Comment: Scaling, collaboration are keys to maintaining U.S. cleantech edge

One of the most telling trends I've seen is revealed through a National Renewable Energy Laboratory chart showing solar cell efficiency versus time using silicon, amorphous silicon, CdTe, copper indium gallium selenide (CIGS), organic, dye-sensitized. The trend lines have a nearly universal slope, with efficiency increasing in the lab at the rate of only about 4 percent per decade.

While there may not be a universal law behind this trend, the sobering fact is that materials-related research takes a very long time. Progress comes in fits and starts, often with serendipitous occurrences. One striking example is the way that CIGS efficiency improved around 1993 when the material was grown on soda-lime glass instead of borosilicate glass. It was later found that sodium from the soda-lime glass was diffusing into the solar cell, improving its performance.

Why is this trend telling? The consequence of such slow materials development is that a new or complex materials like nanostructured photovoltaics do not have a real shot at mitigating global warming. Caltech's Nate Lewis has argued that we will need more than 10 terawatts of carbon-free energy by 2050 " the equivalent of building 1 large nuclear power plant every other day -- for the next 40 years. If we assume that it will take 15 years for a new material to reach the commercial market at 1 megawatt scale, and that the annual production capacity thereafter grows with a 50 percent CAGR (which is greater than solar), then the technology's installed base would still only amount to 0.075 TW by 2050.