Glossary

Terms Explained A-F G-L M-Q R-Z

A - F
Acid Rain	Rain with a harmful level of sulfuric, nitric and other acids. Proven deadly to some ecosystems, it arises from emissions released in burning of fossil fuels.
Alcohol Fuels	Various forms of alcohol, which when blended with gasoline can be used as fuel. Common examples are methanol and ethanol.
Alternating Current (AC)	Electrical energy (such as UK mains electricity) which continually reverses direction at the rate of 50 hertz (50 times per second).
Ampere	A measure of electrical current. It is the number of electrons flowing past a given point in an electrical conductor in a given amount of time.
Array:	The name given to a group of solar modules connected together in a structure.
Base load	minimum energy level a company provides its customers on a constant basis.
Biomass and biomass fuels:	Biologicial, organic non-fossil materials such as wood. Usually defined as being carbon neutral.
Biomass energy:	The energy from biomass materials such as wood when combusted. The emissions are low in carbon dioxide.
Boilers:	Conventional boiler: Conventional boilers burn fuel in a combustion chamber surrounded by a water jacket, thus heating the water for circulation around a heating system. Much of the heat is lost to the surrounding air or up the flue. Condensing boiler: Condensing boilers are higher efficiency boilers that waste almost no heat out of the flue. They are designed to extract more heat from fuel than a conventional boiler. These boilers cool the condensation heat from the flue gas so that the water vapour condenses. The heat produced by this process can be used to heat water. Most brands comply with current UK building regulations. Combination boiler: Modern form of gas boiler which activates on demand usually within a pressurised system to provide instant hot water and central heating (but not at the same time).When hot water is being run there can be no heat to the central heating system. With this form of boiler there is no need for water storage tanks or hot water cylinders. Wood-burning (biomass) boiler: There is a wide variety of wood-burning boilers on the market, utilising differing wood fuels such as wood, wood pellets, or corn (renewable resources). Burning these fuels adds no net carbon to the environment, thus making no contribution to global warming. Log fuelled boilers need to be fed manually and the logs can take up a lot of storage space. Automatic-feed biomass boiler: These boilers use wood chips and/or pellets and come with their own storage container where the top-up fuel can be kept and automatically fed into the boiler unlike log fuelled boilers.
Borehole:	The term used for a drill hole in geophysical exploration. Boreholes can be used as part of a Ground Source Heat Pump system to extract solar heat from the ground.
British Thermal Unit:	Often referred to as BTU, this is the old Imperial measure of heat needed to raise the temperature of one pound of water by one degree Fahrenheit. Sometimes still used to size domestic heating boilers and radiators.
Calorie	Metric thermal unit: the amount of heat energy needed to raise the temperature of one kilogram of water by one degree Centigrade. The word is used in two contexts: large calories and small calorie. The "small calorie" used in fuel research, is the amount of energy needed to raise the temperature of one gram of water one degree Celsius.
Capital costs:	These are the one off initial investment costs such as buying equipment.
Carbon Dioxide:	Often referred to as CO2, this greenhouse gas is mostly produced by the combustion of fossil fuels. Its high atmospheric concentrations are a result of human activity which interferes with the natural CO2 cycle. This can cause negative effects, such as rapid climate change.
Clean Energy	synonymous with renewable energy resources.
Compact Fluorescent Lamp:	Also known as CFLs or energy saving lamps/light bulbs, these efficient lamps generate five times more light than their filament equivalent.
Climate Change:	A significant change from one climatic condition on Earth to another, currently also referred to as Global Warming (see Global Warming).
Climate Lag:	The time elapsed between a factor that causes climate change and the effect it has, such as the release of carbon dioxide from fossil fuel combustion.
Combined Heat and Power:	Also known as CHP or Cogeneration, this refers to the production of thermal energy and electrical power simultaneously.
Conductivity:	This is the term used to calculate heat transfer rates for materials and to measure the extent to which a material can transmit electrical energy.
