - is free. Electricity produced by the turbine is not free however as the turbine has an initial cost as well as ongoing costs which must be recovered during its lifetime. The turbine recovers these costs by producing electricity which does not have to be sourced on the grid.

Maintenance costs are an important factor to consider when deciding on which turbine to purchase. As a rule of thumb, maintenance could cost about 2%-3% of the initial capital cost annually. In principle, good quality turbines have a working life of around 20 years but their actual life expectancy depends very much on a variety of factors such as local wind and atmospheric conditions (e.g. coastal air, turbulence). The strain on a turbine is much higher where turbulent winds are frequent. Maintenance requirements can be less demanding if the turbine is of a higher quality.

A further cost is that of insurance. Home and business owners should contact their insurer to discuss the implications of installing a turbine and mast. It may be advisable to insurance on the wind system itself and also for any accidents due to the wind system. The planning guidelines ensure that a correctly sited turbine is unlikely to cause damage to property within or outside the boundary of the premises.

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Is there a grant available for installing a small wind turbine or other form of microgeneration?

At present there is no national grant or deployment programme available towards the cost of installing a domestic or small business scale wind turbine, PV cells, micro-hydro or micro-CHP unit. During 2009 there was financial assistance available to a small number of sites which will be studied in field trials in 2010/11. The Minister with responsibility for energy launched the field trials in February 2009. The aim of the trial is to, among other things, collect data on the performance and effectiveness of microgeneration in an Irish setting.

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How big are the turbines and masts at this scale?

For a given rated output the blade diameter (and therefore the swept area of the blades) varies from one manufacturer to another. Some manufacturers quote unrealistic figures for the output to be expected from their turbines. It can be easy to spot the more optimistic manufacturers by simply comparing turbines with the same blade diameters. Even if some turbines are more efficient at capturing the energy in the wind when compared to others the disparity can be obvious. The table below provides an indication of the blade diameters to be expected for each size of turbine.

While it is preferable from a performance point of view to use a turbine mast as tall as possible certain restrictions such as planning regulations and cost constrain the use of very high masts. Furthermore turbine masts are generally designed to suit a particular turbine. They need to cope with the particular resonances and vibrations generated by the turbine during operation. You may find that you have limited choice when deciding on a height.

Table 2 below gives an indication of the height of masts for turbines of various heights. Some suppliers can provide a mast option (for example 10m or 15m) to suit different sites, applications and conditions. Suppliers should be fully aware of the requirements for planning exemptions and often size their masts to meet these regulations. The height limits for planning exemptions are discussed elsewhere in these FAQs.

 
Manufacturers' Rated PowerSample Blade Diameters (m)Typical Hub Height (m)
500 W2.26-7m
750 W2.56-7m
1 kW2.86-7m
2 kW4.06-10m
3 kW5.06-10m
4 kW5.26-10m
5 kW5.56-10m
6 kW66-10m
10 kW710-18m
15 kW1010-18m
20 kW1110-18m

Table 2: Typical dimensions of turbines and masts

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Why is the swept area of the blades an important factor in choosing a turbine?

Swept area is a term used to describe the imaginary circular area within the blade tips of a turbine as they rotate. It is probably the most important specification to reference when considering a turbine. If the blades are efficient it can be a clearer indicator of the likely output of a turbine than the manufacturer's rating.

Swept area (A) = π x (R)2 where R is the rotor radius and π = 3.14.(I)

For example a turbine with a rotor diameter of 6m (i.e. radius of 3m) has a swept area of 28.26m2 because:

A = π x (3)2 = π x 9 = 28.26m2 (II)

A larger swept area has more air passing through the plane of the turbine and so greater is the energy that can be harvested. The ability of a turbine to avail of the energy in an air stream is approximately proportional to the diameter of the blades.

The maximum available power in the swept area of a turbine rotor is found using the following formula:

Power = ½ ρx swept area x V3 (III)

Where ρis the air density, V is the wind speed.

If air density and wind speed are made constant it can be seen that the theoretical power available in an air stream is proportional to the swept area. If this area doubles the power available doubles.

It is worth noting that the power captured by the turbine can not be calculated by using the above formula (III). The formula shows how much power is available but the actual power captured is governed by Betz's law, the efficiency of the blades and the efficiency of the generator and electrical conversions. The above formula is shown to illustrate the relationship between power, swept area and wind speed. From the formula it can also be seen that if the wind speed doubles the power output is multiplied by 8! Demonstrating clearly why access to a high average wind speed is so important.

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What are the benefits, disadvantages and differences between the different types of tower?

It is not a good idea to buy a tower or mast not specifically designed for your turbine of choice. Mismatching the turbine to the mast could lead to vibration, noise, failure or collapse of the installation. It is advisable to use masts designed for a specific turbine as these will be designed to cope with the loadings and harmonics created by the associated turbine.

