Design, simulation and validation of small-scale solar milk cooling systems

Besides hygienic milking and collecting practices, which keep contamination levels low, the milk storage temperature is one of the main factors to assure microbiological quality of raw milk. In many African countries, milk production is mainly carried out by small and medium size dairy farms. These farms are mostly constrained by the lack of cooling systems and reduced hygiene standards, often resulting in high microbial contamination of the milk. Under warm climatic conditions, bacteria growth occurs rapidly, which can finally lead to a rejection of milk at the collection centers or dairies, causing significant income losses to the stakeholders of the value chain. In this context, a solar milk cooling solution has been developed, addressing the refrigeration needs of farms in rural and isolated areas. The objective of the dissertation was to assess the solution regarding its availability to preserve milk quality on-farm and during transport. In the first section, the performance of a refrigerator is characterized in relation to its cooling capacity and efficiency. The configuration, based on the use of ice, was assessed to cool down milk under the usually required cooling rate and storage temperatures. The second section implements the previously developed model to design the solar energy supply system for a certain location. A control unit was designed, which converts the studied refrigerator into a smart solar freezer able to adapt to the availability of solar energy. The third section focuses on the use of insulated milk-cans with integrated ice-compartments for the cooling and storage of milk. The bacteria growth was assessed for cooled and uncooled milk in order to obtain the potential of the system to preserve milk quality.