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Where are the 70% Efficient Solar Cells?
Posted by
Cliff
on Wed Jan 08, 2003 04:22 PM
from the better-power-from-photons dept.
from the better-power-from-photons dept.
VernonNemitz asks: "Back in 1984 a patent was granted for silicon chip micro rectennas, which would convert visible photons into electricity in the same way that ordinary rectennas convert microwaves into electricity, at perhaps 70% or greater efficiency. Nobody could make such solar cells back in 1984, but we certainly can today, with sizes of antennas that would capture everything from infrared to the edges of UV -- and the patent has expired. So, where are they?" Currently the most popular type of solar technology is photovoltaics, however PV technology only has an efficiency of about 7-17%. With the potential gains claimed by the technology in the cited patent, has anyone even tried to build one of these units to see if it can live up to the given promise, or at least prove to be a technology than we should be exploring?
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Beats me (Score:5, Funny)
Heres a company - up to 80% efficiency. (Score:5, Interesting)
Also there was a story about 2 weeks ago, mentioning solar energy breakthrough using full-spectrum layering. Does anyone know anymore about this. I was unable to find it in Google News.
Nanotech material, once they arrive, will of course make 90% efficient material practical.
Planet P Blog [planetp.cc] - Liberty with Technology.
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Re:Heres a company - up to 80% efficiency. (Score:5, Funny)
What kind of nanotech material are you talking about? Little nano robots that run around catching photons IN their nano baseball gloves and pitching them into nano furnaces that run nano generataors?
If you want people to take you seriously, a statement like, "nanotech materials _may_ be able to produce 90% efficient material," is more reasonable. "of course" is just silly.
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Re:Heres a company - up to 80% efficiency. (Score:4, Funny)
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Re:Heres a company - up to 80% efficiency. (Score:5, Funny)
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Re:Heres a company - up to 80% efficiency. (Score:4, Informative)
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Rectenna? (Score:5, Funny)
Anyone else get a sorta shifty feeling when they look at that word and picture the consequences of such an invention?
Where the sun don't shine (Score:5, Funny)
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Re:Where the sun don't shine (Score:5, Funny)
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Re:Where the sun don't shine (Score:4, Funny)
</cartman>
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Re:Where the sun don't shine (Score:4, Funny)
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Why we have to have 80%+ (Score:5, Interesting)
You can read about here on my website [floatingplanet.net] for more info. Some in the oil industry are thinking that peak will be hit within the next two years. This might explain our rush to invade Iraq.
Either way, as oil reserve dwindle and demand goes up, it will create a highly destabilized politic - and if you think the repression we've all been feeling lately is bad, it will only get worse... UNLESS:
We wean ourselves (QUICKLY!) off of Oil. The Hydrogen economy is just waiting in the wings. All of the technology is essentially there. The cost factors will become not only competitive, but cheaper and cleaner than oil, once we start migrating our energy infrastructure over to Hydrogen.
Lets hope this happens before we end up in some kind of nigthmarish Oil Fedual/Fascist Global New World Order.
Planet P Blog [planetp.cc] - Liberty with Technology.
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Re:Why we have to have 80%+ (Score:4, Insightful)
My worry is the health of the planet in the mean time. I live in central Minnesota, USA. Our average high temperature this time of year is about 9 degrees F. Yesterday it was 55 degrees F. I know full well one warm winter does not global warming make, but we've had several bizzarely warm years lately. We're s--tting where we eat and it worries me.
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Re:Why we have to have 80%+ (Score:5, Insightful)
Oil demand grows at 1-2% per year. Oil production capacity (current and estimated undiscovered) grows at about the same rate, because that's how economics works. They work just hard enough to keep the demand supplied.
However, at some point the reserves (current and estimated undiscovered) run out. At current rates of growth, that's expected to be somewhere between 2039 and 2066, with a 65% confidence level.
There's no peak. We just run into a wall and it's over.