There are a number of variations on masts for small turbines. These can be categorised into two distinct structures - guyed or freestanding - with variations on the construction of the tower. The key considerations for tower selection are cost, space and suitability with the turbine of choice. The characteristics of each type of support structure are discussed below.

Guyed Pole
  • A narrow tubular pole or joined pipe sections supported by guy wires.
  • Uses less material in its construction and thus reduces material costs.
  • 'Tilt-up' construction with a Tirfor using a gin pole as lever arm around pivot point at the base. A Tirfor is a lifting device or which allows slow winching of a lifting cable. A gin pole is an A-frame lever point which makes it possible to winch the support from a horizontal position.
  • There are usually 2 levels of guys on most towers although the number depends on height.
  • The radius of the guys should never be less than half the height of the tower and can be as wide as there is space beyond that but generally a radius of 75% of the height is satisfactory.
  • No climbing or elevated access is required as the pole can be lowered for maintenance and access.
  • Requires less of a concrete footing than free standing tower variations.
  • Not suitable for mixing with larger livestock due to risk of interference with the wires and anchors.
  • Could be prone to vandalism if in an accessible area.
  • Generally the least expensive type of tower.
Tubular Steel
  • Single tapered pole -street light type- which is usually hot-dip galvanised steel.
  • Scaled down version of typical type of tower used in wind farms.
  • Requires more substantial concrete footing than a guyed pole.
  • No guy wires required and thus minimal risk of structural interference from animals or people.
  • Cranage may be required but as with the other types of tower raising with a gin pole, pivot and Tirfor is a preferable, more preferable option with many variations.
  • Variations which cannot be tilted down require hoist hire or other elevated access for preventative maintenance and repairs.
  • Material costs can be high when compared to other tower types (more steel per metre height).
  • Generally the most expensive form of support for a turbine.
Lattice tower
  • Similar in appearance to common 'criss-cross' towers.
  • Lattice is manufactured by welding tubular, flat or angle profiles together to form a structure.
  • Can use up to half the quantity of material for a similar strength free standing tubular steel tower.
  • Can be guyed or free standing depending on design.
  • Guyed lattice towers warrant similar consideration in relation to site, space, land use and security as guyed pole towers.
  • Installation is in sections and usually requires cranage although some arrangements allow raising with a gin pole, pivot and Tirfor.
  • Base would need to be made secure with fencing to prevent climbing if in accessible area.

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What are the noise levels I can expect and what do they mean?

Each turbine will produce different noise levels and different tones and sounds. The main sources emitted are the sound of the blades cutting through the air and the sound of the generator and shaft turning. Noise may be produced inadvertently by a brake pad rubbing or a squeaky yaw bearing. This can be dealt with quickly and easily with correct assembly, erection and routine maintenance. Noise issues experienced with gearboxes have largely been dealt with as the majority of turbines at this scale do not use them.

The noise the blades, rotors or generator of any wind turbine produces is dependent on the speed of the wind. As the wind speed and the revolutions per minute (RPM) of the rotor increase background noise levels also increase. The increase in noise levels may be cancelled out due to the fact that background noise from the wind itself increases with speed also. Vegetation, which rustles in the wind, can help minimise the noticeable noise emissions from a turbine.

According to the planning regulations (as outlined elsewhere in these FAQs) the level of noise at your premises or the nearest neighbour's premises (whichever is closer) should not be above 43dB(A) - or 5dB(A) above the background noise.

40dB(A) is comparable to the noise levels in a quiet rural area, quiet library or ¼ as loud as ordinary conversation. 50dB(A) can be approximated as equivalent to the noise levels in a quite suburban area, in an average home or with a dishwasher running in the next room. 50dB(A) is roughly ½ as loud as normal conversation. Conversational speech at 1m distance equates to noise levels of 60dB(A).

The specifications a turbine manufacturer supplies should include figures for noise levels to be expected at different speeds at a given distance from the turbine. Ideally these figures should have been certified by an independent or third party test facility.

Noise levels and the concept of dB(A) can be hard to grasp so visiting a supplier's installed turbine is probably the best way to gauge the noise levels to be expected.

The relevant international standard in relation to noise emissions from a turbine is EN61400-11. Evidence of this certification should be sought when choosing a turbine. Only accredited test laboratories' certificates can be given any credence (http://db.european-accreditation.org/).

Blade tip speeds below 75 m/s are advisable as speeds above 80 m/s cause a noise level which, depending on the site and proximity to dwellings, may be an issue. It is possible to calculate the tip speed by using the RPM of the turbine shaft and the diameter of the blade swept area. These specifications should be readily available from the supplier or manufacturer.

