A stand-alone, batteryless, off-grid, solar-refrigerated evaporatively-cooled (SREC) structure for storage of perishables was field evaluated for the first time by smallholder base-of-the-pyramid (BOP) farmers. The SREC chamber achieved daytime temperatures as low as ~5-10 °C when daily maximum temperatures outside reached approximately 45 °C. This technology demonstrated significant potential to enhance the capacity and stability of BOP farmers. The innovations incorporated into the SREC structure included a design suitable for self-building and staged construction, passive evaporation of water from chamber walls for partial cooling day and night, a split evaporator coil system for cooling diversion to a thermal reservoir, and deployment of advanced inverter technology with secure power supply and integrated controls to maximize solar collector efficiency. A cold water reservoir provided low-cost thermal storage instead of batteries for overnight cooling, reducing environmental impact, operational risks, initial capital, and maintenance costs. The chamber's large surface area maximized cooling with minimal temperature differential, increased humidity, and minimized perishable desiccation. A dedicated relay circuit ensured automatic startup following overnight shutdown, with no dependence on the electrical grid for cooling.
Despite its novelty, the SREC structure could be self-built by farmers using inexpensive, locally available materials, minimizing extra labor costs and initial investment requirements. Essential components like solar panels, inverters, and refrigeration systems were readily available in India. This project aimed to replicate initial technical successes through field trials conducted by farmers. The researchers evaluated energy collection and conversion efficiency for refrigeration, assessed the impact on perishable storage quality, measured benefits to farmer households, and evaluated effects on local and regional markets.
Deploying innovative off-grid batteryless SREC structures/chambers in farmers' fields across villages in three hot and dry states of India had several significant impacts. This innovation supported India's transition to a low-emission economy by expanding decentralized solar PV capacity. On-farm cold storage increased BOP farmers' incomes by reducing distress sales, spoilage, and enabling pre-processing of perishables. SREC technology adopters maintained produce freshness without relying on grid electricity, thereby avoiding market disruptions during grid failures and improving market confidence and control. Increased profits enhanced quality of life, boosted purchasing power, supported higher education opportunities for women and children, and improved household prosperity. Educational efforts included training farmers and local tradesmen in SREC chamber construction, enhancing community capabilities, and creating new financial opportunities. Farmers were educated on light processing opportunities for perishables and empowered to operate small processing machinery directly from solar panels. Extension professionals were trained on SREC technology construction and usage fundamentals, encouraging them to promote broader adoption and act as agents of change in their communities.
Final Summary of Project Activities  |
| USAID and NAS staff visit the project in May 2024. Sun Fridge |
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Dr. Chopra and her colleagues successfully designed an off-grid, batteryless solar refrigerated and evaporative cooled (SREC) structure, also called the Farm SunFridge, that can be self-built by smallholder farmers. Several innovative features have been incorporated, including a "water battery" (a thermal reservoir) to provide nighttime cooling, a dual-use refrigeration coil to cool the thermal reservoir and interior air simultaneously, and a solar adaptive controller to regulate power demand by refrigeration compressor based on available solar energy. Two SREC designs were built with frames of concrete (c-SREC) and iron (i-SREC) and evaluated for their ability to regulate temperature and humidity. The Farm Sunfridges were constructed and evaluated in the northern part of India (Delhi, Haryana, and Rajasthan) from 2017 to 2022, and the design proved able to reduce the interior temperature relative to ambient between 5 and 35 °C, varying throughout the day and across the seasons. During the hot, dry season of the year, the temperatures inside the i-SREC structures were lower than those in c-SREC structures; however, when solar insolation declined during the monsoon season, the two structure types performed similarly. The i-SREC out-performed the c-SREC during periods of high solar radiation, likely a result of the much reduced thermal mass of the roofing materials in the i-SREC. A significant reduction in storage temperature and improvement in storability of perishables can be achieved, relative to ambient and relative to evaporative cooling alone, in SREC (Farm Sunfridge) structures, and it has been proven as feasible for perishables storage by smallholder farmers and farmer organizations.
