Research & Development of a Low Cost Solar Thermal Collector DOE Award # EE0003591 Final Technical Report August 2012 Research & Development of a Low Cost Solar Thermal Collector DOE AWARD #: EE0003591 Final Technical Report August 2012 CONTENTS 1.0 Executive Summary .......................................................................................................................................... 4 2.0 Comparison of Actual Accomplishments vs. Goals and Objectives .................................................................. 8 2.1 Project Goals & Objectives .................................................................................................................................. 8 2.2 Actual Accomplishments ..................................................................................................................................... 8 3.0 Project Activities for the Entire Funding Period ............................................................................................. 10 3.1 Investigative Approach ...................................................................................................................................... 10 3.2 Detailed Task Plan ............................................................................................................................................. 11 3.3 Detailed Activities.............................................................................................................................................. 12 3.4 Establish Qualitative Comparative Metrics ..................................................................................................... 12 3.5 Evaluation of the Articulating Planar Fresnel Collector (APFC) ......................................................................... 13 3.6 Benchmarking.................................................................................................................................................... 14 3.7 Development of Concept One: The Optimized Parabolic Trough ..................................................................... 15 3.7.1 Optimized Parabolic Trough Project Results .............................................................................................. 16 3.8 Development of Concept Two: The Bi-Planar Fresnel Collector (BFCC) ............................................................ 20 3.9 Bi-Planar Fresnel Collector Results .................................................................................................................... 22 3.9.1 Bi-Planar Fresnel Collector Cost Analysis ................................................................................................... 24 3.10 Comparison between Concept One and Concept Two ................................................................................... 26 3.11 Test Results ..................................................................................................................................................... 28 4.0 Products Developed under the Award ........................................................................................................... 30 4.2 Fabrication and Testing of Bi-Planar Fresnel Collector .............................................................................. 32 5.0 Description of Analytical Models ........................................................................................................................... 32 5.1 Introduction ...................................................................................................................................................... 32 5.2 Performance Verification - Optical Analysis ...................................................................................................... 33 Tools used ........................................................................................................................................................... 33 5.3 Wind Modeling .................................................................................................................................................. 36 Tools used: .......................................................................................................................................................... 36 5.4 Stress Analysis ................................................................................................................................................... 42 Tools used ........................................................................................................................................................... 42 1.0 EXECUTIVE SUMMARY 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/m2, 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. These drivers included material costs, fabrication costs, shipping costs, and field assembly as well as EPC 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. Typically half the capital cost of a CSP power plant is incurred in the procurement and installation of the solar field. Consequently a 50% reduction in the solar field installed cost could potentially reduce the levelized cost of electricity (LCOE) by up to 25%, assuming all other parameters remained the same. Under this DOE Award program the award was structured into separate three-phases. The intent of the first phase was to focus on the development of a viable conceptual baseline collector design. The actual scope of work completed under the first phase of the award was considerably broader than the proposed scope for the 1st phase of the DOE award. Furthermore this expanded scope was completed by utilizing 40% of the Federal allocated funds for the 1st phase of the project. This investigation was conducted within a broader internally-funded mandate for the design and development of a new class of fully packaged, standardized CSP power plants with specific economic and performance targets. The goal for this CSP development program was to minimize non-recurring engineering and the field-level EPC cost components through standardization and packaging, so as to be able to achieve a fully installed cost target of <$2.25 per watt and a levelized costs of electricity (LCOE) of $0.10 per kWh, in the absence of any Government tax rebates, subsidies or incentives. This co-development opportunity with the DOE Award provided a unique advantage to the DOE Award Project by allowing the candidate collector designs to be examined, not just in isolation as a theoretical study, but enabling them to be evaluated within the context of the detailed engineering being done on an actual 5 MW CSP power plant in California. This provided an opportunity to utilize a highly structured systems engineering approach towards the development and a practical reference to the designs, with greater vetting. This was also one of the main reasons why the actual work completed during Phase One of the award was considerably broader than what was envisioned in the DOE grant plan. 