THINNER IS BETTER?: Thin-film photovoltaic cells, like those in the array seen here in Mainbernheim, Germany, can harvest as much energy from the sun with far less semiconductor material.
Image: COURTESY OF FIRST SOLAR
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The sun blasts Earth with enough energy in one hour—4.3 x 1020 joules—to provide all of humanity's energy needs for a year (4.1 x 1020 joules), according to physicist Steven Chu, director of Lawrence Berkeley National Laboratory. The question is how to most effectively harness it. Thin-film solar cells may be the answer: One recently converted 19.9 percent of the sunlight that hit it into electricity, surpassing the amount converted into power by mass-produced traditional silicon photovoltaics and offering the potential to unleash this renewable energy source.
Prices for high-grade silicon (that can generate electricity from sunlight) shot up in 2004 in response to growing demand, reaching as high as $500 per kilogram (2.2 pounds) this year. Enter thin-film solar cells—devices that use a fine layer of semiconducting material, such as silicon, copper indium gallium selenide or cadmium telluride, to harvest electricity from sunlight at a fraction of the cost.
"The fundamental advantage of thin film comes in the form of the amount of material you need," says electrical engineer Jeff Britt, chief technology officer of thin-film manufacturer Global Solar Energy in Tucson, Ariz. "These are direct bandgap semiconductors. You can get by with one or two microns and still absorb 98 percent of the sunlight." (In other words, it takes at least 100 times less thin-film material to absorb the same amount of sunlight as traditional silicon photovoltaic cells.)
Global Solar uses a technology known as copper indium gallium selenide (CIGS) to make its thin-film solar cells. The company has already supplied the U.S. military and outdoor enthusiasts with portable field chargers, largely for communication and other small electronic devices powered by such cells. In March, the company opened a new factory in Tucson, where it plans to produce enough thin-film CIGS solar cells to generate 40 megawatts of electricity next year—enough to power roughly 15,000 average American homes; it hopes to boost the juice to 100 megawatts by 2010 in response to what it predicts will be a growing market.
"We're focusing on low-cost terrestrial power generation," Britt says. "It's intended for large-scale, ground-based arrays." In other words, the types of solar farms previously dominated by traditional silicon photovoltaics now used to generate electricity from sunshine in states like Arizona and California.
Global Solar is not alone. A host of companies, including HelioVolt, Nanosolar and others, are using CIGS technology in an attempt to cut the cost of producing photovoltaic cells. But there are other challenges. "The first hurdle is cost," says materials scientist B. J. Stanbery, CEO of HelioVolt in Austin, Tex., which is in the process of opening its first CIGS solar cell factory. "The second is efficiency [how much sunlight can be converted to power] and the third is the reliability, [which means the] lifetime of the device."
Researchers at the U.S. Department of Energy's (DoE) National Renewable Energy Laboratory have succeeded in producing CIGS cells that can convert nearly 20 percent of the sunlight that falls on them into electricity. But manufacturers note that mass production reduces their efficiency because chemical processes are not as easy to control on an industrial assembly line.
"Benchtop is a great thing to measure because it tells you about the potential of the technology. It tells you nothing, however, about what people are actually making or can make," says Paul Wormser, senior director of product development for the Solar Energy Solutions Group at electronics manufacturer Sharp Electronics, headquartered in Osaka, Japan. "By the time you go into production, you're going to get about half" of the efficiency demonstrated in a lab under perfect conditions.
Sharp pairs amorphous silicon (fine layers of randomly arranged silicon) with layers of crystalline silicon (whose atoms are in a more structured lattice) to make its thin-film cells. It plans to increase its manufacturing capacity at its plant in Katsuragi, Japan, to produce enough cells to make 160 megawatts of electricity by October—and to bring its total annual output to enough cells to produce 1,000 megawatts by 2010 by building another factory in Sakai, Japan.
He denies speculation that thin-film solar cells will eventually kill the traditional crystalline silicon phtotvoltaics end of the business, noting that they are designed to supplement, not supplant, the old standbys. "Rumors of crystalline's demise are highly exaggerated," Wormser says. "We see thin-film as highly complementary to crystalline and concentrators."
But Wormser says that thin-film cells have the potential to produce more power over time than the older technology, because they resist the sun's heat better and produce more power when the temperature spikes.
Durability may be an issue, however. Consequently, thin-film cells intended for large arrays use lower grade silicon (read: glass) to protect the delicate photovoltaic layers. For example, Tempe, Ariz.–based First Solar, Inc., which employs cadmium telluride in its thin-film solar cells, sells its modules encased in glass for either large arrays or rooftops. "The elegance of the solar business is that you construct a product and it just sits there generating power for 20 to 25 years," says company president, Bruce Sohn.