To illustrate the impact the FSF is having on its users, the young farmer Abhishek and his local farmer producer organization (FPO) near the project site at Cullakpur, New Delhi, use the FSF to store cabbage, tomatoes, and spinach. They have constructed a collection center and light processing platform adjacent to the FSF, and the farmer is buying, storing, and selling his produce from the FSF facility. The farmer and other members of the FPO said that FSF was working better than their expectations. The SunFridge at Cullakpur is working very well, with low temperatures ranging from 0 to 5 °C, when there was no loading/unloading of produce, and 10 to 15 °C when there was significant product movement. The SunFridge and cold room environment has permitted growers to enter the premium market segment for sale of spinach (washed, trimmed, and bound in bunches) and red cabbage (long-term storage), and they are making increased profits thanks to the FSF. The other units built at Chamrara, Haryana, and at the exhibition ground of IARI are working well also, with the latter also serving as a demonstration unit for policy makers, growers, and students visiting IARI. The latest FSF has been built at the village of Choti Bhitarwali, Dehradun, using IARI funds.
The Farm SunFridge has garnered a lot of attention and popularity among growers and policy makers in India. The Director of IARI has provided funds to build two of the structures, and in response to the rising demand for FSF technology, IARI has selected FSF to be built under its revolving fund scheme. Under this scheme, the tenders are floated and based on the bids received, the contractors are identified for construction of the FSF, wherever and wherever there is a demand. The innovative technologies incorporated into the FSF have also attracted attention from other researchers. Two groups of scientists have contacted Dr. Chopra and her group, and together they have prepared three proposals to USAID for the construction of FSF units in Kenya and Ethiopia for smallholder farmers.
Although the PEER grant has now ended, the PI and her colleagues will be continuing their work on further enhancements to the FSF design, including to expand its storage capacity in response to feedback from its users. They will also be supervising students studying the use of the FSF with other mangoes, marigolds, and milk. Further publications on their work are expected, and they have filed for a patent in India. Dr. Chopra and her U.S. partners feel the future for upscaling the FSF looks bright, given that users of the pilot units have demonstrated strong and rapid return on investment and industry and government agencies at various levels have expressed interest.
Supplemental FundsWith funding provided through a PEER Research to Action supplement, Dr. Chopra and her colleagues prepared an FSF construction manual, something that has been requested by farmers and policy makers alike. In addition, they have written a detailed project report with relevant economic analysis that will help interested parties obtain bank loans for building the structure.
Publications
S. Chopra, N. Mueller, D. Dhingra, P. Pillai, T. Kaushik, A. Kumar, and R. Beaudry. 2022. Design and performance of solar-refrigerated, evaporatively-cooled structure for off-grid storage of perishables,
Postharvest Biology and Technology 197, 112212.
https://doi.org/10.1016/j.postharvbio.2022.112212S. Chopra, N. Mueller, D. Dhingra, I. Mani, T. Kaushik, A. Kumar, and R. Beaudry. 2022. A mathematical description of evaporative cooling potential for perishables storage in India.
Postharvest Biology and Technology 183:111727
https://doi.org/10.1016/j.postharvbio.2021.111727
P.S. Mahangade, I. Mani, R. Beaudry, N. Mueller, and S. Chopra. 2020. Using amaranth as a model plant for evaluating imperfect storages: assessment of solar-refrigerated and evaporatively-cooled structures in India.
HortScience 55,
https://doi.org/10.21273/HORTSCI15249-20.
Sangeeta Chopra and Randolph Beaudry. 2018. Innovative composite wall designs for evaporative cooled structures for storage of perishable.
Indian Journal of Agricultural Sciences 88 (11):1692-95.
https://doi.org/10.56093/ijas.v88i11.84895
Sangeeta Chopra and Randolph Beaudry. 2018. Redesigning evaporatively cooled rooms to incorporate solar powered refrigeration in India.
Acta Horticulturae 1194, 609-616.
https://doi.org/10.17660/ActaHortic.2018.1194.88
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