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Holographic Solar Collectors
An anonymous reader writes "The MIT Technology Review is reporting that Prism Solar Technologies has developed a technique to use holograms to concentrate light onto photovoltaic (PV) cells. While the implementation is only about a 10x increase over PV cells without collectors such as mirrors/lenses (mirror/lens approaches can do 100-1000x), it is a great deal simpler, more compact, and cheaper. Also because of the concentration, there is less need for physical PV cell real estate compared to crystalline PV silicon cells of similar output."
10x increase for the holographic cell may sound bad compared to 100x-1000x for mirrors/lens. But in the installations I know that use mirrors or lenses they take up most of the area. If 10% of the whole surface was PV cells and 90% were e.g.. mirrors (a very conservative assumption, I think the PV cells will cover less then 1%) you would gain an effective increase of 100x instead of 10x. (This is not entirely true, since these new PV cells are only part energy creating silicon, most of their surface is just the holographic lense. But still a massive space saver compared to classical mirrors.)
Plus you will usually have to place mirrors on the ground due to their weight and the weight of the motors attached to them to make them follow the sun. In contrast you can place PV cells on almost any surface, although you will loose a lot of efficiency if you can not orient them towards the sun.
If you completely ignore that there are theoretically more efficient methods of concentrating the energy onto PC cells, you still get a 10x improvement over the typical installation (on a roof, with no fancy mirrors at all). And then 10x is huge.
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they just replace sections of PV cells with this hologram stuff-- the panel is the same size, just less silicon
These sound like good old fashioned diffraction gratings to me. 'Hologram' sounds like nothing more than a marketing term. One disadvantage of using diffraction gratings is that the amount of bending is wavelength dependent. And it seems like the marketing department managed to put a spin on that too.
Doesn't it make you feel good to know that our freedoms are protected by politicans, lawyers and journalists.
When you can concentrate the suns energy the collector is more efficient. This is a VERY good thing, especially considering the amount of cloudy / rainy days most places have. Lots of people do not go solar because it simply does not draw enough power for the amount of money they have to use to build the system.
Funnypics
Over the last decade quite a few of these wonderful improvements have been announced yet the commercially available solar-cell still has an efficiency of less than 15% and the price hasn't changed that much either.
I wonder if these announcements are more motivated by an upcoming investment round...
God knows we could use them, but when do we get to see them?
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Finally, a use for Arnold J. Rimmer.
Anything that can provide decent solar generation more cheaply would be good. Sounds like their process improvements in the 2nd gen panels might meet the $1.50/watt figure mentioned in the article. In any case, costs of any solar tech will need to go down quite a bit to support more widespread use, especially in developing countries.
What's stopping me using a holographic collector in conjunction with a mirror/lens affair?
That would be innovative... and they have this thing designed to stop that kind of stuff.
It is called a 'patent'.
--Phillip
Can you say BIRTH TAX
Just when Riker flirts with the inventor's wife.
PV efficiency reduces significantly with increase in temperature (which is why you see solar racer folk pouring water on the PV panels). Thus just cranking up the sunlight by concentration does not give a linear increase in output. PV cells for concentration thus need to be made thicker and differently (to code with the extra current, heat sinking etc.) but hopefully the payback is still there.
Personally I think the PV quest is being approached incorrectly. There's too much emphasis on efficiency. Labs try to out % eachother and the big solar showcase is the solar race which is all about high efficiency cells.
What they should target is $ per Watt because that is the real hurdle to making PV viable. Who cares if it's only 5% efficient, so long as it is cheap? Tile your house with the stuff to get the area.
Engineering is the art of compromise.
The problem with concentrating the light too much is it generates more heat. Like a computer heat causes problems it reduces the efficency of the solar cell. Also the heat increases the rate the cell degrades and will have to be replaced more oftain. 10x is a reasonable amount of concentration because it does not significantly reduce efficency and does not stress the chip.
The issue here is the holograms are a replacing the mirrors/lenses. The actual photo cells are still the same.
The idea here is the holograms could be made flat while mirrors you'll have to link up with motors to track the sun.
If you have mirrors already tracking the sun, then you don't need holograms to redirect the light to the photo cells.
Back in 2001 the Tucson Citizen did a project where they powered a Sun Colbalt Qube 3 off of solar power using a set of panels based on a very similar if not the same technology.
a rexplorer.net/gallery/index.php?TopicID=panels
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The panels they came from a company called TerraSun and the one I have on my desk left from the project looks remarkably like the one in the article.
Archive.org still has some pages from the site which is long defunct http://web.archive.org/web/20010807151516/www.sol
Google finds reference to the technology that TerraSun was developing http://www.wapa.gov/es/greennews/2001/may14'01.ht
It won't save any space compared to regular PV cells, but assuming that area of holorgam is cheaper than area of silicon (The article implied that), then it will save money.
Light side of the Moon? Hunh? The lunar "day" is somewhere around 28 Earth days...fixed installations will be in shadow approximately 2 weeks at a time, and at unfavorable angles for some of the other 2 weeks.
Or do you mean build rails all the way around the Moon and motorize the panels so they can stay on the "light side". Or maybe position at the poles (too lazy to google it...does anybody know the axial tilt of the Moon? shallow enough to stay out of shadow at the poles?)
Better yet, unless you're planning on fabbing the stuff at the Moon, and maybe even if you are (to save on launch costs) just put them in geostationary orbits.
