DOE OSTI2012
This is a Final Technical Report on the Research and Development completed towards the development of a Low Cost Solar Collector conducted under the DOE cost-sharing award EE-0003591. The objective of this project was to develop a new class of solar concentrators with geometries and manufacturability that could significantly reduce the fully installed cost of the solar collector field for concentrated solar thermal power plants. The goal of the project was to achieve an aggressive cost target of $\$$170/m 2 , a reduction of up to 50% in the total installed cost of a solar collector field as measured against the current industry benchmark of a conventional parabolic trough. The project plan, and the detailed activities conducted under the scope of the DOE Award project addressed all major drivers that affect solar collector costs. In addition to costs, the study also focused on evaluating technical performance of new collector architectures and compared them to the performance of the industry benchmark parabolic trough. The most notable accomplishment of this DOE award was the delivery of a full-scale integrated design, manufacturing and field installation solution for a new class of solar collector architecture which has been classified as the Bi-Planar Fresnel Collector (BPFC) and may be considered as a viable alternative to the conventional parabolic trough, as well as the conventional Fresnel collectors. This was in part accomplished through the design and development, all the way through fabrication and test validation of a new class of Linear Planar Fresnel Collector architecture. This architecture offers a number of key differentiating features which include a planar light-weight frame geometry with small mass-manufacturable elements utilizing flat mirror sections. The designs shows significant promise in reducing the material costs, fabrication costs, shipping costs, and on-site field installation costs compared to the benchmark parabolic trough, as well as the conventional Fresnel collector. The noteworthy design features of the BPFC architecture include the use of relatively cheaper flat mirrors and a design which allows the mirror support beam sections to act as load-bearing structural elements resulting in more than a 36% reduction in the overall structural weight compared to an optimized parabolic trough. Also, it was shown that the utilization of small mass-produced elements significantly lowers mass-production and logistics costs that can more quickly deliver economies of scale, even for smaller installations while also reducing shipping and installation costs. Moreover, unlike the traditional Fresnel trough the BPFC architecture does not require complex articulating drive mechanisms but instead utilizes a standard parabolic trough hydraulic drive mechanism. In addition to the development of the Bi-Planar Fresnel Collector, an optimized conventional space-frame type parabolic trough was also designed, built, analyzed and field-tested during the first phase of this award. The design of the conventional space-frame parabolic collector was refined with extensive FEA and CFD analysis to reduce material costs and re-designed for simpler fabrication and more accurate lower-cost field assembly. This optimized parabolic trough represented an improvement over the state-of-the art of the traditional parabolic trough architecture and also served as a more rigorous and less subjective benchmark that was used for comparison of new candidate design architectures. The results of the expanded 1 st phase of the DOE award project showed that both the Optimized Parabolic Trough and the new Bi-Planar Fresnel Collector design concepts failed to meet the primary objectives for the project of achieving a 50% cost reduction from the industry reference total installed cost of $\$$350/m 2 . Results showed that the BPFC came in at projected total installed cost of $\$$237/m 2 representing a 32% savings compared to the industry benchmark conventional parabolic trough. And the cost reduction obtained by the Optimized Parabolic Trough compared to the industry benchmark reference was approximately 16.5% against the industry benchmark. The new BPFC design showed a weight savings of almost 36% compared to the optimized parabolic trough and a 50% reduction in field assembly labor and a 13% reduction in shipping volume. The BPFC design showed only a marginal improvement of 16% over the fully projected installed cost of the optimized parabolic trough benchmark developed as Concept One. During the course of the investigation numerous sensitivity analyses and other analytical studies were conducted to assess potential improvement opportunities, and further optimizations that could lead to cost reductions and performance improvements. Factors that could have a significant impact on high-volume costs were related to production and further improvements in design for manufacturability, automation, assembly jigs, and fixtures, and robotic welding etc. The wind modeling analysis showed that the Fresnel design concept did not reduce the wind load in a significant manner. The stress analysis showed that the design concept with almost a 36% lower weight than the parabolic trough and it was strong enough to withstand the expected wind loads and maintain targeting accuracy. The Initial on-sun optical testing showed that the Fresnel Trough was capable of concentrating sunlight effectively to the desired target and yielding an optical efficiency slightly lower than a parabolic trough.