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Increasing the output of Solar Cells

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dan

Thu Aug 03 2006, 05:29AM

Registered Member #223 Joined: Mon Feb 20 2006, 06:42PM
Location: Ottawa, Ontario, Canada
Posts: 125

One thing that I noticed about solar cells is that they need to be really large to generate any decent amount of electricity. However I came up with a rather crazy idea. Why not use a lens to focus more light energy onto a smaller cell. Obviously you would need to solder them to a copper block to keep them from getting too hot but It sounds feasible. This method would have it's limits but Iâ€™m wondering if it would be worth it. Just as an experiment I have a good sized copper block that would fit two radio shack cells nicely. These cells only put out 0.5v at 0.5V usually. Using one of those page magnifiers (a fernells[sp?] lens) I should be able to at least double the output current. The main problem I would think is keeping them cool. I mean it would have to be passively cooled in order to save any increases made. Maybe I can cheat and use running water from a small stream to cool them off.

Nik

Thu Aug 03 2006, 05:44AM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

The only issue I can think of would be if the cells use a wavelenght of light that the magnifer would block (glass blocks some uv if i remember correctly). I thought of this because I noticed that those radio shack cells don't generate alot of anything when under artificial light (even when close to the source). Just a thought.

Penguin7471

Thu Aug 03 2006, 05:48AM

Registered Member #71 Joined: Thu Feb 09 2006, 08:23AM
Location:
Posts: 63

This method of 'boosting' the output of solar cells is already being used. There are special reflective parabolic dishes that are designed to concentrate sunlight onto a relatively small solar panel. This is cooled with oil pumped around it.

There are a few on experimental runs here in Australia, although I can't remember where.

dan

Thu Aug 03 2006, 06:04AM

Registered Member #223 Joined: Mon Feb 20 2006, 06:42PM
Location: Ottawa, Ontario, Canada
Posts: 125

Well those page magnifiers are made of some sort of plastic so I don't know if it would block a specific wavelength that the solar cell uses. But if that fails I could use mirrors. I never heard about this before it's just a random thought I had. It's a rather simple concept though. I know there would probably be a point of diminishing returns. One thing I'm not sure about is if it possible to saturate a solar cell or will it just generate more and more power the more light you focus on it until it gets too hot. but I guess I'll find out in my little experiment.

Bjørn

Thu Aug 03 2006, 11:15AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Fresnel lenses are fine, I have used one on a solar panel from a garden light and got eight times the normal output. I cooled the panel with water. Solar cells does not generate much energy in fluorecent light. That is why fluorecent lights are effective, they mostly contain energy in the frequencies in the visible band. If you use a normal light bulb a solar panel is probably more efficient than in sunlight because it contains more IR.

One of the problems is the internal resistance of the solar cells, so overdriving them causes a large of loss. There are special cells that are made to be overdriven by 300-1000x, they are probably very expensive.

...

Thu Aug 03 2006, 02:45PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

When we get around to using solar cells to generate energy (hopefully soon, the company I work for has a $60mil contract for terrestrial solar cells) we will be using your method.

However, it will be a much larger magnification factor... I believe they are planning to use a 10' diameter disk focused on to a 4" square of cells (100x) which should give about .5-1kw a peice. To deal with cooling they will plan to use liquid sodium.

I have a few (20ish) old concentrator cells (from when my dad was working at texstar) that are about a 1" square, with about a .8" in diameter active region. I don't have big lenses to try it out, but with water cooling (1'^2 of sun is about 100w) you should be able to get at least 10w of power from 12" fresnel lens.

I wouldn't really worry about blocking out the uv, as a uv photon gives the same amount of energy as a far ir photon, so you aren't really blocking too much out.

dan

Thu Aug 03 2006, 03:51PM

Registered Member #223 Joined: Mon Feb 20 2006, 06:42PM
Location: Ottawa, Ontario, Canada
Posts: 125

Well those page magnifiers are about the size of a letter sized piece of paper. But I had seen some reflective film stuff at a hobby supply store. it was about 2ft wide and was on a roll of 10ft or so. I could build a support frame for it a make it into parabola. Sort of like this. But Iâ€™ll try the magnifier first. These solar cells are about 2cm x 4cm and only put out 0.25W in full sunlight normally! If I could get even 5W with a page magnifier and two small solar cells that would be a huge improvement! One thing i'm conserend about is soldering them to the copper block. First will they be able to survive the tempratures needed to solder them (~200C). Secondly their backs are soldered to a copper bar only so only a parallel configuration is possible limiting the output voltage. They only put out out 0.5V under normal sunlight so I'm hoping under the lens it will boost it to at least 1.5V. This would at least be a usable voltage. Current shouldn't be much of a problem and would probably be able to supply a few amps.

Bjørn

Thu Aug 03 2006, 04:44PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

The voltage will not rise a lot when you overdrive it. You need several cells in series or an efficient DC-DC converter.

dan

Thu Aug 03 2006, 05:34PM

Registered Member #223 Joined: Mon Feb 20 2006, 06:42PM
Location: Ottawa, Ontario, Canada
Posts: 125

Rats.. With only 0.5V the max current (and power) I can get from it will severely be limited. Plus getting a DC-DC converter to run off of 0.5v would be a very challenging feat if not impossible. So it seems like I can't just solder them to a copper block after all. I would need some sort of insulation between the cell and the heat sink in order to wire them in series. Although finding something that is non-electrically conductive and still has good thermal conductivity will be rather difficult. Hmm seems like a fruitless effort then.

...

Thu Aug 03 2006, 05:39PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

That is the problem with heat sinking solar cells, they need to be electrically isolated

I wonder what it would cost to get a big sheet of a high conductivity ceramic that is tinned on both sides so you could etch it into some seperate pieces, solder it to the heatsink/waterblock, and solder the cells...

Yo could always use seperate heat sinks for each cell...

On that note the cells should take the heat fine, but it is probably best to minimise the time they are at temp. The real concentrator cells had the contacts welded becuase they ran too hot for solder

Or you could use some triple junction cells which would give a little over 3v... I know I have a few arround here somewhere, but considering that they were sold for thousands of dollers a cell...

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