But that assumes demand will be constant. It won't. As the visible end approaches, the surviving producers will start gouging on the scarcity. Consumption will drop, stretching out the date at which the oil dries up. Possibly indefinitely, since at that point other energy technologies become feasible. But still at a much higher $/kWh than we now pay for oil. There's your peak: when the consumption curve turns down due to market economics and substitution of alternatives and deprivation.
Petroleum will become a minor energy product, like whale oil is now (whale oil used to be a major energy product; go look it up).
Which is something the oil companies see coming, but know they can't profit from, so they deprecate alternatives and then secretly work to develop them, so they can continue to control your energy supply after the oil finally becomes deprecated itself.
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Re:What about Biodiesel? (Score:5, Insightful)
Honestly, bioethanol has much more short term potential than biodiesel. Lignocellulosic feedstock is available in bulk, and the baseline economics are pretty good - a modest scale facility using existing technology could be built today that would make ethanol at a total cost of probably 1.30-1.60 per gallon if feedstock availability is good and cost is cheap (this works out to probably 1.70-1.90 per gallon equivalent of standard gasoline). In other words, with another 15-20% efficiency improvement followed by scale increases to reduce the amortized fixed cost of plant+facilities per gallon, it could be price competitive with gasoline. And there are already well over 1 million FFVs (Flexible Fuel Vehicles) on the road today that could burn E85 (85% ethanol, 15% gasoline mix) without modification - most people who own these cars don't even realize it.
Ethanol has real potential and some of us are working on making it into a business reality.
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Re:Ethanol is not good (Score:4, Informative)
What my post talks about if you read it, is what is generally referred to as "bioethanol". Of course, ethanol from corn sugars is biological in origin, but what most people call bioethanol is ethanol produced from biomass or lignocellulosic feedstock.
That means _waste_ cellulose. Such as corn fibers, not the corn iteself, or pulp/wood chip byproducts from the milling/cardboard industries, and "waste" crops such as bagasse in Louisiana that grow in swamp land (i.e. land not arable for production of more valuable crops and that grow with very little external water and energy input and thus are very low in terms of actual feedstock cost including any energy input).
The cellulosic chains are broken down and the constituent glucose and xylose sugar molecules are fermented - there are several processes such as SSF (Simultaneous Saccharification and Fermentation), steam-cracking weak acid hydrolysis, and recirculating strong acid hydrolysis, which are all more-or-less viable for this process.
I shall not defend the corn ethanol industry - you are correct in saying that they exist because of federal subsidies. I am promoting a process for taking otherwise "valueless" biomass that would end up in land fills or lie unused elsewhere that can be obtained at relatively low cost and converted into a relatively high value energy product.
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Re:Rectenna? (Score:5, Funny)
Here's the best that Google could come up with for picturing a rectenna [google.com], but the exact image I wanted wasn't found. As demonstrated in episode 101, rectennas are powerful, but also put out a lot of heat.
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Re:Rectenna? (Score:5, Funny)
I asked her, "Are you sure you want to know?"
"Yes, show me."
So I covered my eyes and shift-clicked.
"Eeewwwww," she said, "is that real?"
"Yes dear, it's real and the burning sensation in your eyes will clear in a few days."
It's scary shared-experiences like these that really solidify a relationship.
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Goverment rebates (Score:3, Informative)
It seems someone is working on them... (Score:5, Informative)
I know where they are (Score:5, Funny)
Is it here yet? How about now? How about now? (Score:5, Funny)
Research (Score:5, Insightful)
Who elected George Bush anyway?
Re:Research (Score:4, Funny)
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Re:Research (Score:5, Funny)
Notice anyone threatening the Netherlands lately, Wisebeing?
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Re:Research (Score:5, Insightful)
So even a "Manhattan Project" style affair will be worthless unless we also make a concerted effort to dramatically improve the energy efficiency of our society -- our cars, our appliances, our homes, etc.
With not much effort, by not a huge percent of the population, California was able to fairly significantly reduce its energy needs during the whole Enron-initiated "power crisis." Not to sound polyannaish, but just imagine what would happen if we all actually did some simple, painless, things that saved energy.
