Absolute Humidity 
The ratio of the mass of water vapour to the volume occupied by a mixture of water vapour and dry air. 
The component of a solar thermal collector that absorbs solar radiation and converts it to heat, or, as in a solar photovoltaic device, the material that readily absorbs photons to generate charge carriers (free electrons or holes). 
The ratio of the radiation absorbed by a surface to the total energy falling on that surface described as a percentage. 
The passing of a substance or force into the body of another substance. 
Acid Rain  
Rain mixed with sulphuric, nitric and other acids which arise from emissions released during the burning of fossil fuels. 
Without loss or gain of heat to a system. An adiabatic change is a change in volume and pressure of a parcel of gas without an exchange of heat between the parcel and its surroundings. In reference to a steam turbine, the adiabatic efficiency is the ratio of the work done per pound of steam, to the heat energy released and theoretically capable of transformation into mechanical work during the adiabatic expansion of a unit weight of steam. 
Unicellular or multicellular plants, occurring in fresh or salt water or moist ground, that have chlorophyll and other pigments but lack true stems, roots, and leaves. The group includes the seaweeds, diatoms, and spirogyra. 
A mixture composed of two or more elements, at least one of which is a metal. 
Alternating Current  
Electric current that changes direction at regular intervals. 
Ampere (amp)  
The number of electrons flowing past a given point in an electrical conductor in a given amount of time; this is the electrical current. 
A device that operates by electricity. Includes lights and heaters, not just machines with moving parts. 
A rock formation that allows water to move through it, such as a layer of sandstone. The aquifer must occur above a layer that prevents the water seeping away, such as clay. In an aquifer deep below the surface the water will be hot. 
Gases that surround the earth. 

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Waste plant fibre left after the juices have been removed from sugar cane. 
A charging device in fluorescent lights which gives a "jump start" to the gas inside the tube to make it start glowing steadily. 
Band gap  
In a semiconductor, the energy difference between the highest valence band and the lowest conduction band. 
Band gap energy  
The amount of energy (in electron volts) required to free an outer shell electron from its orbit about the nucleus to a free state and, thus, to promote it from the valence level to the conduction level. 
A human-made barrier built across a water course. 
Barrier energy  
The energy given up by an electron in penetrating the cell barrier; a measure of the electrostatic potential of the barrier. 
The term generally used for a dry cell used to power a torch or small appliance. In science it refers to several electrical cells connected together to increase the voltage. 
Beaufort Scale  
The scale devised in 1805 by Sir Francis Beaufort, a British Admiral, measures wind strength on a scale from force 1 (light air) to force 12 ( hurricane) on land and to force 17 for winds at sea. 
The term biofuels refers to fuels used for the generation of electricity and fuels for transportation. Biofuels are alcohols, ethers, and other chemicals made from biomass such as plants, domestic, agricultural and forestry wastes. 
The wires from a battery that will touch the armature of a motor. 
BTU British Thermal Unit 
British Thermal Unit is a measure of heat energy; the amount needed to raise the temperature of one pound of water by one degree Fahrenheit. 

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Metric thermal unit: a measure of heat energy; the amount needed to raise the temperature of one kilogram of water by one degree Centigrade. This is the large Calorie (used relating to food energy content) definition. The small calorie of fuel research is the amount of energy needed to raise the temperature of one gram of water by one degree Centigrade. 
Are a type of food made up of carbon, hydrogen and nitrogen. Carbohydrates, such as starch and sugar are quick-release energy rich food substances. Other food types necessary for a balanced diet are proteins, fats, fibre, vitamins, minerals and water. 
A Molecule that's present in all living things, rocks and fossil fuels 
Carbon dioxide 
A colourless odourless incombustible gas present in the atmosphere and formed during respiration, the decomposition and combustion of organic compounds and in the reaction of acids with carbonates: used in carbonated drinks, fire extinguishers, and as dry ice for refrigeration. Formula: CO2. Also called: carbonic-acid gas. 
The Celsius scale is used to indicate temperature. Other scales are the Kelvin scale, and the Fahrenheit scale. 
Weather patterns over time. 
Solid fuel of plant origin formed millions of years ago. The vegetation died and became swamped by water where it decayed, was compressed and slowly turned into coal. Coal is mined and brought to a power generating station to be burned to produce energy. 
The method of switching the electrical connections to a rotating coil so that the side of the coil facing a particular direction is always magnetic north. 
Achieving the use of less energy, either by using more efficient technologies or by changing wasteful habits. 
A chamber where steam is cooled and condensed to water. 
The process by which heat travels through some substances without the substance moving. For example, leave a teaspoon in a cup of tea and the handle gets hot because heat moves from the tea, up through the spoon. 
Conductors have loosely bound electrons in their outer electron orbits. These are free to move through the metal. Once a small voltage is applied the electrons move: thus electricity flows. Conductors have a low resistance. 
To make impure by touching or mixing; pollute. 
Heat travels by moving particles in a liquid or substance. For example, heat is carried from an electric heater around the room because the air moves. 

