Nature Materials 7, 825 (2008); published online: 27 October 2008; corrected after print: 4 November 2008.

In the version of this Editorial originally published online, the second sentence of the first paragraph should have referred to 'electricity' needs, and to a total area of '100 km × 100 km', not '100 square kilometres'. The sentence has been corrected in the HTML and PDF versions of the Editorial.