Quick question: would you interpret quantum dots as disruptive technology for light absorbing solar energy, or concentrating solar power (CSP)? One is a fairly recent topic in the photovoltaic world, and the other has been around for over one hundred years.
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Nanomech in Photovoltaics
An interdisciplinary exploration of third generation photovoltaics, environmental technology, and scientific philosophy.
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What is disruptive technology?
- Date:
- Wednesday, 02 Jul y 2008 - 19:47 UTC
A quantum dot is a nanoparticle in which the excited states (high energy electrons and holes) are “confined” by the very small dimensions of the particle. This leads to increased energy in the excited states (no where to go but up in energy), and has resulted in many new technologies. One proposed technology would use quantum dots as light absorbers for a photovoltaic effect, where one could collect mulitiple electrons (increased photocurrent) or very high energy electrons (increased photovoltage). The up side is that quantum dots sound sooo cool, why not make them into PV devices? The down side is that the rates of charge carrier extraction (collecting the electrons to do work) are still way too high to get much efficiency out of them. A lot of research needs to occur before you start seeing purely quantum dot PV. The disruption appears to be far away.
On the other side, if you concentrate the sun’s power, you can use it effectively for multiple applications, and often you don’t need radical new technologies. Rather, a combination of straight forward technologies in a new way may lead to something disruptive. You can concentrate the sun’s visible light (48% of the suns power, or 656 W/m2) for photovoltaics, OR you can concentrate the sun’s infrared light (45.6% of the total power, or 623 W/m2) and use the thermal heat to do work! Either way, by concentrating you take a diffuse source and, well, concentrate it. Certainly, you would need to cool a PV collector, but what about a thermal collector powering a turbine to generate electricity? In 1878, a solar power collector was exhibited at the World’s Fair in Paris, France. Between 1907 and 1913, an American engineer (F. Shuman) developed solar powered hydraulic pumps with a concentration ratio of about 4.5:1.*
And the kicker, CSP is getting closer and closer to being the first economically viable solar technology—opening the doors to the following technologies? Is this disruption, by opening the possibilities of solar power beyond the single junction photovoltaic device?
- D. Y. Goswami, F. Kreith, and J. F. Kreider Principles of Solar Engineering 2nd Ed. (2000) Taylor & Francis, Philadelphia, PA.
Last updated: Wednesday, 02 Jul 2008 - 19:47 UTC
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Comments
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Jeffrey – I think I’m missing the point. Are you saying because the relatively low-tech CSP has more immediate benefit that we ought to ignore quantum dot technology (though, of course it will remain of interest in other applications)?
Can’t we do CSP and other developments as well – e.g. new PV technologies using much lower cost materials or higher efficiency PV? I’m not totally clear why it excludes other approaches?
Thanks for the question and comment Brian. CSP, in the form of CPV certainly does have a more immediate benefit than quantum dot photovoltaic technology (in terms of cost per watt). That’s the trick with CSP: multiply the power gain while using low cost materials. You just need to get a higher performance than a sc-Si cell at a reduced price.
But this is not an either/or situation. I am also saying that we should be pursuing all solar developments (I’m an energy diversification advocate). We should definitely pursue quantum dots for future technology. In fact, I would suspect that a CPV system using small cells of quantum dot materials is entirely possible in our future.
My question was more along the lines of estimating the odds of CSP being the initial disruptive technology for the solar field, or quantum dots?