Development of a decentralized solar assisted milk pasteurizer and improved chiller for rural communities

Renewable energy is the only way to cope with changing climate for under-developed countries like Pakistan, particularly solar energy must be opted out due to plentiful sunshine hours. Being a natural liquid food, milk is a complete nutritional diet containing all of the essential minerals such as protein, fat and vitamins. However, improper post milking handling and storage resulting in wastage due to microorganisms and bacterial multiplication. The present study enables the application of decentralized solar-based milk pasteurization and chilling unit for the rural communities in Pakistan. To this end, in order to achieve pasteurization, innovative and efficient medium temperature solar technologies using solar concentrator (SC) and evacuated tube collectors (ETC) were employed, while one tonne of refrigeration unit powered by PV panels (2kWp) using variable refrigerant flow (VRF) technology enabled the chilling process. Finally, the microbial quality analysis of processed milk was carried out in comparison to locally available fresh and packaged milk. Energy required to pasteurize 100 litres of milk were calculated to be 4.68 and 4.22 kWh respectively for a temperature difference of 35-40°C. Under practical conditions, heat energy consumed for the milk pasteurization system coupled with SC and ETC was recoded to be 3.56 kWh and 3.91 kWh respectively; this value lies from 3.78 – 4.32 kWh to pasteurize the same milk batch size for a temperature difference of 35-40°C. Experiments were conducted using different batch sizes (50, 100, 150 and 200 liters) to cool down the raw milk from 30ºC to 4ºC. During the optimization phase, the comparative power required to run various types of compressors (reciprocating, rotary with capacitor and rotary with VRF) were found to be 1.8 kW, 1.2 kW and 0.8 kW respectively whereas the torque loads were noted to be 3.3 kW, 1.6 kW and zero kW. The developed solar based technologies showed promising quality of milk processing in physical, chemical, hygienic, adulteration and consumer acceptability aspect over the compared milk sources. Fat (5.4%), solid-not-fat (9.1%), salts (0.7%), protein (3.9%), lactose (4.2%), total solids (14.5%), pH (6.85), density (1.031 kg/l) and freezing point (-0.532°C) of solar processed milk were found within the standardized ranges. The processing cost per liter of milk, both for chilling and pasteurization, was calculated to be 0.003 USD with these solar powered technologies. In a nutshell, the present study addressed the raised research question in successful manner by accomplishing all research objectives by developing decentralized SMP, SMC, comprehensive milk quality and economic analysis for dairy farming communities.