• A
  • B
  • C
  • D
  • E
  • F
  • G
  • H
  • I
  • J
  • K
  • L
  • M
  • N
  • O
  • P
  • Q
  • R
  • S
  • T
  • U
  • V
  • W
  • X
  • Y
  • Z
Term Definition

An electrical storage device which uses an electric cell, or group of cells, to convert chemical energy into electrical energy by means of reversible chemical reactions.


Bioenergy is the renewable energy created from biomass or biofuels.


Fuel derived from biological sources, so in some respects this term is synonymous with biomass. Biofuels come from recently deceased sources (e.g. as distinct from fossil fuels). The term biofuel is also used to refer to the energy created from these fuel sources.


Biomass is material from biological sources such as wood, straw, manure, sugar cane etc. which has stored sunlight in the form of chemical energy and can be used as a biofuel to create bioenergy.

British Thermal Unit (BTU)

The amount of heat energy required to increase the temperature of one pound of water by one degree Farenheit. It is equivalent to 1055 Joules.


Carbon footprint

A measure of the impact of human activities on the environment, especially global warming, due to the amount of greenhouse gases produced, and expressed in units of carbon dioxide. On a personal level this is generally dived into two areas, the primary footprint (our direct emission of carbon dioxide due to burning of fossil fuels, eg for heating and transportation, which is under our direct control) and the secondary footprint (due to indirect emissions resutling from the product lifecycle of any items which we buy or consume).

Co-generation (CHP)

Co-generation or combined heat and power (CHP) refers to the use of a power station or heat engine to produce both electricity and useful thermal energy. Conventional power stations have always produced heat as a by-product, and in the past this has been vented into the environment. CHP technologies allow this heat energy to be captured and used for domestic or industrial heating.

Energy density

Energy density is the amount of energy stored in a given system or region of space per unit volume or mass. It therefore has units of energy per length cubed or energy per mass. Higher energy densities are typically better for the consumer, as you pack more energy into a given weight or volume.

Energy intensity

Term used to refer to the ratio between energy consumption and economic or physical output. On a national level, energy intensity is the ratio of total domestic primary energy consumption or final energy consumption to gross domestic product or physical output.

Fossil fuel

Fossil fuels are hydrocarbon deposits found in the Earth's crust which were formed by the decay and fossilisation of ancient living animal and plant matter.

Fuel cell

A device that converts the chemical energy of a fuel such as hydrogen and an oxidant into electrical energy.

Hydroelectric power

Hydroelectricity involves the production of power created by the gravitational force of falling water. In general this requires the constuction of a dam which drives a water turbine and generator.


Photovoltaic power generation systems harness solar energy and convert it into electricity. This process involves photons of light interacting with the material of the photovoltaic panal to knock electrons into a higher state of energy, thus creating an electric current.

Solar thermal

Solar thermal power generation systems harness solar energy and convert it to thermal energy (heat).

Solid state lighting

This term refers to the use of light emitting diodes (LEDs) as a light source in place of electrical filaments or gas. The light in an LED is created from a solid object (a semiconductor or in some cases layers of polymers or organic compounds), in contrast to the vacuums or gases employed in traditional light bulbs or fluorescent lighting. The use of a solid state source means that LEDs lose less energy as heat, and such systems are also generally more resistant to physical shock and therefore have an increased lifespan.

Steam trap

A steam trap is a valve designed to discharge condensates, air and other non-condensable gases from a steam system whilst trapping the live steam.


A superheater is a component in a boiler system or steam engine which reheats steam to above its saturation temperature, increasing its thermal energy and ensuring that it does not recondense. This increases the efficiency of the system.

Thermal destratification

Thermal destratification is the vertical equilibration of air temperature within a building or enclosed area, generally though the use of fans. Since hot air rises, the main advantage of an effective thermal destratification system is that it prevents loss of thermal energy at floor level, creating a more comfortable environment and potentially reducing heating bills.

Tidal/hydrokinetic power

Power generated via windmill-like turbines from swiftly flowing rivers or tides. Unlike traditional hydroelectric power, does not require the construction of dams.


A transformer is an electrical device which increases or decreases alternating current (AC) voltages. It consists of two or more insulated coils of wire wrapped around a magnetic core, and uses the principal of mutual induction to convert the AC in the primary windings into AC of a different current and voltage in the secondary windings.


A turbine is a rotary engine which converts the kinetic energy of a moving fluid into mechanical energy through the rotation of a bladed rotar. 

Wave power

Wave power technologies capture energy from ocean surface waves, as distinct from tidal power.

Wind farm

A collection of wind turbines in one location used for the generation of electric power.

Wind turbine

A rotary engine which converts the kinetic energy of wind into motion which is then transferred to an electric generator shaft to produce electricity.