Patenting growth, R&D investment and market expansion for (A.) Solar (photovoltaic) worldwide, (B.) Wind worldwide and (C.) Coal, US only.

<p>Innovation, proxied by (cumulative) patent applications, is well described (grey dots) by a production function that includes both the effects of cumulative production and cumulative public R&D investment for all technologies. This relationship holds at various stages of maturity. A restricted <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0067864#pone.0067864.e001" target="_blank">Eq. (1)</a> accounting for public R&D investments alone gives a poor description of the trends observed (open squares), failing in particular to account for the uptick in patenting (and upwards curvature) in wind and solar technologies over the last decade. Full details of the fit parameters and statistical goodness of fit are given in the SI. The best fit for solar has <i>α</i> = 0.22, <i>β</i> = 0.41, and p-values <. The best fit for wind has <i>α</i> = 0.51, <i>β</i> = 0.30, and corresponding p-values and , respectively. The best fit for coal has <i>α</i> = 0.18, <i>β</i> = 0.43, and p-values <.