Conservation:	Reducing the use of energy by combatting waste and increasing energy efficiency.
Cost effective:	When the money saved by renewable energy and energy efficiency more than pay for the capital and maintenance costs over a given period .
DC:	Electricity that flows continuously in one direction such as from a battery or a solar powered system.
Deep cycle battery	A battery designed to tolerate up to 80% discharge of its capacity.
Depth of discharge (DOD)	the amount of energy (expressed in percentage of its rated capacity) withdrawn from a battery, a battery bank or a cell.
Demand management:	Also known as demand side management. Refers to control of energy consumption to better match generation capacity & efficiency.
Direct Current (DC)	Electric current flowing in one direction in invariable amperage. This is most often associated with battery power.
Distributed Generation (Distributed Energy Resources)	Electricity that is provided by small power generators located at or near end users
Emissions	In the context of global warming, this is the release of radiatively relevant greenhouse gases (one example is the release of carbon dioxide during fuel combustion in an automobile engine.)
Energy	The capacity to do work.
Energy efficiency:	The ratio of energy input to energy output. 'Energy efficient' usually refers to any change in energy use that results in an increase in net benefits per unit of energy used, thus reducing waste.
Energy sources:	There are three categories: Fossil fuels (oil, coal, gas); Nuclear (fission of fusion); Renewables (wind, hydro, geothermal, solar, biomass and wave).
Evacuated tube solar collectors:	These utilise parallel rows of glass tubes to absorb energy from the sun. Each tube is transparent and consists of an outer tube and a metal absorber tube attached to a fin. The coating of the fin absorbs energy from the sun.
Evacuated tube:	The absorber tube in a solar thermal collector through which collector fluid flows.
Flat Plate Collector:	A device, usually a box, in which sunlight is collected and converted into heat by a dark absorber plate under glass or plastic, without the aid of reflecting surfaces to concentrate the rays.
Fossil fuels:	Natural hydrocarbon fuels (oil, coal and gas) and their derivatives such as petrol.
Fuel:	Any material that is capable of releasing energy when its chemical or physical structure is altered.

G - L
Geothermal	Heat from the earth. Customarily applied to energy from geysers and hot springs (which is now better characterized as hydro-geothermal), in recent years, this term is applied to any heat stored in earth and available as a renewable energy resource.
Global warming:	An increase in the average near surface temperature of the Earth. Usually used to describe the predicted rise in this temperature due to the increase in emissions of greenhouse gases.
Ground Source:	Solar heat stored in the ground that can be utilised by heat pumps (see Borehole).
Heat Pump:	An energy efficient electric compressor that takes a high volume of low-level heat from one source. This is then transferred to another place as a lower volume of high-grade heat. It operates as a heating and air-conditioning system that uses a refrigeration cycle (where a refrigerant is compressed as a liquid and expanded as vapour to absorb and emit heat.) The heat pump transports heat to a space to be heated during Winter and reabsorbs heat from the same space to be cooled during the Summer. Heat can be absorbed from the air, ground or ground water (see Borehole). Types of heat pump: Air Source Heat Pump: The most common type of heat pump, it absorbs heat from the outside air and transfers it to the space to be heated. Or, in cooling mode, the heat pump absorbs heat from the space to be cooled and rejects it to the outside air. Back up heating is needed if outside air temperatures are likely to fall to 32 degrees Fahrenheit or below. Ground Source Heat Pump: A heat pump in which the refrigerant exchanges heat with a fluid circulating through the ground or ground water. The fluid is contained in a variety of vertical and horizontal pipe layouts depending on the temperature of the ground or water and the ground area available. These heat pumps can use the waste heat from an air conditioning system to provide hot water in the Summer. Geothermal heat pumps are more expensive to install but are more energy efficient than air source heat pumps and have lower emissions. Closed loop: A heating or cooling system where the heat transfer fluid circulates from the heating or cooling components to a heat exchanger thereby transferring heat away.
Hydroelectric:	The generation of electricity where the energy of running water is converted into electric power.
