China is outpacing many countries in patenting renewable-energy technologies (see J. E. Trancik Nature 507, 300–302; 2014). But this achievement has arguably been inflated by the country's patenting laws.

For example, according to the Espacenet patent database, from 1978 to 2008 China was awarded 21,192 patents on solar photovoltaics. Of these, 99% were granted by China's State Intellectual Property Office. By contrast, the US Patent and Trademark Office granted just 83 patents in this field over the same period (C.-Y. Wu Scientometrics 98, 429–446; 2014).

The overwhelmingly domestic focus of China's patenting activity is a result of its patent-law system, which is designed to promote indigenous innovations. Chinese firms tend to file as many patents as possible for a single equivalent invention, encouraged by extra public subsidies and administrative support (see, for example, A. de la Tour et al. Energy Policy 39, 761–770; 2011).

This factor needs to be borne in mind when evaluating Chinese patent figures for the purposes of technological ranking.