Some silicon solar cell makers have been able to hit 21% on their best days, but doing so consistently and in high volumes are far more difficult. (Panel efficiency is usually a bit lower than cell efficiency).

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That is not great compared with the 20% and more achieved by a silicon-based solar cell, the 40% managed by a solar-thermal turbine, or even the 18-20% of one of the new generation of cheap and cheerful thin-film solar cells.

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But last year solar cell manufacturers bought more silicon wafers than chipmakers--and solar's demand for wafers is growing three times as fast as demand from the rest of the electronics industry.

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