Thinking About Solar

Q: I am on the main grid in Sydney, Australia. I have been thinking about using solar to help reduce my power bill which is around $2,500 per year. I run a massage clinic and use lots of heating and dries for towels etc. I found a build your own solar cell plans at http://www.fuellesspower.com/ and was wondering if these actually work prior to spend $20 to find out. Has anyone here build solar cells with silk screen methods as mentioned in the above address. My neighbour runs a large silk screen printing business and may be able to help me here. Any comments or thoughts welcome.

A: You may want to look at building (or even purchasing) solar thermal collectors. That is, something to produce hot air directly from the sunlight. This hot air could be used to dry your towels and provide heat without having to be made into electricity first. This is much cheaper and maybe even more efficient than using solar generated electricity. Simple hot air collectors are easy to build from common parts available at most any hardware or home improvement store. Plans for such collectors abound on the internet. http://www.jrwhipple.com/sr/solheater.html http://www.ncsc.ncsu.edu/fact/23body.htm#space Looks like this process buys a silicon wafer (perhaps a reject). I have no idea where you can get these or at what price, but I believe they are available if you shop hard enough. Then you make a diode out of it by baking in the oven with an arsenic, or phosphorous compound on the surface to drive in a doping. If you do it right, you get a large diode which will generate photocurrent quite nicely (this is basically what the photocell manufacturers do, they just use nicer ovens). Now you need to metalize the back (you may be able to buy the wafer already metalized) and you need to construct an electrode on the other side to collect the photocurrent. This can be done with vapor deposited aluminum, all you need is a vacuum chamber and some way of etching off the aluminum you do not want. This is what the big boys use. You can also use some tin salts that are conductive and transparent (an unusual feature). What you will need is a comb of metal to collect all this power but cover up very little of the photocell junction area. Silk screen inks can be used, either laying down a conductive epoxy, or an ink that has to be baked out to become a conductive layer. You will want to make sure that this ink does not diffuse into the silicon and short out the diode or cause other long term reliability problems. The process description is probably not worth $20, but the education in silicon processes could be a lot of fun. If you want practical, I would suggest the direct use of solar heat (confirming what another has already said).

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