crazy idea with solar cells

[Stynus]

I was thinking about buying solar cells of 20Watts but then i was thinking about a 2W solar panel that i have in my shack.

If I get an old sattelite dish and place peaces of mirror on it and i place te solar cell in the fire point would i get a higher power output then?

sorry for my bad english

[mlt2]

Hello, I am new to the whole solar power idea. But from what I hear the added heat will lower the output of the cells a lot. Also I have been told the added heat will kill the solar cells a lot faster. From what I have read solar cells really don't like temps over 80-100f. Please don't make fun of me if I am wrong. This is just what I have read.

Mike

[pyrocasto]

Mlt, no one's here to make fun of you, your right. Solar cells hate heat, but they get in the high 100s, so 80-100F is a little low.

Stynus, it would work, but yes it would kill the cell almost instantly probably. If you could figure out a way to keep it under 200 degrees, it should work, at least a little bit.

They have something called a concentrator cell for this type of thing, which is built into a heatsink that you pump liquid through to cool it.

[JW]

I have stumbled across this idea several times, while searching the internet for "parabolic recievers". Actually I saw an episode(documentary) on discovery channel a few years back about exactly this. Thats what prompted my searching a couple of years ago. It was some high tech start-up that was custom making a power-dense solar cell to be placed on a parabolic reciever(very simular looking, to an old sat dish) and the cell was right in the fire point. There are some problems with trying this, using conventional solarcells.

 Actually I have an aluminum smelter and am planning on building some recievers for parabolic type dishes. I plan to post a story on this when I cast them. They will simply be copper tubing submerged in a round aluminum casting. The only problem that has come up for me is that I want to use 17in dia disks with 3 in thickness. These reciever are intended to heat water. I have the molds. some on the board have expressed interest in such a project, so I will make a batch of 10. But from the way its looking so far, a 16ft dia  parabolic reflector dish will be needed for these. I can make the recievers as small as 12in diameter with the molds i have.

more on this later.

JW

[Vtbsr]

Why don't you produce steam at the focal point of the old dish. Then you could use that to run something else.I think some of the power companies tried the idea,but with a flat  tracking mirror to double the infiltration.The PV's were discolored and lost some of there output when they tried to sell them. With the dish you could get 700 deg and melt everything. The problem i see is how to get the dish to track.

[Aelric]

You can find tracking programs and tracking gear for your mirror on the internet.  Might even be able to get the motor and the mount from an old satellite dish.  They have loads of tracking hardware for PV's, just would be a matter of adapting it over for your dish.  I think it would be very neat to see how much steam it could make, or even use a sterling engine.  One idea on using a PV, what about using a peltier (the water cooler idea is good too) it would take a little power but I suppose it would get down to just how much power you could produce and how much surface area you could light up.  Please post any findings you have, would love to hear more.

[Ungrounded Lightning Rod]

Actually I have an aluminum smelter and am planning on building some recievers for parabolic type dishes. I plan to post a story on this when I cast them. They will simply be copper tubing submerged in a round aluminum casting. The only problem that has come up for me is that I want to use 17in dia disks with 3 in thickness. These reciever are intended to heat water.

If all you want is hot water you don't need a concentrator.  A dark collector in an insulated box under glass works just fine.

If all you want is "process steam" you don't need a dish (a "two-dimension concentrator" which must be aimed by the minute).  A trough (a "one-dimension concentrator" which must be aimed by the season) works just fine.

Dishes are for extreme temperatures:  They'll get you superheated steam (for getting more out of heat engines than lower temperature process steam), smelt metal, and the like.

A given area of collector grabs the same AMOUNT of heat regardless of whether it concentrates.  The difference is the TEMPERATURE of the heat it collects.

[JW]

Hi ULR,

 Ya umm, im going to try an experimental 'LaMont style' steam power boiler. Id be curious to know pounds per hour of steam capability(volume generation) in direct sunlight. Bear in mind, this is a LaMont recirculating(pressurized) forced circulation type of steam generator. the water, must remain water, when circulating in the heat exchanger, and 'actual feed water temp' is negligable with this power boiler design. since it feature's reserve battery capability. : )

JW

[Ungrounded Lightning Rod]

That would be the one where you have a big tank of superheated water with a little steam on top that you store under pressure until needed.  It boils when you release the steam to run your engine, providing more steam and cooling off until it gets down to the boiling point, at which point you have a partial tank of almost-boiling-hot water.  Right?

(Steel mills used to have steam locomotives for halling stuff around, with a big tank refilled a couple times a day with superheated water manufactured from the heat available in the plant's systems.)

Noon would be about a kilowatt of heat per square yard (varying with time-of-day on a non-tracking collector according to the cosine function clamped at zero, but averaging the equivalent of maybe 5 noontime-hours-worth per day - see "solar hour" map for your area and seasons), less any inefficiencies.  You should be able to figure it out from there.

[JW]

Sweet,

 Thanks for that ULR, about a 1kw per flat yard sounds reasonable. considering losses with a 16ft dish, that should be about 1kw. was thinking about 250, 251 psi(whatever it takes) and a small reaction turbine, like the ones used for onboard lighting of the ships of old.

