and performance of all renewable energy generation technologies. Moreover, some combination of intelligent, two-way electric grids; scalable and cost-effective methods for large-scale and distributed storage (either direct electricity energy storage or generation of chemical fuels); widespread implementation of rapidly dispatchable fossil-based electricity technologies; and greatly improved technologies for cost-effective long-distance electricity transmission will be required. Significant, sustained, and greatly expanded R&D focused on these technologies is also necessary if this vision is to be realized by 2035 and beyond.

Resource Base

Solar and wind renewable resources offer significantly larger total energy and electricity potential than do other domestic renewable resources. Although solar intensity varies across the nation, the land-based solar resource provides a yearly average of more than 5 × 1022 J (13.9 million TWh) and thus exceeds, by several thousand-fold, present annual U.S. electrical energy demand, which totals 1.4 × 1019 J (~4,000 TWh). Hence, at even modest conversion efficiency, solar energy is capable, in principle, of providing enormous amounts of electricity without stress to the resource base. The land-based wind resource is capable of providing at least 10–20 percent, and in some regions potentially higher percentages, of current electrical energy demand. Other (non-hydroelectric) renewable resources can contribute significantly to the electrical energy mix in some regions of the country.

Renewable resources are not distributed uniformly in the United States. Resources such as solar, wind, geothermal, tidal, wave, and biomass vary widely in space and time. Thus, the potential to derive a given percentage of electricity from renewable resources will vary from location to location. Awareness of such factors is important in developing effective policies at the state and federal levels to promote the use of renewable resources for generation of electricity.

Renewable Technologies

Over the first timeframe through 2020, wind, solar photovoltaics and concentrating solar power, conventional geothermal, and biomass technologies are technically ready for accelerated deployment. During this period, these technologies could potentially contribute a much greater share (up to about an additional 10 percent of electricity generation) of the U.S. electricity supply than they do today. Other technologies, including enhanced geothermal systems that mine the heat

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