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Heat Pump — by Mark Kragh — last modified Jan 15, 2010 03:47 PM

A heat Pump is an electrical heating system which used the heat which is readily available outside and moves this inside. The principle of operation is the same as in a fridge or freezer

Hydro-Electric Power — by Joe Baylis — last modified Jan 04, 2010 05:59 PM

A form of renewable energy derived from the flow of water.