has anyone thought about using a Fresnel lens (well a lot of them really) for the glazing on solar hot water panels, if so what were your thoughts. is it worth it.
If the amount of heat going into your collector is the same whether or not you are using concentrating lenses, it may be more trouble than it's worth. If you can concentrate the heat on the fluid going through collector pipes, that might work. Too much in the way of hot spots might be a problem.
A fair number of people are and have been playing with concentrating designs--there's even a yahoo group dedicated to them--non-members like me can read, last things I've seen have been about heat-proof but long lasting and inexpensive materials for parabolic mirror arrangements. Heat-proof, long-lasting (resistant to UV damage--an issue for those plastic film jobs, or to the silicone or whatever alternative liquid there is in the collector, I'd think) and inexpensive would be issues here too.
You may get water too hot for most purposes with, say, a black garden hose wandering over your roof in the summer.
And where you are located (does it freeze in the winter or can you ignore that because it's a summer cabin) is a big deal.
The nice thing would be to have a system that soaks up enough light-and-heat to work more or less when there hasn't been any sunshine for a week or two. Most if not all of the solar hot water systems I know about have backups in place.
a good place to start is visit the following alternative energy discussion forum http://www.otherpower.com/
or
opt for a goole search of the discussion board.
http://www.google.com/custom?q=fresnel+lense&sa=Google+Search&cof=S%3Ahttp%3A%2F%2Fwww.otherpower.com%2F%3BGL%3A0%3BAH%3Acenter%3BLH%3A69%3BL%3Ahttp%3A%2F%2Fotherpower.com%2Fimages%2Ftitle.jpg%3BLW%3A593%3BAWFID%3Aba35deb1811a3d8e%3B&domains=otherpower.com%3Bfieldlines.com%3Bwondermagnet.com%3Bwondermagnets.com&sitesearch=fieldlines.com
Otherpower is "the cutting edge of low technology."
What a nice way to put it.