Passive Solar EnergyPassive solar energy, also called solar thermal, can cut the majority of the worlds heating bills. Simple complience to its demands are all that is required. All sunny windows equal electric space heaters when the winter sun is allowed to shine through. If that light reaches a dark colored thermal mass, that energy will be stored for night time heating. Also, shade trees and basement space can be used for cooling. Improvised building techniques would greatly reduce the amount of electricity needed for cooling and natural gas for heating. A small amount of electricity is needed for fans to direct the heat (or cool air from basement area) to increase upon natural convective air currents. If a house is built generally east to west, it will recieve heat from more windows facing south and it will not have to heat as much space per window. During the summer, the eves and the high position of the sun in the sky prevents over heating through windows.I have not yet built a solar thermal heater. It would consist of "hot boxes" made out of an insulated metal backing with glass in front and black metal in between. Baffles inside would force air to maximize surface contact. A fan would force the hot air into a bin of (cleaned) 1 inch rock that would be about the size of a shed. I've read that it is close to 50% efficient if sized right and if fans blows the right amont of cubic feet per minute. This means that on a bright and cold winter's day, about 220 sq ft of hot boxes would provide 10 sq meters worth of sunlight (10kW). So 5 hours would store 50kWh. A normal wall heater is rated at 35,000 Btu an hour and each kWh is equal to 3,414 Btu. = about 4 to five hours of continuous heat! I don't know about how to insure that air quality does not get fouled from an old bin of rocks... But the following links may help explain solar thermal energy in more detail. Solar Energy Heat Storage for Home... Solar Hot Water, Heating and Cooling Systems
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