Print 32 comment(s) - last by jbartabas.. on Aug 4 at 3:52 PM

This tech is too hot for old, drab silicon.

Although photovoltaics have seen marked advances in recent years, they are still remarkably inefficient when it comes to harvesting the energy they receive. Even the best production silicon photovoltaics convert less than 20 percent of the light they receive to electricity.

Silicon photovoltaics suffer a compound problem in energy generation. First, they can only capture a narrow spectrum of the sunlight they receive, producing immediate waste energy from the unused light in the form of heat. Second, silicon photovoltaic efficiency suffers from heat. In essence, a cell's own waste energy cripples it. Silicon photovoltaics produce zero energy at temperatures even below 100 degrees Celsius, regardless of how much light they receive.

Rather than trying to improve the efficiency of these already self-hobbled solar cells, Stanford researchers, led by materials sciences and engineering assistant professor Nick Melosh, have created a new material that can harvest both incident light and heat energies. Their paper has been published in the August 1st edition of Nature Materials online.

To create a solar cell that would flourish under both light and heat, they broke away from the familiar silicon semiconductor platform and instead looked to gallium-based photovoltaic surfaces. But in order to harvest the heat generated by the waste energy, they needed to add an additional layer of material, for which they used a thin coating of cesium metal. They have dubbed the energy harvesting process PETE, for Photon Enhanced Thermionic Emission.

Unlike traditional silicon cells, Melosh's group's don't hit their peak efficiency until temperatures in excess of 200 degree Celsius--well above the point where silicon cells have already been rendered inert. To make the best use of the material's properties, they could be used in solar concentrators, where temperatures regularly exceed 800 degrees Celsius. Further waste heat could then be used in thermal exchangers, much in the same way solar heat is currently harvested to create energy.

Melosh's team is looking to hit 50 to 60 percent conversion between the cesium layer and semiconductors like gallium arsenide. And to make the material and process even more promising, fabrication costs for a standard six inch wafer of the material put it theoretically on par with oil-based energy generation by output.

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By bug77 on 8/3/2010 4:43:09 AM , Rating: 2
Maybe I'm nitpicking here, but last I checked cesium was radioactive?

RE: What?
By namechamps on 8/3/2010 8:14:16 AM , Rating: 1
I believe Cs133 is the naturally forming isotope and it is stable.

Cs135 * Cs137 are byproduct of nuclear fission reactors and nuclear fallout.

RE: What?
By bug77 on 8/3/2010 8:54:54 AM , Rating: 2
I see. So last I checked, I checked the wrong cesium. Apparently, there's a Cs134, too, but the article almost certainly refers to Cs133.

RE: What?
By Shadowmaster625 on 8/3/2010 10:25:55 AM , Rating: 4
Sure its not radioactive, it just happens to explode on contact with water.

RE: What?
By geddarkstorm on 8/3/2010 3:09:07 PM , Rating: 2
Just like potassium, sodium, and oh so much so lithium metals :P.

RE: What?
By UnWeave on 8/3/2010 4:22:19 PM , Rating: 2
Yeah, but have you seen a water caesium reaction? It's boomtastic. If these one day become mainstream and, say, ended up on my roof, they had better be water-tight.

Below 100 C???
By jhb116 on 8/2/2010 10:19:39 PM , Rating: 2
Did you ABOVE 100 C?

RE: Below 100 C???
By jlips6 on 8/3/2010 3:14:49 AM , Rating: 2
no, he meant above 9000

RE: Below 100 C???
By Flail on 8/3/2010 4:09:09 AM , Rating: 4
no, he meant OVER 9000!!!

RE: Below 100 C???
By TSS on 8/3/2010 7:16:28 AM , Rating: 2
no, he ment "not even reaching 100 C before producing zero energy", as the limit for that to happen is below the 100 C mark, but above say, 60 C.

But i agree it's very poorly worded. I too thought "you have to freeze these things to get energy? that can't be right..."

Too good to be true...
By theArchMichael on 8/2/2010 9:24:51 PM , Rating: 2
fabrication costs for a standard six inch wafer of the material put it theoretically on par with oil-based energy generation by output

Yeah, but do they mean over the lifetime of the six inch wafer? Per year?
If it were per year and assuming it's MTBF is longer that would probably create enough savings to really get everybody on board... or at least offset the other costs associated with improving infrastructure for rolling something like this out nationwide.

RE: Too good to be true...
By LeviBeckerson on 8/2/2010 10:26:51 PM , Rating: 2
They did not include that information in the information I had access to. I will see about obtaining it though!

RE: Too good to be true...
By Amiga500 on 8/3/2010 2:45:38 AM , Rating: 2
Yeah, but do they mean over the lifetime of the six inch wafer? Per year?

Almost certainly over the lifetime of the wafer unfortunately.

If it could (right now) match the cost of oil infrastructure and cost within a year, then this article would not just be on Dailytech, it would be all over the news.

RE: Too good to be true...
By topkill on 8/3/2010 11:59:29 AM , Rating: 3
That is exactly the question that needs to be answered. They always give some bogus number on price per kWh without qualifying ANY of the assumptions they used:
- Did they assume the dessert in Arizona or somewhere in New York state?
- What life span did they assume?
- did they include the cost for some type of storage mechanism for solar (or wind) if they are comparing cost per kWh against other sources like nukes. Hey, the sun doesn't shine 24/7 so you have to level the load to do an apples to apples comparison
- did they include any subsidies in the price

I would love to see solar and wind take over the world. But throwing out bogus numbers that don't apply in the real world is not helpful.