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The total amount of electricity required by users at any one time. 
Depletion layer 
A p-n junction area that has few charges available for conduction and so acts as a barrier to the movement of charges. 
Direct current 
An electric current that flows steadily in one direction around a circuit. Batteries produce direct current. 
The addition of a small amount of another element to a pure emiconductor to increase its conductivity. 
A machine for converting mechanical energy to electrical nergy.Common name used for direct current generators.

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A Community of plants, animals and microorganisms nterdependent on each other and their environment. 
Eddy currents 
Electrical currents produced in a conductor by a variation in the trength of a magnetic field. 
The ratio of desired work-type output to the necessary energy input, in any given energy transformation device. An efficient lightbulb for example uses most of the input electrical energy to produce light, not heat. An efficient heatbulb uses most of its input to produce eat, not light. 
Electric current 
A flow of electrons moving along a wire or conductor. 
Electrical energy 
The ability of the electric current to do work. Measured in kilowatt hours. 
A device consisting of an iron core surrounded by a wire coil that produces magnetic effects only when an electric current is flowing in the wire coil. 
The negatively charged particles that are part of an atom. 
The release of waste by-products produced from the generation of electricity (gases) into the air. 
Energy is something which makes things happen, it is also known as the capacity to do work. Almost all the energy used has its origins in the sun. All life depends on sunlight and heat. 
Energy flow 
The transfer of energy from one organism to another through the feeding levels, or trophic levels, in an ecosystem. About 90% of the energy is lost at each transfer. 
Energy resource 
A resource is something that can be used to provide energy e.g. coal, food, gas, geothermal, manure, nuclear, oil, peat, sea, sewage, sun, waste, water, wind or wood. 
Electrical lighting devices which produce the same amount of light(lumens) using less electrical energy than incandescent electric light bulbs. Such devices are usually of the fluorescent type, which produce little heat, and may have reflectors to concentrate or direct the light output. 
To change or cause to change from a liquid or solid state to a vapour. 
Extrinsic conduction 
The movement of charges through a doped semiconductor

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Any type of material that is attracted to a magnet. 
Flat Plate 
A photovoltaic surface installed to face south at a tilt angle equal to the latitude. 
Flat-plat tracker 
A device mounted under a photovoltaic panel that moves the panel to follow the path of the sun. 
Flue gas desulphurisation  
Removal of sulphur oxides from oil and coal burning boilers by washing the flue gas with a solution of lime. The sulphur is removed as calcium sulphate, which is used to make gypsum plasters and hence has a commercial value.  
Fluorescent light 
A device which uses the glow discharge of an electrified gas for the illuminating element rather than an electrically heated glowing conductive filament. 
Food chains 
A chain of organisms in an ecosystem in which each is food for the next member. The first in the chain are plants or bacteria which make their own food (primary producers). These are eaten by herbivores (primary consumers) which are in turn eaten by carnivores (secondary consumers) 
Food web 
Connected food chains which represent energy flow in an ecosystem. 
Fossil fuels 
Sources such as coal, oil and natural gas are referred to as fossil fuels. They are formed from the remains of dead plants and animals. 
A resistance encountered when one body moves relative to another body with which it is in contact. 
Fuel cell 
A device which produces electricity with high efficiency (little heat by using a fuel and a chemical which reacts with it (an oxidizer) at two separate electrical terminals. An electric current is thereby produced. 
Fuel efficiency 
The amount of work obtained for the amount of fuel consumed. In cars, an efficient fuel allows more miles per gallon of gas than an inefficient fuel. 

