  Understanding the factors driving innovation in energy technologies is of
critical importance to mitigating climate change and addressing other
energy-related global challenges. Low levels of innovation, measured in terms
of energy patent filings, were noted in the 1980s and 90s as an issue of
concern and were attributed to low investment in public and private research
and development (R&D). Here we build a comprehensive global database of energy
patents covering the period 1970-2009 which is unique in its temporal and
geographical scope. Analysis of the data reveals a recent, marked departure
from historical trends. A sharp increase in rates of patenting has occurred
over the last decade, particularly in renewable technologies, despite continued
low levels of R&D funding. To solve the puzzle of fast innovation despite
modest R&D increases we develop a model that explains the nonlinear response
observed in the empirical data of technological innovation to various types of
investment. The model reveals a regular relationship between patents, R&D
funding, and growing markets across technologies, and accurately predicts
patenting rates at different stages of technological maturity and market
development. We show quantitatively how growing markets have formed a vital
complement to public R&D in driving innovative activity; these two forms of
investment have each leveraged the effect of the other in driving patenting
trends over long periods of time.
