Solar Energy Driven Cold Storage

 

 SOLAR ENERGY OPERATED SMALL CAPACITY COLD STORAGE

 

FARM SUN FRIDGE

 

Indian farmers producing fruits, vegetables, milk, egg have no commercial storage facility available at their farm or household. Also the supply of electricity from the grid is not reliable. Power cuts are quite common. The quality of the electricity is also not good. Low voltage is quite common.

 

During storms or other extreme weather events, the power cables get snapped and the system also develops snags. Restoration of electricity takes time.

Scientists under Indian Council of Agricultural Research (ICAR) had developed some cold storage structure (capacity approx. 2 tonnes) based on the principle of evaporative cooling.  It is a fact that during hot and dry weather conditions, evaporation of water causes cooling. This concept was commonly used by artisans to make clay containers (surahi, ghada) to cool the water stored in these containers. The cooling effect due to evaporation is limited and it also depends on the ambient temperature and humidity. Under best possible conditions we can achieve a reduction in temperature up to say 15 to 18 deg. C. Although it helps in extending the shelf life of perishables to some extent, but this cannot achieve the optimum temperatures (10 - 12 deg C) for storage of tropical fruits and vegetables. These structures only need water to cool their walls and operate without electricity.

Further research was conducted to improve the storage structures of small capacity (two tonnes) by augmenting them with refrigeration. It led to the development of Farm Sun Fridge (as shown in pictures above).

The Farm Sun Fridge is an innovative, off-grid, battery-less, cold storage facility for perishables that uses a combination of evaporative cooling and solar refrigeration to store harvested farm products on farmers’ fields or in farm communities. This facility offers smallholder farmers inexpensive access to cold storage even without electrical connection and improves their control over the marketing of their crops.

It incorporates several innovative features into its design: it uses wetted fabric over iron mesh walls for passive, evaporative cooling, autoclaved aerated concrete blocks (AAC) and styrofoam panels for insulation, a solar-powered, mini split inverter air-conditioning unit for refrigeration, water-based thermal storage in place of batteries for nighttime cooling, and a novel solar sensor that better balances refrigeration demand with available solar energy.

Unique among clean energy storage concepts, the Farm SunFridge can be conveniently constructed all at once or developed in stages, as time and finances allow. In the first stage, farmers build the evaporative cooling (EC) chamber with locally available materials, which provides modest cooling. In stage two, solar refrigeration is installed with minimal additional investment and no major structural modifications.

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The approx cost (year 2021) and brief specifications are as under:

Cost: ~Rs 5 Lakhs (~ $7000)

Photovoltaic Wattage: 5 kW

Refrigeration Capacity: 18,000 BTU/hr  (1.5 tonnes)

Construction Area: 35 m²

Construction Time: one month

Size: 3 x 3 x 3 meters.

Storage Capacity: 2000 kg produce

Internal Daytime Temperature: 8 – 10°C

Internal Nighttime Temperature: 12 – 14 °C

* when the daily ambient maximum temperature is approximately 45 °C