Concentrating light onto PV cells has been done before. The main problem is that the PV cells get too hot and degenerate quickly. Bulky panels using mirrors or lenses can be solved using flat fresnel fenses. Now the question remains, how to cool these things. It dawned to me that the panel created so far is in fact very similar to the solar water heaters. Why not combine the two? A fresnel lens concentrates the light onto a PV panel that is protected against heat by water flowing up between two layers of glass (Hot water rises) circulating as it does in traditional solar hot water systems. The water takes out the heat producing IR radiation leaving all the good electricity generation radiation for the PV panel. This way you can put up one panel producing both hot water and electricity.
the article states that they are shooting for a price around $2.4/watt, which I can assume ytou is well below what we are currently paying. i was recently quoted a price of $8/watt from solarsave (http://www.solarsave.com/) for a pv installation, so having to pay a third of that price is extremely reasonable from a cost per watt perspective, even if you don't get any added efficiency due to heat losses.
Thats a great idea.
And then when Bush Jr. Jr. Jr. decides that he doesn't like [bad country here], he'll just tell the opperators to point the giant microwave systems at [bad country] country for a while.
This scheme removes one of the principle benefits of photovoltaic power: namely that it's omnidirectional: it'll still have a decent energy production even if the light source is diffuse. like.. say.. light, but full cloud cover (seems half the weather in the NE is light full cloud cover...) or fog. if you're going to bother lensing the light, you might as well use a solar collector to drive a heat engine, which is far more efficient than PVs are right now.
Can you be Even More Awesome?!
Um, hey guys. I think you'll find that many high quality differaction gratings are in fact *holographic.*
When it comes to making diffraction gratings, phase-delaying gratings beat out amplitude-reducing gratings (parallel opaque parts) for transmission. It's easy to make both phase and amplitude gratings with an interferometer (to make fringes) and some holographic film. For phase gratings, you just bleach the film/plates after you wash them in developer and before you use the stop bath.
Three dimensional graings also be used to achieve high efficiencies. I've made some by projecting interference fringes into an optically active crystal (see the photorefractive effect). Optical quenching is a wild effect.
~opticsdoug
Concentration is highly overrated from a cost standpoint. A typical solar cell runs about $3/peak watt produced at 1 sun illumination. A 10 to 1 concentration ratio would reduce solar cell area to $0.30 if you could continue to use the same cell and it can handle the concentration. You have achieved 90% of the possible cost reduction for the solar cell. A 1000 to 1 concentration ratio only buys about you another 29.9 cents or so cost reduction of the cells and you have to pay for a much more complicated concentrator setup.
OK, it's not quite that simple. What actually happens is that to design cells that can make use of a 10 to 1 concentration ratio may cost a little more than a standard cell. And today, these are a somewhat special product, so lack of an economy of scale further increase the cost compared to the standard cell. Cells designed for a 100 to 1 or a 1000 to 1 concentration ratio are an extremely specialized product and cost a mint, although you need very little total area of the cells themselves. The balance of the concentrator becomes a key cost in the system.
The other thing that happens is that when you are going for a high concentration ratio, some of the cells inherently get more efficient (as long as you can keep them cool... more of the "other costs" to deal with). In addition, because you are using just a little bit of specialized solar cell, you can pay a bit more for fancy triple junction cells that are more efficient by as much as a factor of two (up to say 30% efficiency at converting light to electricity compared to the standard silicon cell). However, the losses in the optics and the need for active cooling will take their toll on the system efficiency.
What it all seems to boil down to is that you have to design and cost out the system as a whole before you can say what makes sense for the market.
Pyron Solar http://www.pyronsolar.com/US/index.htm has got a great little system put together that uses fresnel lenses to focus sunlight on high efficiency solar cells.
They float the entire assembly in water to cool it and to assist in rotation so that the apparatus can follow the sun.
Our energy problems are licked, I hope.
An invasion of armies can be resisted, but not an idea whose time has come. - Victor Hugo
My first thought reading the headline was that this was just called a "hologram" to get some buzz, over what is a very generic, straightforward way of increasing the power delivered to the expensive part, the solar cell. But (for those too lazy to RTFA) this is different for three reasons:
1) It is almost omnidirectional - a Fresnel lens is a flat subsititue for a regular lens, with limited off-axis focusing ability. This seems to use the glass as a lightguide instead, with a broader angular reach (in exchange for limited scalibility - bigger the glass width to thickness ratio, the more light lost because of increased internal reflections & distance from entrance to cell)
2) It uses a hologram to selectively reject useless frequencies like infrared, which is 80% (IIRC) of the energy of sunlight, but generates no electricity from the cell. In fact, infrared is harmful to the cell, because it increases its temperature, which reduces its effeciency!
3) Because of the above features, it does not need a turning mechanism to follow the sun, the solar cell (which is the most expensive part) lasts much longer because it is not heated as much even though it is capturing much more useful light and converting that into electricity, it is flat and relatively easy to handle, unlike traditional solar cells with large, bulky, moving "capture" mechanisms placed in front of them....
In summary, it is cheaper per kilowatt-hr, AND more effecient, AND more practical for installation (no moving parts or seperated pieces). This is pretty neat.
This idea has already been implemented several years ago where this kind of setup (solar panels and holographic gratings) was incorporated into office windows, directing the usable light frequencies towards the panels but still leaving enough normal light through so rooms don't get too dark. I think they even deflected the far infrared away so the heat stayed out of the building!
Can't remember the report too clearly but I think it was an office building in France...