Small-Scale Milk Pasteurization and Chilling Using Hybrid Solar–Thermal and Photovoltaic Systems for Off-Grid Areas

Due to the lack of access to grid electricity, milk preservation is a significant challenge in pastoral and rural areas of most African countries, despite the large volume of milk produced. Integrating milk pasteurization and chilling with a hybrid solar–thermal and photovoltaic system can enhance milk preservation, enabling milk to reach the market and generate income for pastoral and rural communities in off-grid areas of Africa. In this study, a MATLAB program was developed based on a transient model of a solar heating system and refrigeration system that uses a DC compressor powered by a photovoltaic panel for dynamic adaptive simulation of milk preservation temperature. The model facilitates reliable sizing of the evacuated-tube solar collector area, the PV array, and the DC compressor capacity for pasteurization and chilling based on the given milk volume for a particular location. Moreover, the annual performance of the system with a 50-L milk capacity at Semera, Ethiopia, was investigated. The simulation results show that milk can be effectively pasteurized at temperatures of 63°C and higher after water is heated for 30 min at 10 a.m. Consequently, in less than 3 h, the milk chilling system can lower the milk's temperature to 4°C. During the critical month, the time required was around 3 h and 10 min. Furthermore, the results show that the refrigeration cycle's coefficient of performance (COP) at the start of operation at 1800 rpm is 1.65. For the 24-V compressor, the highest COP recorded was 2.16 at a maximum speed of 3600 rpm. Nevertheless, when using the same compressor model with 48 V, the COP begins to decrease as the rpm exceeds 3600 rpm and eventually reaches a maximum speed of 6500 rpm. Hence, it can be concluded that solar-powered milk pasteurization and chiller can be used to alleviate the problem of milk preservation and market inaccessibility facing pastoralists and small-scale dairy farms in off-grid areas of semi-arid tropical regions.