This summary of the Concentrating Solar-Thermal Power (CSP) portion of the 2022 Solar Energy Technologies Office (SETO) Peer Review covers discussions between reviewers and their discussions with SETO’s awardees. See descriptions of all CSP projects that were analyzed as part of this review.
The first section covers the overall CSP review, taking all projects into account. The subsequent sections cover specific topics within the CSP portfolio.
The following reviewers participated in the CSP portion of the Peer Review:
- Dale Rogers (Chair, author of the CSP Overall Portfolio Review section)
- Anoop Mathur (Lead Reviewer, author of the CSP Collectors Portfolio Review section)
- Lin-Wen Hu (Lead Reviewer, author of the CSP High-Temperature Components Portfolio Review section)
- Theodore Bergman (Lead Reviewer, author of the CSP Systems Portfolio Review section)
- Minghui Chen (Lead Reviewer, author of the Power Cycles Portfolio Review section)
- Peter Pfromm (Lead Reviewer, author of the Industrial Process Portfolio Review section)
- David Denkenberger
- Don Gervasio
- D. Todd Griffith
- David Jeong
- Ron Kent
- Cheng-Xian Lin
- Keunhan Park
- Nate Schuknecht
- Nathan Siegel
- Michael Simpson
- Elias Stefanakos
- Sungwoo Yang
- Weihuan Zhao
CSP Overall Portfolio Review
Goals and Strategy
Although a few different versions of the SETO mission and its corresponding research and development (R&D) goals and strategy can be found, the general messaging is consistent. The higher-level SETO mission is to accelerate the development, advancement, and deployment of solar technology to support a transition to a decarbonized electricity system by 2035 and a decarbonized energy sector by 2050. Key enabling factors for achieving this will be technology and product offerings that lead to rapid deployment of low-cost and reliable electricity and energy beyond electricity. In support of this higher-level mission and at the CSP-specific level of SETO-sponsored R&D, SETO provides funding that supports early-stage research to improve CSP performance, reduce cost, and improve lifetime and reliability. The intent is to advance the CSP technologies in a way that makes CSP more attractive for commercial deployment.
SETO’s approach has been to build a portfolio of projects that are diverse (e.g., supporting a variety of technology advancements relative to materials, components, subsystems, and integrated solutions) and that are focused on achieving SETO-established targets for performance, lifetime, and cost. This approach appears to be appropriate and should enable continued advancements and accelerated commercial deployment of CSP technologies. This, however, assumes that appropriate targets have been defined, there is adequate diversity within the portfolio, projects within the portfolio have meaningful potential impact if successful, and there is a reasonable likelihood of project success. Currently, there is a SETO CSP priority focus on the development and advancement of Gen3 technology, perceived as a viable option for achieving lower cost (thus, greater market interest) by leveraging higher operating temperatures and efficiencies.
Alignment with Goals
Overall, it seems that there has been a concerted effort by the SETO CSP staff to build a portfolio of projects that do align well with stated CSP goals. However, at the individual project level, this was sometimes difficult to assess based upon inputs provided in project presentations. Although Principal Investigators (PIs) were specifically directed to address this in their project summaries, the manner in which they did so varied significantly. In some cases, this was not explicitly addressed while in other cases, it was addressed but in a very high-level, qualitative manner that didn’t adequately demonstrate alignment with goals.
When judging project and portfolio alignment with stated goals, key considerations should include “potential impact” and “likelihood of success.” This specific insight, however, was generally not conveyed well in the project presentations. Instead, there appeared to be a primary focus on conveying technical progress with little or no discussion relative to how (or if) the project will meet SETO CSP goals. At any point in time during project execution, the PI should be able to clearly and concisely articulate why the work being done can be impactful and why there is high confidence that the project objectives can be achieved. These claims should be defensible and, where feasible, quantitative.
There is room for improvement in this specific area with one option being to require that all PIs explicitly address these two considerations for their project showing traceability back to SETO CSP goals.
Funding and Resource Allocation
SETO’s current CSP portfolio for the 2022 Peer Review has a total of 84 projects that were divided into five separate topic areas as follow: 1) Collectors; 2) CSP High-Temperature Components and Characterization; 3) CSP Systems; 4) Power Cycles; and 5) Solar-Heated Industrial Processes. The allocation (i.e., funding and number of projects) across these five topic areas is considered to be appropriate, especially given SETO’s current emphasis on advancing Gen3 CSP solutions at temperatures that drive higher efficiency power cycles (e.g., sCO2 Brayton cycles). It was, however, somewhat surprising that there were not more projects addressing Collector System advancements. Regardless of the CSP application (e.g., electricity production or industrial process heat) and regardless of the operating temperatures (e.g., Gen2 CSP versus Gen3 CSP), cost-effective collector systems that meet performance and lifetime requirements will be an integral part of the overall plant-level solution. Collector System cost is a very large portion of the overall plant cost, and cost-effective solutions will be critical if accelerated deployment and longer-term commercial success are to be achieved.
It should be noted that, while the number of Collector System projects within the CSP portfolio is small, there is one heavily funded project that is clearly focused on progressing technology in this area. This large-scale consortium is led by one of the U.S. National Labs and has both domestic and international participants. Although there has been an advisory committee established that does include industrial participants, it is suggested that this project include more private sector participation and be more focused on commercial market pull (e.g., implement a market-based, design-to-cost methodology that drives product development decisions).
Across the five topic areas for CSP, there appears to be a good mix regarding the number of projects, project sizes, and funding allocations. A caution, however, would be that perhaps, in general, there can be too much diversity in a portfolio. Often, there are more good ideas and funding requests than there is available funding. Therefore, for effective portfolio management, it is imperative that only those projects that can clearly demonstrate alignment with SETO goals (i.e., have the potential to be impactful and have a reasonable likelihood of success) should be selected for the portfolio and retained during project execution.