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 “conventional” parabolic trough, as well as the conventional Fresnel collector. In addition to delivering the design of this new class of collector architectures, the project also delivered hardware in the form of a full-scale fabricated prototype, along with proto-production assembly tooling. The fabricated tooling and prototype collector served as a validation of the designs manufacturability and its projected fabrication costs. Furthermore on-sun field tests were also conducted on this prototype to evaluate performance and validate shipping and field “installability” costs. 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. It also helped to eliminate any subjectivity surrounding “industry standard” costs for the conventional solar parabolic troughs. A methodical investigative approach and rigorous design process was followed during the course of this project. The design process involved first opening-up the line-focus solar collector design space to identify a large number of geometries and architectures that could be evaluated against a matrix of cost and performance parameters that had been established to identify potential improvement opportunities. A starting point for this study was provided by a novel new design concept developed previously without the use of DOE or other Government funds and has been termed as the “Articulating Planar Fresnel Collector”, (APFC). During the design process in order to curtail the number of variables, and provide convergence, the number of control variables was limited to six key dominant design and cost drivers. Furthermore, the design and development process was further influenced by an assumption that minimizing wind loads, build tolerances, fabricated part sizes and the number of unique parts, as well as minimizing EPC costs would lead to lower cost designs. Detailed engineering analyses were conducted on each of the design candidates. These included computational fluid dynamics analysis (CFD) to examine the sensitivity of geometries to wind loads, finite element analysis (FEA) to optimize structures for weight and stiffness. Also, optical ray-tracing analysis was conducted to evaluate the optical performance of the candidate design architectures. After final down-selection the two final design candidates, Concept One, the Optimized Parabolic Trough and Concept Two, the Bi-Planar Fresnel collector emerged as viable candidates and were selected for further detailed analysis. Detailed engineering, detailed assembly drawings and fabrication drawings for collector components, assembly tools and fixture were prepared for each of the collector concepts. First, Concept One, the Optimized Parabolic Trough was fabricated along with its tools and fixtures. This was followed by the fabrication and assembly of Concept Two, the Bi-Planar Fresnel Collector. Both the Concept One Optimized Parabolic Trough and Concept Two, the Bi-Planar Fresnel Collector were further evaluated during on-sun field testing at a test site near the Mojave Desert in California. The goal of both Concept One and Concept Two builds and tests was to provide sufficient fidelity to allow a critical evaluation of the main features of these designs against a “standard” design (Parabolic Trough). The results of the expanded 1st 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/m2. Results showed that the BPFC came in at projected total installed cost of $237/m2 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. These studies showed that most of the dominant factors that could reduce cost were largely optimized during the course of this investigation. 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. These further optimizations were originally planned for Phase 2 of the award. The wind modeling analysis showed that the Fresnel design concept did not reduce the wind load in a significant manner. This was a surprising result as it had been assumed that the gaps between the mirror sections would provide pressure relief which would reduce wind loads. The pressure relief was noticed in the middle sections but was considerably diminished away from the center. 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. Although, Suntrough Energy has decided not to pursue further development of the Bi-Planar Fresnel Collector design architecture under phase 2 of the current DOE award program. But it believes that the preliminary results show that the design offers sufficient promise as well as certain unique design features. Further work is needed to refine the design, build and test more prototypes to improve its performance, and simplify manufacturing processes to further reduce the costs. Suggestions for factors to be considered for further investigation on the Bi-Planar Fresnel design architecture during any follow-on activity: 1. BPFC is an unproven design and requires considerable more test and evaluation. 2. Long term reliability has to be established 3. Accuracy during assembly in mass-production requires further development 4. Optical efficiency is low and needs further optimization 5. Mirror shading and edge losses need further optimization 6. High NRE & tooling costs 7. High part count – high costs 8. Optimize geometry to further reduce wind drag 2.0 COMPARISON OF ACTUAL ACCOMPLISHMENTS VS. GOALS AND OBJECTIVES 2.1 PROJECT GOALS & OBJECTIVES The proposed objective of this project was to evaluate a number of solar collector designs and select a baseline design for a solar concentrator with geometries and manufacturability that can significantly reduce the fully installed cost of the solar collector field for concentrated solar thermal power plants. As typically half the capital cost of a CSP power plant is in the installed solar field the targeted goal for cost reduction was 50% in the solar field installed cost compared to the Industry benchmark installed cost of the parabolic trough. The goal of the project was to optimize the collector design for the following parameters: a) Optical and thermal performance b) Material cost c) Fabrication cost d) Transportation cost e) Field assembly and installation costs 2.2 ACTUAL ACCOMPLISHMENTS The actual accomplishments were considerably broader than the proposed scope of phase one of the DOE award and included delivering a full-scale integrated design, development, and manufacturing solution for a new class of solar collector. Through the support of the first phase of this DOE award two new classes of Linear Fresnel Collector Troughs were evaluated. The first design concept evaluated was a new solar collector design called the Articulating Planar Fresnel Collector (APFC) developed independent of the DOE Award, but its performance was evaluated using the parameters developed under the project. The second was another new