Thermal Conversion
By deltaend on 8/3/2010 5:01:04 AM , Rating: 2
The thermal conversion could also be accomplished by the Eneco power chip, although there is much debate as to if this chip is the most recent "super conductor at room temperature" type fiasco.

We really, really, really need to figure out a better way to generate energy with heat. So much of it goes to waste. Imagine deserts turning into light/heat farms overnight and converting their value from worthless to highly profitable?

RE: Thermal Conversion
By Kurz on 8/3/2010 8:50:55 AM , Rating: 2
There has to be a natural process in nature that converts the lowest state of IR into something.

It seems to be a waste that the universe doesn't have a mechnism that allows the easy and natural conversion of heat.

RE: Thermal Conversion
Where can they be used?
By JediJeb on 8/3/2010 4:17:51 PM , Rating: 3
Unlike traditional silicon cells, Melosh's group's don't hit their peak efficiency until temperatures in excess of 200 degree Celsius--well above the point where silicon cells have already been rendered inert.

I'm guessing from this they probably would not be the best things to use in the Arctic regions. I know you could insulate them and they would self heat, but 200c is quite a bit above ambient in many places.

Another question I have is could you wrap a thermocouple around these and generate even more electricity with any heat that escapes?

RE: Where can they be used?
By jbartabas on 8/4/2010 3:52:13 PM , Rating: 2
[...] 200c is quite a bit above ambient in many places. [...] Another question I have is could you wrap a thermocouple around these and generate even more electricity with any heat that escapes?

The PETE process has been studied for solar concentrator systems, hence the search for high efficiencies at high temperatures. As for using some of the waste heat, that's actually a substantial part of what they propose in order to reach 50%+ overall efficiency (by use of a thermal cycle in addition to the PETE).

Not enough information
By Senju on 8/2/2010 10:25:31 PM , Rating: 2
Although Interesting, there is simply not enough information in this article for us to get excited about. As you can see from the above posts, this article leads to 10 more questions.

By kwrzesien on 8/3/2010 3:04:35 PM , Rating: 2
My roof shingles are 100% efficient at converting solar rays into heat (or 0% at converting it into electricity). How much cooler would my house be if that heat wasn't there? I bet the savings from running the HVAC less would make ANY solar panel roof system worthwhile in the long run.

WOW! What we need.
By Belard on 8/3/2010 9:03:19 PM , Rating: 1
More Tech like this is what we need for the future.

Make it cheap by mass production so everyone can have it on their homes... recharging their cars, etc. We will eventually run out of oil... in 100 years, we'll look quite different than today.

good luck
By shin0bi272 on 8/2/10, Rating: -1
RE: good luck
By san1s on 8/3/2010 12:46:41 AM , Rating: 2
what? you didn't know you could buy solar panels for your home?

RE: good luck
By Dr of crap on 8/3/2010 9:06:29 AM , Rating: 1
I have to agree. Can we stop with the breakthoughs and accually build these things up and PROOVE them to the masses?
If this so called breakthough were that good, lets build up a football field full of them to TRY IT OUT AND PROOVE it to the unbelieving - me!

RE: good luck
By shin0bi272 on 8/3/2010 5:59:55 PM , Rating: 2
no re-read my comment... when THESE new "breakthrough" panels hit the market I'll care... till then STFU. No one is making panels with any of the hundreds of breakthroughs we've seen on DT... they're all still using silicon. Though some have moved to thin film silicon... but if youve checked the prices lately a 230w panel is 1800 US! Get with the making of the cheap high efficiency panels already! Its been years since I heard about lead selenium which was supposed to be 40% efficient but where are those panels? No where that's where!

RE: good luck
By cesium62 on 8/4/2010 4:56:14 AM , Rating: 2
Sunpower creates silicon solar panels that convert 22% of sunlight. [ ]
That was three years ago.

First Solar creates thin film cadmium-telluride panels. Not even remotely silicon. CIGS (copper, indium, gallium, selenide) is another thin film technology that also doesn't use silicon.

First Solars panels are convert 10% of sunlight, and even that low conversion efficiency is sufficiently practical for them to be one of the biggest producers of PV.

By iceonfire1 on 8/2/10, Rating: -1
RE: Efficiency
By SunTzu on 8/2/2010 10:01:39 PM , Rating: 2
And no info on how much light would be needed to get them profitable.

RE: Efficiency
By LeviBeckerson on 8/2/2010 10:25:05 PM , Rating: 4
As stated in the last paragraph, the efficiency of the gallium arsenide panels should be around 50 to 60% under ideal conditions. For comparison, the source stated that current silicon panels can be as good as about 20%, as stated in the first paragraph.

RE: Efficiency
By Shadowmaster625 on 8/3/2010 10:38:25 AM , Rating: 2
20% is an upper limit. Most cheap solar panels that are competitively priced on the market right now are about 12-14%. If this tech could really do 60% it would be nearly 5 times more watts per square foot. Most el cheapo solar panels deliver power around 10 watts per square foot. The power density is too low to be practical. But at 60W per sq ft, well that could be something.

RE: Efficiency
By shin0bi272 on 8/3/2010 6:03:10 PM , Rating: 2
well no because if the silicon panel is maxing at 20% for these to max at 60% if the silicon panel goes down so will these... probably by a more drastic curve too since they have to be 200C to operate efficiently.

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