The problem is that most people need a real incentive -- dramatically higher costs -- before they will conserve.
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U-235 vs. U-238 (Score:5, Informative)
Then there's a wide variety of other radioactive substances that can be burned in reactors. For example, breeder reactors can actually breed plutonium from the very common U-238 (U-238 is one of the most common elements in the Earth's crust), creating an almost infinite supply of fuel. Military breeder reactors work fine for producing lots of plutonium for atomic bombs. Research on commercial breeder reactors (basically the military reactors tied to turbines to power electric generators) was stopped by worries about arms proliferation (it is much easier to seperate Pu-239 from U-238 than it is to seperate U-235 from U-235 in raw uranium ore, thus makes it easier to get enough fissile material to crete atomic bombs), but could be re-started pretty swiftly if necessary. Which would not be for 50 or 100 years, as you mention.
Regarding 100 and 400 years of oil, my own best estimates are somewhat lower than that. My estimates are that we will experience shortages within 20 to 25 years, and that within fifty years we will have basically exhausted all economically accessible oil resources (i.e., there will be oil out there, but it will take more energy to extract it than can be obtained by burning it). However, hopefully by that time the current taboo regarding nuclear power will have eased, and we will be able to replace the lost petrochemical resources with synthetic hydrocarbons or other such creations. (Don't laugh, we use petroleum as feedstock for chemical plants because it's cheap, available, and readily "cracked", but there are certainly other feedstocks that could be "cracked" into various petrochemicals if necessary, including coal, for that matter -- after all, both the Nazis and the South Africans did it).
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Where are they? (Score:5, Interesting)
The patent just expired. It takes a while to develop and prove out a new technology.
I see lots more work on windmills for alternative power. Many have shelved solar panels because the current ones have poor performance.
Re:Where are they? (Score:5, Interesting)
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Re:Where are they? (Score:5, Interesting)
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Re:Where are they? (Score:5, Interesting)
The downspout on an office building is going to produce proportionally less electricity. Let's assume you have a 4000 square meter roof 100 m high and you get 100 cm per year of rain. That's 4 million kg of water dropping 100 m. Since E = mgh, you get a potential annual power yield of 4 gigajoules. Over the whole year, this comes out to an average of 126 watts. Factor in unavoidable generation losses, and you'd be lucky to power a single light bulb with the rainwater from an entire office building.
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cost? (Score:5, Insightful)
Possibly overlapping Patents? (Score:4, Interesting)
Perhaps impractical to actually build? (Score:4, Informative)
Assuming the applicant built a prototype and proved this device works, creating metal coatings in the exact thicknesses he mentions with the detail he describes is still something that would be very expensive to do now. That technology hasn't improved very drastically in the last decade or so.
What, or rather Who keeps this off the market? (Score:5, Funny)
Who keeps the metric system down?
We do, we do.
Who keeps Atlantis off the maps?
Who keeps the Martians under wraps?
We do, we do.
Who holds back the electric car?
Who makes Steve Guttenberg a star?
We do, we do.
Who robs cave fish of their sight?
Who rigs every Oscar night?
We do, we do!
Not with semis (Score:5, Informative)
E=hw
Silicon is actually a rather poor photomaterial, being an indirect material, it's limited to about 60% effeciency at any wavelength. The electron must not only gain energy, but also move a slight bit within the crystal in order to reach the conduction band. Direct materials, such GaAs, being direct, can be > 95%
Perhaps the are other techniques??
Re:Not with semis (Score:5, Informative)
Whoops, I think you're confused. w (which is actually an omega) is angular frequency, not wavelength. And h is really h-bar, which is Planck's constant over 2 Pi, not Boltmann's constant.
But the actual equation is correct :-)
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Here it is. The inventor calls it lepcon. (Score:5, Informative)
It looks as if this is all still very blue-sky, and there is no reason to think that these nifty ideas will work in practice. The first page I linked to tells us: ``Dr. Marks is in negotiation with U S. government to fund Lepcon research and development.'' Probable translation: ``He's applying for grants, because he can't sell it to the venture capitalists.''
