Wednesday, December 06, 2006

Sunlight Hype: 40% Efficient Solar Cell


Boeing-Spectrolab's announcement that they had broken the 40% efficiency mark with a new solar cell was enough to wake me from my slumber and write a very long-overdue post. Let me start by saying I'm at the top of the list of solar enthusiasts that would love to believe the breakthrough is going to have a huge imapct on the solar industry in the near future. But I'm a bit skeptical.


Most solar cells use silicon as their principle semiconductor. Without hitting you with excessive jargon, the semiconductor is basically the material that turns photons of sunlight into electricity. The problem with silicon is that it has gotten more expensive in recent years. The solar world has been growing in leaps and bounds, and silicon refineries haven't kept up. There are plenty of plans for expansion, but even as refineries ramp up their production, most analysts don't expect supplies to level out the costs until 2008. So we'll have relatively high costs of solar modules for at least another year or so. In the meantime, plenty of startups have begun investing in alternative semiconductors in hopes of discovering a cheaper alternative to silicon, and that's what Boeing-Spectrolab has done.


I shouldn't be completely dismissive. Boeing-Spectrolab is using a multi-junction solar cell, which is a new technology that has a lot of potential. Silicon cells basically have one layer that transforms anywhere from 12%-22% of all sunlight into DC electricity (depending on the silicon crystal). These multi-junction cells feature multiple layers, each of which transforms a different wave from the entire spectrum of light into electricity. That's where the 40% efficiency comes from. This past May, Sharp announced they had reached 37% with a multi-junction cell that uses gallium-arsenide as its semi-conductor, and Boeing-Spectrolab is probably using something similar.


(Surprise, surprise, Boeing-Spectrolab isn't telling anyone yet what they're using)


But here's why I'm skeptical. Throughout the entire history of solar cells, there's a plethora of researchers and scientists that have reached high percentages in the lab. But the difference between what's possible in a lab under certain specific conditions, and what's economically producible on a large scale is often significant.


Even aside from that, let's say, hypothetically, that the technology does turn out to be commercially viable, most of these alternative semiconductors are rare metals. Not only do most US Geological Surveys indicate that there aren't enough supplies of raw materials of these semiconductors to meet solar market targets for the next thirty years, but most of these metals are also byproducts from other mining processes. If these semiconductors (again, hypothetically) were to become profitable enough that the byproducts became main products, the result could be hundreds and thousands of tons of mining waste that could cause an ecological disaster.


Silicon will never have these problems. It's the most abundant element in the earth's crust, and can be collected and refined with a minimal environmental impact.


But I'm not trying to be captain of the player-haters for the multi junction cells. The truth is that this probably will be the technology of the future. But there are a lot of issues that need to be ironed out before we get there.


Once we find out what exactly Boeing-Spectrolab is doing with these cells, we might be doing carwheels in the streets. This could be the biggest breakthrough in the history of solar cells. But even if it is, I still wonder how many years away we are from working out the kinks to get the product on the market.


Time will tell.


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