The speed or velocity of the blade tip (VT) is equal to the RPM multiplied by the diameter divided by a constant (19.1):

VT = RPM x D/19.1

Taking an example where the blade diameter is 5.5m and the rated RPM is 200 (i.e. at rated output the turbine will be turning at 200 RPM) we can calculate the blade tip speed at rated output (VTrated) thus:

VTrated = (200) x (5.5/19.1) = 58 m/s

So when this turbine is producing its rated output the blade tips will be moving at 58 m/s.

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Is it expensive to get grid connected?

Apart from the cost of employing a RECI/ECSSA certified electrician to connect the system to the grid (which will be included in the price of the system) there will typically be no additional charge from ESB Networks. However in some instances, there may be additional physical works required, and such works would be chargeable.

An import/export meter (interval meter) is required to avail of payment for export. ESB Networks is providing the first 4,000 microgenerators with free interval meters.

Refer to the Your Guide to Connecting Micro-generation to the Electricity Network for further information.

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How do I go about organising a tie-in/connection to the grid?

Your chosen supplier could take care of the documentation necessary. It is a quick form so should be done at no extra cost. They should also take care of the hiring of a RECI or ECSSA certified electrician to carry out the connection to ETCI standards as part of their service.

Form NC6, available from the ESB Networks website, should be submitted well in advance of any grid tie-in.

NC6 is a straight forward one page form which includes:

  • Name, address and co-ordinates of the site
  • Contact details
  • MPRN number
    • Unique number assigned to each meter point
    • Printed on the top of your bill
  • Installer contact details
  • Make, model and serial number of inverter (grid connected electronics)
  • Declaration of conformance with "Conditions governing the connection and operation of microgeneration" including EN 50438.
  • Details of generating unit
    • Make and model
    • Type of technology (wind, PV, micro-hydro, micro-CHP etc.)
    • Unit Rating and phases generated
  • Details of inverter unit.

Type-test certification for the inverter (the unit tying the system into the grid) should accompany the NC6 form. The certification required should declare conformance with EN50438 which is the appropriate standard for grid connected units. The suppliers should provide you with this paper work if you are submitting the NC6 form yourself.

You will need an import/export meter to avail of any payment for exported energy. The import/export meter currently available in Ireland is referred to as an 'interval meter'. It is now supplied automatically and for free to customers when they submit the NC6 form.

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Can I get a smart meter installed or how can I get involved in the smart metering pilot?

It is worth pointing out that the interval meter which is available from ESB Networks is different from the smart meter which will be piloted around Ireland in 2009/2010. The interval meter is existing technology and the smart meter will be a new technology with new supporting infrastructure. Microgenerators are not included in the smart metering pilot. The microgeneration field trials are separate from the smart metering pilot.

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Can I get an import/export meter from ESB Networks?

The distribution system operator (ESB Networks) has made available, at no cost to the customer, 4,000 electronic import/export meters which are more intelligent than the standard electro-mechanical meter. These 'interval meters' should not be confused with the smart meters which will be piloted from 2009. The interval meters were made available as an interim measure to facilitate payment for export of excess power prior to a decision on a national roll out of smart meters. The availability of interval meters removes the key technical barrier to payment for export. The interval meter is necessary to access any available payments for exported energy. Interval meters will be supplied at no cost to the first 4,000 microgenerators applying over the next 3 years.

An interval meter is supplied automatically once you submit form NC6 to ESB Networks. Existing microgenerators who wish to be grid connected in accordance with current regulations should submit NC6 also.

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Should I choose to add batteries instead of getting grid connected?

Batteries are used in off-grid or charging applications. Off-grid systems are employed when the cost of connecting to the grid is prohibitive or the customer chooses to remain off-grid. As off-grid systems don't have the back-up of the national grid to call on during times of low or no wind they need some form of storage if they are to have a constant source of electricity.

The capacity of the storage can be just enough to smooth out the short term variances in wind availability or it can be enough to provide power to the premises if there is no electricity produced by the turbine for periods of days. The amount of energy stored depends on the size of the generator installed, how long the customer wants to satisfy their on-site demand and on how much they are willing to spend on battery cells.
Batteries are an arrangement of cells. Cells can be purchased separately (e.g. 2 Volt) and can be assembled to create batteries of almost any required voltage (e.g. 24 Volt).

The type of batteries used with wind turbines are known as 'deep cycle' batteries (or deep discharge). These are not like car batteries which are designed to deliver a large current or be called on to deliver a large amount of energy over a short period of time, for example during ignition.

There are variations of deep cycle batteries which are less suitable for long slow charges and discharges such as 'leisure' and 'semi-traction' batteries. Full 'traction batteries' are the most suitable type of deep cycle battery and are the most commonly used in off-grid systems. They are the type used in fork-lifts and submarines. Electric fork-lifts are typically charged slowly overnight and depleted during the day which is close to the likely operation of an off-grid power system.