PVs can exceed 35% efficiency (Score:4, Interesting)
This article mentions Tecstar--apparently the leading supplier of high-output PV cells for space missions. They made the cells for the Mars lunar rover, among other projects.
The difficulty is that manufacturing the cells is very difficult and expensive, requiring multi-million dollar Metal Oxide Chemical Vapor Deposition (MOCVD) machines. Due to variations in the rather elaborate manufacturing process, the yields vary greatly, and also produce cells that have widely varying efficiencies. Some cells fall below a given spec, while others exceed the spec.
In order to achieve a given power output for a space system, they are able to mix the under and overperforming cells into an array that provides the necessary power.
So, although some cells may only provide 30% output, a few will exceed specs, and thus provide > 35% efficiency. The challenge is delevoping manufacturing processes that improve yield and thus reduce costs.
Why aren't we ever going to see these type of cells on earth? Cuz they cost millions of dollars to produce, and there is a multi-year order backlog for them for planned space missions. Unless hundreds of millions of $ gets directed towards making them a commodity, well, you know the story...
Solar cells (Score:4, Informative)
The cost and deposition speeds already eliminate a number of materials from practical application; and, there are a number of other issues that must be taken into account (especially among modern solar cell materials):
1) For sunlight, the maximum intensity occurs at 550nm, which means that a device bandgap of 1.35eV is needed to give a maximum electron/hole pair generation rate. One of the best known solar cell materials, c-GaAs, has an Eg = 1.4eV, but its high cost makes it prohibitive. c-GaAs can be grown by epitaxy, but requires high temperatures for deposition -- it can be difficult to grow uniformly over large surface and on more desirable substrates (like plastics).
2) c-Si, which is cheaper than c-GaAs, must be deposited in very thick layers for max efficiency, and has an Eg = 1.1eV, making it difficult to deal with and not that efficient. Like c-GaAs, impurities in the crystalline latice can have large, detrimental performance effects.
3) a-Si is a great material as it can be grown over large areas very inexpensively, but it has a number of disadvantages. Being amorphous, it suffers from metastability (the Stabler-Wronski effect), which means that its performance degrades over time as more light hits it. It also has Eg = 1.8eV, which makes it less than perfect for sunlight-based solar cells.
There are other issues facing solar cell designers, such as:
1) reflection at the surface
2) series resistance due to impurities and scattering within the semiconductor
3) non-radiative recombination (phonon recominbation) in the semiconductor
4) incomplete extraction of carriers in the semiconductor
5) interface and contact losses in the p-i-n or Schottky barrier structure
Triple-tandem solar cells made of p-i-n structures of a-SiGe, uc-Si, and a-Si:H (which have bandgaps like 1.2eV, 1.45eV, and 1.85eV in the same package) can be used to target as much of the solar spectrum as possible, and can still be grown "relatively" cheaply by PECVD reactors. They get somewhere around 17% efficiency in sunlight.
Performance of solar cells would undoubtedly be better if cost were not an issue, and if single-wavelength light were being used, as exotic material devices could then be targeted for these specific conditions. Alas, real life is not so ideal.
-kris
Lets get realistic about the cost. (Score:5, Insightful)
Maybe the price needs to come down to a few THOUSAND dollars...with some government tax credits and utility savings, it might be worth it.
-ted
Theoretical problems with optical rectennas (Score:5, Informative)
Sunlight at the earth's surface has a power flux density of about 1 kilowatt per square meter. To convert that to an electric field strength, we take the square root of the power flux density times the impedance of free space, 377 ohms. This gives 614 volts/meter.
Yellow light has a wavelength of 570 nm. That means the electric potential over that distance is only about 350 microvolts. This is approximately the voltage you'd see at the terminals of a 50 ohm half wave dipole, and it's far below the voltage needed to switch a rectifier. Silicon rectifiers take about 600-700 millivolts of forward bias to begin conducting, even if one could be constructed to work efficiently at optical frequencies. Germanium takes about 300 mV, and silicon Schottky diodes take about the same.