Technical Diversity
In reviewing the CSP project portfolio, it is clear that the SETO staff has made a meaningful effort to provide for technical diversity within the portfolio. Given the higher-level program goals and strategy, having the appropriate mix of technology options will enhance the likelihood of ultimate portfolio success. However, as a portfolio manager, finding that appropriate balance can be a significant challenge. For example, for the SETO CSP portfolio, factors that should be considered include: 1) “technology push” versus “market pull;” 2) projects led by industry versus those led by National Laboratories and universities; 3) Gen2 CSP versus Gen3 CSP; and 4) Gen3 Solid Particle Receiver Technology versus other Gen3 options.
Given SETO’s desire to accelerate commercial deployment of CSP, there is a recognition that technology enhancements will be needed to stimulate additional market pull. While there has been some commercial success with Gen2 CSP, this has been somewhat limited to areas having favorable policies and financial incentives. To be more competitive in the marketplace, CSP technologies will have to achieve continued improvements in performance, lifetime, and cost. One option for doing so is to push toward higher operating temperatures for Gen3 CSP. The SETO CSP project portfolio appears to be structured in a manner that recognizes that the upside potential associated with Gen3 CSP warrants priority attention and funding. However, the portfolio structure appears to also recognize that commercial deployment of this technology option is still perhaps a few years away given current technical and cost hurdles. As a result, the portfolio balance between Gen3 and Gen2 CSP technologies and the balance between Gen3 particle receiver technology and other Gen3 CSP options seem appropriate at this time. It is, however, suggested that the project portfolio be frequently reviewed for an appropriate level of industry participation to ensure a “market pull” priority over “technology push.”
A final observation is that perhaps an underrepresented area in the portfolio is the Collector System (i.e., heliostats, etc.). Although, as previously mentioned, there is one heavily funded project in this area, it appears to have limited private industry involvement. Given that this system is a large cost driver for a commercial plant and given its potential impact on either Gen2 or Gen3 systems, this single project should be considered a top-priority for SETO and should be frequently monitored for progress against stated goals.
Advancing the Mission
Given SETO’s higher-level program mission and given the CSP-specific goals and strategy, it appears that the scope of the CSP portfolio of projects effectively matches the defined mission. The portfolio has a good mix (as previously discussed) and appears to be largely focused on the right technology advancements to further stimulate CSP market interest and to accelerate deployment.
It should be noted, however, that having project scope that aligns with the SETO mission may not, by itself, be adequate to successfully “advance the SETO mission” and “serve the interests of the U.S. solar industry and American people.” As previously discussed, the CSP portfolio of projects should have the potential for significant impact and should also have a reasonable likelihood of success, and all project PIs should be required to address, in detail, both items in a defensible manner. “Advancing the mission” is accomplished as these projects are successfully executed. Ensuring that projects are being executed in a smart, efficient manner with appropriate risk management is a critical part of attaining the longer-term goal.
Areas of Improvement
The SETO CSP staff is well qualified and has a deep understanding of the technology. There has been an obvious, concerted effort by the team to develop a portfolio of projects that align well with the defined CSP goals. However, a significant observation during the project reviews is that many of the project PIs appear to be largely focused on addressing and resolving technical issues and perhaps not paying enough attention to future marketability. This is a pattern frequently seen in technology development and has certainly been consistently witnessed over many years of CSP technology advancements. While performance and lifetime have experienced meaningful improvements over the past several years, the cost of CSP has simply not been able to achieve competitive levels that can truly stimulate the marketplace.
A helpful step toward this end is that SETO has defined cost targets at the plant level, system level, and component level. However, it is not readily obvious that project PIs are consistently tracking to these goals. The general sense is that, although PIs likely understand the importance of achieving competitive costs with acceptable risk, the tendency is to worry about cost and risk only as an afterthought. It is, therefore, recommended that, where feasible, CSP portfolio projects be required to have interim "Go/No Go" decision points that are "market"-based (e.g., commercial-scale cost targets). There should then be a focused effort during project and peer reviews on determining whether PIs are indeed looking beyond solving the immediate technical issues. Thus, for project continuation, PIs should be required to make a defensible argument demonstrating that the project can lead to a marketable product. This discussion should include considerations given to and assumptions regarding scaling to commercial sizes. This will perhaps be more difficult for projects that are at early-stage Technology Readiness Levels (TRLs). However, it is recommended that this still be a requirement in that it forces the PI to justify his project’s longer-term value.
A final observation is that perhaps more attention should be given to leveraging cross-cutting technologies where feasible for advancing CSP technologies. An obvious area of potential overlap would be with the nuclear industry (e.g., high-temperature components and material needs, molten salt and liquid sodium expertise and data bases, etc.). It is suggested that the SETO CSP staff explore options for sharing data and for potential collaboration with other segments of DOE and with other industries.
Stakeholder Engagement
Based upon some of the project presentations reviewed, it was not readily obvious that project activities were being driven by a “market pull.” Instead, several of the project summaries were focused on technical progress and issue resolution and failed to adequately address how market considerations and stakeholder involvement were influencing the project. Stakeholders could include component or system-level providers, EPCs, project developers, plant owner-operators, or bankers. These longer-term players can be critical to project and portfolio success, and early engagement is highly encouraged to ensure there is a clear understanding of what the marketplace requires for successful commercial deployment. It’s important that the flow of information be in both directions with these stakeholders being made aware of technology advancements and with technology/product developers being made aware of what will be required by these various stakeholders for marketplace deployment.
