The presented work proposes a calculation method to estimate the transient performance of a small on-farm milk cooling system for PV applications. The system employs 3 kg ice for fast cooling of 17 L milk in conventional 20-L-milk-cans. Two units of a commercial DC refrigerator operate at −10 °C and at 4 °C for ice production and milk preservation respectively. The development of milk temperature and energy consumption during a cooling event was studied experimentally at different ambient temperatures of 20 °C, 30 °C and 40 °C. A computational model was developed and validated where thermal resistances and COP were adjusted with experimental data. The results between 20 °C and 40 °C ambient temperature show a COP reduction of around 30% and a total daily energy consumption increase of around 100%. The specific total energy consumption of the system per litre milk was between 30 Wh/L and 58 Wh/L for the studied ambient temperature range. The suggested model can be used for the optimisation of photovoltaic stand-alone systems at specific locations.