BTU (British Thermal Unit) - A unit of measure of the energy in fossil fuels. A gallon of gasoline has approximately 126,000 BTUs in one gallon. Propane has 91,600 BTUs in one gallon. Number 2 heating oil has approximately 132,000 BTUs in one gallon.

Heat Exchanger - A device used to transfer heat. In many solar hot water or "thermal" systems, a heat exchanger transfers thermal energy from the fluid circulating in the collector to the water in a storage tank that is later used in showers, laundry, etc.

Hybrid Systems - These are systems that combine two or more renewable energy technologies. A combination photovoltaic and wind system, or a photovoltaic system that recovers and utilizes heat from the panels for space or water heating are hybrid system examples.

Inverter - A device that converts photovoltaic or wind generated electricity to a form that is compatible with your electrical appliances, clocks, etc. Most houses use 120volt Alternating Current electricity, and all the appliances in the house are designed to operate on this type of electricity. Most photovoltaic and wind generated electricity is 12, 24 or 48 volt Direct Current. The inverter will transform the Direct Current into Alternating Current.

Photovoltaic (pv) Panels- These are the devices that convert sunlight into electricity.

Photovoltaic (pv) System - A complete set of components for converting sunlight to electricity. A system may include the following components: photovoltaic panels, wiring, inverter, controller, batteries and other components depending upon the sophistication of the system.

Solar Collector- These are the rectangular panels that are used to convert thermal energy from the sun, which is then used for space and/or water heating.

Solar Hot Water System - A complete set of components for converting thermal energy from the sun into space and/or water heating. A system may include the following components: solar collector, pump, heat exchanger, and storage tank.

Watt - A unit of measure of electrical energy. Most electrical devices will have a label that states what their energy needs is in watts. (A microwave made need 1000 watts to operate). A kilowatt is 1000 watts.

Watt-hour- A device that needs 1 watt to operate, and runs for one hour, will use 1 watt-hour of electricity. A kilowatt-hour is 1000-watt hours. Your electric meter records the number of kilowatt-hours you use every month.

Wind Energy Conversion System- Usually known as a windmill or a wind turbine. WECS convert energy from the wind into electricity. A complete set of components may include the following components: Wind Turbine, wiring, inverter, controller, batteries and other components depending upon the sophistication of the system.