During project and/or peer reviews, project PIs should be able to clearly convey that their efforts are addressing "market pull"/“commercial readiness” of their product (e.g., meeting customer requirements relative to cost, performance, and lifetime with acceptable risk). It is suggested that future peer reviews have presentation content requirements that direct the PIs to explain, not just what stakeholders are involved but how they are contributing to commercial readiness. It is also suggested that the SETO staff consider options for enhancing stakeholder involvement in funded projects and for facilitating the flow of information across projects within the portfolio. Although competition-sensitive information will not likely be shared, there is value in having portfolio PIs aware of general technologies and products being developed and of common challenges that may exist across projects.
Final Feedback
SETO has done a commendable job at building a portfolio of projects that appear to align well with the higher-level program mission and with CSP-specific goals. Successful achievement of these goals, however, is largely dependent upon the following two key characteristics associated with each project within the portfolio: 1) potential impact assuming project success and 2) likelihood of success. These two characteristics need to be clearly articulated by project PIs when preparing proposals and when supporting project reviews. When doing so, claims being made need to be defensible. It is recommended that the SETO staff make these expectations clear, and that PIs be held accountable for providing this information.
A second key point relative to portfolio management is regarding the difficulty in finding the appropriate portfolio balance. The ultimate goal is to achieve performance, lifetime, and costs that can further stimulate and accelerate market pull for CSP technologies. This means that, at a commercial project level, a business case will have to close and “project bankability” will have to be achieved. Factors such as technology uncertainties, product risk, and strength of warranties and performance guarantees will be critical considerations. It is, therefore, imperative that a portfolio have the right mix of technology options and have the right balance between “technology push” and “market pull.”
A final point to be made relative to this track, is regarding the peer review process. The 2022 review was based upon presentations that were uploaded to a website and did not allow for oral presentations to be made. There was, however, time allowed for reviewers to schedule individual meetings for questions and clarifications. This approach was reasonably effective, but it is recommended that, when feasible, future peer reviews be conducted with oral presentations being required. Also noted for this year’s review, is that the mix of reviewer backgrounds appeared to be skewed toward academia. It is suggested that, where feasible, there be a more balanced mix that includes more industry representation, especially individuals having experience in commercial product development or those having been specifically involved in development and deployment of CSP components and systems.
CSP Collectors Portfolio Review
Goals and Strategy
The SETO has stated CSP goals as: Low cost solar-thermal electricity by using a greater than 50% thermal to power efficiency cycle, reliable electricity using thermal energy storage, and energy beyond electricity using solar thermal (heat) in process industries. Specifically, the goal is to reduce the life cycle cost of electricity (LCOE) from the current 9.8 cents/kWh to 5 cents/kWh by 2030.
For the collector subsystem topic, which accounts for over 40% of the capital expenditure (CAPEX) in the CSP plant, the goal is to reduce over 40% of the 4.8 cents/kWh reduction in LCOE (2.1cents/kWh) is expected from reducing the CAPEX and operating expenditure (OPEX) cost of collector subsystem.
The strategy is to form a consortium of national labs, universities, developers and gather the existing knowledge base and fund research, design and demonstration projects in this topic area with an aim to reduce both capital expenditure (CAPEX) and operating expenditure (OPEX). Specifically,
- Reduce the first cost of heliostats by using advanced and automated manufacturing (CAPEX)
- Significantly reduce the cost to install the field of heliostats with standardized installation methods with improved site preparation (CAPEX)
- Improve the performance of the solar field by increasing the plant output by effectively operating and maintaining the solar-field so we collect more energy and produce more heat energy (OPEX)
- Extend the life of the plant by reducing the stress on materials – structural materials for heliostats and fatigue due to temperature fluctuations caused by varying solar conditions resulting in varying incident flux from heliostats. (OPEX and CAPEX)
The strategy, even though aggressive, is appropriate and achievable but requires effective use of emerging technologies in sensors, control, data analytics, and high-fidelity mathematical modeling in addition to improving installation and collaborating with industry partners and a wider workforce from other industries.
Alignment with Goals
About 75% of the projects currently funded under this topic are well aligned with the goals and strategy. There is one major program with 80% of the funds (HelioCon – Heliostat Consortium) and most of our comments are based on this project.
The Helicon project included broad stakeholder engagement from industry, academia, and national labs with prior experience in the CSP field to fix the gaps in field engineering, define standards for measurements and design, establishing automated manufacturing, and making the field deployment process from breaking ground to more robust.
The HelioCon project stated its three goals as follows: 1) Form center of excellence on heliostat technologies; 2) Establish core validation and modeling at national labs; and 3) promote workforce development. However, these goals as stated are weak because they do not quantify specific goals for CAPEX (example: reduce manufacturing cost by 25%), and specific goals for OPEX reduction (example: by improving performance or solar output and effective maintenance and/or extending the life of the plant to >50 years). Using the available expertise and data, these targets should be specified.
To achieve the 2035 and 2050 mission, the centers of excellence in five years must have:
- produced a standard optimized collector and receiver design;
- defined and standardize installation and siting procedures;
- developed an agile manufacturing workforce; and
- engaged emerging technologists with expertise in machine learning and mobile miniature sensors.
The project team did very well to gather all the available expertise in CSP from universities, labs, and CSP developers to identify the gaps in engineering issues, established a path to standards and manufacturing methods to automate manufacturing, and expanded the vendor base. These are important for lowering capital cost for Gen3.
However, because emerging technology industries were not engaged, there was little discussion on emerging technologies (such as machine learning, model predictive control, miniature drones) that can fill these gaps. I hope the first task of defining the roadmap in the HelioCon project will leverage these technologies to solve issues that impact performance such as material fatigue due to fluctuations in elevated temperatures on receiver tubes, and lower performance due to optical errors in heliostats. These are important for Gen3.
