Bengaluru: Keep it cool, fresh and cheap, Mr Farmer

Bengaluru: When the time came for them to start working on their final-year engineering presentations, Rashmi U., Suhas D.S., Vinay K.S. and Ravi Kiran S., all students at RV College of Engineering, decided to make an impact.

Their interdisciplinary project is a zero operational cost, fully sustainable solar-biogas hybrid cold storage unit that enables farmers to store their vegetable produce for up to 15 days. At the moment, storage facilities in and around Bengaluru charge around Rs 2 per kilo, so the farmer storing around 100 kilos of produce will have to pay Rs 200 per day, which he simply cannot afford.

The solar-biogas hybrid cold storage unit, which is being kept at RV College for the moment, works completely on sustainable energy sources, which means farmers no longer have to worry about erratic power supply and over-the-top operational costs. It also stores vegetables at the optimum temperature – between 5 and 8 degrees Celsius. “Near-freezing temperatures cause ‘chilling injury’, while the vegetables rot in anything higher than 8 degrees C,” said Vinay.

The four students started from scratch, visiting farmers in and around the city to understand their problems. Their aim was simple – to connect the farmer and the customer, so that the profit to the farmer increases. “We went to Malur, Ramanagar, Magadi, Mysuru and Kolar and understood that wastage was the biggest problem,” Vinay explained. Since they have no way of storing their produce, which is highly perishable, farmers are forced to sell at the day’s prices, even if they are low. “The price of vegetables fluctuates on a daily basis, but this is something they can't take advantage of,” said Rashmi. “Better storage meant better prices.”

Gujarat is the only state using zero energy cold chambers, they found, but these bring the ambient temperature to less than 10 degrees Celsius, which was not enough. “We actually constructed one ourselves but it didn’t work,” said Vinay. When they visited existing cold storage facilities, they found they were extremely high maintenance. "Farmers are paying a very high amount every day and they are given no guarantee that their produce will be intact. If there is no power and one vegetable rots, everything else will too. The farmer has to pay irrespective of this."

“We worked with principal scientists at the Indian Institute of Horticultural Research to understand the optimum conditions for storing the produce," said Rashmi. "Our college was extremely supportive as well – most institutes don't encourage interdisciplinary projects." Dr K.N. Subramanya, Vice-Principal, Department of Industrial Engineering and Management, and Dr R.S. Kulkarni, Professor and Head of the Mechanical Engineering Department, worked with them as their guides. "Principal Dr B.S. Satyanarayana also gave us a lot of support, he agreed at once to our idea," she said. Interestingly, the storage unit, which can be built on site, uses a compressor-ejector cascaded refrigeration cycle with R134a and water as refrigerants respectively. The ejector cycle is driven by solar thermal energy through solar evacuated tubes and an auxiliary heater driven by biogas during the night. The vapor compression cycle works on electrical energy that is generated by the solar PV cells.

“The cascaded technology, which uses an ejector cycle, is still being researched by the biggest companies across the world," said Vinay. "We visited an air-con expo after we built our hybrid unit and asked some of the participants if they used it. None of them did," they say, smiling. Their prototype, which they tested by storing beans, works just fine, however and has a capacity of 50 kg and 500 litres.