In addition to offering solar modules at $1.25 a pop (compared with at least double that per module for traditional photovoltaics), First Solar has also instituted a process for recycling them at the end of their active lives.
"Glass can be returned to the glass industry. Metals can be repurified and given back to us in the form of the cadmium telluride compound. Even the wires can be reused," Sohn says. "We really can recycle in excess of 90 percent of the weight of the product today in a perpetual, environmentally friendly life cycle."
In fact, cadmium telluride solar cells are currently the most ecofriendly devices, even though they use a toxic heavy metal, primarily because they require the least energy—typically provided by burning fossil fuels—to manufacture, says environmental engineer Vasilis Fthenakis, senior scientist at Brookhaven National Laboratory's National Photovoltaic Environment Research Center in Upton, N.Y., and Columbia University.
Yet, cadmium telluride commands only about 30 percent of the thin-film market, according to DoE statistics, compared with amorphous silicon cells (such as those produced by Sharp and ECD Ovonics), which account for more than 60 percent; CIGS cells make up just about 1 percent of this market.
But CIGS has the most potential efficiency (converting as much as 25 percent of incoming sunlight to electricity) of any of the thin-film technologies as well as of traditional photovoltaic cells, Heliovolt's Stanberry says. Würth Solar in Germany has mass-produced such cells that can convert as much as 13 percent of sunlight, according to Lawrence Kazmerski, director of the DoE's National Center for Photovoltaics in Golden, Colo.
All of the thin-film technologies also offer the potential for ubiquity. That is, says Sharp's Wormser, "you have the opportunity with thin film to make what people refer to as a semitransparent photovoltaic module in place of a window on a building. It allows you to see out through the window, but from the outside it looks like tinted glass."
The thin-film solar cells can be used in more flexible applications, such as so-called solar shingles, roofing materials that double as electricity generators. "It's going to serve the purpose of keeping out the elements, but it's also going to generate power for you," Global Solar's Britt says. This also eliminates the significant cost—typically at least doubling the price of a given module—of adding solar photovoltaic systems to already existing buildings.
Alternative forms of electricity generation—or some kind of efficient energy storage, such as better batteries—would be necessary for those times when the sun is not shining. But thin-film solar cells hold the promise of harnessing the sun's power in an efficient and sustainable way—and displacing the burning of fossilized sunlight for energy that is contributing climate change–causing carbon dioxide to the atmosphere.
"Combining this highest efficiency, lowest cost and most reliable thin-film technology directly into building construction materials will be the beginning of a revolution in solar power," HelioVolt's Stanbery says. "I worried that I wouldn't live to see the day when solar became an economically substantive part of our energy mix, but I think we're on the road to that happening finally. The best is yet to come."
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25 Comments
Add CommentThis is the next big step in reducing our dependence on fossil fuels. Everyone talks about giant solar arrays, but the average joe really doesn't care about them. What we want is to see personal solar arrays, one's that affect our lives directly. And most of us don't want to wait forever to get them!
Reply | Report Abuse | Link to thisWe currently have the technology to build safe, fast, electric cars. Now with the introduction of thin film solar cells we have the technology to make those electric cars "cordless". You drive to work, you park your car in the sun and eight hours later you drive home. Most cars sit out in the sun eight hours a day, which would mean eight hours of charging for an electric car with a thin film solar roof. So you'd never have to plug in your car again, or at least very rarely.
Since the longevity of the thin film solar cells has yet to be determined it just requires a bit of decent design to make them a modular part of the car. A roof designed to hold and protect the solar cells and yet make their removal and replacement easy would be the order of the day.
And why stop with the roof of the car, why not design the trunk and hood to also house thin film solar cells. And if there is enough electricity generated by solar film in the doors and other body panels, why not include them as well?
It's really nice to hear about the "potential for ubiquity" and solar shingles and other visions of the future, but what the man on the street is looking for is something practical. Something that impacts their life now, not ten to twenty years from now. Thin film solar cells are the technology that can vastly reduce our dependence on fossil fuels, we just have to start using them.
As the article correctly notes, cost per watt hour is much more important than conversion efficiency in creating a demand for solar electric. How about long-run roofing rather than solar roofing tiles. That would really bring down costs.
Reply | Report Abuse | Link to thisDoes one assume a megawatt is what UK engineers call a megawatt.hour?
Reply | Report Abuse | Link to thisHow many kilowatt.hours in a 'pop'?
Definitions used to be important in the transfer of understanding.
Andrew
In the News as one possible answer to our dependence on fossil fuels.
