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."

Comments

Only 10x? That's huge!

[chriss]

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.

Re:Only 10x? That's huge!

[Ungrounded Lightning]

It sounds [like the improvement is] to make it cheaper by only having to use ten percent the amount of PV cells in the same area of solar panel.

Yep.

a one square yard panel of naked PV cells shouldn't get any more energy than one square yard with holographic cells... right?

A square yard of naked cells (or cells imbedded in a classic panel), a square yard of focusing concentrator onto a smaller area of cells, and a square yard of holographic panel containing some smaller area of cells, would all potentially collect the same power (neglecting concentrator inefficiencies).

The point is that:
  - doing a square yard of collection with a square yard of cells costs.
  - A normal focusing concentrator focuses not just the useful light, but the non-useful far-infrared, so you need serious cooling of the cells to run at a high degree of contentration, and the concentrator is bulky, heavy, and may need to track the sun.
  - This thing is WAY cheap to make, doesn't focus useless infrared below the cells' bandgap frequency, and doesn't need to track. It loses some of the light, so you may need a little extra area to make up for that. But you use only 10% of the cells compared to a classic panel for a given amount of power.

As I read the drawings this is basically a glass plate with solar cells glued to 10% or so of the back and the remainder covered with a holographic coating.

The holographic coating diffracts the desired frequencies so they become trapped between the faces of the glass plate by total internal reflection (as light is trapped in a fiber optic light pipe) and it bounces back and forth between the surfaces until it hits a place where a cell is glued to the back. At that point the glue's index of refraction is high enough that the light can escape into the cell. So you just need enough cells that most of the light encounters one before it gets to an edge or leaks out where a dirt speck sits on the glass. (I'm not clear how they keep the holographic coating from diffracting it back out toward the sun but I presume they've got that covered.)

Far infrared doesn't bend enough to get trapped so it escapes out the front or back of the panel.

This is VERY nice. With maybe 90% of the infrared passing through the panel or bouncing out the front of it you don't get the massive greenhouse effect of a classic panel.

Holograms?

[exp(pi*sqrt(163))]

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.

Re:Holograms?

[chriss]

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.

Re:Holograms?

[thePig]

And it seems like the marketing department managed to put a spin on that too
Not sure whether that is a spin. Heating is a real problem for Solar concentrators.. A lens will concentrate light, but also IR. These are quite high temperatures we are talking about. If they can actually take out IR from the question, then this indeed is a good idea..
Also, I can see pratical applications on window sills etc. In our place, temp can go up to 110. Think of a cheap window which will let in only light (similar to the current double pane windows)...
It has future.

Solar collecting is good.

[crazyjeremy]

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.

Re:Solar collecting is good.

[shmlco]

"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."

I can see solar as a potential option for some businesses, but for home use you still have the small problem of no power output during the night. And that's usually just when you want some lights, television, heat, and so forth.

If they want solar to REALLY catch on someone is going to need to develop not just a cost-effective solar cell, but also a cost-effective way to store and reuse the energy collected during the day.

Re:Solar collecting is good.

[Glonoinha]

If only there was a way to store all that electric power. Maybe massive plates of lead and zinc in a acid solution, in big heavy square things with little plugs on top to add distilled water from time to time (I have no idea why, but I envision that there would be a good reason to do so on my mythical device.) Give it a catchy name like 'Deep Cycle Truck Battery' and sell them at Wal*Mart for ~$50 apiece, letting us fill an entire room with them for under a thousand dollars.

Someone should invent that.

Re:Solar collecting is good.

[networkBoy]

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

Re:Solar collecting is good.

[pellis23]

That's what grid-connected solar arrays are for. You use the grid as your battery. In California at least, with a grid-connected array, PG&E buys any surplus electricity you generate during the day (while you're at work and the sun is shining) for the more expensive daytime retail price and when youg et home and actually consume, you buy back from the grid for the cheaper, night time price.

Re:Solar collecting is good.

