Spectral beam splitting for solar collectors : a photovoltaic-thermal receiver for linear concentrators
Creators: name: Mojiri, Ahmad
Publisher: name: RMIT University
Year: 2024

description: There is an unprecedented need to transform energy production methods from fossil fuel based to renewable sources. Among these sources, wind and solar energy have gained significant momentum by cost reduction and system efficiency improvement. The cost of silicon PV cells has dropped from 76 dollars per watt in 1977 to below 30 cents per watt in 2015. Photovoltaic electricity has already reached grid parity in some countries including parts of the US and Australia. Solar energy is anticipated to be the world's largest power production method by 2050. However the transition won't be smooth and some challenges are perceived.<br><br>Utility scale PV fields can generate cheap electricity but their penetration can be curtailed once they reach 10% of total electricity supply. This is due to the lack of cost effective electrical energy storage. Even ambitious battery cost reduction in the next few years doesn't seem to be able to tackle this issue in short term. Hence, there is a significant need for innovative solar thermal power generators to be combined with PV converters to take advantage of cheap PV electricity and cost effective thermal energy and storage concurrently.<br><br>The stored thermal energy can be converted into electricity cost effectively when there is no PV output due to absence of solar radiation. Collectors that simultaneously capture sunlight with PV cells and a thermal collector are called PV-T collectors.<br><br>Traditional PV-T collectors are made of a PV receiver coupled to a thermal fluid. Since commercial PV cells convert about 15-20% of the sunlight to electricity, the remainder of the light energy dissipates as heat in them. The dissipated heat can be collected by the thermal fluid and delivered as useful energy.<br><br>For low temperature applications this can be a suitable method. For high temperature cases such as thermal power plants or industrial heat generators, the PV cells should be thermally decoupled from the thermal absorber because their efficiency and durability deteriorate at high temperatures. This can be achieved by employing spectral beam splitting between the PV cells and the thermal absorber.<br><br>In this thesis, a new method for effective spectral beam splitting for high temperature, greater than 120 C, hybrid PV-T receivers for linear solar concentrators is introduced. For this purpose, direct absorption and spectral light filtering using selective thermal fluids and semiconductor doped glass have been employed to achieve a relatively cost effective design for such receivers. The receiver was built and tested on a parabolic trough which is the first scalable experimental spectral splitting PV-T receiver built and tested in the literature.<br><br>The system achieved a 4% electrical conversion efficiency at about 120 degree C thermal output using silicon solar cells while keeping the cells operating at temperature below 60 degree C. A high level of thermal decoupling between the cells and the thermal absorber as well as an optical efficiency of over 60% was observed in the proposed system. Some recommendation for improving the systems' efficiency is also provided at the end of this work.