<em>Image courtesy of Yuliyan Velchev/istockphoto</em>

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Solar Greenhouse with Solar Chimney for Electrical Power Generation

This project involves the purchase of a commonly available small greenhouse (10' x 12' or 120 ft2) that we then convert to harness a convection current. The theory is simple and has been applied on a large scale before. As the air in the green house heats up, it pressurizes the green house or gets lighter if the pressure can escape. By placing an insulated chimney at the apex of the greenhouse. The heated air wants to escape out the chimney. To create a cycle, one or more small opening are created at the base of the greenhouse. Thus the air escaping out the chimney draws cool air into the greenhouse. This air is then heated and escapes and the cycle continues. This current of air is basically a locally created wind than we can use to spin small turbines. The point of this experiment is to determine exactly how effective this can be on a small scale. The area of the greenhouse is approximately 13 m2 This means on average it is receiving 13,000 watts of energy from the sun in a typical US state. However, the temperature difference between the cold and hot side of our "engine" is very small. Probably only 8 deg K. Thus, the Carnot equation would limit or maximum power generation at ( 1 - 273 / 281 ) * 13,000 or 370 watts. This is approximately 1/2 horsepower. But that assumed our system was as efficient as it could be. In reality, there will be many other losses in our system. I think we will be lucky to get 100 watts out of this device. The up side is that we get a usable greenhouse out of it. It all goes well, we should end up with data indicating what size of greenhouse would be required to say power a typical household.

I am starting with a 10' x 12' green house kit available from Harbor Freight Tools. (www.harbourfreight.com) Prices vary for this kit depending upon the time of year but it usually costs around $800.00. Though this kit is considered a bargain by most who buy it, it is also considered pretty difficult to assemble and needs some modification to function really well.

 

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