[networkBoy]

Just for the record, those batteries _suck_ for solar energy collection.
Something more like this:
http://www.ibsa.com/estore/search.asp?details=1&ms cssid=KS9FNAJCUXGV9LBH81QUWL707VKN9LB0&Ntt=mining& N=0&Dx=mode+matchallany&part_number=4D-XHD&Nty=0&D =mining&Nu=Part+Number&Ntx=mode+matchallany&part_d esc=Workaholic+-+1000+CCA&Ns=product+Type%7C0%7C%7 CRank%7C1&Ntk=SearchGroup
Though that's with an ultra quick search.
-nB

Re:Solar collecting is good.

[Anonymous Coward]

thats a good link, can you read it back for me over the phone ?

Re:Solar collecting is good.

[networkBoy]

"thats a good link, can you read it back for me over the phone ?"
Sure:
ache tee tee pee colon whack whack dub dub dub aw fuckit dot see oh em

Re:Solar collecting is good.

[Anonymous Coward]

You need to physically go and see some houses that have "whole house" solar installations, talk to the people there. Sigh... I can yammer about it all day long, say I lived with it for years, that the battery banks (cheap normal flooded lead acid storage batteries) could go for four days with heavy clouds, that on sunny days the batteries would be fully chrged by 1 PM in the afternoon despite heavy usage, that the payback period is less than ten years, etc...it won't do any good. Not a damn bit of good, This is the same FUD from the 70's, probably based on "true science facts" from rush limbeau and the US electric monopoly company..

The tech is here, it works, and it's affordable tied into the 20 year note, and the tech usually has at least that long a warranty, 30 years is common now. A lot of folks are now getting less than a ten year payback because rates are so high for electricity, and do you really think electric rates will be going DOWN in the future?

There are THOUSANDS of installations in the US and millions world wide. It is not "theoretical" it really doesn't need any more "study", we are at the marginal improvements stages now, like with computers, roughly when they went over a couple gigahertz CPU speed. They got good enough and affordable enough at that point most anyone who wanted one could get one, now computers are common landfill trash..

This is not anything weird anymore, or "in the mysterious future", solar PV is mainstream proven robust technology. It WORKS and got cheap enough around ten years ago, even cheaper if you just do a meter spinning backwards grid tie with it. Which coincidently works when AC demand is the highest in the summer, "the heat of the day", the more nice hot sunny days, the more AC is needed, the more solar PV slaps the power into the grid or your batteries at the right time.So you have two basic ways to do it, store it (I recommend that, much nicer), or sell it back cheap. Either way it works now. And the US is falling behind places like germany,japan and china when it comes to the alternatives, because they *aren't stupid*. They can check out the news and see energy is rising in price a LOT faster than most anything else, oil has gone up around 25% in one year. Knock knock, hello, this is your wallet speaking. The other energy forms will be close behind, oil is always the base energy pricing indicator.

That's why japan, germany and china are in massive solar upgrades-along with wind and anything else they can do NOW, because they "get it" on looking past one fiscal quarter, and in the US-we mostly don't. Two days is a push here, this is the short attention span short bus to school nation, ipods and video games are the only thing important technologically speaking..these other nations can see the handwriting on the wall and are getting in hard, fast and early when it is still cheap. Also why they pump out a lot more engineers than we do, and why they actually reward "brains". We reward sports heroes, movie stars and corporate CEO thieves.

You are paying an electric bill anyway, tell me, when will that bill be PAID OFF? When do you get to "own" your electric production if all you have is the grid source? Oh, never? Is that so, so how is there any "payback" and how is it "affordable" if you never get to own it? If solar needs a payback, how about all other forms of sold electricity? When is your payback, what sort of deal did the local electric company give you? What is your "payback" time frame at your house with just relying on some company like enron? 50 years paying to RENT? Say you start at age 20 and pay an electric bill for 50 or 60 more years-what do you have to show for it after all that time?