novel class of Fresnel architecture which has been termed as the the Bi-Planar Fresnel Collector (BPFC) as an evolution of the original Articulating Planar Fresnel Collector which was designed, built, analyzed and field-tested under the DOE award. Also, as part of this DOE award an optimized conventional space-frame type parabolic trough was designed, built, analyzed and field-tested to seek potential advancements in the proven parabolic trough architecture. This optimized parabolic collector was also used as a benchmark for comparison against advanced candidate collector designs to eliminate any subjectivity surrounding “industry standard” costs for the conventional solar parabolic troughs. A comprehensive set of evaluation criteria and metrics were also established during the course of this investigation to compare the different collector designs. These criteria included the following parameters: 1. Wind Loading 2. Structural Stiffness 3. Optical Performance 4. Cost Analysis The main accomplishment of this project was the development of a viable alternative to the conventional parabolic trough collector. This was done through the successful design validation, build and testing of a new class of Linear Planar Fresnel Collector, that is being termed as the Bi-Planar Fresnel Collector which showed significant promise in reducing material costs, fabrication costs, shipping costs, and on-site field installation costs compared to the benchmark “conventional” parabolic trough collector. A benchmark parabolic trough collector was also designed and fabricated after significant optimization with extensive FEA analysis to reduce material costs and re- designed for simpler fabrication and more accurate field assembly. Where the results failed to meet the primary objectives of the project was in achieving the aggressive target of a 50% cost reduction from an industry reference total installed cost of $350/m2. The actual cost reduction obtained from the industry reference by the Bi-Planar Planar Collector is estimated to be 32%. And the cost reduction obtained measured against the Optimized Parabolic Trough benchmark reference was approximately 16.5%. During the course of the investigation numerous sensitivity analysis and other analytical studies were conducted to assess potential improvement opportunities, optimizations that could lead to further cost reductions and performance improvements. These studies showed that most of the dominant factors that could reduce cost were largely optimized during the course of this investigation. Factors that could have a significant impact on high- volume costs were related to production and further improvements in design for manufacturability, automated assembly jigs, and fixtures, and robotic welding etc. These further optimizations were originally planned for Phase 2 of the award. The overall summary of the findings of the project were:  Wind modeling analysis showed that the Fresnel design concept did not reduce the wind load in a significant manner.  Stress analysis showed that the design concept was strong enough to withstand the expected wind loads.  Initial on-sun optical testing showed that the Fresnel Trough was capable of concentrating sunlight effectively to the desired target.  Initial cost estimates were higher than the goal of $170 / sq meter. Further work is needed to refine the design, build and test more prototypes to improve its performance, and to reduce the costs of the Bi-Planar Fresnel Collector design. Despite the considerable promise of the Bi-Planar Fresnel Collector Suntrough Energy has decided to not pursue the subsequent phases of this project under the DOE award program. 3.0 PROJECT ACTIVITIES FOR THE ENTIRE FUNDING PERIOD 3.1 INVESTIGATIVE APPROACH This investigation was conducted within a broader mandate for the design and development of a new class of fully packaged, standardized CSP power plants that could minimize the field-level EPC cost component, and be able to achieve a fully installed target cost of <$2.25 per watt. Furthermore the goal was to achieve a levelized cost of electricity (LCOE) of $0.10 per kWh or less, in the absence of any Government tax rebates, subsidies or incentives. As the solar field represents roughly 50% of the installed cost of a CSP power plant it was critical that a new low cost solar collector be developed to achieve these aggressive targets. The DOE award funded the portion of the project which focused on the low-cost solar collector development. The research and development for a low-cost collector was being undertaken within the broader mandate of an internal self-funded program to develop a low- cost CSP development with specific targets for economics and performance. The investigative team was able to take a highly structured systems engineering approach to the collector development. Hence this provided an opportunity for collector design concepts to be examined, not just in isolation, but to be modeled and tested in the practical context of the detailed engineering, overall performance and plant economics being conducted for a 5 MW CSP power plant planned in California. The approach taken by the investigating team was to initially open-up the line-focus solar collector design space to identify a large number of geometries, and architectures that could be tested against a matric of parameters to identify improvements against the traditional parabolic trough design standard as set by the SEGS plants. A starting point for this study was provided by a novel new design concept which was previously developed by the team which was termed as the Articulating Planar Fresnel Collector (APFC). This design was a radical departure from conventional parabolic troughs, and offered some unique characteristics such as a planar light-weight frame geometry with mass-manufacturable elements, a stationary receiver and rapid, low cost installation. In order to curtail the number of variables, and provide convergence to the design process a fundamental premise was made that the solar collector costs are influenced by the following six variables: 1. Aerodynamic loads & moments’ drive: a. Material costs b. Foundation design c. Installation cost 2. Factory assembly is cheaper than field assembly; a. Which favors designs that provide greater factory assembly 3. Manufacturing and shipping costs can be reduced by; a. Mass production of smaller sections b. Smaller sections can be packed and shipped more cost effectively. c. Smaller sections can be assembled without the use of expensive lifting equipment 4. Reduced manufacturing tolerances reduce manufacturing costs a. Develop in-field assembly fixtures that can provide accurate and rapid final field assembly and erection 5. Identifying options that would allow the use of flat mirror sections to replace costly curved ultra- clear glass mirrors used in parabolic troughs - imperative to reduce cost