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Gaia Hypothesis 
The idea that Earth and the atmosphere is a living organism. Life helps create the environment it needs in order to live. Gaia is the ancient Greek word for "Mother Earth." 
An instrument for measuring an electric current. 
Gases released by burning fossil fuels pollute the atmosphere, which is the air surrounding the earth. Some are called 'Greenhouse gases' because they act as insulators, keeping heat trapped close to the earth. 
A machine that produces electricity. 
Heat from the earth's hot rocks (molten rock). 
Global warming 
The gradual warming of the earth due to the "greenhouse effect". 
Greenhouse effect  
The trapping of the sun's radiant energy, so that it cannot be reradiated. In cars and buildings the radiant energy is trapped by glass: in the earth's atmosphere the radiant energy is trapped by gases such as CFCs and carbon dioxide. 
Greenhouse gases
Gases that prevent heat from escaping from the atmosphere. This makes the earth warmer. 
A system of transmission lines which interconnect the generating stations and distribution centres of local electricity authorities. 

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Hybrid system 
In a hybrid power system different methods of producing electricity are combined to ensure a continuous power supply. Gas or diesel fuel generators may be combined with solar cells or wind generators. 
A prefix meaning produced by or derived from water or the movement of water, as in "hydroelectricity". 
Hydro Power 
Running water provides the power to drive turbines which generate energy. This power results in electricity being produced. 
A class of compounds containing hydrogen and carbon formed by the decomposition of plant and animal remains. These compounds include coal, oil, natural gas, and other substances occurring in rocks. 

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Immersion heater 
This is screwed into a large opening usually on the top of the cylinder. The central rod contains a thermostatic sensor which switches the heater on when the water in the cylinder drops below a certain level. Usually rated at 3kw, there are different types for different purposes. 
Not able to be penetrated, as by water, light, etc.; impermeable. 
Incandescent light  
A bulb which uses the ohmic resistance in a conductor to produce light upon the passage of an electrical current through it. The conductor is usually in the form of a wire or filament. 
The solar radiant energy impinging on the earth. 
Doesn't let heat pass through easily. 
Intrinsic conduction 
The movement of charges through a pure semiconductor. The intrinsic current is very small and depends on the temperature of the semiconductor. 
A device which changes direct current (DC) into alternating current(AC). Direct current is created by photovoltaic modules or batteries and converted to AC through the use of an inverter. 

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The basic unit of work or energy. 

The measure used for electrical energy. One kilowatt hour is the amount of electrical energy transferred to an appliance in one hour by one kilowatt of power. 

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Normally refers to a lagging jacket, which surrounds the hot water cylinder. The following example emphasises the importance of a lagging jacket.  A 130 litre unlagged copper cylinder maintained at 600°C will waste 86 units of electricity per week. Provide the cylinder with a 50mm thick lagging jacket and this loss will be reduced to 8.8 units per week. Increase the thickness of the lagging jacket to 75mm and the weekly heat loss will be reduced to 6 units. 75mm has been found to be the optimum thickness. Increasing it further does not provide a worthwhile saving. 


A piece of iron, cobalt or nickel (or an alloy of these) that can attract other pieces of the same metals. 
Magnetic field 
An area where magnetic forces can be detected. 
Mechanical energy 
Energy of the moving parts of a machine. Also refers to movements in humans. 
Tiny creatures such as bacteria that are too small to see with your eyes 
Two or more atoms combined chemically, for example a Carbon dioxide molecule (CO2) or a glucose molecule (C6H12O6). 
A machine that converts electrical energy into mechanical energy.

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Non renewable resource 
Non renewable means that the resources are finite resources, they will not last forever. Once they are used up they cannot be replaced.e.g fossil fuels 
N-type semiconductor 
A semiconductor in which electrons are the majority carriers. 
Nuclear energy 
Energy from radioactive material, such as uranium, which is found in some rocks. 
Nuclear fission 
Atomic nuclear processes which involve the splitting of nuclei with the accompanying release of energy. 
Nuclear fuel 
Energy derived from atomic nuclear processes during fission or fusion. 
Nuclear fusion 
Atomic nuclear processes which involve the fusing of nuclei with an accompanying release of energy. 
Nuclear Power  
When the Uranium (U) contained in fuel assemblies in the core of the reactor is encouraged to undergo fission (break apart), heat and radiation are released and this is called nucler power. Only a tiny fraction of the uranium fuel is actually capable of fission, the U-235 fraction. The bulk of the fuel does not break down. 

