Quantum Dots Could Double Solar Energy Efficiency 112
dptalia notes the recent publication in Science of research demonstrating a way to use hot electrons in solar cells, resulting in an overall energy conversion efficiency of 66%. Here is the abstract in Science; access to the full article requires a subscription. "A team of University of Minnesota-led researchers has cleared a major hurdle in the drive to build solar cells with potential efficiencies up to twice as high as current levels, which rarely exceed 30 percent. ... Tisdale and his colleagues demonstrated that quantum dots — made not of silicon but of another semiconductor called lead selenide — could indeed be made to surrender their 'hot' electrons before they cooled. The electrons were pulled away by titanium dioxide, another common inexpensive and abundant semiconductor material that behaves like a wire."
Summary Skips over important piece from the story (Score:5, Informative)
"The next step is to construct solar cells with quantum dots and study them. But one big problem still remains: “Hot” electrons also lose their energy in titanium dioxide. New solar cell designs will be needed to eliminate this loss, the researchers said."
Re:How much energy are we talking about? (Score:2, Informative)
RTFA, about 66%
Re:But by when? (Score:4, Informative)
Meanwhile, partially as a result of various breakthroughs in solar cell technology, solar cell prices are finally dropping despite unprecedented demand.
Re:How much energy are we talking about? (Score:5, Informative)
I'm no expert, but probably a lot more. Some facilitating factors:
1. PbSe is pretty easy to synthesize as nanorods. TiO2 is even easier. Lower production cost.
2. Higher efficiency (theoretically) than the 40% record achieved using triple junction cells (which have extreme costs and are likely never going to be practical) and the ~25% achievable using single-junction silicon cells (maximum theoretically about 31%).
This should lead to a great increase in the achievable power. The only thing that I'm unsure of is whether you can concentrate the light in nano-confined cells as much as you can in bulk material cells. The (I believe) issue becomes current density saturation either within the material or at the connector interface. Not altogether familiar with the R&D in this area. Since high-efficiency cells can be concentrated efficiently by a factor of ~1000x, this could be a significant effect if nano-confined cells can't be concentrated very much.
Probably not going to happen. (Score:5, Informative)
I wrote a paper on this idea last semester, and as interesting a find as it is, I don't think it's ever going to lead to enhanced power conversion efficiencies (PCE). The "Double Solar Energy Efficiency" is actually a theoretical doubling of the thermodynamic limit on PCE, and it doesn't take non-radiative losses into account. These losses have been minimized in the record breaking silicon and multi-junction solar cells, but quantum dots bring lots of problems with them.
It's definitely worth further investigation, but currently I'm not convinced that it will ever bring improvements.
Re:Econuts will be torn over this one (Score:3, Informative)
Re:But by when? (Score:3, Informative)
We are also seeing some cool developments to make solar better. Not just big efficiency gains like this article mentions but also more environmentally friendly processes to make the panels (although replacing silicon with lead "quantum dots" may not be a step in that direction but even the normal production players like sunpower are hitting new efficiency records). As it stands, a lot of petroleum products go into the parts that make the panels...a cool development I saw a press release about a few weeks ago is from somebody called BioSolar [biosolar.com] who have designed a panel backing film based on some bio products rather than oil.
We are also seeing 3rd gen solar tech pick up which will drop costs even if it isn't as efficient (and really, when you are almost at 30% on commercial panels, cost is a bigger issue since we have a LOT of rooftops ready for panels)
Re:But by when? (Score:3, Informative)
The ones that are dropping are because of two reasons...
1 - china made junk flooding the market. There is a metric crapload of really low grade Solar panels on the market from china. These low grade panels are also of the worst designs that are easiest to make that flat out suck in real world use.
http://www.amazon.com/Sunforce-50044-60-Watt-Solar-Charging/dp/B000CIADLG/ref=sr_1_1?ie=UTF8&s=hi&qid=1276875660&sr=8-1 [amazon.com]
for example is complete garbage. It's all marketing hype and they fail to tell you that any shadow, even a line from a cable across the panel reduces output drastically.
They do admit to being Amorphous.. I.E. the cheapest to make solar panel. They are about 6% efficient. However, there’s a reason why thin film solar panels haven’t replaced older types yet. They’re just not as efficient. With about a six percent conversion rate for energy drawn from the sun, they can only draw about half the wattage from sunlight that mono and polycrystalline panels do, making them take up twice as much installation space for the same amount of power.
Plus most of these are also built poorly. so the 6% is assuming they were built perfectly. The most I have seen from any of the cheap china panels out there has been around 4%...
I had better luck with really old burned industrial used ones from the solar farms out west. I have a pair of 6 foot panels I bought for $340.00 that are a dark brown from being in the sun for years that put out more power than 4 of the kits' linked above do.
Re:But by when? (Score:3, Informative)
It still takes about 5 years to recoup the cost of a residential solar system-- even with huge government subsidies!
But energy is free after that whereas you have to keep paying for distributed power, even with huge government subsidies to coal, natural gas, and other fossil fuels. Solar panels are warrantied 20, 25, even 30 years. I think the shortest warranty for hardware are on batteries, yet Surrette/Rolls [wholesalesolar.com] has a 10 year warranty. On the other hand Enersys Batteries [solar-pane...energy.com] only have a 5 year warranty. Even if you have to replace the batteries every 5 years, you still save money.
Some, like you?, complain about subsidies for alternative energy but you say nothing about subsidies for "conventional" energy. Coal? It gets billions of dollars in subsidies, here's, Chevron's CEO agreeing with the Sierra Club to lobby to end coal subsidies [grist.org]. Rep Edward Markey practically brags that My Climate Bill 'Has Huge Subsidies For Clean Coal! Huge!' [youtube.com]. He details some of the subsidies nuclear power and other's get. How about this: Global Dirty Energy Subsidies Top $550 Billion Per Year [politifi.com]. A blog entry on the Financial Times website says The cost of fossil fuel subsidies: $557bn [ft.com]. How about the US? The Policy Archive [policyarchive.org] says that between 2002 and 2008 "Fossil fuels benefited from approximately $72 billion over the seven-year period, while subsidies for renewable fuels totaled only $29 billion."
If you want to complain about subsidies complain about the subsidies conventional energy, and agricultural businesses, get. A Reason blog entry says Agricultural Subsidies: Corporate Welfare for Farmers [reason.com].
Falcon