Hybrid concentrator photovoltaic-thermal (CPV/T) systems generate both electricity and process heat by splitting concentrated sunlight onto CPV cells and a thermal receiver utilizing a heat-transfer fluid. Such energy co-generation increases total conversion efficiency and reduces system costs to compete with more widely used electricity and heat-generation methods in target markets. Here, we design and prototype a sunflower-like CPV/T system that collects a portion of the incoming sunlight using triple-junction CPV cells operating with an average temperature of <85°C. In the same receiver, thermal output >245°C may be generated from both waste heat from the CPV cells and a spatially separated fraction of the incoming concentrated light illuminating a heat-exchanger coil. In total, >65% of incident sunlight is converted to electricity or process heat. On-sun field tests validate this model and guide future development, and a techno-economic model demonstrates a US average levelized cost of heat of 2.5 ¢/kWth.

Hybrid concentrator photovoltaic-thermal systems can cogenerate electricity and heat by beam-splitting incoming concentrated light onto photovoltaic cells and a thermal receiver to increase total conversion efficiency and potentially reduce system cost. To demonstrate this, we have designed and prototyped a transmissive spectrum-splitting concentrator photovoltaic module that maximizes solar energy conversion by utilizing the entire solar spectrum. Visible light is collected using infrared-transmissive triple-junction photovoltaic cells to achieve an in-band module efficiency of 43.3% for light of wavelength lambda < 873 nm, while 44.2% of out-of-band light with lambda > 873 nm is transmitted through for collection by a thermal receiver. During testing on a dual-axis tracked parabolic concentrator dish at up to 166 suns, cell temperatures were maintained at 119 degrees C or below via a novel active cooling method. This cooling system strictly flows silicone oil directly across both sides of the cells, without inhibiting optical transmission, as verified through experimentation and simulation. The module was validated outdoors for 572 sun?hrs, and achieved a maximum thermal receiver temperature of 180 degrees C. 86.1% of incident solar power is collected at 166 suns average concentration collectively among the electrical, cooling, and thermal receiver subsystems. The remaining 13.9% is lost to mirror reflectivity, dish shadowing, receiver reflection, and thermal losses. The ability to directly cool the cells with an inert silicone oil offers the potential for reduced system cost relative to previous transmissive hybrid concentrator photovoltaic-thermal systems, including microfluidic-cooled designs. This solar cogeneration capability is valuable in a wide range of commercial and industrial applications.

Side-by-side installations of flat plate photovoltaics and parabolic trough collectors consume significant space and have high system losses; by using an all-in-one, spectrum-splitting hybrid receiver, electricity and high-temperature heat can be generated with a single efficient system. Here, the performance of a transmissive concentrator photovoltaic/thermal (tCPV/T) system is demonstrated on-sun, with a total energy efficiency of 85.1% +/- 3.3%, 138 W electric power at 304 suns (with average cell temperatures <110 degrees C), 903 W hot water output (average 34 degrees C and 1.7 bar, peak temperatures to 56 degrees C), and 1,139 W high-temperature steam output (average 201 degrees C and 45 bar, peak temperatures up to 248 degrees C). The spectrum-splitting hybrid receiver uses a sparse array of III-V triple-junction solar cells on GaAs substrates contained within a transparent microchannel water cooling stack, followed by a structured flow path thermal receiver cooled with pressurized water. System economics based on a 2.72-m(2) prototype performance is shown to be at or near market competitiveness to natural-gas-produced process heat for a variety of locations, with a levelized cost of heat of 0.03 $/kW(t)h for an installation in San Diego, California.

Hybrid photovoltaic-thermal systems can decouple IR light from visible light, allowing it to be collected separately by spectrum-optimized mechanisms for increased total efficiency. To demonstrate this, we have designed and prototyped a transmissive spectrum-splitting concentrator photovoltaic module that maximizes solar energy conversion by utilizing the entire solar spectrum. The system first collects visible light using IR-transmissive triple-junction photovoltaic cells to achieve an in-band module efficiency of ηmIB = 34.7% for light of wavelengths λ < 870 nm. Simultaneously, 58.8% of light with λ > 870 nm is transmitted through the cells for collection by a thermal receiver. By combining electrical and thermal power collection, 75% of incident solar power is collected, far surpassing the collection capability of only photovoltaics. The module was tested on a dual-axis tracked parabolic concentrator dish at up to 160 suns for 60 cumulative on-sun hours while maintaining photovoltaic cell temperatures at an average of 50 °C via active cooling. The system performed as expected based on modeled values, and represents a cost-effective path forward for dual-generation of electricity and high-temperature heat with increased total efficiency. The capability is valuable in a wide range of commercial and industrial cogeneration applications.