Reply | Report Abuse | Link to thisMillions of years supplying the Earth's needs...
http://www.quazen.com/Science/Technology/Solar-Power-Source-of-Endless-Energy.21176
Solar Power, Source of Endless Energy
I have not made any calculations, but I think that even with 100% efficient solar panels the surface of average car is not sufficient to charge it's battery for any significant mileage. And then there are those not so sunny days that make it even worse. So in reality the solution for cordless car could be made by installing those solar panels onto a house, that has many times the potential surface area, at the roof for example. Those panels would charge a battery, that in turn would charge the car battery when it is near to be plugged in, for example during the night. Or those panels could feed the grid during day and grid electricity would be used at night to charge the car battery.
Reply | Report Abuse | Link to thisBeside this car issue, I wonder how feasible it would be to use combined PV and thermal panels? It could be made by placing PV cells on top of watercooled thermal panel. That way the energy wasted in PV cells as heat could be harvested to provide wam water etc and it would also boost the efficiency of PV by keeping it cooler. And total harvested radiant energy efficiency should be better. How much better will probably determine whether such combined harvesters are worth making up.
This is nothing but a shell game and SA should know better (wait. They do. They're just environmentalist ideologues).
Reply | Report Abuse | Link to thisLet's use more realistic numbers than total solar radiation hitting the earth, because no one is going to pave over the oceans.
Incident sunlight under ideal conditions is 1 kilowatt per square meter. That 's it.
An electric car equivalent to a 150 hp internal combustion engine need about 100 kilowatts of energy peak and about 25 kw for cruising.
At 100% efficiency, you would need 100 square meters of solar panels to run your car in real time. Current cell efficiency is 20% at best. So, practically you need 500 square meters. A car's surface area is about 3 square meters. A 5000 square foot two-story home (a McMansion) has about 280 square meters of roof for solar panels.
So, on a perfect day you would have to take the entire output of the roof for 16 hours to give your car an 8 hour charge.
Here's the dirty little truth and is why solar power fails over and over again commercially.
There isn't enough energy density in sunlight to support an industrial society.
If you want energy density, you use supernova fragments. Our planet is full of them. They're called Uranium and Thorium.
Yes, it's a great step forward for solar power. Still, the tree huggers haven't answered the simplest question: What happens to the power grid when the sun isn't shining?
Reply | Report Abuse | Link to thisThis is great news for the renewable energy and effective reduction of CO2 emissions (power generation with no CO2 emissions) -- an effective tool when dealing with global warming and meeting growing demand for green power ...
Reply | Report Abuse | Link to thisThanks,
Gordan
> An electric car equivalent to a 150 hp internal
Reply | Report Abuse | Link to this> combustion engine need about 100 kilowatts of energy
> peak and about 25 kw for cruising.
> So, on a perfect day you would have to take the
> entire output of the roof for 16 hours to give your
> car an 8 hour charge.
Most people interested in a practical electric car don't feel any need for "150 HP performance"! So I think your calculations start with an energy use assumption that is 2 to 3 times higher than necessary.
The other inumeracy is "an 8 hour charge": That would be reasonable for someone with a delivery service, but the vast majority of us spend less than 2 hours per day driving. The 5-6 hours of peak-equivalent power that most PV systems generate yielding a 2.5 hour charge would be fine.
The analysis also ignores the fact that PV systems can put power into the grid at precisely the time of day with the highest demand, the afternoon air-conditioning peak during hot summer days. Conversely, a commuter's car can then be charged with current drawn back from the grid during the night when a lot of excess capacity is available. If home users were actually paid for the value of their power sent into the grid during the day and charged for the value of the power they draw at night, home PV systems would quickly pay for themselves.
Here in Northern California, "solar roofs" are already a reality. New homes have offered them as an option for some time now. Even with glowing testimonials of people saving hundreds of dollars on their utility bills, tax incentives and so on, they still remain a "hard sell". Why? Because of the high initial cost of the installation. With a typical family only living in a house 7 years or less it's difficult for them to justify this "investment". I'm encouraged however, with more progressive thinking and lower manufacturing costs this technology will eventually become more commonplace. I think the previous commentator got it right, that the average person would like to get off "the grid", if for no other reason than to have more control over costs, etc. (Remember ENRON?) Even if "solar cars" never become a reality, wouldn't it be nice to have say 30% of it's power supplied from "free electricity" you generated yourself? New innovations come about mostly from necessity.
Reply | Report Abuse | Link to thisDown with big solar farms! There is no need to centralize expect to support the monolopy - collect it where you need!
Reply | Report Abuse | Link to thisYes, of course we expect clueless idiots here to say this means on-site thin-films will destroy other solar technologies. However the article is correct, for the next 30+ years silicon, thin film, and solar thermal especially will all play vital roles, none of them exceeding the demand for any of them.
