Staying cool: A liquid metal cooling system developed by IBM could help allow concentrated photovoltaic cells to have more solar energy focused on them. As a result, more electricity could be produced without vaporizing the cells.
IBM T.J. Watson Research Center
A technology developed by IBM to cool computer chips could be a boon for solar energy.
By employing a trick normally used to cool high-performance computer chips, IBM researchers have found a way to make concentrated photovoltaic cells that are more efficient in converting the sun's energy into electricity.
The researchers have shown that it is possible to increase the concentration of light on photovoltaic cells by about ten times without causing them to melt. This, they say, makes it possible to boost the amount of usable electrical energy produced by up to five times.
IBM is not known for its work in solar energy, but that has changed recently, with the rising cost of fuel and the growing interest in renewable alternative energies, says Supratik Guha, lead scientist of photovoltaic research at IBM's T.J. Watson Research Center, in Yorktown Heights, NJ. "About a year and a half ago, we decided to start looking at photovoltaics," he says.
The principle behind concentrated photovoltaic cells is to use a large lens to focus light onto a relatively small piece of photovoltaic semiconductor material. The benefit is that only a fraction of the semiconductor material is used, thereby reducing costs.
There are a number of companies marketing such technologies, but one of the main challenges is in coping with the vast amounts of heat produced by the focused sunlight, says Guha. "You're really heating the chip up. As you raise the temperature of the chip, its efficiency drops, so you've got to keep the temperature down." There are generally two ways to do this: either by using passive heat sinks--metal blocks that draw the heat away from the cell--or, for higher-temperature systems, by using water cooling, in which water is pumped through a metal heat sink to draw the thermal energy away more efficiently.
In many respects, this is a problem very similar to cooling computer chips--something with which IBM has a long history, says Guha. State-of-the-art chips now kick out about 100 watts per square centimeter, which is similar to what concentrated photovoltaic cells have to endure, he says.
So Guha adapted an IBM-developed material currently used for chips to improve the heat transfer between the photovoltaic cell and a water-cooled heat sink.
"If you place the chip on a copper heat sink, the interfacial heat transfer isn't good enough to keep the temperature down," says Guha. This is because microscopic indentations in both surfaces means that there will be relatively little surface contact between the faces. So photovoltaic companies tend to use various organic pastes to act as thermal interfaces. The problem is that such materials aren't particularly efficient at transferring heat.
Sunrgi claims that its concentrated photovoltaic system outshines the competition.
The silicon shortage that has kept solar electricity expensive is ending.
Best Solar Uses Scarce Materials
I'm concerned that the latest thin film and concentrated PV rely on some scarce minerals like, Cadmium, Indium, Gallium, Selenium, Tellurium, and so on. Reserves of some of these metallic elements are numbered in mere tons. They already have uses in the electronics industry that could potentially consume them. So, how far can we really stretch them for use in solar panels? Probably not nearly as far as we imagine. Costs come down and use of materials goes down, but in the end, can we achieve the potential of solar by relying on these scarce materials?
For this reason, I am most impressed by technologies that move Silicon PV cells forward. We have Silicon in great abundance. Efforts to bring down costs of Silicon production, reduce waste, improve its quality and to use far less of it to produce the same or more energy deserve the greatest attention in the long run. When combining the best of the latest innovations, it seems certain that Silicon-based cells could compete on cost.
After a little research, I found the following paper online. Here's one of its conclusions:
"Today it appears unrealistic to expect that a PV system based on either CdTe, CIGS or
ruthenium-dye-sensitised cells could produce more than 10 000 TWh/year
corresponding to some 6 TWp in the year 2100 and an average growth of 60
GWp/year sustained over 100 years. According to most energy scenarios this would
correspond to less than 5% of the total energy supply. A potential that is a factor of
ten lower is perhaps more realistic, that is significantly below 1% of energy supply.
Amorphous silicon, with germanium, is much less constrained, and without
germanium it is not material constrained, in our sense, at all."
http://frt.fy.chalmers.se/PDF-docs/BA_thesisWoP.pdf
Re: Best Solar Uses Scarce Materials
why waste the heat thats valuable energy ! either used to generate more electricity or to heat your home/factory...
Re: Best Solar Uses Scarce Materials
That's a good thought, but it would be a difficult trick to concentrate heat when your most important objective is to dissipate it as rapidly as possible.
Re: Best Solar Uses Scarce Materials
Agreed, there are many ways for waste heat to be used to create more power - everything from simple Stirling engines to some of the promising solid state thermal technologies.
The heat from collector systems can be extracted to generate power via low pressure (wet steam) or it can be used to heat salt beds for later extraction at night (see Nevada Solar 1).
There are ways to take the heat and increase the velocity of the fluid via orifice or venturi for extraction by a low pressure steam system to drive an auxiliary generator. It's a sound principle that is currently used in today's co-generation power plants. Use the exhaust heat of a gas or coal fired engine to drive a secondary low pressure steam system.
The remaining or residual heat can then be dumped to atmosphere using cooling vane technology. Sometimes the best solutions are old tech.
Can the technology being developed to produce electricity from waste heat in internal combustion engines with thermoelectric [paint] materials in exhaust (pipes) be used to enhance the production of electricity in photovoltaics? It seems a shame to just waste all that heat! When can we expect an inexpensive photovoltaic system for home use which can compete with the local electric utility?
nanosolar already has the system and the price to do this (home elec at grid price), but all their capacity is bought up by big companies.
One thing slowing home adoption is that the cheapest techs will be bought up by major projects to sell to the grid (with tax and other incentives, it competes in many places). The more expensive technologies that cannot compete even with incentives are left for homow's to buy ... because they don't have to compete with the cost of a coal plant, they have to compete with the cost of delivered kw/h's at their meter, a much lower standard.
Also, although the info above is correct as conventionally calculated, the truth is even the worst techs on the market can compete with bulk/grid electricity in an absolute sense. But investors don't ask, can we sell this power at coal rates and pay off the plant before it dies? They ask, can we sell this power at coal rates and pay off the plant in 5 to 7 years so we can have 20+ years pure profit?
Many of the PV techs are rated 25 years but in fact will be generating more than 80% of their nominal output 50 years from now. That can still give 20+ years of pure profit...but to the kids of the investors, not to the investors themselves.
The fact that PVs costs are all up front skews the profit equation to make them appear less attractive than they might be in absolute terms and/or to long-term thinkers.
Many thanks for this interesting discussion.
I was wondering what the capabilities are of polymer based photovoltaics. I found some thread on this site at: discussion on polymer properties, specifically: polymer based phtovoltaics. But this doesn't help me much.
Thanks
Rod
Concentrated sunlight can drive a laser. Then, the laser light can be converted into electricity much more efficiently. A solar cell can utilize laser photons better because only one frequency allows coatings to be optimized.
Possibly, a coherent beam could drive a laser diode.
Possibly, sunlight could pump a maser, and diodes could then rectify the microwaves to obtain electricity!
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10 Comments
Complementary manufacturing
It is surprising that IBM would make a comment that they "don't plan to make [concentrated photovoltaic] systems", given that the two technologies have much in common :
- both require thin-film substrates of silicon
(either amorphous, poly-crystalline or mono-crystalline)
- both utilise nano-scale features (see http://www.technologyreview.com/Energy/19696/,
http://www.technologyreview.com/Energy/18415/ and
http://www.technologyreview.com/read_article.aspx?id=20163)
- both employ multiple layers of various materials (semiconductors and metals) to act as electrical pathways and improve efficiency
I would have expected there to be enough complementary overlaps in manufacturing techniques that there are significant benefits to incorporating the two technologies within the same development environment.
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