Constraints and Opportunities

Research and development (R&D) conducted by the government and industry over the past 12 years has developed impressive new technologies and has reduced technical and financial risks. As previously described, first generation solar thermal systems have been successful and are proving the viability of the technology. However, deployment of these systems could be greater. Low fuel costs, changes in the availability of federal and state tax incentives, and other market factors have constrained solar thermal technology's potential to significantly penetrate the domestic electric generating market And in some cases, the availability of power (primarily fossil fuel derived) from many third-party suppliers, combined with conservation (which has reduced demand), has left many t}tilities with excess generating capacity.

International markets also provide opportunity for solar thermal technology. Small systems, like the Stirling, have potential to be competitive in either grid-connected or stand-alone applications in many third-world countries. However, other developed countries are threatening to challenge the United States in tapping these markets. European countries are significantly increasing their investments in solar thermal research. At the same time, the U.S. budget has steadily declined over the past decade. This situation may make it difficult for U.S. industry to exploit its current leadership in marketing solar thermal technology in foreign markets.

Two related factors currently limit increased implementation of solar thermal electric systems: cost and the lack of pilot-plant demonstrations of technological improvements in a utility setting. Significant cost improvements have been achieved by reducing component and system costs while improving system performance; the cost of energy from solar thermal electric systems, which was 600/kWh in 1980, has been reduced to 80 to 120/kWh today. Components that provide further improvement have been developed and are currently being evaluated. Dish electric systems utilizing a stretched-membrane dish integrated with a reflux receiver and a reliable Stirling engine, when developed and mass produced, are projected to cost $l,200/kWe. Cost estimates for energy from such a dish electric system are projected to reach 50/kWh, low enough to be competitive in a substantial market'5'. For central receiver technology, there is a need for a 30 to 100 MWe pilot-plant demonstration incorporating improved receiver concepts (molten salt, direct absorption, or air) and stretched-membrane heliostats; both offer significant improvement in performance and energy costs. These advanced technologies are a direct result of the government-sponsored research, development, and demonstration (R,D&D) work, and continued improvements will depend directly on the continued vitality of the R,D&D program.

To take advantage of continuing component improvements and attain further cost reductions, system demonstrations are necessary. The utility market environment requires demonstration of any new technology on a scale that is readily expanded to full-size plants. Reliable system performance is being demonstrated and cost improvements realized with each successive parabolic trough system. Similar operation and experiences are necessary for both central receiver and dish electric concepts where the advanced technologies that are proven on a component scale can be integrated into a system in an industrial setting. Utility participation in such projects on a cost-shared basis is considered critical to success.

Research efforts in the DOE Solar Thermal Program are developing the foundations necessary to further enable a viable solar thermal technology. These efforts are focused on concepts, processes, and materials for a broad range of applications and on the identification and proof of concept of advanced applications for highly concentrated solar energy. Some of these include research on (1) optical materials and advanced optical techniques to improve conversion efficiencies and reduce costs, and (2) high-temperature materials to enable receivers to more effectively absorb concentrated sunlight. R&D of prototype hardware applies these new materials and reduces system costs. Testing of the hardware provides field experiences that lead to improvements in reliability. R&D in this area has led to the development and testing of the following systems: (1) low-cost, lightweight membrane heliostats and parabolic dish collectors; (2) advanced molten-salt receivers for central receiver systems; (3) high-flux sodium reflux receivers for dish systems; (4) high-performance, low-maintenance Stirling engines for modular dishes; and (5) direct absorption receivers for central receiver systems.

Future solar thermal systems are expected to be used in either a peaking mode without the use of storage or with an integral thermal storage system for intermediate and base-load plants. The lowest levelized energy costs are expected to be achieved by use of a thermal energy storage system. However, to realize these lower energy costs, additional R,D&D of storage systems will be necessary. Research in higher density phase-change storage concepts should lead to low-cost storage systems in the future. Furthermore, storage systems at commercial scale capacities have not yet been demonstrated. In today's trough systems, a hybrid mode of operation, with natural gas, is used to provide dispatchability and achieve a higher capacity factor and lower cost of delivered energy.

To bring additional solar thermal technology to the market, a strong interaction between government and industry is required. Specific efforts to facilitate this process include providing technical assistance to suppliers and users of solar thermal technology, and implementing joint-venture projects in which industry and government share the risk of developing a solar thermal technology for a specific market. As part of this effort, the federal program and some utilities are studying the benefits of demonstrating new solar thermal technologies on a scale that is readily expanded to full-size plants. One benefit of these system demonstrations is that these field experiences help improve reliability and reduce operation and maintenance costs.

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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