There are a few projects that are assessing field-heliostat quality using image processing and polarimetry and projects using quantitative and mathematical models to operate the plant under variable solar conditions (partly cloudy days, windy days, etc.), while extending receiver material lifetime, and projects to model impact of wind. These projects can have a sizable impact on improving system performance by operating the plant at its best and reducing OPEX with use of data-driven or machine learning and by closing the loop between the solar field and receiver by making real-time adjustments in heliostat aiming.
However, there is very little emphasis on operation and maintenance of the CSP system by leveraging data from field characterization of collectors to using established mathematical models, and learning from the data and math models, and closing the loop between an agile solar field and receiver. These methods can reduce flux spillage and reduce forced outages or downtimes during cloud transients.
Funding and Resource Allocation
The diversity of projects and funding level is adequate, but this area needs more projects in automation, field sensors, automated operation, learning, and decision-aiding technologies.
SETO should increase the funding for projects for field monitoring and assessment, modeling, machine or deep learning and control, and should tap into the expertise from other industries, such as aerospace and defense. The aim is to ensure that the plant performs at its best at all solar (varying degrees of clouds) and wind conditions.
Technical Diversity
The projects in this topic area generally cover all the areas that must be addressed in the short run. There is adequate technical diversity, however, there should be more emphasis on field control and monitoring.
Automated and mobile manufacturing are areas mentioned in Helicon and this will be important in reducing CAPEX cost. Manufacturers and designers from industries should be engaged. HelioCon aims to establish manufacturing methods for heliostats. But there are many heliostats designs available and many more that may hit the market. A design team should inform the manufacturing team about next generation needs. Consider movable heliostats, flexible membranes etc., as they may require different manufacturing methods than what might be considered conventional. The facets are the highest cost part, so this may be one of the primary areas for reducing cost with innovative design and manufacture.
The investments in technologies made for more challenging power plant application will trickle down to less challenging applications in the process industries and water desalination. The projects that are currently funded for these low-temperature applications have very little impact on the SETO mission and very little likelihood of success because the end customer is not engaged. Hence, SETO should plan to focus its investment on projects that support power generation.
Advancing the Mission
SETO is likely to achieve its mission, if the consortium plans the Centers of Excellences (COEs) with specific and aggressive high level goals, if the National Labs establish the core capabilities in field measurement and modeling, and if all stakeholders agree on standard scalable, replicable design and field deployment methods and are willing to share data to improve the soon-to-be installed CSP systems.
More aggressive and quantifiable goals and timelines are required to meet the 2035 mission. A key strength of the consortium is that it maintains a base of heliostat knowledge and workforce in the U.S. It addresses industry standardization, setting up means and methods for manufacturing and assembly to ease entry for new commercial entities. The stakeholders and members represent a good swath of labs, universities, small businesses, and major developers.
The low temperature collector projects are a ‘technology-push.” They do not fit the SETO mission or meet market needs.
Areas of Improvement
One blind spot is not aggressively using the emerging technologies from other industries (such as aerospace and defense) to develop field sensors that can provide real time assessment of every heliostat in the field.
Also, consider heliostat designs that are future looking rather than limit to those in use today. The consortium seems to be building a consensus amongst national lab personnel. The consortium should disseminate to the commercial world as well.
Typical electric utilities expect the plant to be designed to perform predictably and reliably, requiring only routine maintenance with easy-to-use tools. However, the fuel source (i.e. the collector-receiver subsystem in CSP plant) has many uncertainties due to uncontrolled disturbances from cloud transients, solar field partially covered with clouds, which effect plant performance and require continuous attention from operators.
Advanced sensing, field characterization, and automation technologies must be developed to make this subsystem (fuel) resilient to these transients and information packaged to help the plant operator make only high-level decisions. This is important for ready acceptance of CSP to achieve the growth levels planned for 2035 and 2050. Very little attention is being paid to develop and package these technologies already available and in use in other industries.
Stakeholder Engagement
The projects generally have the right mix of academia, utilities, developers, plant owners, component suppliers, vendors, subject matter experts, and global institutions with strong involvement of National Laboratories. A stronger participation from utilities is required to developing high-level requirements of solar fields and receivers.
The HeliCon project promises to engage a wider workforce. This must include technologists and designers from other industries who have successfully used machine learning and developed miniature unmanned vehicles (drones), optical sensors, and synthesized control systems.
Advanced manufacturing of components for heliostats is mentioned as a gap and is being pursued. It is important to engage the manufacturers and system designers of components (other than the lab personnel). The roadmap that the consortium is developing should be reviewed with the industry and all stakeholders.
The consortium or SETO must clearly specify the metrics for reducing costs for example, x% CAPEX for each component or each subsystem and y% OPEX from operation and from maintenance.
Final Feedback
The objective should be to design an agile Solar field and Receiver together as a subsystem, which can provide reliable, predictable heat flux or heat rate and maintain the desired heat map on the receiver within specified limits of receiver temperature and rate of change of temperature, under all solar conditions (cloud cover, degraded heliostats, etc.).
Once this control objective is achieved and we are getting the best performance from the system, then we can start looking for ways to reduce cost by trading-off performance, if required.
There is more than adequate control authority available in the field and the sensing technology has advanced to a point where we can assess heliostat performance in real time and estimate the energy incident on receivers from individual or subgroups of heliostats. SETO has rightfully funded projects using drones and polarimetry to assess the optical efficacy of heliostat fields. This technology can be advanced much further. For example, the U.S. Department of Defense has successfully developed and used mini-drones fitted with cameras to provide intelligence in battlefield. We should consider developing swarms of mission-specific mini-drones (iPhone sized or smaller than palm sized) fitted with cameras and sensors that can take off from the pedestal of the heliostat, scan for optical quality and determine how each facet of heliostat will map its flux on the receiver, record the data, and park itself to be recharged and transmit the data to the center.
