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

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?

[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.

[Gyga]

Most enviromentalist don't advocate pure solar, they advocate using it the take strain off other systems, I look at AC in the desert as big strain to be removed.

Put a solar farm on several people's roofs, put a wind farm here and there, coastal cities get wave generators, and everything else can be nuclear. That is the future, not pure solar.

If this new system could be inmproved to focus the light to a small line I wonder if panels could be hid inbetween roof shingles? Removing the ugly factor entirly, though thick black lines could be cool.

Re:Solar collecting is good.

[topham]

Yes, but you can let the water out at night and still have power...

Dams are really large storage cells. (Batteries)

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

Re:Solar collecting is good.

[cridanb]

a pump storage facility which pumps water up a hill is operational in wales and connected to the national grid in the UK

it is used to balance out extreme loads reacting quickly to smooth out demand so that more power stations are not kept idling

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:Alternative to each other?

[Phillup]

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'.

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

[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.

Re:10x input != 10x output

[Anarchitect_in_oz]

Given that in most places we want power we also want hot water.
I'm not sure why they don't combine PV Solar with absorption panels linked to a heat pump and the hot water system, or heat the pool.

Finding uses for heat, in most building isn't all that hard.

Deal with PV's problems by teaming with other technologies instead of trying to solve all the problems in isolation.

Re:Promising...

[Jeremi]

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.

The other possibility is that the price of the alternatives might go up. If that happens, then solar will look more attractive even at its current pricing.

Re:Hologram, eh?

[dubbreak]

Finally, a use for Arnold J. Rimmer.

If you didn't find that absolutely hilarious you really need to watch some Red Dwarf.

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.

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.