There are environmental issues to consider when looking at batteries. Much of the battery material can be recycled but elements such as lead and cadmium are toxic and their use should be minimised in the first instance even if they can be recovered. Batteries can be dangerous (explosive acidic fumes, liquid acid, shorting of terminals) and every precaution should be taken in safe storage and ventilation. Professional expertise should be employed.

Control of the charging and discharging of batteries is crucial if the batteries are to last a reasonable length of time. An expensive battery bank can be damaged beyond use if not employed correctly. Batteries need to be accompanied by a wind turbine specific charge controller to prevent damage as manual control with meters and switches is not a realistic option for most people. Most batteries are designed to deliver only a portion of the stored energy and not be discharged fully under normal operation. Full discharge will shorten the life of the battery considerably.

For grid connected wind turbines where the user has back-up electricity available in times of low or no wind, albeit at the retail price per unit, adding batteries is sometimes considered. It is considered when electricity suppliers will not pay for excess electricity exported on to the grid. If no payment is available then customers may wish to store the electricity for use later. The economics of such a decision need to be carefully considered however in light of the decision by ESB Networks and ESB Customer Supply to pay some categories of customer for exported energy. Payment to the remaining categories of customers is under consideration. When the export tariff is equal to or greater than the import tariff the grid effectively becomes a storage device- you sell to grid when you don't need it and buy it back when you do. When the export tariff is greater than the import tariff then there is a clear financial benefit to being grid connected over using batteries.

Battery storage is expensive and a well maintained bank may last only half as long as a good quality, well maintained turbine. Depending on the size of the turbine installed and the amount of storage required batteries can add €2,000 to €5,000 to a domestic scale system. Second hand deep cycle traction batteries have become increasingly difficult to source.

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Can I heat water or the building by using electricity produced by the turbine?

Enthusiasts of small scale wind power have found a multitude of ways to utilise the power produced by the turbine. Some use batteries to store electricity for when the wind isn't blowing, others are grid connected, some are pumping water, others are charging electric vehicles, some are powering heat pumps, others are heating water and some are even doing a number of the above from one turbine. Furthermore there is any number of ways to do each of the above.

For a generator that is producing excess electricity, but not able to access the grid or avail of payment from electricity suppliers, storage is often considered. Battery storage is covered elsewhere in these FAQ's. Charged batteries hold the electricity in the form of chemical energy until it is needed and it is released once again as electrical energy.

Some microgenerators who can not avail of an export tariff opt for a system that will heat water. In this arrangement the electricity is passed through an element in a well insulated water storage tank. The electrical energy is converted to heat energy by the element and the heat is stored in the water tank to be used as needed. The water may need to be heated further by using electricity from the grid before use.

It should be noted that those with access to the export tariff of 9c/kWh or 19c/kWh should probably not consider the added expense of a water heating system from their turbine or microgenerator. Instead they should consider exporting the excess to the grid, receiving the payment, and import the required energy for heating on a reduced night-time tariff.

For those who do not have the option of an export tariff there are three main methods used to heat water from a wind turbine. One way is to just use a mains equivalent supply coming through the existing wiring loop from the grid connected inverter (or direct from an off grid controller) into the immersion element.

Another method is to heat the water via a small bank of wind charged batteries. The batteries provide a buffer from the fluctuations of the wind and provide low voltage direct current (12V, 24V, 48V) for a DC low voltage immersion element which would be a modification added to the well insulated hot water tank. This system could also be incorporated with an inverter and switching mechanism so that the load could be switched to mains voltage AC appliances in the house.

A third method would use a direct heating controller to heat the water tank with a switchover to either heat storage heaters at night or power the home during the day. This method has the advantage that batteries are not needed.

Careful consideration must be given to the method chosen. The demand profile of the premises and the size of the turbine are the key factors. Where no export tariff is available the goal is to design a system which will use every unit of electricity produced without the additional cost of storage.

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What should I expect of a turbine supplier/installer?

Site assessment

A comprehensive site assessment during a site visit by a competent, trained representative is a basic necessity. Buying a turbine in a DIY store or online, regardless of site suitability, could turn out to be a mistake. The key elements of a site assessment are covered elsewhere in these FAQs.

Feasibility study

The site assessment will feed into a report which will indicate if the site is technically and economically viable. If the site is not economically viable or is borderline the customer may wish to go ahead to capture other benefits such as clean and independent energy. Site demand and the timing of that demand will be crucial to the viability of the site. More detailed information on site assessment and viability is available elsewhere in these FAQs.

