Glossary of terms - Renewable Energy

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[A - D]

AC:
Electrical energy (such as UK mains electricity) which continually reverses direction at the rate of 50 hertz (50 times per second).

Array:
The name given to a group of solar modules connected together in a structure.

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.

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.

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.

Demand management:
Also known as demand side management. Refers to control of energy consumption to better match generation capacity & efficiency.

[E - H] | back to top

Emission:
Any substance discharged into the air, Earth or water.

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.

Geothermal:
Energy from reservoirs in the Earth’s surface, such as geysers or ground water that is ‘heat energy’.

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:
The power captured from the natural movement of water for energy purposes.

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Inverter:
An appliance used to convert direct current (DC) into alternating current (AC) for standard household use.

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.

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.

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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.

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.

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’.

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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.

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.

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.

[U - Z] | back to top

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.

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.

Wind energy:
Wind energy comes from moving air which is converted to electrical power by a rotor and generator to create electricity or mechanical energy. This can be used for driving pumps and generators.

Wind turbine:
Machine for converting the wind’s kinetic energy into a useful form. Usually refers to an electrical energy machine.