JW

[Ungrounded Lightning Rod]

Note that the temperature of your storage will top out as it approaches the temperature of the collector, and energy collection rate will taper off.  If you want to run at high temperatures and pressures you might need the dish, or some dish.

On the other hand, you can use a BIG storage tank at moderate temperatures and pressures.  The square-cube law is your friend.  B-)

[ignesandros]

You could even use a peltier device at the focal point if you could get it small enough. This would require a good heatsink of course...

-Andrew

[richhagen]

Say a large long trough reflector with a thick piece of aluminum bar stock on the focal line coated with black on the side to absorb the radiant energy, and insulated on the backside except where the peltiers were clamped to large shaded heat sinks.  The spacing of the Peltiers could be determined empirically to maximize output/cost ratio.  If you could hit a few hundred degrees Farenheight on the bar, and move the heat away quickly enough on the backside (maybe use insulated heat pipes to transfer heat to large heatsinks shaded by the reflector) to maintain a significant temperature drop, you might be able to generate a useable amount of power.  Rich Hagen

[commanda]

Water cool the cold side. Even fan assisted heatsink fins wont move enough heat. If the cold side can't disperse the heat, the temperature differential will drop & so will your output. Also the average peltier temperature will quickly reach destructive temperatures.

Someone posted a link here recently to an article about generating power with peltiers. The amount of energy to remove from the cold side is really scary. They only turn about 5% of the applied heat into electricity, the other 95% has to be removed from the cold side.

Oh yeah, spring load the clamps.

And put insulation between the peltiers, so the heat on the front heatsink doesn't jump across the air gap to the cold sink.

Amanda

[commanda]

Oh yeah, another thing. The cold side heat sink needs to be in the order 0.0x degC/watt. Have a look at any catalog, and see what regular aluminium heatsinks are rated at. Orders of magnitude about a hundred times greater. The biggest non-fan-assisted heatsink in the Jaycar catalog is 0.5 degC/watt. And cost AU$21.95.

Amanda

[richhagen]

Ok, take a large piece of barstock aluminum, take a megaflat heat pipe ( http://www.cheresources.com/htpipes.shtml ), say 18" by 5.5", clamp it to a huge aluminum heat sink on the back side. I have some five and a halve inch wide heat sink bar stock extrusion on hand, so if you take a foot and a half of it you ought to be able to disipate a large amount of heat.  If its still not enough, then water cooling, but that would probably make the system even less efficient to move that much water about.  With the cost of the heat piping, I'm pretty sure that this would not be cost competetive with normal solar panels though, and it would be much more particular on the seasonal aiming of the trough.  It would also have a lower MTBF due to the series connections of a bunch of peltiers to generate charging voltage, or if a boost converter was used, that circuitry would reduce the reliabilaty as well.  Rich

[bparks]

I've wondered if it might be cost effective to use a fairly mild version of this to minimize the number of solar cells required.  Instead of using a large parabola to focus huge amounts of sunlight on a cell, and designing a powerful heatsink & cooling system to keep from frying the cell, what about parabolic troughs sized to double or triple the amount of sun on each cell.  It seems like you might be able to get by with just a good heat sink & no liquid cooling.  I think the point is to find a concentrator & cooling system that is cheaper than just buying more pv cells.

[ghurd]

It will still kill them in short order.

Even if it doesn't, which it certainly will, the heat may drop the output to not much more than normal.

G-

[ignesandros]

If you're not getting the sun's full force, your PV's would love a little more light reflected on them... think of places in CA and Alaska, for instance. More light would just bring these cells to a normal operating current. In fact, if think about it, the natural air cooling effect would increase the effiency at above-spec power densities.

-Andrew

[Bruce S]

The idea of putting the PV at a focal point would fry the cells in short order as some have already said, but if you're looking to merely make sure the PVs where getting as much sun light as possible then reflectors/mirros would be the better.

The open air would help keep the heat down, I've done this to charge SLAs using a free ( I love that word) PV that you see being sold to put in your car to keep the bat fully charged. I use plain cheap( not as good as free) mirror pieces and just angle them so the light is always on the PV.

IF however you are wanting the heat then you need to think 100s of degrees, which is good for making steam and such but heven those will need a tracker and a trough type unit is far far better that a dish type.

I think on one of the older posts there was one that showed how to make a home made tracker.

If you go the route of using peltier units care must be in the planning to make full use of everything you get with it. The heat that you would get with a dish pointed at a peltier device could then be used to heat the water that is used to remove the heat being thrown off by the "HOT" side of the device.

I once saw a report that Greenland ( I think) did something like this but they used the cold/heat difference to make the power to light lights. There the difference was REALLY cold out side and a wood stove for the HOT side.

Good luck;

 Let us know how it goes.

Bruce S

[robfirth]

You say that it would fry the solar cell, but I found a link to a company that makes solar concentrators for solar cells. They call theirs the sunflower.

It is true, it would fry the cell, but these people claim that they cool it to 30 degrees above ambient temperature.

Their idea is that mirrors are cheaper that solar pannels

http://www.energyinnovations.com/concentrator.html