Certification

At present the key applicable standard associated with microgeneration in Ireland is EN 50438. This standard's scope is limited to the point at which the turbine connects to the grid. Therefore the standard applies to the inverter. ESB Networks must be furnished with evidence of compliance with EN 50438 for the grid connection to be approved. ESB Networks' main concerns are that the turbine will not export power to a de-energised grid and that the power produced under normal operation will not reduce the quality of the supply to other customers in the area. A de-energised grid, during a power outage (planned or otherwise), will be worked on by technicians. If the inverter allows electricity to be exported to the grid at this time it is a danger to the technicians.

The turbine itself should be certified to perform in accordance with EN 61400-12 and designed safely to be compliant with EN 61400-2. EN 61400-2 includes the classification of small wind turbines with regard the wind speeds and conditions for which the turbine is designed. Class I winds are common in Ireland and many turbines are not designed to withstand the high gusts or average wind speeds experienced in our climate.

 
ClassIIIIIIIIIIIIIVIV
 m/smphm/smphm/smphm/smph
Vref5011242.59537.5843067
Vave10228.5197.517613
Table 3: Small wind turbine classes


Table 3 shows the classification of small wind turbines as prescribed in EN 61400-2. Vref is the reference wind speed for each turbine. A turbine designed with a Vref of 112 mph is designed to withstand climates for which the extreme 10 minute average wind speed with a recurrence period of 50 years at the turbine hub height is lower than or equal to 112 mph. Vave is the annual average wind speed at hub height.

The performance of the turbine in relation to noise should be in line with EN 61400-11. These are international standards. A manufacturer can self-declare compliance with the safety standard EN 61400-2. Proof of compliance with EN 61400-12 and EN 61400-11 is achieved by putting the turbine through rigorous tests. The test must be carried out by an accredited test facility and not the manufacturer or a non-accredited facility. Customers should check the accreditation of the test facilities appearing on the test reports because they may not be as professional as the document may portray.

The CE mark should also be in evidence on the major elements of the microgeneration system (turbine, inverter and controller). The CE mark is not a symbol of quality but does show that certain standards have been satisfied by the manufacturer.

Training

Action Renewables in Northern Ireland has developed a training course for wind and hydro micro-turbines and PV panel installers. At present there is no legal requirement for installers to have undergone this training in order to operate in the Republic of Ireland. There will be a compulsory training requirement in place for any equipment and installer registration in the future- similar to current arrangements for wood pellet boilers and solar thermal panels. The training is run by the Renewable Energy Installers Academy (REIA) in Northern Ireland and it is open to electricians from the republic. The awarding body is City & Guilds.

Some of the established turbine manufacturers offer training courses for installers of their equipment. In an effort to protect their brand some manufacturers will only supply turbines to installers who have undergone this training. A combination of the training provided by the REIA and the practical training provided by a quality turbine manufacturer should equip a supplier well to provide a good service to its clients.

A number of private training providers are offering wind turbine training courses in the Republic but many of these are not recognised by City & Guilds, FETAC or the SEAI field trials at present. For a list of recognized training sites please refer to the list on the SEAI website: Microgeneration Training Providers. SEAI is developing training and certification requirements with a view to having a FETAC qualification in place as soon as possible. For the purposes of eligibility for the small scale field trials the REIA training and manufacturer training will be required. Prospective customers should aim for this standard when choosing a supplier or installer whether they intend to apply for inclusion in the trials or not.

The final wiring and sign-off of a grid connected turbine must be completed to ETCI standards. The electrician should be a member of a certified trade body such as RECI and ECSSA. Ask your prospective supplier for evidence of training or experience within the company.

Health and Safety

The Safety, Health and Welfare at Work (Construction) Regulations 2006 prescribe the duties and responsibilities of all parties (client and provider) engaged in construction activities with regard health and safety. One of the main duties of a client is the appointment of project supervisors for the design and construction stages of a construction project (PSDS and PSCS). Domestic works are exempt from this requirement unless a trade or business is undertaken on the premises. Turbine suppliers and installers should provide an undertaking that the works will be carried out in line with the requirements of the 2006 regulations. Clients should make themselves familiar with their duties under the regulations.

Warranty

Some manufacturers and suppliers offer warranties with major equipment and parts. Ask a selection of suppliers what warranty they offer. Some offer warranties of up to 5 years.

After sales service

Turbines may not always operate to desired performance levels following initial installation. Certain issues may not become apparent until certain wind speeds are reached or certain actions are required (braking for example). The response of the installer to a request for a call-out from a customer can be a key factor in determining if the customer has a good experience. If at all possible, customers should make contact with existing customers to gauge their opinion on a supplier or equipment. It is vital for the turbine to be kept operating so that the energy in the wind is not wasted while electricity is imported from the grid.

The availability of after sales service is an advantage local or national suppliers and installers have over cheaper, international online suppliers.

Maintenance

Most turbines require some level of maintenance and a schedule for routine maintenance will be recommended by the manufacturer. Some claim to be maintenance free and some turbines require more maintenance than others.

