Increasing the output of Solar Cells
dan, Thu Aug 03 2006, 05:29AMOne 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 I’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.
Re: Increasing the output of Solar Cells
Nik, Thu Aug 03 2006, 05:44AM
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.
Nik, Thu Aug 03 2006, 05:44AM
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.
Re: Increasing the output of Solar Cells
Penguin7471, Thu Aug 03 2006, 05:48AM
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.
Penguin7471, Thu Aug 03 2006, 05:48AM
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.
Re: Increasing the output of Solar Cells
dan, Thu Aug 03 2006, 06:04AM
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.
dan, Thu Aug 03 2006, 06:04AM
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.
Re: Increasing the output of Solar Cells
Bjørn, Thu Aug 03 2006, 11:15AM
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.
Bjørn, Thu Aug 03 2006, 11:15AM
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.
Re: Increasing the output of Solar Cells
..., Thu Aug 03 2006, 02:45PM
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.
..., Thu Aug 03 2006, 02:45PM
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.
Re: Increasing the output of Solar Cells
dan, Thu Aug 03 2006, 03:51PM
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 I’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.
dan, Thu Aug 03 2006, 03:51PM
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 I’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.
Re: Increasing the output of Solar Cells
Bjørn, Thu Aug 03 2006, 04:44PM
The voltage will not rise a lot when you overdrive it. You need several cells in series or an efficient DC-DC converter.
Bjørn, Thu Aug 03 2006, 04:44PM
The voltage will not rise a lot when you overdrive it. You need several cells in series or an efficient DC-DC converter.
Re: Increasing the output of Solar Cells
dan, Thu Aug 03 2006, 05:34PM
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.
dan, Thu Aug 03 2006, 05:34PM
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.
Re: Increasing the output of Solar Cells
..., Thu Aug 03 2006, 05:39PM
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...
..., Thu Aug 03 2006, 05:39PM
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...
Re: Increasing the output of Solar Cells
Ben, Thu Aug 03 2006, 05:50PM
Ben, Thu Aug 03 2006, 05:50PM
Re: Increasing the output of Solar Cells
Coyote Wilde, Fri Aug 04 2006, 03:33PM
Don't photocells get less efficient as they get hotter?
Coyote Wilde, Fri Aug 04 2006, 03:33PM
... wrote ...
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.
Please, please, please tell me they're also going to use all that heat, too. Conventional turbogenerator, sterling, thermocouple... otherwise, the amount of energy untapped is tragic. Liquid sodium!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.
Don't photocells get less efficient as they get hotter?
Re: Increasing the output of Solar Cells
..., Fri Aug 04 2006, 04:29PM
I hope so, considering that the most efficient solar cell is <40% efficiency. Assuming they are using the GaAs cells (but not triple junction cells which cost mucho dinero) they could get about 30% efficiency tops in the sun, which leaves about 60% for the thermal energy, which will probably be down to <20% after you run it through a turbine. Not a whole lot, but it does almost double the energy put out... An advantage to using thermal is that you can store it quite efficiently by heating up a huge mass of something during the day, then using it at night...
..., Fri Aug 04 2006, 04:29PM
I hope so, considering that the most efficient solar cell is <40% efficiency. Assuming they are using the GaAs cells (but not triple junction cells which cost mucho dinero) they could get about 30% efficiency tops in the sun, which leaves about 60% for the thermal energy, which will probably be down to <20% after you run it through a turbine. Not a whole lot, but it does almost double the energy put out... An advantage to using thermal is that you can store it quite efficiently by heating up a huge mass of something during the day, then using it at night...
Re: Increasing the output of Solar Cells
Bjørn, Fri Aug 04 2006, 05:28PM
The cells lose efficiency at about 0.5% for every Kelvin increase in temperature above 25 deg C. The internal resistance goes down and the voltage goes down so in some special cases they can almost cancel each other out.
There is often a need for warm water so there is usually no problem putting the excess heat to use.
Bjørn, Fri Aug 04 2006, 05:28PM
The cells lose efficiency at about 0.5% for every Kelvin increase in temperature above 25 deg C. The internal resistance goes down and the voltage goes down so in some special cases they can almost cancel each other out.
There is often a need for warm water so there is usually no problem putting the excess heat to use.
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