active solar system
	A mechanical system that actively collects, concentrates, and stores solar energy.
cogeneration
	The simultaneous production of electricity and steam or hot water in the same plant.
energy efficiency
	A measure of energy produced compared to energy consumed.
eutectic chemicals
	Phase-changing chemicals used in heat storage systems to store a large amount of energy in a small volume.
gasohol
	A mixture of gasoline and ethanol.
geothermal energy
	Energy drawn from the internal heat of the earth, either through geysers, fumaroles, hot springs, or other natural geothermal features, or through deep wells that pump heated groundwater.
low-head hydropower
	Small-scale hydro technology that can extract energy from small headwater dams; causes much less ecological damage.
micro-hydro generators
	Small power generators that can be used in low-level rivers to provide economical power for four to six homes, freeing them from dependence on large utilities and foreign energy supplies.
net energy yield
	Total useful energy produced during the lifetime of an entire energy system minus the energy used, lost, or wasted in making useful energy available.
ocean thermal electric conversion (OTEC)
	Energy derived from temperature differentials.
passive heat absorption
	The use of natural materials or absorptive structures without moving parts to gather and hold heat; the simplest and oldest use of solar energy.
photovoltaic cell
	An energy-conversion device that captures solar energy and directly converts it to electrical current.
run-of-the-river flow
	Ordinary river flow not accelerated by dams, flumes, etc. Some small, modern, high-efficiency turbines can generate useful power with run-of-the-river flow or with a current of only a few kilometers per hour.
tidal station
	A dam built across a narrow bay or estuary traps tide water flowing both in and out of the bay. Water flowing through the dam spins turbines attached to electric generators.
wind farms
	Large numbers of windmills concentrated in a single area; usually owned by a utility or large-scale energy producer.

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