Evaluation of a solar photovoltaic thermal (PVT) system in a dairy farm in Germany

Abstract

Livestock farms are a major contributor to CO2 emissions. The use of renewable energy sources (RES) is an important step to mitigate emissions from farms. This paper develops and evaluates a market-integrated, cost-effective, and case-sensitive RES solution for livestock farms. For this purpose, the dairy farm at LVAT-ATB in Germany; which includes three barns for milk production with a total area of 3950 m2, was considered. A solar PVT system is designed to most effectively use the heat recovery of the milk coolers and to use the thermal heat from the PVT system to lift the inlet temperature of an electric boiler (E-boiler) and reduce grid electricity consumption. The performance and monthly thermal output of the designed PVT system are evaluated using two different PVT collectors; Solarus (concentrated) and Dual Sun (flat plate). A preliminary analysis was performed to determine the PVT collector most suitable for the livestock farm here studied. The DualSun collector generated a higher electricity output than the Solarus C-PVT, however, the C-PVT was able to reach higher temperatures. Since the LVAT-ATB farm site included an existing heat recovery system, the integration point was carefully defined and a semi-automated system was incorporated to (1) use the heat from the heat recovery system as the inlet heat for the PVT system and (2), to use the PVT buffer tank as additional storage to store excess heat from the heat recovery system. Using this approach, a maximum amount of thermal energy can be stored. The PVT system would further raise the temperature from the heat recovery system and thus minimize the electricity consumption of the E-boiler. Furthermore, a draft layout of all the components and outdoor enclosure was presented. 24 Solarus PVT collectors running at mean temperature of 45 °C meet 16% of the annual hot water demand of the dairy farm by direct solar heat and this number of PVTs can supply up to 38% of hot water demand in summer months. The payback period for this system is less than 6 years and annual electrical energy utilization ratio and highest solar thermal fraction are 9.7 and 51.9%, respectively. Furthermore, 24 PVTs on an annual basis, generate slightly more than 4,200 kWh of electricity that can be used to offset electricity consumed by electric boilers in the LVAT farm.