Hydro power:	Power obtained from the (typically gravitational) movement of water.
Insolation	Solar radiant energy impinging on the earth in any given region or area.
Inverter:	An appliance used to convert direct current (DC) into alternating current (AC) for standard household use.
Kilowatt (kW)	One thousand watts of electricity (See Watt).
Kilowatt hour:	A unit or measure of energy consumption of 1,000 Watts (one kilowatt) over one hour. Written as KWh. Can be used to measure electricity generation and use as well as the heat energy of fuels such as gas.
Lead-acid battery	Slightly larger than a car battery, these have internal plates made of lead or a lead alloy, surrounded by a sulfuric acid electrolyte. Car batteries are made with softer plates. Lead-acid batteries are commonly used in solar and wind energy systems.
Life Cycle Cost (LCC):	The total of all costs relating to a system, product, structure or service during its life time. Lifetimes are typically 20 years for a renewable energy system)
Light emitting diode (LED):	LEDs produce light at low temperatures. This reduces wasted heat energy and makes them very efficient.
Line wire loss	Voltage or power lost due to the resistance of wires in an electric circuit. Power loss is often proportional to wire length and is far greater in DC than AC.
Load	The electricity required and used by any single or collection of electrical item(s).
Load Profile	Collected information on a customer's usage over a set period of time

M - Q
Maximum power point (MPP)	The voltage at which a PV array is producing maximum power.
Maximum power point tracker (MPPT)	A power conditioning unit that increases the power of a PV system by ensuring operation of the PV generator at its Maximum Power Point (MPP). The ability to do so can depend on climate and the battery's state of charge.
Megawatt (MW)	One million watts of electricity (See Watt).
Nuclear fusion	A potentially limitless source of energy in which nuclei are fused, with an accompanying release of energy.
Open Loop:	A system where water is pumped from a water well, pond, lake or other surface source for a ground source heat pump or solar water heater. The water is heated or cooled for use.
OTEC	Ocean Thermal Energy Conversion. Heat engines produce electrical power from the differential in temperature between the ocean's warm surface and cold deep water.
Ocean energy	The use of the vast potential energy within the oceans. Several kinds are possible, including OTEC and wave power.
Off Peak/ On Peak	Times when energy demand and price is low (off-peak) or high (on-peak).
Ozone	A major agent in the formation of air pollution, this is actually a form of oxygen. Ozone is a result of photochemical reactions involving emissions from automobile and industrial processes. Ozone does occur naturally in earth's upper atmosphere (the ozone layer) where it protects the earth's surface against harmful effects of the sun's radiation. Ozone accumulation close to the earth's surface is harmful. Ozone depletion in the upper atmosphere is also harmful, as the ozone layer is essential to the preservation of the earth.
Parabolic Dish	A high-temperature (above 180 degrees Fahrenheit) solar thermal concentrator, generally bowl-shaped, with two-axis tracking.
Parabolic Trough	A high-temperature (above 180 degrees Fahrenheit) solar thermal concentrator with the capacity for tracking the sun using one axis of rotation.
Passive solar:	The design of buildings so that they capture or exclude the Sun's heat in order to reduce fossil fuel consumption for heating or cooling.
Payback:	The time it takes for positive cash flow to match capital costs. Can be from energy efficient or renewable energy measures.
Peak Watt	A manufacturer's unit indicating the amount of power a photovoltaic cell or module will produce at standard test conditions (normally 1,000 watts per square meter and 25 degrees Celsius).
Photovoltaic (PV) solar cell:	A device for changing light from the Sun into electricity. Can be integrated into large structures for buildings or PV 'solar farms'.

R - Z
Renewable energy	Energy from sources that cannot be used up or that are naturally replenishing: sunshine, water flow, wind and vegetation. Some add the qualification, "cannot be used up in one lifetime." Still other note that these are "flow-limited," in that there is a limited amount of energy per unit of time.
Renewal Obligation Certificates (ROCs):	Digital certificates which hold details of how a unit of electricity is made, who made it and who consumed it.
