Atmosphere - the gaseous envelope of air surrounding planet Earth.
Active solar heating - a process that uses devices to collect, store, and circulate heat produced from solar energy.
Biomass fuel - a fuel, such as wood, formed from the products of living organisms.
Current - the rate of flow of electricity.
Energy conservation - the practice of extending the useful life of the Earth's energy resources through reduced and more efficient energy use.
Energy - the ability to do work.
Fossil Fuels - fuels originating from geologic deposits of ancient plant and animal life. (Examples are oil, natural gas, coal.)
Heat - a form of energy that causes a rise in temperature, or changes the object from solid to liquid or from liquid to gas.
Helium - a chemical element usually in gaseous state.
Hydrogen - a chemical element. Two atoms of hydrogen are found in every water molecule (H2O).
KWH - a kilowatt hour is a unit of energy. It is equal to 1000 watts being used for one hour. This would be equivalent to having ten 100-watt light bulbs on for one hour or one 100-watt light bulb on for ten hours.
Light energy - the kind of energy that travels as visible radiation consisting of units called photons.
Mechanical energy - the energy of motion used to perform work. For example, when a person peddles a bicycle, the energy from their body is used to put the bicycle into motion.
Passive solar system - a means of capturing, storing, and using heat from the sun. Unlike active systems, passive solar systems do not require the use of pumps and controls. For example, putting a cover over the water in a swimming pool is a passive solar system that helps to trap the sun's heat in the pool water.
Photon - an elemental unit of light energy or a tiny particle of light.
Photosynthesis - the process by which green plants convert carbon dioxide and water into sugars (chemical energy) using the energy in sunlight.
Photovoltaic array - a group of solar electric modules connected together.
Photovoltaic cell - the basic building block in photovoltaic systems that turn sunlight directly into electricity. Sometimes called "solar cells."
Renewable energy - sources of energy which are inexhaustible because their use today does not diminish their availability tomorrow. Solar, wind and hydropower are examples.
Solar collector - a device used to gather and absorb solar energy in the form of heat.
Solar energy - energy in the form of light, or radiation, from the sun falling upon the Earth's surface. This source of energy is free and renewable.
Thin film photovoltaics - photovoltaic technology that involves depositing silicon or other semiconductor materials onto glass, metal or plastic. These films are flexible and less expensive to manufacture, but lower in efficiency than the older crystalline technologies.
Voltage - measure of the "push" of electric current. The higher the voltage, the more force there is to push the current through the wire.
Watt - a metric unit of power, which gives the rate at which work, is done or energy is expended.