This information on heliostats from the field, along with incipient weather and cloud cover and mathematical models (being developed at the University of Wisconsin and elsewhere) can be used to control the solar field to achieve the desired heat map by tactically adjusting the solar field aiming on the receiver. Such capability is available now or can be readily adapted for CSP. This can potentially eliminate weather-related outages and spillage losses and improve performance by as much as 25% (as stated in one of the projects).
In summary, the emerging machine or deep learning techniques, miniature drones and sensors, dynamic mathematical models, and model predictive control technology should all be used to ensure the collector and receiver subsystems operate to maintain temperature limits and capture the maximum possible heat flux. This data will also help with economical preventive and predictive maintenance of the solar field. Decoupling the harsh effects of uncontrolled heat flux fluctuations makes it easy to design materials for receivers.
CSP High-Temperature Components Portfolio Review
Goals and Strategy
This topic area meets SETO’s goals by supporting research, development, characterization, design, fabrication, and evaluation of CSP high-temperature materials and components behavior and reliability including heat transfer media, containment materials to achieve lower costs, increased efficiency, and more reliable performance relative to current technologies. SETO’s strategy for this topic area is to drive technology advancement and to bridge fundamental research and development to full-scale applications through funding a broad range of projects including characterization of thermophysical properties of liquid, solid, particle beds, sensor development and calibration, materials corrosion measurements and control, development of diagnostic and modeling tools, failure risk management of thermal energy storage (TES) components, and technoeconomic analyses. The research projects supported under this topic should have broad impacts relevant to other TES-enabled systems, in addition to CSP, such as nuclear thermal storage.
Alignment with Goals
Projects selected and managed under this topic area cover research and development of materials, components, sensors, and modeling tools to support CSP system deployment. These projects range from fundamental research in materials corrosion and thermocouple physical properties measurements of high-temperature salts to design-build-test of particle-based receivers, solar heat flux sensors, and material coatings and failure degradation analysis. Research funded under this topic area is aligned with SETO’s defined goals and strategy for Gen3 CSP deployment in 2030 towards the 5 cents/kWh target.
Funding and Resource Allocation
Funding levels in this topic area vary with research objectives and appear well-balanced and complementary to other CSP topics. For example, heat transfer media properties, materials degradation mechanisms, particle bed solar receiver design and testing, and low-cost solar sensor development contribute directly to collectors and CSP integrated system development. Principal investigators and sub-awardees represent a good mix of national labs, university, and industry collaboration. On the individual project level, reviewer feedback indicated appropriate funding for research projects funded in this topic area. Overall, the number of projects appears appropriate and represents a logical approach to achieve the CSP system deployment goals.
Technical Diversity
Research projects in this topic area address broad technical challenges including materials degradation characterization under harsh service conditions, endurance testing, thermo-physical property measurements, particle bed heat exchangers, materials and system failure mechanism assessment, and technoeconomic evaluation. These are all directly relevant to achieve SETO’s objectives in the deployment of next generation CSP systems. Diversity of these projects represents the various technical and economic challenges in the CSP system design, performance, reliability and operations. Somewhat underrepresented is the high-temperature materials development, testing, and scalability to ensure fabricability, endurance, and lifetime performance.
Advancing the Mission
Research projects selected under this topic area address various technical and economic challenges associated with CSP deployment. These projects range from fundamental research in materials corrosion and thermocouple physical properties measurements of high-temperature salts to design-build-test of particle-based receiver, solar heat flux sensors, and materials coatings and failure degradation analysis. Some examples of direct impact to the solar industry in increasing efficiency and reliability and reducing cost are the development of affordable solar heat flux sensors and system modeling tools. All the projects funded under this topic area are generally aligned with SETO’s mission and serve the interest of the U.S. solar industry as a whole.
Areas of Improvement
While most projects strive to achieve the program goals, several projects focus on developing and evaluating innovative high-temperature materials, coatings, insulating material, and additive manufacturing fabrication for CSP in lab-scale. These materials and approach appear to have low TRL and are difficult to quantify the manufacturing cost and may not be viable for full-scale fabrication. This may pose significant challenges to achieve SETO’s goal to deploy CSP by 2030 at 5 cents/kWh.
Another issue raised by reviewers was the research outcome applicability to industry. A reviewer commented on a project that studies in-situ materials corrosion mechanism that it is mostly oriented towards basic science and dissemination of information through publications. The project has been very successful in its scientific contributions. However, it is important to take the final step and translate academic research into a cohesive and comprehensive document that can be useful to CSP Gen3 system industry developers.
Stakeholder Engagement
Research projects awarded in this topic represent a well-balanced technical approach and most projects have a good mix of national labs, university, and industry collaboration to achieve the CSP system goals. The projects in general are well informed by the appropriate level of stakeholder engagement and collaborating organizations. For example, the solar flux sensor and particle receiver test bed development being carried out can be directly utilized in the CSP integrated system testing at Sandia National Laboratories. Industry engagements are critical for intermediate and late-stage development in order to directly benefit the U.S. solar industry; therefore, SETO should encourage principal investigators to engage industry partners.