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Ocean energy 
The vast amount of potential energy within the oceans. 
Millions of tiny marine creatures and some plant life became embedded in mud on the beds of shallow seas. The remains of these plants and animals changed into oil by the action of bacteria and the pressure of deposits. 
Ocean thermal energy conversion technology, which uses the temperature differential between warm surface water and cold deep water to run heat engines to produce electrical power.

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Able to cause or produce disease. 
Organic material built up by the partial decay of vegetation in acid water of bogs. Peat represented the first stage in the transformation of vegetation into coal. 
To penetrate or pervade (a substance or area). 
How green plants, algae and some bacteria make their own food. Carbon dioxide and water are taken in and using sunlight and a substance called chlorophyll, chemical reactions take place to produce glucose and oxygen. The chemical formula of this reaction is: 6CO2 + 6H2O ----sunlight & chlorophyll C6H12O6 + 6O2 
Photovoltaic cell 
Device made of semiconductor materials which produces a voltage when exposed to light. 
Point of consumption 
Where a product, such as food, is finally used. 
Point of production 
Where a product, such as food, is originally made. 
Polar ice-caps 
At the north pole and south pole, water is frozen as ice. 
The rate at which electrical energy is used, measured in watts (w) or kilowatts (kw) 
Rain, snow, sleet, dew, etc., formed by condensation of water vapour in the atmosphere 
p-type semiconductor 
A semiconductor in which holes are the majority carriers. 
To free (something) of extraneous (not essential), contaminating, or debasing matter.  

Photovoltaic; pertaining to the production of electricity from light. 

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The rays given off by the sun including heat, light and ultra-violet rays. 
Renewable energy devices 
Solar collectors, wind machines, hydroelectric turbines are typical examples. 
Renewable resource
Renewable means that the supply will never be exhausted. They can be used over and over again.e.g wind, water. 
A natural or artificial lake or large tank used for collecting and storing water, e.g. community water supplies or irrigation. 
Process by which all living things break down food to release energy. Involves exchange of carbon dioxide and oxygen and so is made possible in many animals by the breathing system. The chemical formula of respiration is: C6H12O6 + 6O2 ----------?6CO2 + 6H2O + energy 

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The deposition or production of sediment.  
Substances with outer electrons that are not free to move but require little energy to free them for conduction. Semiconductors have a resistance between conductors and insulators. Their electrons are not free to move but do not need a great amount of energy to free them for conduction. It is important to realise that it is the electrons which actually move in n-type and p-type semiconductors. 
Solar cell 
Device made of semiconductor materials which produces a voltage when exposed to light. 
Solar cooling 
The use of devices which absorb sunlight to operate systems similar to gas-fired refrigerators. 
Solar electricity 
Electricity produced directly by the action of sunlight. 
Solar heating 
Processes, active or passive, which derive and control heat directly from the sun. 
Solar power 
The sun gives us light and heat. We can capture and magnify the sun's energy. 
Solar thermal energy systems  
Systems using concentrating collectors to focus the sun's radiant energy onto or into receivers to produce heat. 
A coil of wire used to produce a magnetic field by the flow of electrons. 

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The measure of how hot a body is. 
Rotors or blades that spin when driven by steam, gas, water or wind.

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Utility-Interactive System 
A PV installation connected to a utility power line. 


The volt is the basic unit for electric potential. The higher the electric potential, or volt, the greater the amount of electrical energy that can be transferred through a circuit. 

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The unit of electrical power. It is a measure of the rate at which an appliance uses electrical energy. One watt is equal to one joule per second. 
The result of unequal heating of the earth's atmosphere, as a function of terrain, latitude, time of year and other secondary factors. 
Wind machines 
Devices powered by the wind which produce mechanical or electrical power.

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