Reply | Report Abuse | Link to thisWhy is it when we think of innovation like this, we think large industrial structures taking up lots of land & resources. Look at some pictures from the 1890s in a typical city then with all the wires, telephone poles, etc. Today we have a thousand fold increase in communications & power sources with none of these eyesores. Just suppose, in the near future, every new house sold in this country was required to have a solar roof. People would predictably balk at the initial cost, but would see benefits in reduced utility bills, and most importantly see immediate feedback on their conservation efforts. This technology will not arrive overnight, but incrementally as costs go down and people grasp the benefits of more empowerment over their personal lives.
Reply | Report Abuse | Link to this"The sun blasts Earth with enough energy in one hour4.3 x 1020 joulesto provide all of humanity's energy needs for a year (4.1 x 1020 joules), according to physicist Steven Chu, director of Lawrence Berkeley National Laboratory. The question is how to most effectively harness it." This statement is the equivalent of something like "there is enough hydrogen in ocean water molecules to provide energy through fusion for thousands of years." There is much more to the question than just a source term.
Reply | Report Abuse | Link to thisSteven Peterson, Ph.D.
Silicon makes up 27% of the Earth's crust. The current high cost is just due to a glitch in supply/demand planning, where conservative polysilicon suppliers were reluctant to believe the rapid growth of Si PV, having been recently burned by the dot com bust of the late 1990's. Thin film PV semicondutors may use 1/10 or so material but are much rarer, often toxic, and ultimately higher in cost for truly large-scale use than silicon. Selenium is 0.000009% of the Earth's crust and tellurium is 0.0000002%.
Reply | Report Abuse | Link to thisMake oil old technology should be the goal of pursuing photovoltaic cell technology.
Reply | Report Abuse | Link to thisWe took the plunge 3 years ago and released equity in our London home to install a 4.8Kwh photovoltaic system, which currently provides 100% of our electricity. The excess electricity is exported into the national grid which we get paid for, if every home had solar panels the need for generating stations would be reduced. My argument is simple, our national governments should be offering financial incentives to everyone to purchase solar technology and enhanced rates for the electricity produced that is exported to the national grid. This model works in Germany where they have been able to encourage a new industry which manufactures and develops solar technology. The fact that we produce our own electricity has changed the way we use electricity, in that we replaced all the tungsten and halogen lamps in our house with LED's and turn off all non essential usage of all equipments, including standbys.
Reply | Report Abuse | Link to thisAs fas as storing solar energy is concerned - the answer is to use Hydrogen Balancing technology. This is used for Wind Power Generation and could easily be adapted for use with solar power. See here :
Reply | Report Abuse | Link to thishttp://www.energyefficiencynews.com/power-generation/i/643/
http://whlenergy.com/
This would allow the treehuggers to use solar generated electricity at midnight - but without any harmful emissions - radioactive or chemical..
REGARDING:
Reply | Report Abuse | Link to thisAndrewMcG at 08:24 PM on 04/25/08
"Does one assume a megawatt is what UK engineers call a megawatt.hour?
How many kilowatt.hours in a 'pop'?"
A "'pop&apos" can be whatever you want it to be since it looks like a typo of some sort to me.
A watt is one joule of energy per second.
A megawatt is one million joules of energy per second
A megawatt-hour is one million joules of energy per second for one hour or 3600 seconds, therefore is 3.6 billion joules of energy.
And if there is any question, a joule of energy is the energy required to raise a one kilogram mass one metre against an acceleration of one metre per second per second of accleleration.
to put it into perspective, a 2 litre bottle of water would mass about two kilograms and the acceleration of gravity is about 9.8 metres per second squared, so raising a two litre bottle of water one metre would require about 2 x 9.8 or 19.6 joules of energy.
Definitions used to be important in the transfer of understanding.
Andrew"
can anyone tell me the true cost of installation and length of time this thin film technology will last. also who is installing this thinfilm technology in the seattle,wa area and is this a good area for solor cells????
Reply | Report Abuse | Link to thiscan anyone tell me the true cost of installing a thin-film system in the seattle, wa area and is this a good area to use this kind of power supply? also who is currently selling and installing this technology?
Reply | Report Abuse | Link to thisThere is a new technology for solar panels that will be ready in five years. It will utilize nearly 95% of the sunlight that reaches it.
Reply | Report Abuse | Link to thisHi Dragon, sound interesting.
Reply | Report Abuse | Link to thisDo you mind to share the information regards your statement.
Thanks.
Eason
That's good news. I like that. I always think that it can be happen and now it is. Thank You for sharing such a awesome news.
Reply | Report Abuse | Link to thisWe have to reduce our dependence on fossils fuel and take steps to turn into solar power. Otherwise in future there will be a crisis of energy everywhere. Here is a solution to get solar power @ solar power phoenix
Reply | Report Abuse | Link to thishttp://www.americanpv.com/solar-power-phoenix.php