This report describes the work that was performed during a three-phase project to establish a concentrating solar power (CSP) approach to boosting the chemical energy content of methane, a chemical fuel that is available from multiple sources, including natural gas, landfills and anaerobic digesters. The system makes use of parabolic dish solar concentrators, which had previously been developed for possible electrical power generation, and a compact, process-intensive chemical reaction system based on micro- and meso-channel process technology (MMPT).
The Solar Thermochemical Advanced Reactor System (STARS) has the potential of being useful for a number of applications. Combined with parabolic dish concentrators as Dish-STARSTM, the system provides a solar augment to the incoming methane stream, increasing its chemical energy content by 20-30% while decreasing its carbon intensity, measured as mega-joules per gram of carbon dioxide (MJ/gCO2). When the immediate chemical product, known as syngas, is used for power generation, the result is electricity with approximately 20% less CO2 emissions.
Similarly, when the syngas is further reacted to produce valuable chemical products, such as hydrogen, the reduction in carbon emissions is retained and reduced carbon intensities can be attained for the chemical products. In a co-production mode, low-carbon electricity and/or hydrogen plus various hydrocarbons (for example, methanol, olefins or plastics) can be produced.
Prior to this project, the initial integration of high TRL parabolic dish concentrators with highly efficient, MMPT components for steam-methane reforming was previously demonstrated under an earlier project, obtaining a Technology Readiness Level of 3 (TRL 3) and a world record, solar-to-chemical energy conversion efficiency of 63 +/- 4%.
During the course of the current project, the solar-methane reforming (SMR) system was successfully advanced, including the following accomplishments:
• The Solar Thermochemical Advanced Reaction System (STARS) technology platform was advanced from TRL 3 to TRL 6. Approximately two to three more years of development are needed to advance the system to TRL 9, which corresponds to commercial readiness.
• In on-sun tests, STARS’ solar-to-chemical energy conversion efficiency was increased from 63% to 70%. Test results combined with analyses indicate that higher efficiencies, as high as 80%, are obtainable through the use of higher performance concentrators and moderately higher temperature operation of the SMR.
• The STARS technology platform received an R&D 100 Award in late 2014.
• Mass production manufacturing methods for STARS components, particularly for MMPT reactors and heat exchangers were investigated. Additive manufacturing was proved for multiple microchannel heat exchangers, including a high-temperature, highly effective heat exchanger, as part of the project.
• Technoeconomics for power generation and hydrogen production confirmed the potential for electricity production in a hydrid solar/natural gas powerplant at about 6-7 ¢/kWh and hydrogen production in the range of $1.25-$2/kg.
As a result of the success of this project, two additional cost-shared projects have been proposed and accepted. One is focused on advancing a Minimum Viable Product (MVP) version of Dish-STARSTM for hydrogen production in California to TRL 8 over a two-year period. The other is focused on developing and proving MMPT manufacturing methods that are mass-producible and, if successful, are targeted to further reduce costs below those identified in this report.