The required maintenance of a turbine can depend on local conditions such as the amount of turbulence experienced by the turbine and the corrosiveness of the air (sea air contains salts for example). A good quality turbine will have key mechanical and electrical components constructed out of marine grade or corrosion resistant materials such as stainless steel and brass.

Turbulent airflow will demand more of a turbine. The loading and unloading of blades and bearings and the extra movement associated will increase wear and tear. An analogy with cars can be used. The shocks of a car which travels with light loads on smooth roads will last much longer than the same model car on rough roads with heavy loads.

Suppliers may offer a period maintenance contract or offer a per-visit charge. Annual maintenance may be as simple as re-greasing wearing surfaces. Ask prospective suppliers what maintenance is required by their turbine manufacturer and ask for an estimate for call-out charges beyond the period covered by the warranty.

Turbines have potential to be dangerous so maintenance should only be carried out by trained individuals. Especially as the turbine will have to be accessed by lowering with a crane or winch or accessed via a raised platform.

Who oversees the import and supply of small wind turbines?

SEAI has developed recommended quality and certification criteria for consumers and has implemented the Triple E register of products to show consumers which products achieve a minimum standard. Outside of recommending to customers that minimum standards are consulted when choosing a product, and limiting access to tax incentives to qualifying products, SEAI does not have a remit or means to control what products are sold on the market.

With any electrical machinery there will likely be a Low Voltage component for which the National Consumer Agency has market surveillance authority. Likewise, with any device that has a Low Voltage component there will be an Electromagnetic Compatibility aspect for which ComReg has market surveillance authority.

However, for the purpose of overseeing small wind turbines the Health and Safety Authority (HAS) has market surveillance responsibility for 99% of the functionality of such wind turbines and the HSA will engage with NCA or ComReg in its market surveillance activity if required

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Is there a list of registered suppliers or installers and what training should an installer have completed?

At present there is no register of installers or products published. Criteria for inclusion on such lists are being finalized as is the methodology. SEAI has in the past published an un-vetted list of microgeneration suppliers. We no longer publish such lists because without qualifying criteria there is a risk that un-trained service providers will be seen as approved by SEAI. SEAI does not approve installers or suppliers on any of its registers. Rather the registers are lists of people and companies who have satisfied minimum training and other requirements.

Suppliers were required to demonstrate that they have undertaken training and certification to be included in the SEAI field trials. There is currently micro-wind training available in Northern Ireland with the Renewable Energy Installer Academy (REIA) which can be attended by suppliers from the Republic and leads to a City & Guilds qualification. This course is also now offered by Chevron Training. FAS in Galway and Finglas offer accredited PV training.

Some wind turbine manufacturers also insist that installers of their turbines attend manufacturer run training courses before they will supply them with equipment for sale. A combination of the training provided by the REIA and the practical training provided by a quality turbine manufacturer should equip a supplier well to provide a good service to its clients. Prospective customers should aim for this standard when choosing a supplier or installer. SEAI will shortly publish a list of installers trained to this standard on its website. It should be pointed out however that this sector is not unique in that the completion of training indicates only a minimum standard and does not guarantee quality.

A number of private training providers are offering wind turbine training courses in the Republic but many of these are not recognised by City & Guilds, FETAC or the SEAI field trials at present. For a list of recognized training sites please refer to the list on the SEAI website: Microgeneration Training Providers. SEAI has assisted in the development of training and certification requirements for wind and PV with a view to having a FETAC qualification in place as soon as possible. The details of the awards have been published and training providers are progressing their applications to become approved sites.

It is always a good idea to try and gauge the satisfaction of previous customers of a supplier and installer before making a purchase. These installations may need a number of re-visits to get running at peak performance due to the nature of wind. The supplier's response to these call-outs is often a good indication of their customer service.

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How long should the turbine last and how much maintenance is required?

Once installed, the source of the power produced is free. However, it should be remembered that the turbine is not free and the actual unit cost of the electricity produced is equal to the total costs of the turbine over its life-time divided by the amount of useful units it supplies (neglecting any payment for export to the grid).

Clearly it is important to keep a turbine running for as long and as well as possible if the financial and environmental benefits are to be accrued. Maintenance costs are an important factor to remember. In principle, the best quality turbines have a working life of up to 20 years but their actual life expectancy depends very much on design, materials, the quality of the installation and maintenance as well as local wind and atmospheric conditions (e.g. coastal air, turbulence). Poor quality turbines may be destroyed in the first high gust of wind or after 2 - 3 winter storms. Equally, a good quality turbine which is poorly or incorrectly installed could be destroyed or damaged within a short period.