It is not possible to construct a diode that doesn't require a forward bias, otherwise we could rectify the noise from room-temperature resistors and convert ambient heat to useful work. This is specifically prohibited by the second law of thermodynamics.
Oil is solar power! (Score:4, Interesting)
I think it is a good idea, anyway. The only energy that is not solar is geothermal and nuclear.
Re:Ask yourself... (Score:5, Funny)
90% of slashdot just simultaneously realized that these solar panels havent been developed because they are too busy looking at porn and playing warcraft.
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Re:Where are the 70% Efficient Solar Cells? ask GW (Score:4, Insightful)
If GWB is so concerned about keeping the Texas oil economy going and appeasing the Texas oil companies, wouldn't he want to avoid increasing the supplies of oil, especially foreign oil? If GWB annexed Iraq and started sucking out all the oil for US use, that would just tank the prices of oil and lower the demand for Texas oil.
Plus he's POTUS now, not Governer of Texas, he has more people to appease then just the Texans. (And if it was so easy to invent alternative energy he'd score far more points across the board then he would lose in Texas)
Bush & Cheney both sold off their stocks (at a loss at the time), to limit their conflict of interest with the oil companies.
It isn't GWB holding up electric cars in some oil conspiracy, it's the population as a whole - who collectively don't seem all that interested in alternative fuel vehicles or higher fuel usage vehicles. Then there's the money for whatever new infrastructure is required by alternative energy...
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Re:Where are the 70% Efficient Solar Cells? ask GW (Score:5, Insightful)
t0qer's argument is correct, though, just not formulated quite accurately. It's not support for Texan oil. There really isn't any more Texan oil. What oil the US produces is mostly offshore or Alaskan, but even so it's small fraction of what we use.
Bush isn't trying to support pumping of oil; imported crude goes straight into the US petrochemical industry. Many of the refineries are in Texas, but even where they aren't, GWB is a friend of the industry. It's where he made his millions, and it's all he knows.
It's not simple selfishness and wanting to pad his wallet. It's just that that industry is where he grew up. He's conditioned to think of it as central to US wealth and prosperity, the driver of the economy. In his mind, whatever is good for the oil companies is good for every American. He really honestly believes he's doing the right thing for all of us by suppressing alternative technologies and making war with Iraq.
Bush is not smart and worldly enough to see the bigger picture, or to take the long view.
Getting the Iraqi oil fields under a friendly regime means the US has more *control* over oil prices and fewer "bad guys" to worry about messing up the economics for his favorite companies.
It isn't GWB holding up electric cars in some oil conspiracy, it's the population as a whole - who collectively don't seem all that interested in alternative fuel vehicles or higher fuel usage vehicles.
Yes and no. US consumers don't want a wimpy EV1, for the most part. They want the bulk, power, and capacity of an SUV. Thus, the consumer is to blame.
But... The government spends many billions on petroleum research, exploration, and foreign policy to support the petroleum economy. The cost of just the first war with Iraq and the subsequent decade-long airspace occupation is estimated in the back hall of congress to be in the range of $100 to $200 billion [washingtonpost.com]. Billions more are spent every year to subsidize activities (research and exlporation) that benefit the oil companies. I've seen figures (can't find them right now) that estimate you pay $5 to $8 per gallon of gas in income taxes to support petroleum
Now... if over the last fifteen years the government had spent that same half a trillion dollars on electric, fuel cell, and hybrid vehicle research, don't you think we'd already have big powerful SUVs that don't depend on oil? We'd have a cleaner country, consumers just as happy, and fewer foreign policy messes. What if we'd been doing that since 1920? Shouldn't we start now so we're not asking the same question again in 2040?
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Re:Where are the 70% Efficient Solar Cells? ask GW (Score:5, Interesting)
Do you have a URL for Bush's guidelines on electric vehicles?
