Solar Electric Power

Sunpower Stirling engine mounted on a solar concentrator in Houston, TX

Sunpower Stirling engine mounted on a solar concentrator in Houston, TX

Current solar solutions (both solar thermal and photovoltaic) are well suited to delivering peak power efficiently since peak demand typically correlates with daylight. However, they severely suffer for providing baseload power. On average, solar farms install 8x the capacity needed to meet the average demand. This is in order to ensure power can be provided through the evening and when clouds block the sun. In addition to this increased need for “excess” capacity, a suitable method to store the energy must be implemented. Cost effective, reliable energy storage continues to be a technology challenge for PV markets. Finally, the excess capacity also requires excess land resources.

Stirling offers the advantage of being indifferent to the source of heat. During the day, it can operate using solar radiation, and during the evening, an alternative fuel source (biomass, natural gas, etc), can be used to produce electricity. This permits much greater effectiveness of capital assets for electricity production. For base-load power production, Stirling is 23% less expensive than photovoltaics.

Additionally, Stirling is more efficient in converting solar energy to electricity. Stirling engines are proven to be in excess of 38% efficient, and even in systems designed for lower-cost rather than peak performance, 25% is easily obtainable. Comparatively, commercial PV panels are 14-18% efficient.

While Stirling can be competitive in large, utility-scale fields of use, it is uniquely advantaged in smaller, distributed locations. Solar-thermal using conventional steam turbines are an equally effective mechanism for large scale production. However, steam turbines do not scale down well in terms of cost and efficiency. Further, smaller distributed fields of use can generally not support the operating requirements of super-critical boilers. Stirling scales down well, and in fact has a “sweet spot” below 10kw. For larger installations, multiple Stirling engines can be ganged together to achieve power requirements, and at the same time provide partial redundancy in the event of any single-point failure.