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Renewable Energy Solar Cells Ain’t So Renewable

Sanyo’s just announced that it’s going to build a new factory in Japan dedicated to solar photovoltaic cell manufacture–the company plans to double its solar cell output to meet rising demand as the world slowly catches on to the idea of renewable energy. But in the light of some thinking about the rarity of chemical components, perhaps Sanyo actually shouldn’t be planning a project like this at all.

Sanyo’s just announced that it’s going to build a new factory in Japan dedicated to solar photovoltaic cell manufacture–the company plans to double its solar cell output to meet rising demand as the world slowly catches on to the idea of renewable energy. But in the light of some thinking about the rarity of chemical components, perhaps Sanyo actually shouldn’t be planning a project like this at all.

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The new Sanyo plant will produce more modern-tech photovoltaic (PV) cells than the company currently manufactures, with a higher power-output per incoming sunlight. The factory, planned for Osaka prefecture (along with a second factory which will make cheap PV cells for developing nations,) will effectively double the total power output from Sanyo-made solar cells to around 680 megawatts annually (for comparison, the Hoover Dam’s peak power output is about 2 gigawatts.)

But while these plans are pretty admirable from an eco-friendly point of view, thanks to the environment-saving low-carbon-footprint nature of solar power, there’s a growing body of scientific thought that’s concerned about how renewable this, and other “renewable energy resources” actually are.

For high-power solar cells the issue boils down to a single element used in their manufacture: indium.

While PV cells are manufactured a little like any other semiconductor device on a silicon frame, the power efficiency of silicon-only cells is pretty limited. By doping the silicon with other elements and creating multi-junction devices, the efficiency can be pushed way up to around 40%. One element used for this purpose is indium, which is also used in indium gallium arsenide-based infrared detectors and mini lasers, and to make LCD screens.

But indium is actually an amazingly rare metal: It’s present in very few mineral ores, and makes up just 0.25 parts per million of the earth’s crust–compared to the 63,000 ppm of iron. Some researchers estimate that if we continue to use indium at the current rate there may be just a 10-year supply left.

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There’s a similar problem for fuel cell technology. Part of the magic that turns hydrogen into electricity in a fuel cell is the use of platinum as a catalyst: It promotes the chemical reaction that generates power and thus boosts the efficiency of the resulting cell. 

But platinum, which is also a precious metal used decoratively and commonly elsewhere in electronics manufacturing, is thousands of times less abundant than even indium–it’s present at around 0.003 parts per billion in the crust. 

So if there’s a radical rethink of the way we’re exploiting the unrenewable and eco-harming energy resources of our planet, and a massive shift towards renewable energy resources, then the useful lifespan of both of these rare metals as electronic components is frighteningly short. 

There are other chemical alternatives for use in both semiconductors and fuel cells, of course. Carbon nanotubes are looking like an increasingly useful supermaterial. Just last week researchers at Dayton University demonstrated they could be used to replace platinum as a catalyst in hydrogen fuel cells, and there’s work to use nanotubes and graphene to create a better hydrogen fuel tank and a super-battery to store electrical power. Nanotubes are even showing potential as solar photovoltaic solar-cell materials.

Instead of building a factory to use up our precious indium resources at double the rate, perhaps Sanyo would be better off spending the money on researching carbon nanotube-based technology instead. After all, carbon makes up around 1,000 parts per million of the earth’s crust, and there’s plenty of it greenhousing-up the atmosphere as CO2.

[via Physorg, NewScientist]

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