Solar EnergyMaterials 14 (1986) 299-325 299 North-Holland, Amsterdam SPECTRAL SELECTIVITY APPLIED TO HYBRID CONCENTRATION SYSTEMS D.E. OSBORN, M.A.C. CHENDO, M.A. HAMDY and F. LUTTMANN Solar and Energy Research Facility, University of Arizona, Tucson, Arizona 85721, USA M.R. JACOBSON, H.A. MACLEOD and R. SWENSON Optical Science Center, University of Arizona, Tucson, Arizona 85721, USA Spectral selectivity applied to hybrid quantum/thermal solar systems can improve the overall conversion efficiency of concentrated solar energy. The solar spectrum can be separated into spectral regions or windows matched to specificphotoquantum processes and the balance used for photothermal conversion. Higher conversion efficiencies can then be maintained in the photo- quantum converter while photons inefficient for its use can be channeled directly to a thermally decoupled photothermal loop at an elevated temperature. Various quantum conversionprocesses utilizing different portions of the spectrum can also be optically coupled through the use of spectral selectivity in a quantum/quantum hybrid solar system. The basic approaches of spectrally selective beamsplitters (SSBS) using dichroic filters and liquid absorption filters developed by the authors are presented. Various SSBSquantum/thermal hybrid systems are discussed. A detailed analysis is developed for one example, a spectrally selective hybrid photovoltaic/photothermal concentrating system. The analysis shows definite benefits of a spectrally selective approach, 1. Introduction The efficiency of utilizing the broad band of available solar energy by photo- quantum (PQ), photovoltaic (PV), or photochemical (PC) solar energy converters can be improved by combining those converters with a photothermal (PT) con- verter. For example, such hybrid systems are being developed to overcome the high unit area cost and inefficiency of PV conversion by employing concentrated sunlight to reduce the PV cell area required and recover the waste heat in a PT loop in series using the photovoltaics as a thermal absorber (fig. 1). In such thermally coupled quantum/thermal conversion systems, the PV conversion efficiency is limited by the broad wavelength range of the incident radiation, and the PT efficiency is con- strained by the need to avoid overheating the PV cells, which would reduce their efficiency further, Solar energy converters differ in their conversion efficiency as a function of wavelength. Photothermal converters are designed to absorb all wavelengths of the solar spectrum efficiently. However, photoquantum converters exhibit widely differ- ing spectral response curves which may be strong functions of wavelength. Photo- 0165-1633/86/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)