A concentrating solar simulator is a laboratory-scale tool that is useful in the development of processes to generate solar fuels. Such a device, which produces a concentrated radiative output replicating that of a solar dish, has been designed, built, and characterized at the University of Minnesota to facilitate the testing of prototype solar receivers and reactors. The concentrating solar simulator consists of seven commonly-focused radiation units, each consisting of a xenon arc lamp close-coupled to a reflector in the shape of an ellipsoid of revolution. A systematic design procedure has been developed as part of this work, which involves determining the location and orientation of each of the radiation units by requiring that the target focal points of all reflectors coincide. A set of unique geometric relations have been developed that ensure this requirement on a general scale and provide the framework for further designs by allowing the specification of detailed practical requirements dealing with the space available and manufacturability concerns. After the location and orientation of each of the lamp-reflector modules is established, the shape of the reflector is optimized with the use of a Monte Carlo ray tracing model. The shape of the ellipsoidal reflector is varied by the eccentricity, and sensitivity analyses are carried out to determine the effect of the reflector specular error and effective arc size and shape on the resulting flux distribution and magnitude. The completed facility consists of a dual enclosure specially designed to protect the researchers and the simulator, the array of lamps and reflectors, and the electrical systems necessary to power and control the lamps.
The radiative output of the solar simulator constitutes the energy input to the prototype solar receivers and reactors, and therefore must be well-characterized. The output has been measured with respect to its spatial and temporal variations by using an optical technique in which a CCD camera views radiation reflected from a water-cooled Lambertian target through neutral density filters and a lens. The image recorded by the camera is calibrated such that the recorded grayscales correspond to measured values of incident radiative flux, as measured by a circular foil heat flux gage that has been calibrated in-house. Using this method, it was determined that the solar simulator can output up to 9.2 0.4 kW of thermal power to a focal area 60 mm in diameter, corresponding to an average flux of 3240±390 kW m-2. The peak flux, as averaged over a 10 mm diameter focal area, is 7300±890 kW m-2. The UMN solar simulator facility is an excellent tool for testing prototype solar receivers and reactors on a laboratory scale.