Final Feedback
Research projects funded in this topic area have broader scientific and engineering system contributions that should be highlighted in this report. Well characterized high-temperature salts, particle beds, and material thermo-physical properties and heat transfer performance obtained from SETO-funded research produce valuable databases and have high impact for peer-review publications. Innovative materials and coatings developed for CSP are also applicable for other thermal energy storage and systems such as nuclear thermal storage. Furthermore, the failure mechanism, risk assessment, economic analysis tools and assessment developed for CSP are also relevant to high-temperature thermal energy storage systems. Overall, SETO research contributions for this topic area can be leveraged for other DOE programs and industry applications. Other selected comments from reviewers for SETO to consider are outlined below:
- The solar sensor project needs a commercial partner; an entity that is communicating a clear need for this product in the marketplace.
- Challenges for several projects should be identified to increase the TRL level to inform improvement on materials and components design, manufacturability, and scalability for CSP deployment.
- Intellectual property rights limit sharing technical information obtained from some SETO-funded projects and reduce the impact of SETO for industry applications.
CSP Systems Portfolio Review
Goals and Strategy
SETO’s goal for CSP Systems is to ultimately provide technological pathways that will promote significant reductions in the LCOE. The pathways are primarily two-fold. First, Gen3-related activity has the potential to lower the LCOE (electric) by raising the high temperatures of the associated thermal power cycles, hence increasing solar-to-electric conversion efficiencies. In addition, development of supercritical carbon dioxide (sCO2) power cycles specifically for Gen3 has the potential to reduce the size and cost of the power block. Second, lower-temperature opportunities exist to reduce the LCOE (thermal) of CSP for process heat and other industrial applications.
Common to both of the preceding pathways is the need to improve the performance and reduce the cost of various components of CSP systems including but not limited to heat exchangers, energy storage devices, working fluids, and heliostats. Strategies to reduce maintenance and operation costs are also important. SETO’s strategy is to support application-specific research, testing, and development in areas such as but not limited to new materials, new materials-handling schemes, and new fluid flow as well as heat transfer processes in severe operating environments.
SETO’s strategy also includes an expectation that project principal investigators (PIs) engage with a broad range of stakeholders, from researchers who might provide expertise that is otherwise lacking, to potential commercial end-users of the technologies who are perhaps best equipped to identify practical issues associated with the various proposed concepts. Finally, SETO expects the PIs to disseminate the new discoveries, methodologies, and technologies as appropriate.
Alignment with Goals
The projects selected and managed under the CSP Systems topic align tightly with SETO’s goals and strategies.
The majority of the projects are directly relevant to the Gen3 concept and address research and development challenges such as high-temperature heat exchange processes involving solid particles, gases, or liquids. Both traditional (for example, various molten salts) and more non-traditional working fluids (for example, sCO2 and liquid sodium) are being investigated for possible usage at various locations within the Gen3 system. Efforts continue on the sCO2 and particle heat transfer front, since these media offer the potential to reduce the size and cost of the power cycle hardware, and accommodate high Gen3 receiver temperatures, respectively. Two projects that directly support Gen3 research are related to the development and management of the National Solar Thermal Test Facility, which provides PIs with a unique capability to perform on-sun testing. Most of the Gen3 related projects in the CSP Systems topic are at the large prototype, or pilot scale.
Several projects have applications to lower-temperature CSP systems. For example, one focuses on developing inexpensive thermal energy storage to be used in conjunction with an organic Rankine cycle. Several projects are relevant to a broad range of solar applications. Of these, one project deals with the development of software to assess spatial and temporal non-uniformities of the irradiation of the receiver due to, for example, passing clouds in order to inform maintenance operations. The opportunity to extend this effort to other solar applications is readily apparent.
Again, the diversity of the individual projects is appropriate, and is consistent with SETO’s goals and strategies. The breadth and depth of the scientific and technical aspects of the projects in this topical area are both appropriate and impressive.
Funding and Resource Allocation
The funding levels of individual projects in this topical area exhibit large variation. The budgets of individual projects span orders of magnitude, ranging from hundreds of thousands of dollars for university-based research, to many tens of millions of dollars for pilot plant development. On a project-by-project basis, the funding levels appear to be appropriate and correlate nicely to the anticipated expense of the activities.
Funding within the CSP Systems topical area is skewed toward Gen3-related activity. In contrast, the dollar amounts allocated to the lower-temperature CSP work for industrial applications are relatively small. SETO is encouraged to continue to invest in low-cost, lower-temperature CSP projects of practical importance that could yield a respectable return on investment such as through the Small Innovative Projects (SIPS) program. This type of support might be provided with little negative budgetary impact on the higher-budget Gen3 and pilot scale projects.
Technical Diversity
The project-to-project technical diversity in this topical area, CSP Systems, is appropriate and is addressed above. Within each individual project, however, technical diversity is sometimes lacking. Whereas many projects were balanced with appropriate technical diversity, there is a need for some of the industry-based projects to engage with experts in academia and the national labs for technical assistance. Alternatively, there is a need for researchers in academia to engage with experts in the national labs or industry for assistance with, for example, cost analysis.
Advancing the Mission
The scope of the projects within the CSP Systems topical area matches SETO’s mission and serves the interest of the CSP component of the US solar industry. The projects do not, in general, relate to other solar industries such as those associated with photovoltaic energy generation or battery storage.
Areas of Improvement
The LCOE (electric) for some competing renewable technologies is dropping rapidly and is approaching the SETO target LCOE (for thermal). This economic dynamic suggests that SETO should carefully assess the ultimate competitiveness of CSP for electric power generation. If other renewable sources, for example wind, present customers with an emerging opportunity to economically convert electric power to stored thermal energy, and then use the stored thermal energy to generate electric power on demand utilizing existing technology, the nascent CSP power-generation industry must be aware and informed of the possible fallout.
