Inter-technology knowledge spillovers for energy technologies

Both anecdotal evidence and the innovation literature indicate that important advances in energy technology have made use of knowledge originating in other technological areas. This study uses the set of U.S. patents granted from 1976 to 2006 to assess the role of knowledge acquired from outside each energy patent's technological classification. It identifies the effect of external knowledge on the forward citation frequency of energy patents. The results support the claim above. Regression coefficients on citations to external prior art are positive and significant. Further, the effect of external citations is significantly larger than that of other types of citations. Conversely, citations to prior art that is technologically near have a negative effect on forward citation frequency. These results are robust across several alternative specifications and definitions of whether each flow of knowledge is external. Important energy patents have drawn heavily from external prior art categorized as chemical, electronics, and electrical; they cite very little prior art from computers, communications, and medical inventions.