The Moon Village and similar concepts are strongly reliant on in-situ resource utilisation (ISRU), primarily associated with the extraction of water and oxygen from regolith ice and lunar minerals respectively. However, there is great interest in harvesting solar power locally leveraged from in-situ resources. To that end, there have been proposals to “print” solar cells from lunar regolith using a heat source - nominally a Fresnel lens, mirror or laser - mounted on a rover which traverses the lunar surface fusing regolith into solar cells. There are several potential difficulties with this notion: (i) anorthite yields lunar glass at high temperatures which will be coloured by iron impurities; (ii) pure silica is rare on the Moon where it is in silicate form unlikely to yield Si with sufficient purity for solar cells; (iii) although group III acceptor dopant Al may be extracted from the lunar mineral anorthite, group V donor dopant P will be much more difficult to extract from KREEP minerals and will require supply from Earth; (iv) the photovoltaic conversion efficiency from in-situ manufactured solar cells is unlikely to be >5%. There are several approaches that can alleviate these difficulties but they require pre-processing of regolith rendering the mobile rover-mounted 3D thermal printer unviable. Silicates such as anorthite can be treated with acid to yield alumina and silicic acid in solution from which pure silica can be precipitated. Pure silica when heated to high temperature yields fused silica glass which is transparent - fused silica glass may be employed to manufacture Fresnel lenses and/or mirrors. Both silica and alumina may be input to the Metalysis FFC Cambridge electrolytic process to yield near pure Si and near pure Al respectively. Finally, a metal-semiconductor junction forming a Schottky junction may substitute for a pn junction. Enhancement of the poor efficiency of the solar cell may be implemented using a local solar concentrator Fresnel lens but such enhancement will be modest. We present an alternative lunar resource leveraged-solar power production system on the Moon which can yield a conversion efficiency of >10% - solar Fresnel lens-thermionic conversion. The thermionic vacuum tube is constructed from lunar-derived materials and NiFe asteroidal ores on the Moon. Given that the majority of energy required for ISRU is thermal, thermionic conversion exploits this energy source directly.

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70th International Astronautical Congress, IAC 2019
Department of Mechanical and Aerospace Engineering

Ellery, A. (2019). In-situ resourced solar power generation and storage for a sustainable moon village. In Proceedings of the International Astronautical Congress, IAC.