NOTHING, you rented! Same as if you rented an apartment for 50 or 60 years instead of buying a house, no equity, nothing. It's *dumb*, retarded now that we have a variety of workable alternatives. What is your electric bill by the kilowatt hour in 5, 10 years, 15 years years? Oh, you don't kn

So many stories but where are they?

[Zaai]

Pardon me for being sceptical about the actual commercial feasability of this.

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?

Re:So many stories but where are they?

[crazyjeremy]

Products like this decrease the amount solar panels needed. Many of the wonderful improvements are available, but at a very high cost. This development specifically reduces the cost needed to attain the same amount of power.

Comment removed

[account_deleted]

Comment removed based on user account deletion

Hologram, eh?

[LochNess]

Finally, a use for Arnold J. Rimmer.

Re:Hologram, eh?

[Tumbleweed]

Finally, a use for Arnold J. Rimmer.

Rimmer Directive 271 states clearly, "No chance, you metal bastard."

10x input != 10x output

[EmbeddedJanitor]

Silicon solar cells are still too damn expensive and power hungry to manufacture to be a useful mainstream generation tool. The only places they're really being used is where mainstream supply is not available/practical or where they are heavily subsidised for political/marketing ends. Increasing concentration to reduce the silicon are does reduce the amount of silicon and therefore potentially reduces the $ per W. However...

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.

Re:10x input != 10x output

[trixillion]

From the article it is clear that this technology is specifically designed to address two of your concerns. Admittedly it helps to have a background in physics in order to understand some of the concepts (particularly the optics.) Firstly, the holographic lens and waveguide have been designed to direct certain ranges of wavelengths to the silicon and the other wavelengths away from it. This helps to prevent overheating of the silicon cells. Secondly, the lens system is there in order to collect more light per area of silicon used. This causes the $/Watt to increase, while the efficiency (Watts converted per Watt theoretically availlable) remains the same (well, in a perfect world, it sounds like this will work significantly better in their second generation.)

Re:10x input != 10x output

[syphax]

Who cares if it's only 5% efficient, so long as it is cheap? Tile your house with the stuff to get the area.

You are almost absolutely correct. Except for two things:

1. Low efficiency leads to higher indirect costs- specifically, the infrastructure that holds the cells and connects them to the grid. As you get down to lower efficiencies, these costs become significant.

2. Even at 10% efficiency, you need a huge area to produce a significant amount of juice. Sure, we could in theory generate all the energy we need in the U.S. by covering "only" around 1% of the U.S. land area with 10% efficiency PV (practical issues aside), but that still works out to be a huge area. Like, say, Maine. So even if we had a nice, cheap, low-efficiency solar technology, it's usefulness would ultimately be limited by land use constraints.

We used a similar product in 2001

[goldarg]

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.

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.sola rexplorer.net/gallery/index.php?TopicID=panels

Google finds reference to the technology that TerraSun was developing http://www.wapa.gov/es/greennews/2001/may14'01.htm

Re:We used a similar product in 2001

[Anonymous Coward]

This company is apparently the spawn of TerraSun. They acknowledge this in the PDF mentioned above (http://www.nrel.gov/technologytransfer/entreprene urs/pdfs/prism_solar.pdf), slide 3 gives the company timeline and lists TerraSun.

That's not the point

[m85476585]

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.

How about Fresnel lenses?

[dinther]

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.

Re:How about Fresnel lenses?

[bensch128]

If you read the article, it says that lens don't work because they have to be always facing the sun -> heavier/more expensive.

The hohlgraphic plates can redirect light coming in from any direction and cause it to eventually (after much bouncing around) fall on a photovoltaic cell. It also has the benefit of filtering out bad (unhelpful) IR light.

Cheers,
Ben

cost per watt

[maino82]

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.

many diffraction gratings are holographic

[Anonymous Coward]

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

Skeptics: this is NOT just a glorified Fresnel lnz

[Starker_Kull]

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.