A concentrating solar power system is presented which uses hillside mounted heliostats to direct sunlight into a volumetric absorption molten salt receiver with integral storage. The concentrated sunlight penetrates and is absorbed by molten salt in the receiver through a depth of 4-5 meters, making the system insensitive to the passage of clouds. The receiver volume also acts as the thermal storage volume eliminating the need for secondary hot and cold salt storage tanks. A small aperture and refractory-lined domed roof reduce losses to the environment and reflect thermal radiation back into the pond. Hot salt is pumped from the top of the tank through a steam generator and then returned to the bottom of the tank. An insulated barrier plate is positioned within the tank to provide a physical and thermal barrier between the thermally stratified layers, maintaining hot and cold salt volumes required for continuous operation. As a result, high temperature thermal energy can be provided 24/7 or at any desired time. The amount of storage required depends on local needs and economic conditions. About 2500 m 3 of nitrate salt is needed to operate a 4 MW e steam turbine 24/7 (7 hours sunshine, 17 hours storage), and with modest heliostat field oversizing to accumulate energy, the system could operate for an additional 24 hours (1 cloudy day). Alternatively, this same storage volume can supply a 50 MW e turbine for 3.25 hours without additional solar input. Cosine effect losses associated with hillside heliostats beaming light downwards to the receiver are offset by the elimination of a tower and separate hot and cold storage tanks and their associated pumping systems. Reduced system complexity also reduces variable costs. Using the NREL Solar Advisor program, the system is estimated to realize cost-competitive levelized production costs of electricity.

Abstract:A low cost, high flux, large area solar simulator has been designed, built and characterized for the purpose of studying optical melting and light absorption behavior of molten salts. Seven 1500 W metal halide outdoor stadium lights are used as the light source to simulate concentrating solar power (CSP) heliostat output. Metal halide bulbs and ballasts are far less costly per-watt than typical xenon arc lamp solar simulator light sources. They provide a satisfactory match to natural sunlight; although 'unfiltered' metal halide lights have irradiance peaks between 800-1000 nm representing an additional 5% of measured energy output as compared to terrestrial solar irradiance over the same range. With the use of a secondary conical concentrator, output fluxes of approximately 60 kW/m 2 (60 suns) peak and 45 kW/ m 2 (45 suns) average are achieved across a 38 cm diameter output aperture. Unique to the design of this simulator, the tilt angle and distance between the output aperture and the ground are adjustable to accommodate test receivers of varying geometry. Use of off-the-shelf structural, lighting and electrical components keeps the fabrication cost below $10,000.

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A spectrum splitting, transmissive concentrating photovoltaic (tCPV) module is proposed and designed for a hybrid photovoltaic-solar thermal (PV/T) system. By utilizing III-V triple junction solar cells with bandgaps of 2.1eV/1.7eV/1.4eV, ultraviolet (UV) and visible light will be absorbed and converted to electricity, while infrared (IR) light will pass through and be captured by a solar thermal receiver and stored as heat. The stored thermal energy may be dispatched as electricity or process heat, as needed. According to the numerical analysis, the tCPV module can perform with overall power conversion efficiency exceeding 43.5% for above bandgap (in-band) light under a standard AM1.5D solar spectrum, under an average concentration ratio of 400 suns. Passive and active cooling methods, keeping cells below 110°C, are also investigated and discussed, indicating that a transparent active cooling design could improve the CPV module efficiency by around 1% (absolute), relative to a passive design, by reducing the maximum cell working temperature by around 16°C.

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