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Get Powered Up! Certified Energy Manager Jeff Yago answers your alternative energy questions

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Archive for the ‘Fresnel lens’ Category


Fresnel lens

Wednesday, December 17th, 2008

Hi Jeff,

I’m a disabled senior citizen who has discovered solar energy, love it!

I am toying with the idea of using a fresnel lens to heat a large piece of concrete or steel (maybe railroad track) and have the heated object on a movable system so that in the evening I could transport it into my garage and extract the heat to my home. I thought I could use a Heliostat to track the sun for heating purposes. Am I nuts? Suggestions?




Sounds like a lot of work on your part. You can obtain the same energy with a lot less effort. For years people have heated greenhouses by placing large 30 and 55 gallon metal drums of water on the back walls. The drums are painted black and absorb the heat of the sun that has entered the glass and shines on the back wall away from the plants. Then at night, the heated drums give up their heat to offset the heat that is being lost.

Remember that any lens does not “increase” the solar energy available, it just concentrates it on a smaller area. For example, if you take a 1 sq. ft. thick steel plate and place it in direct sunlight, it will absorb the exact same solar energy as taking a 1 sq. ft. concentrating lens and shining the sunlight onto the same metal plate. Yes, the point where the lens has concentrated the sunlight will get hotter, but the rest of the plate that would have received at least some sunlight will not. The lens cannot increase the energy falling on each square foot of area, it only concentrates it onto a small point when increases the temperature. However, the same total energy (BTU) of heat is available.

Hope this helps and good luck dragging that railroad rail in and out of the house,

Jeff Yago



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