Energy intensity: The amount of energy needed to produce a unit of output (which can be measured in terms of gross domestic product).  The lower the energy intensity, the more work done per unit of energy.

Feed-in tariff: Tariffs that require extra payment for renewable energy, usually solar, that goes to the electrical grid.  Usually, the money goes to individuals who have installed solar panels. This system incentivizes not only solar installation, but installation of the most efficient solar possible.

Gigawatt: A unit of energy equal to a billion watts. A watt is equal to one joule per second. A Gigawatt is not the same as a gigawatt-hour, which equals a gigawatt expended over an hour.  According to answers.com [http://wiki.answers.com/Q/How_many_homes_can_a_gigawatt_power], a gigawatt can power roughly 750,000 to 1,000,000 U.S. homes.

Grid parity: The point where a renewable source becomes no more expensive than electricity on the power grid, most of which is generated with fossil fuels.

GW: See gigawatt.

Kilowatt hour: A unit of energy equivalent to the work done by one Kilowatt (1 KW) of power expended for one hour. This is more formally expressed in joules: one Kilowatt-hour equals 3,600,000 joules.

kWh: See kilowatt hour.

Photovoltaics: Technology employing layers of semiconductor material, usually silicon, to capture power from the sun for use as electricity.  Thin film is an alternative photovoltaic form that uses metallic compounds.

Solar thermal: A parabolic (inverted cone shaped) mirror used to collect the sun’s energy and convert it into usable energy.  Solar thermal water heaters are a basic, and inexpensive, form of solar energy.  Solar thermal power plants are a large-scale version of the same concept used to produce power for the electrical grid.