Techno-economic comparison and environmental impact assessment of a hybrid photovoltaic thermal solar system and a thermosiphon solar thermal hot water system with electric back up element, under Windhoek, Namibian conditions

A thesis submitted in fulfilment of the requirements for the degree of Master of Science (Renewable Energy)

Lack of accessible data on technical and economic evaluation of thermosiphon solar water heater (TS-SWH) and hybrid photovoltaic thermal (PVT) water heaters under Namibian conditions is limiting options available to decision makers on locally economic and opportune systems. This study compares the technical, economic aspects, and environmental impacts of TS-SWH and PVT water heaters. The TS-SWH installed in Otjomuise suburb, in Windhoek, were compared to PVT studied by others, in the UK and India. TS-SWH data was collected by Namibia Energy Institute using measuring instruments coupled to the systems. Both TS-SWH and PVT systems have the same technical make up, but the PVT system has solar PV cells on its collector. The findings of this study are that global radiation plays a major role in the operation of both solar water heaters and has influence on other parameters. TS-SWH of 1.2 m2 collector area results in about 6.3t of avoided CO2 as opposed to the PVT of the same aperture area that results in about 12.8t of avoided CO2 over their life span of 20 years, by interpolation of results by Herrando et al (1). PVT systems are cost effective, they cover domestic hot water demand completely and generate electricity simultaneously, in comparison to TS-SWH of same aperture area. TS-SWH has shown a solar fraction of 100%, specific solar energy yield of 470 kWh/m2 annually and return on investment of 7.7 years, in comparison, a PVT system has solar fraction is of about 68.6%, payback period of more than 20 years (2), a better energy yield of about 515 kWh/m2 annually and cogeneration efficiency of 66% (3). Installation of PVT systems for both domestic and commercial use country wide is recommended to reduce electricity demand and environmental impacts arising from generation of electricity from conventional methods. A study of PVT systems installed in Namibia and analysis of all year round data for TS-SWH is recommended for more reliable comparisons.