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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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Since you can create multiple refractions inside a hologram, you can create a much better lense than with diffraction gratings. So while both are basically flat lenses, the holographic version is much more efficient.
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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.
Since plain ol solar will never meet our energy needs, just use the grid as a storage device. Durring the day the grid is fed by solar energy with the shortfall made up of anything else available, at night the total demand for energy is lower so those same reserve sources can feed the grid. If there ever is a time that our entire grid can be solar (I doubt highly that this will ever happen) then you can charge a kinetic sourcew against a gravity well* or charge a massive flywheel with the excess power.
-nB
* for example pump water up a mountain to a storage lake and let it run down durring the night for power
-nB
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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
Have you ever seen http://www.homepower.com/ magazine?
Funnypics
It takes a few hours (at least) for most power stations to significantly alter their output - and over a day to completely turn one on/off. When other power stations are overproducing, they provide somewhere for the spare energy to be stored. When others are underproducing, they take up the slack.
While the grid might not be a battery, it certainly contains some fairly large ones. Even if it didn't, being able to turn off a fossil fuel power station or two[2] during the day would be a significant environmental benefit.
[1] While you, as an end customer, may only see a flat rate (or maybe a peak/off-peak rate) for electricity, your supplier sees a significant variation in prices from minute to minute and from power station to power station.
[2] Of course, you would not actually turn one off, but you might reduce the load (and hence fossil fuel usage) on 10 by 10%.
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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.
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.
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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
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
I always think about solar power while on the freeway... here in CA it's the 405 and the 5 freeways that do it for me... 12 car lanes of completely open space traveling hundreds of miles up and down the state, with a lot of already built infrastructure, ie: wiring, conduits, maintenance terminals, etc.
Covering over the freeways with a half tube grid of cheap material... put up solar cells in grid cells where they make the most sense, let light, air and weather filter through the rest... feed it into the local grid, voila.... a huge huge solar cell array, located in the one place where it can't do anything but improve the aesthetics.
Use the cheapest stuff you can get and upgrade as those become more efficient over time...
A fool throws a stone into a well and a thousand sages can not remove it.