Stakeholder Engagement
Nearly all of the projects in this topical area would benefit from closer engagement with the potential end-users of the technology; that is, electric utilities. Such engagement is especially important for the large-scale pilot plant projects, and is critical if CSP is to ultimately play a significant role in power generation. Other observations are related to the need for better cost estimating, again suggesting the positive benefits of individual investigators collaborating with the appropriate experts.
Although not critical for success, it is noted that various individual projects would benefit if the investigators would communicate directly with investigators of other projects within the SETO CSP portfolio. There are common technical and techno-economic challenges shared between various projects, and inter-project communication might accelerate the rate of progress and ultimate success of the entire CSP effort.
A few of the projects, especially those in industry, might benefit by more effectively engaging experts who are most knowledgeable about the engineering sciences that are at the heart of some CSP-related technologies. Some projects in this topic area build on decades of engineering science that may have been developed for industries that are only peripherally related to CSP. Examples include the benefits that might accrue if investigators were to engage with experts in high-temperature heat exchanger design and high-temperature heat transfer fluids in, for example, the nuclear industry; or with experts in the deep science of particulate transfer in, for example, the pharmaceutical industry.
Final Feedback
On the whole, the CSP Systems portfolio of projects is most impressive. New and exciting technologies are being developed that can accelerate the nascent CSP industry. Although there are some notable exceptions, most of the PIs of the individual projects should make an increased effort to disseminate their research and development activities to: (i) the scientific and engineering research communities through publications and patents, (ii) potential end-users through various modes of outreach and engagement, and (iii) other CSP researchers. SETO can play a pivotal role in promoting or coordinating such activities. While the importance of, for example, engaging with potential end-users is broadly acknowledged, dissemination through publications and patents play a key role in exciting future generations of bright scientists, engineers, and technologists to consider careers in the CSP industry of tomorrow.
Power Cycles Portfolio Review
Goals and Strategy
Power cycles are used to convert heat generated by the sun into electricity in CSP plants. Conventional power cycles use steam as the working fluid to drive turbines with steam temperatures up to approximately 550°C. Higher temperature input to a power cycle leads to a higher efficiency to convert heat to electricity. The Gen3 CSP program expects to advance high-temperature components and develop integrated assembly designs with thermal energy storage that can reach operating temperatures of greater than 700°C. Advanced power cycles, such as supercritical carbon dioxide (sCO2) cycles, have the potential to achieve low capital costs of less than $900 per kilowatt for cycles that have the thermal-to-electric efficiency of greater than 50%, which is much more efficient than the existing steam-based cycles. The combination of Gen3 CSP systems with sCO2 cycles is expected to lower the cost of a CSP system by approximately $0.03/kWh, which is 60% of the way toward SETO’s 2030 cost goals of $0.05/kWh for baseload configurations that have a minimum of 12 hours of energy storage. The CSP Power Cycles topic area focuses on advanced, high-efficiency power cycles that explore components of sCO2 turbomachinery, high-temperature/pressure heat exchangers designs, and manufacturing techniques.
The SETO goal for the Power Cycles topic area is to achieve thermal-to-electric efficiency of greater than 50%, temperatures of greater than 700°C, and low capital costs of less than $900 per kilowatt. An advanced power cycle that hits these targets will help meet SETO’s LCOE target of $0.05/kWh for baseload CSP plants with more than 12 hours of storage and $0.10/kWh for peaker CSP plants with less than 6 hours of storage. The strategies to achieve these goals are to fund projects to develop and demonstrate key power cycle components, such as high-temperature heat exchangers, turbomachinery, seals, and bearings, and to fund research in developing cost-effective manufacturing methods to achieve SETO’s cost goals.
Alignment with Goals
All the projects under this topic align well with defined goals and strategy. The projects focus essential components for sCO2 power cycles, including heat exchangers, turbomachinery, high-temperature materials, bearings, seals, and manufacturing methods, to achieve the target goals. Projects in heat exchangers and turbomachinery respectively represent about 62% and 28% of the total funding, and the remaining 10% goes to material joint techniques. Among the 14 heat exchanger projects, seven are based on additive manufacturing, four are for diffusion bonding, and three are based on conventional methods. In addition, there are two projects for seals, one for bearings, and two for compressors. In particular, four are particle heat exchanger projects, which are well aligned with the DOE selected solid-particle heat-transfer pathway. All the teams have established good collaborations with appropriate expertise and experienced principal investigators.
Funding and Resource Allocation
The funding level and number of projects for this topic seem appropriate. The funding of this topic area is approximately $40 million for a total of 21 projects; 32.3% of the total funding goes to national laboratories, 21.5% goes to universities, and the rest goes to industries and research institutions. However, the funding level has a big gap between $300,000 and $1.2 million where potential projects could be awarded.
Technical Diversity
The technical diversity seems appropriate. However, reviewers noticed some redundancy in projects, especially with the additive manufacturing and diffusion bonding based heat exchanger projects, representing 50.2% of the total funding in this topic area. Some areas are underrepresented. For example, no project focuses on operation and maintenance of a power cycle. Additionally, some projects appear to be more impactful than others. Particle heat exchangers are key to the solid-particle heat-transfer pathway for Gen3 CSP and potentially are more impactful than molten salt heat exchanger projects.
Advancing the Mission
If the projects in this topic are successful, the resulting innovations/improvements in heat exchangers, turbomachinery, and manufacturing methods will substantively advance the SETO’s mission and the U.S. solar industry as a whole by paving the way toward commercialization of sCO2 power cycles for Gen3 CSP. However, the specific ways and the amount of cost reduction from the proposed technologies are not clearly presented for some projects.