A supplier may offer a maintenance agreement or contract for a set period after the installation. Alternatively they may give an indication of what they might charge for a call out or regular service. Some turbines may not need to be serviced until a number of years (2-3) have passed since the installation. Manufacturer's guidelines should clearly state the maintenance schedule which will be in compliance with a warranty. Routine maintenance may simply be a case of greasing wearing surfaces and checking fasteners. Major maintenance may be required less frequently, for example a blade may need to be replaced after a number of years.

Because wind turbines are erected during the weather and wind conditions existing on the day they may need some fine tuning in the days or weeks following. For obvious safety reasons a turbine may be erected during a period of no wind and the installer or electrician may have to return to commission the system on a windy day to ensure everything is operating as designed. Furthermore some teething problems may be experienced in the weeks after commissioning. You need to be sure that you have chosen an installer that will respond to your requests for a site visit under these circumstances. Getting the view of existing customers is one way of gauging a supplier's customer service.

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What is the financial payback period for such an investment?

Under current circumstances economic payback for a micro-scale wind turbine - a long term investment - may not be achieved for more than ten years. The

  • Capital outlay
  • Demand for electricity and the timing of the demand
  • Load factor
  • Maintenance costs
  • Average wind speeds
  • Turbine performance
  • Cost of alternative sources of power
  • Life-time of the turbine and associated equipment
  • Value placed by prospective buyer on Building Energy Rating
  • Payment or credit for excess electricity exported.
Capital Outlay

Quality turbines of any scale are not cheap. A good quality 5kW - 6kW turbine can cost over €25,000 to purchase, install and connect. A well maintained good quality 6kW unit in an excellent site will produce around 13,000 units of electricity per annum. Depending on the proportion of this power which is consumed onsite, exported for 9-19c/kWh or exported for free it has a value from anywhere between €1300 and €2400 to a domestic customer of ESB Customer Supply.

13,000 kWh would have the value of around €2400 if all of the units produced were consumed onsite and the site was supplied by ESB CS with the 24-hour rate (rather than the night-saver). However a typical house in Ireland might consume around 5,500 units of electricity per annum and not 13,000. The electricity generated would have the value of €1760 if the turbine matched demand for 3,000 kWh of a typical houses demand (at 18.6c/kWh per unit) and exported the balance (3,000 kWh at 19c/kWh and 7,000 kWh at 9c/kWh). The house would then still have to import 2,500 kWh at 18.6c/kWh (or €465 worth of electricity).

Demand for power and the timing of demand

Clearly the proportion of power consumed/exported/imported can vary widely from premises to premises. Customers could monitor their own energy use for a period of months to get an idea of the timing of their demand. A variety of DIY energy monitors are available and the data collected can be uploaded to a computer for analysis.

Well sited consumers who remain high demand customers after employing all appropriate energy efficiency measures may be best placed to benefit most from the addition of microgeneration. Wind microgeneration is suitable to sites where there is a constant 'base-load' demand for electricity. That is where demand rarely drops below a certain level, even at 5 a.m. If a turbine is installed it can displace imported power required to meet the base-load demand. It should however be remembered that 'night-saver' or other economy tariffs are available and these should be included as appropriate when analysing the economics of the site.

Load factor

Every demand customer has a 'load factor. In electrical terms a load factor can be expressed as the ratio of the maximum electrical demand versus the average demand over the same period (peak v. average). A rugby club with floodlights may have a very small demand for 95% of the week. For a few hours every week during 6 months of the year the demand reaches its peak when floodlights are turned on for training. Installing a wind turbine on a site such as this is far from ideal from a demand and cost reduction point of view unless an appropriate export tariff can be availed of.

Maintenance costs

Maintenance costs and contracts should be discussed with a number of prospective suppliers. A routine maintenance schedule should be supplied by the manufacturer as well as estimates for future costs of major parts. The schedule should be sufficient to ensure long and productive operation under local conditions. Some turbines require more maintenance than the manufacturer recommends while others may survive with less. As is the case with all machinery, the more frequent the maintenance and care the longer the turbine is likely to be of use. The ultimate aim is to reach beyond the break-even point. A turbine system which does not reach a break-even point has in effect produced power during its lifetime that has been more expensive than would have otherwise been available from the grid.

Maintenance costs usually include a call out charge as well as costs to cover access to the turbine for greasing and other light maintenance. After a period of years parts such as blades or brushes may need to be replaced. Estimates for the lifespan of such parts and the cost of such non-routine maintenance should be provided by the supplier or manufacturer. Again local conditions, turbulent air flow or storm damage may require replacement of parts outside of any schedule.

The more mechanically and electronically complex the turbine is the more elements there are that can go wrong, therefore the more maintenance which may be required. Simplicity should be a factor in choosing a turbine.

