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FOCUS Technology Snapshot - Cogenra Solar's Hybrid Solar Converter with Light-Filtering Mirror

In this project Cogenra Solar develops DoubleFOCUS (DF), an innovative solar power system that integrates multiple state-of-the-art technologies from a broad cross-disciplinary fields, in order to maximally exploit energy from the sun. The DF concept combines concentrating photovoltaic (CPV) and thermal concentrating solar power (CSP) in a novel way that leverages the strengths of each technology, more optimally utilizes the solar spectrum, and shares system components to generate more exergy and energy value with minimal incremental hardware. DF is a platform technology ideal for both small, distributed applications as well as utility-scale generation, and it can easily incorporate complementary advances in PV and CSP, thereby creating a new learning curve that will drive down the cost of dispatchable solar power faster than PV or CSP alone. Exergy efficiency of the DF converter will be ~42% despite its moderate temperature.

DoubleFocus is conceptually similar to a conventional parabolic trough CSP system. Parabolic mirrors track the sun and concentrate direct normal incident energy to 40-50 suns. The CSP absorber tube runs along the focal line of the system.  However, in this innovative optical design, a dichroic filter (fabricated inexpensively from polymer layers with alternating high and low index of refraction) preferentially reflects the short wavelength energy (<950 nm) onto one of two photovoltaic/thermal receivers.  The PV/T receiver incorporates inexpensive single-junction, high-efficiency, single-crystal GaAs cells lifted off from reusable substrates.  The cells will be laminated directly onto an aluminum baseplate that is extruded with an internal void; heat transfer fluid circulates through this conduit and collects the energy that the PV cells do not convert directly to electricity.  The two PV/T receivers are deliberately offset from the mirrored focal line, reducing the effective concentration to 20-25 suns.  The system delivers heat at two different temperatures to two separate thermal storage/conversion systems. For utility scale deployments, the CSP absorber tube will deliver heat at 350-400°C to a steam turbine and the PV/T receiver will deliver heat at 175-200°C to an organic Rankine cycle (ORC) engine. For industrial, commercial, and district heating deployments, the lower temperature loop can alternatively provide industrial process heat, heat domestic water or air, or drive a double-effect adsorption chiller air conditioner.