Areas of Improvement
Reviewers found many delays in the achievement of the milestones due to various reasons including the COVID-19 pandemic. No project considers operations and maintenance and there are limited efforts on utilizing machine learning technologies to improve materials and heat exchanger designs. In addition, reviewers also suggested that it would be necessary to have long-term durability testing to understand and mitigate failure modes.
Stakeholder Engagement
The projects are well informed by the appropriate level of stakeholder engagement. Reviewers agreed that industry stakeholders, such as component manufacturers, are critical to ensure the projects’ success. Many projects in this topic area have an industry partner. Additionally, some projects could benefit from leveraging outside expertise, wherever it exists, in aerospace or nuclear field.
Final Feedback
Reviewers believe that no project is clearly superior or inferior to the others, and all projects are supporting SETO’s goals to a certain point. The researchers have done a good job identifying many scientific and practical challenges. However, it is unclear whether a manufacturing method is reliable and cost effective. As the technology of sCO2 power cycle is not mature yet, it is suggested to revisit Rankine cycle or other power cycles while waiting for the commercialization of sCO2 cycles.
Industrial Processes Portfolio Review
Goals and Strategy
For reference from SETO's website: “The goal of the U.S. Department of Energy (DOE) Solar Energy Technologies Office (SETO) is to accelerate the development and deployment of solar technology to support an equitable transition to a decarbonized electricity system by 2035 and decarbonized energy sector by 2050.”
Industrial processes are a rather new area for the application of CSP (power towers, parabolic reflectors for the purpose of this review) in SETO. Some of the projects reviewed in this area generally do not make use of high (say, >500°C) temperatures but use thermal energy at lower or much lower temperatures (down to 80°C in one case). Other projects (nitrides for ammonia, molten salt electrolysis etc.) do use high temperatures.
On a fundamental level, it seems that the unique capability of CSP to reach high temperatures (albeit intermittently with need for storage if continuous processing is required) needs to be exploited or the effort may fall prey to lower capital and operating costs for, say, renewable electricity from wind and solar photovoltaics, hydroelectricity, or perhaps available low-quality heat sources (industrial process heat dissipation).
Overall, the industrial processes reviewed here (ranging from nascent projects initiating benchwork to mature technology deployment at industrial scale) can certainly be an outlet for energy from CSP, but there is no strong economic driving force for this to happen. Other renewable energy sources will do with the only issue being cost per unit energy, and tolerance (or absence thereof) to intermittent processing. In short, it seems for example not likely (and reality seems to support this) that a solar tower and collector field will be constructed to drive membrane distillation at 80°C if low-cost wind power is available. Note that organizations such as the Southwest Power Pool will readily contract for renewable energy for, say, a planned industrial installation such as renewable ammonia synthesis, with a guarantee for continuous supply of renewable electricity at any level of reliability if that is desired. This negates the argument brought up by some CSP/storage advocates that wind power is intermittent.
The reviewed projects, if powered by CSP rather than fossil-derived energy certainly support the goal of SETO (above). Economic driving forces, however, will push most of the projects toward using other renewable energy sources. CSP should be reserved for processes that require the extraordinarily high temperatures easily available through CSP, such as silicon production for semiconductors in the carbothermal reduction of silicon dioxide at 2200°C.
Alignment with Goals
The goal of using CSP for purposes other than generation of electricity is certainly well supported by the projects in this topic. Commodity chemicals production (ammonia, hydrogen), a number of variations on desalination ranging from conceptual to full-scale deployment, and some more detailed projects support this goal.
Availability of low cost renewable energy from other sources, however, threatens the impact of any project not taking specific advantage of the unique high-temperature range that is easily accessed with CSP.
Funding and Resource Allocation
The funding in this area (compared to SETO's funding in other areas) seems appropriate. The project portfolio shows some tendency to duplication, however, with duplication in the desalination area. This area is either subject to devastating commercial competition (seawater: reverse osmosis), or it is difficult to see how actual applications emerge, especially in light of very challenging economics for zero liquid discharge desalination (in addition to often neglected issue/cost of disposal of solid mixed-minerals residue). Since no use is made of the main distinction of CSP in desalination, this is a good example of the conundrum of being non-competitive with other renewables.
Technical Diversity
Water purification projects are somewhat overrepresented. Projects that make at least indirect use of high-temperature thermal energy would probably do better regarding competitiveness with other renewable energy sources. Specialty high-temperature alloys and materials, inorganic materials (especially high purity for semiconductors), and specialty glasses may be examples.
Advancing the Mission
The match with SETO's mission is good. Since there is little in the way of CSP industry in the U.S. as far as solar towers or other solar thermal collector applications, a match with industry can only be seen as a "push" at this time since "pull" by industry seems not present. Again, a "pull" is most likely (besides through consistent subsidies) through "can be done easily in a CSP process, hard to do otherwise" case.
Areas of Improvement
Each project needs to be clearly and very early on benchmarked against existing technology and existing renewable energy options. A go/no-go should be established based on economics if no truly inevitable use of CSP is made.
Stakeholder Engagement
Economics are very often paramount in industrial applications. One might simply require an applied economist as part of a team, especially the large-budget efforts. Static CAPEX/OPEX calculations are what is supplied at most in this portfolio (if that), while an economist will bring a neutral and fact driven view to projects. In addition, time-dependent economics including estimated technology advances, regulatory environment, and market fluctuations provide an advanced view, just like dynamic simulations are often more enlightening than steady state work.
Final Feedback
This review process and the information provided (as expressed by reviewers and myself) could benefit from more structured information that is comparable for each project. If the slideshow format is used again, a template should be provided to the PIs before the review so a basic range of information is provided in a standardized manner. The review suffered from very inconsistent information via the slideshows.
See more review summaries from SETO’s 2022 Peer Review.