Back in July, I announced the start of a new series of posts on Sustainable Energy, but I haven't had a chance to actually write about the topic until today. No time like the present, then, to launch into my favorite diatribe: Solar Heresy.
My concern about solar cells -- specifically silicon photovoltaic cells -- is that it takes a great deal of energy to make silicon.
The starting material is sand (silicon dioxide, SiO2) which is a wondrously stable material. It takes a lot of energy to reduce SiO2 to silicon. It requires additional energy to purify the starting material into the superpure form of a true semiconductor. To make the higher-efficiency single-crystal solar cells, one also needs to crystallize the material, requiring melting it at 2577 °F (1414 °C) and slowly pulling a crystal out of the melt. Then there's the energy needed to create the solar cell including patterning, doping, and annealing. The solar cell then needs to be packaged, mounted, shipped, and installed.
How many years do I need to run a solar cell before I payback the energy consumed in making it?
I'm not the first person to pose the question. In fact it has been addressed by a number of studies, with widely varying conclusions. Bankier and Gale reviewed a group of assessments that ranged from 0.7 to 25.5 years. Each study had different assumptions -- mostly about the mounting frame and type of silicon (polycrystalline or single crystal). It seems that none of the studies included the energy cost of the sand-to-silicon conversion.
For many years it was acceptable to start the energy cost calculation from polysilicon. After all, polysilicon is a waste product from the manufacturing of silicon wafers for the computer chip industry. But this changed in 2008 when several plants were put on line to produce polysilicon just for solar cells (NYSE:YGE). China is now a leading producer of polysilicon. Last time I checked, the main source of energy in China is coal, much of it with a high-sulfer content.
The big picture is that we're burning high-sulfer coal in China at tremendous rates to make supposedly "green" silicon solar cells.
Until someone can show me a conclusive study that solar cells are energy net positive, I remain a solar skeptic.
Science is sexy
So why all the fuss about solar? Governments around the world are subsidizing solar production.
Rich nations like to fund solar because it looks like they're creating high-tech jobs and advancing technology (ESLR, FSLR*). Emerging nations fund it to try to jump-start their nascent technology infrastructure (CSUN, STP, SOL, TSL).
I'm very much in favor of governmental funding of the science behind alternative energy solutions, but subsidizing the manufacturing and installation undermines the market forces that should select the best solution in a technological meritocracy. I would rather use Uncle Sam's money to figure out which of the bazillion solar cell configurations currently under development (or on university sketchpads around the world) is the best solution, rather than burn our limited fossil fuels creating thousands (millions?) of metric tons of mediocre stuff right now.
So what should we do instead?
There are a hundred better ways to save and create energy today. I'll write about some of them in future posts in this series.
And now I'll climb down off my soapbox. (For now.)
*FSLR. First Solar, Inc. makes CdTe photovoltaics, not silicon. They do benefit from government support of solar programs.
Full disclosure: No positions.
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