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the opposite direction (a - b). For example, a simulated difference of +1.5 for Texas
biofuels patents over New York patents (Table 5, line 2) denotes that we expect that
patents from Texas receive 1.5 more citations than patents from New York (i.e., patents
from Texas are on average 30% more highly cited). Inversely, New York biofuels
patents are 24% less highly cited and therefore less technologically important than
patents from Texas. Data herein is preliminary and represents a limited set of identified
energy patents. However, it does provide interesting evidence of differences between
technology areas and paths for future exploration in clean energy patenting and
innovation. In the following sections, we provide descriptions of the sources of technical
and commercial breakthrough patents in the solar, wind, and biofuels technology areas.

3.3.1 Solar
For technical importance, unassigned solar patents from independent inventors are
significantly less cited than patents owned by universities, national labs, and corporations
[29] (Table 3 for all solar data). Drawing on the previous discussion (§3.1.2.), while
most solar patents came from corporations compared to independent inventors, it appears
that those patents from corporations were more technically important. There likely may
be some data artifacts here due to the technological differences between photovoltaics
and solar thermal innovations, but the differences between sources of total patents
compared to breakthrough patents is still relevant. Solar patents owned by corporations
and universities are the most highly cited patents, with an insignificant citation increase
to university patents. We do not observe any strong relationship to funding sources.
Increasing team size correlates with increasing technical breakthroughs. In terms of
geographic effects, patents from California and Massachusetts are both highly cited. The
effect in California is likely due to the predominance of the semiconductor industry and
resultant solar-applicable technologies that are heavily concentrated there, [77] while the
effect in Massachusetts is more likely driven by universities and a few highly innovative
solar firms (e.g., Konarka and Evergreen Solar). Colorado patents are less highly cited
relative to patents from other states. This observation may be due to the higher
percentage of solar patents in Colorado originating from independent inventors than in
the whole solar dataset (46% versus 33%, respectively). Singh and Fleming [29] have
previously demonstrated that independent inventors often face challenges in bringing
their technologies to fruition. However, the patents from these independent inventors
enjoy an average citation count higher than the patents from the national laboratories (6.7
versus 6.1, respectively), indicating that perhaps these patents are more technically
relevant.

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