Sunvapor Inc. (Livermore, Calif.; www.sunvapor.net) was awarded a grant from the U.S. Dept. of Energy (DOE; Washington, D.C.; www.energy.gov) last month to scale up its Green Parabolic Trough Collector, a solar thermal technology that cuts construction costs by half compared to existing solar thermal systems. The new grant builds on the success of the prototype system (Chem. Eng. June 2017, p. 7; www.chemengonline.com/low-cost-solar-collectors-provide-renewable-process-heat). The Sunvapor collectors use a patented low-cost spaceframe structure built from lumber instead of steel to support the parabolic mirrors, and an advanced alignment process to maintain the accuracy of the parabolic assembly.
For the new project, the solar collectors will generate 150-psi saturated steam for an industrial food-production process. The solar collectors will be coupled with a thermal-energy storage technology that will allow steam generation at times of low or no sunlight. Sunvapor is working with the U.S. National Renewable Energy Laboratory (NREL; Golden, Colo.; www.nrel.gov) on the storage solution. It is based on a set of phase-change materials (PCMs) that are specifically chosen for high latent heat, a melting point tuned for the steam pressure, low cost and environmental safety.
“As the excess steam generated by the solar collectors is introduced to the heat exchanger, the PCMs melt, effectively storing the thermal energy,” explains Philip Gleckman, CEO of Sunvapor. “Later, when no sunlight is present, the stored energy can be used to generate steam as the PCMs freeze.” The near isothermal heat exchange reduces the mean fluid temperature in the solar field, leading to lower heat losses, higher efficiency and lower costs, he says.
Although the first deployment of the solar-steam and energy-storage system will be a food-processing application, the steam conditions are similar to those used for the most efficient desalination processes for brackish water that include heat recovery in the last distillation effect, Gleckman notes, so the platform can also be applied there in the future, as well as many other industrial applications where steam is required.
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