Renewable resource:	A resource that can be renewed or replenished over a human time scale.
Renewable energy:	Energy from sources that are naturally replenished such as water, sunlight or wind. Includes sustainable biofuels.
Renewable energy technology:	Devices that utilise renewable energy resources, such as solar panels and wind turbines.
Return on Investment (ROI):	The comparative term used to assess the return on initial capital investment. Often expressed as a percentage return per year.
Resistance	Property of a material that resists the flow of electrons when a potential difference is applied across it. This is measured in Ohms. Resistance is the quality that causes electricity to produce light in a filament or heat in an electrical heater of any kind.
Resistor	Any electronic component that restricts the flow of electrical current in circuits. These are often used intentionally to produce heat or light (e.g. a stove element or a light bulb filament).
Ribbon Silicon	A type of single-crystal silicon that produced in sheets or ribbons.
Silicon	Semiconductor material made from silica, purified for photovoltaic applications.
Single Crystal Silicon	An very pure (and very expensive) form of crystalline silicon produced by the Czochralski method. This involves dipping a single crystal seed into a reservoir of molten silicon under refined conditions and slowly withdrawing a solidifying single crystal rod of silicon that is then fabricated into single-crystal photovoltaic cells.
Solar cell:	See Photovoltaic (PV) solar cell.
Solar cooling:	The use of solar thermal energy by devices that absorb sunlight to operate a cooling appliance.
Solar electricity:	The conversion of sunlight into electricity. Also known as photovoltaics or PV.
Solar greenhouse:	A greenhouse which is converted to include double glazing and heat storage.
Solar heating:	Processes that convert the sun's heat into heat for other uses such as hot water.
Solar thermal:	Term used to describe systems that capture the sun's heat for other uses such as hot water.
Solar panel:	A panel that produces either electricity or heat when light shines on it.
Stand-Alone system	A solar PV installation that is not connected to a utility power line (the grid).
Thermal	Pertaining to heat gain and heat retention.
Thin-Film PV:	A thin layer (less than one micron thick) of material that is deposited onto a metal, ceramic or semiconductor base and is used to make photovoltaic cells. The film can be conductive or non-conductive and can be made of amorphous or polycrystalline material.
Transmission System (Electric)	Lines or wires of electricity that transmit electrical energy from points of origin to end users.
Turbine	Any machine used to generate rotary mechanical power from the energy of a stream of fluid (such as water, steam, or hot gas) or air (wind power). Turbines convert kinetic energy into mechanical energy.
Uninterruptible power supply	A device (likely containing batteries) that stores power for use when conventional power is unavailable (e.g. during a blackout).
Volt	The unit of electric potential (intensity) and potential difference. It is also a relation of current to resistance: i.e. 1 volt is the potential difference across a resistance of 1 Ohm when a current of 1 Amp is flowing.
Voltage drop	The voltage lost along a length of wire or conductor due to resistance. The voltage drop is calculated using Ohm's Law. Voltage drop is also measured for resistors.
Voltage regulator	A device to control the operating voltage of a photovoltaic array.
Voltage	The measurement of the "intensity" of electricity.
Watt (W):	A unit of electrical power used to describe the rate of energy consumption of an electrical appliance. One Watt equals one joule per second.
Waveform	The shape of a wave that represents a vibration or AC current.
Wind energy	Energy from wind motion converted into mechanical energy by the action of a wind turbine driving a generator with its central shaft.
Wind turbine:	Machine for converting the wind's kinetic energy into a useful form. Usually refers to an electrical energy machine.
Wind Farm	This is a group of turbines interconnected to a common utility system via a system of transformers, distribution lines, and a substation.
Wood energy:	Wood and wood products used for fuel, such as wood chips, sawdust and charcoal.
Wood pellets:	Sawdust, firewood, wood chips or untreated offal timber compressed into uniform diameter (approx. 6mm diameter, 10 to 30 mm length) pellets to be burned in a heating stove.

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