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Re:Where are the 70% Efficient Solar Cells? ask GW (Score:4, Informative)
What would happen if all the major automakers decided tomorrow to start building electrics?
We would burn about the same amount of oil, and increase our use of coal.
We would burn about the same amount of oil, because you wouldn't be replacing very many gasoline powered cars on the roads; electrics are still too small and have too short a range to be useful for the majority of Americans. None of this is going to change until there is a dramatic improvement in the stored energy densities of batteries, and/or a reduction in the toxic waste produced in the creation and disposal of the batteries themselves. The last time I saw statistics, the sum total of all the "alternative fuel" vehicles sold in the world over any time period you choose to look it was LOWER than the increase in the number of vehicles in the world ... that is, even with increased sales, we continue to fall further behind.
We would burn more coal because electric cars need to get the electricity to recharge their batteries from somewhere, and the cheapest source of electricity generation (that can be built today in North America and Asia (and even Europe, I believe)) is coal.
This is not to say that there aren't loads of technologies available to improve efficiency of fossil fueled vehicles, but most of them make vehicles MUCH more expensive (by almost any metric you choose) ... and the vast majority of people (Americans AND non-Americans) have little incentive to spend more when they can get the same capabilities for less, EVEN IF it would be to their benefit in the long run (why else would people be willing to lease instead of buy vehicles? It is far far more cost effective in the long run to buy than to lease ... ). Some of these technologies include hybrids, light composite frame and body materials, ceramic and aluminum engine blocks, high efficiency diesels, exhaust scrubbers, biofuels, superconducting electricity distribution grids, etc. etc. etc.
But none of them are perfect, and none of the forseeable technologies will eliminate our reliance on petroleum ... not even that "holy grail" of environmentalists, the "Hydrogen Economy". Hydrogen isn't free after all ... there are no large supplies of the stuff to drill or mine for, and there is none in the atmosphere to distill. You have to generate it by cracking water ... using electricity, that you have to generate by some other means. And currently, the only good way to do THAT is to produce the electricity using nuclear (which the environmentalists ALSO hate and also has a time horizon before the exhaustion of the fuel), hydropower (environmentalists hate this too) or fossil fuels ... and the inefficiencies involved in the seperation, storage, shipment, and sale of hydrogen currently would would require just about the same amount of fossil fuel usage as currently for the same energy extracted by the automobile (although we might be able to use different forms, such as more coal and less oil, and there would be far fewer plants to police). In other words, we'd be burning the same amount of fossil fuel to make the hydrogen as we currently burn to make the cars go in the first place.
There are no simple answers and very few real conspiracies, and I don't understand why otherwise intelligent people continue to believe that there are.
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Re:Anyone know the energy in sunlight? (Score:5, Informative)
This is from Here [electrochem.org]
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Re:Anyone know the energy in sunlight? (Score:4, Interesting)
if you take all the unused building space in america and covered them with solar cells (of today's technology and efficiency) you could generate (more than) all the power we use (even if we convert all cars to electric cars). the neat thing is that the "unused building space" doesn't mean "cover the desert with solar cells" is just means to put solar cells on every roof top, on the top of the medians along the highways. granted this is a difficult task, but what if every residential house that was built had to have it's roof coated in solar cells and put on the grid. after a while you'll be generating quite a lot of power.
another cool thing that is in development is turning the huge windows of office buildings into solar panels. in high-rise office buildings, it's not uncommon to have 10 foot tall windows that span the entire room. usually these windows are tinted and the office generally has blinds or curtains to keep all the sun out (to reduce cooling costs in the summer, and having that much sun in the office would make it to bright anyway). so rather than just using some type of tinting that reflects the light partially, i've seen some cool work with dithering (very) small solar cells in the windows, these will absorb light and turn it into electricity. so you'll get two benefits: tinted window and extra electricity for the building.
just simple solutions like that could help our upcoming power crisis when we run out of oil.
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