For the time period from the present to 2020, there are no current technological constraints for wind, solar photovoltaics and concentrating solar power, conventional geothermal, and biopower technologies to accelerate deployment. The primary current barriers are the cost-competitiveness of the existing technologies relative to most other sources of electricity (with no costs assigned to carbon emissions or other currently unpriced externalities), the lack of sufficient transmission capacity to move electricity generated from renewable resources to distant demand centers, and the lack of sustained policies.77

The second major area in which optics can contribute to energy security in the United States is through solid-state lighting.

Key Recommendation: The DOE should strongly encourage the development of highly efficient light-emitting diodes (LEDs) for general-purpose lighting and other applications.

For example, the DOE could move aggressively toward its 21st-century lightbulb, with greater than 150 lm/W, a color rendering index greater than 90, and a color temperature of approximately 2800 K. Since one major company has already published results meeting the technical requirements for the 21st-century lightbulb, the DOE should consider releasing this competition in 2012. Major progress is being made in solid-state lighting, which has such advantages over current lighting alternatives as less wasted heat generation and fast turn-on time. The United States needs to exploit the current expertise in solid state lighting to bring this technology to maturity and to market.

Recommendation: The DOE should:

1. Develop high-temperature solar cells suitable for use in conjunction with CSP systems. These solar cells can provide sunlight conversion to electricity in addition to the CSP thermal conversion. Moderate-efficiency solar cell electricity generation in addition to thermal electricity generation could drive total efficiency greater than 50 percent;

2. Develop more efficient, and less expensive, methods of solar power concentration for both low and high levels of concentration;

3. Develop methods to reduce LED costs, such as growing LEDs on silicon, or increasing SiC wafer sizes, or other LED substrate cost-reduction approaches; and

4. Develop efficient green LEDs to support quality RGB LED color rendering.

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77 NAS-NAE-NRC. 2010. Electricity from Renewable Resources: Status, Prospects, and Impediments. Washington, D.C.: The National Academies Press, p. 4.



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