High Efficiency Solar to Electric Energy Conversion through Spectrum Splitting and Multi-channel Full Spectrum Harvestin
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High Efficiency Solar to Electric Energy Conversion through Spectrum Splitting and Multi-channel Full Spectrum Harvesting Lirong Zeng Broderick1, Tiejun Zhang2, Marco Stefancich2, Brian R. Albert1, Evelyn Wang1, Gang Chen1, Peter Armstrong2, Matteo Chiesa2, Lionel Kimerling1, and Jurgen Michel1 1 2
Massachusetts Institute of Technology, Cambridge, MA, USA, 02139 Masdar Institute of Science and Technology, Abu Dhabi, United Arab Emirates
ABSTRACT A system combining photovoltaic (PV) and solar thermal approaches is designed to convert solar energy to electricity with high efficiency across the full solar spectrum. Concentrated solar spectrum is split into two parts: PV and thermal. The PV part of the spectrum is further split into several subbands directed to bandgap appropriate solar cells on an inexpensive Si substrate. Epitaxial Ge on Si is used as a virtual substrate for III-V semiconductor growth. At long and very short wavelengths where PV efficiency is low, solar radiation is directed to a high temperature thermal storage tank for electricity generation using heat engines. The potential of using PV waste heat due to thermalization of high energy photoelectrons for electricity generation is also investigated. Detailed optical and thermal analysis show that with optimized design and neglecting optical component loss, system power conversion efficiency can reach 56%, including more than 16% absolute contribution from thermal storage. INTRODUCTION Traditionally there are two ways to convert solar energy to electricity: the photovoltaic (PV) effect and the solar thermal effect. In the former, semiconductor materials absorb sunlight and generate photoelectrons which are collected by an external circuit. The advantage is high efficiency (~44% so far under 1000 suns [1]), and no moving parts. However, in the very short and long wavelength ranges, PV has low efficiency. In the latter, solar energy is used to heat up a working fluid which generates electricity through heat engines. No expensive semiconductor materials are involved, and by using high temperature thermal storage, electricity can be generated even at night. The drawback is low efficiency (
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