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Across 3. A flat box which absorbs sunlight to heat circulating water in tubes.(3 words) 4. The practice of allowing individuals on the power grid to subtract the cost of the energy they get from photovoltaics or wind turbines from their electric bills.(2 words) 7. An award that is given to public and corporate edifices for using 40% less energy.(2 words) 8. Energy produced by burning plant-related materials such as firewood.(2 words) 9. A small system that consists of a set of parabolic concentrator dishes that focus sunlight onto a receiver.(3 words) 11. Reflectors, in the shape of a parabolic trough, that reflect sunlight onto a tube of oil at thefocal point of the trough.(3 words) 13. A house that uses the earth as a natural insulation.(3 words) 17. Energy sources-namely, solar, wind, and geothermal.(2 words) 18. Devices that convert light energy into an electrical current.(2 words) 19. Electricity created by free falling water on a turbine generator. 20. An array of suntracking mirrors that focuses the sunlight falling on several acres of land onto a receiver mounted on a tower.(2 words)

Down 1. A policy that requires a percentage of power from renewable energy sources.(3 words) 2. Devices in which hydrogen or some other fuel is chemically revombined with oxygen in a mannerthat produces an elctrical potential rather than initiating burning.(2 words) 5. Gasolinewith oxgen-containing addictives to enhance clean burning.(2 words) 6. A combustible gas derived from decomposing biological waste. 10. Useful energy derived from water heatedby the naturally hot interior of Earth.(2 words) 12. A wind driven generator that has a propeller shaft.(2 words) 14. The ability to do work. 15. Energy derived from the sun.(2 words) 16. The use of electrical energy to split water molecules into their constituent hydrogen and oxygen atoms.