We present the design, fabrication, characterization, and field testing of transmissive active cooling for use in a point-focus spectrum-splitting hybrid concentrator photovoltaics/thermal (CPV/T) system. Seven parallel-path 100 mu m thick microchannels are made using polydimethylsiloxane and attached to a CPV module containing a 6 x 6 array of 5.5 mm transmissive CPV cells on a sapphire substrate. Water is flowed through the micro-channels to actively cool the CPV cells. The total transmittance of the CPV module reduces by 5.2% with the addition of the active cooling microchannels, relative to the module transmission with no microchannels. The peak cell temperature is measured as 69 degrees C with a thermal resistance of 9.351 K/W at 157 suns, well below the 110 degrees C maximum allowed temperature. A maximum flowrate of 16.7 g/s is achieved from a 13 psi pressure drop across the microchannels and manifold assembly. The flow characteristics within each microfluidic channel show maximum fluid velocity of 4.3 m/s (Re = 953) with a calculated convection coefficient of 1.7 x 10(4) W/m(2)K (Nu = 5.36). The CPV/T module and cooling system performance was validated during week-long outdoor tests under varying solar conditions up to 250 suns using a 2.7 m(2) parabolic dish collector mounted to a two-axis tracking system.

A hybrid solar energy conversion system has been developed for converting sunlight into electricity and thermal energy. The system increases efficiency and reduces cost by utilizing a transmissive, spectrum-splitting concentrator photovoltaic module featuring triple junction III-V solar cells. This enables cell temperatures to be maintained below 100 degrees C while thermal temperatures may rise as high as 600 degrees C. The presentation will discuss module and system design, a series of prototype iterations, and multi-day outdoor field testing. Techno-economic analysis will be presented in a variety of locations and industrial process heat contexts.

We present three-dimensional numerical simulations to quantify the design specifications of a directed thermoplate expanded channel heat exchanger, also called dimpleplate. Parametric thermofluidic simulations were performed independently varying the number of spot welds, the diameter of the spot welds, and the thickness of the fluid channel within the laminar flow regime. Results from computational fluid dynamics simulations show an improvement in heat transfer is achieved under a variety of conditions: when the thermoplate has a relatively large cross-sectional area normal to the flow, a ratio of spot weld spacing to channel length of 0.2, and a ratio of the spot weld diameter with respect to channel width of 0.3. Experimental results performed to validate the model are also presented. (C) 2018 Elsevier Ltd. All rights reserved.

A three-dimensional ANSYS-FLUENT Computational Fluid Dynamics (CFD) model of the central receiver in a compact hybrid solar-thermal collector is presented. The small scale cavity receiver is conical in shape, laser welded from Inconel 625 with a 38 mm entrance aperture, and uses pressurized water as the Heat Transfer Fluid (HTF) within a thermoplate serpentine flowpath. The coupled thermofluidic CFD model examines a simplified unrolled version of this dimpleplate heat exchanger, representing the laminar flow within 10 x 1 mm expanded flowpath serpentine channels complete with intrachannel spot welds and non-uniform concentrated solar irradiance heating. The computational model is validated against experimental results with the receiver at the focus of a 2.7 m(2) parabolic dish, two-axis tracking rooftop solar collector. For steady state conditions with the outlet HTF reaching temperatures in excess of 200 degrees C, the HTF temperature rise predicted by the computational model is in agreement with the experimental data. In order to accurately capture the heat losses from the heat exchanger to its surrounding, we present an additional three-dimensional CFD model including the heat exchanger and surrounding thermal insulation. Contours of temperature and velocity at the midplane of the dimpleplate receiver heat exchanger are presented. (C) 2018 Elsevier Ltd. All rights reserved.