Average wind speeds

The output of a wind turbine is dependent on the energy in the air flowing over the blades and through their swept area. Power output for a given turbine is proportional to the cube of the wind speed i.e. if the wind speed doubles the power output increases by a factor of 8. Another way to look at it is that a doubling of the power output can be achieved by an increase in the wind speed of just 25%. So it is clear that the power output and its value can vary substantially from site to site. Average wind speeds are more important than the occasional high wind speeds which might be available at a site.

Turbine performance

Manufacturers and suppliers should supply all of the technical specifications and expected performance figures for the turbine and system. Each turbine has a power curve which will give an indication of the turbines output at different wind speeds. A power curve which an accredited third party test or independent test facility has developed is more reliable than a manufacturer supplied one. Customers should always check the accreditation of test facilities providing certification. A power curve will show information such as cut-in wind speed, peak power, rated power, rated wind speed and cut-out wind speed.
A low cut-in wind speed is desirable to capture as much available energy as possible. At cut-in the turbine will produce little power but it is better to be producing something rather than nothing. Before cut-in turbines may be rotating but the generator is not producing any power. A typical cut-in wind speed for small turbines is 3m/s.

Peak power is the maximum the turbine will produce in infrequent circumstances such as exceptionally high winds or momentary gusts. Over-speed controls should prevent too much power being conducted through the electronics but peak power could cause damage if the turbine is not designed or prepared to respond quickly or if the mechanism fails. The electronic controller and inverter are designed to cope with currents and voltages within a range and a momentary breach of upper limits will damage or burn out components, if not the entire unit. The inverter must be sized appropriately to cope with peak power production.

The key performance indicator for a wind turbine is the amount of energy it produces over its lifetime and not the rated power/nameplate rating.

Cost of alternative sources of power

The power produced will replace imported electricity at the retail rate available at the moment it is produced. At present domestic customers generally have access to just two types of tariffs. One account has a flat tariff throughout the day and night. The other option is a day/night tariff with the meter differentiating between units consumed at night and during the day (ESB's 'Nightsaver' product for example). The day-time tariff in the day/night option is slightly more (6.8% more) than the standard 24 hour tariff but the night-time tariff is significantly less (47% less). The day/night tariff option is suited to homes with electrical storage heating.

Commercial and residential commercial customers have a range of tariff suites available from a choice of suppliers. Anyone, commercial or domestic customers, considering their tariff options need to consider carefully their consumption patterns and factor in extra standing charges applicable for the required metering. There is also a charge for the required meter.

Some microgeneration sites may chose to use the power produced onsite to heat water, be it for washing or for space heating -direct water heating. In this case the fuel cost comparison is carried out against available heat fuel sources such as oil, natural gas and biomass boilers or stoves. For situations where just the excess electricity is used to heat water it is just that portion which is compared to other heat sources with the remainder compared to electricity imports as before.

Life-time of the turbine and associated equipment

By definition a turbine that lasts beyond its break even point or payback period has paid for itself. It is also clear that a turbine that only lasts a small few years is a wasted investment. Turbines need maintenance and it is in the interest of the owner to keep the turbine generating for as long and as efficiently as possible to get to a point where the turbine has paid for itself and it is producing clean energy at a cost less than the retail price of electricity.

Value placed by prospective buyer on Building Energy Rating

Adding microgeneration to a property will improve its rating under the Building Energy Rating (BER) requirements. The output from electricity producing photo-voltaic (PV) panels will be estimated as per a prescribed formula. For wind turbines there must be at least one year's output data before it can be factored into the buildings performance. This is to account for a wide variation in performance of turbines- from good sites to poor sites and from maintained turbines to defective ones.

Prospective buyers, leasers of a premises or tenants will place a value on the energy rating of a building. Running costs can be a key consideration when valuing, purchasing or renting a new property.

Payment or credit for excess electricity

Payment by electricity suppliers willing to buy excess electricity will reduce the payback period and improve the viability of the technology. With a payment of between 9c and 19c/kWh being offered by some of the ESB Group every unit of electricity produced has a value and units will no longer be exported to the grid for free.

To give a simplified example: A house in an excellent site for availing of wind has a 3kW turbine installed. The turbine produces around 6,300 units of electricity (kWh). The house has an annual demand of 5,000 kWh but the turbine only matches this demand for 40% of the time i.e. 2,000 kWh of the house demand comes from the turbine. The remaining 3,000 kWh comes from the grid.

If no export tariff was available the turbine output would have the value of €372 (retail price of electricity (e.g. 18.6c) x 2,000) as the amount exported (4,300 kWh) would have no value. With payment for export available to domestic customers each of the 4,300 units now has a value. The first 3,000 kWh has a value of 19c/kWh (equal to €570) and the remaining 1,300 kWh has a value of 9c/kWh (equal to €117). Thus the payback period is reduced by earning €687 from exports annually. This export payment is on top of the payback accruing from displaced imports (the 2,000 kWh mentioned above).

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