Chill Challenge: Affordable, Off-Grid Refrigeration
“Our mission is to lift people out of poverty and reliable, affordable and sustainable refrigeration is key. Successful solutions to our Refrigeration Challenge could be a game changer for millions of people. We are extremely proud to catalyze innovative solutions and bring affordable refrigeration to improve the lives of those far removed from the grid.”
— Cathy Leslie, former EWB-USA Executive Director
Background
In 2019 Engineers Without Borders USA launched its “Chill Challenge,” an initiative to explore affordable refrigeration technologies for off-grid communities. Although refrigeration has been a cornerstone of global economic and social development for more than a century, reliable refrigeration remains out of reach for many in developing countries, including for many of EWB’s partnering communities. To address this “refrigeration gap” EWB USA received a grant from Open Philanthropy to explore innovative refrigeration technologies that could be significantly more affordable than current options for off-grid communities. The competition was open to all interested parties and to all refrigeration technologies. Innovators were asked for proposals along two design tracks:
- Development of a 150-250 liter refrigerator capable of chilling 20 liters of water/day to 3ºC, and costing less than $12/month to own and operate, or
- Development of an icemaker capable of producing 100-1000 kg of ice per day at a cost of $0.03 per kg or less.
Both units would achieve these targets while operating on off-grid energy sources and meeting several design parameters.
In response to the call for proposals, EWB received 43 submissions from teams in ten countries, representing universities, companies, NGOs, and individuals. The proposed technologies ranged from conventional vapor compression refrigeration to various thermal sorption technologies and Stirling cycle, thermoelectric and evaporative cooling. Of the forty-three proposals submitted, fourteen were shortlisted for further consideration, and in April 2020 EWB awarded grants, totaling $305,000, to seven proposals that were ranked highest by the grantee review panel.
Research Results
Although COVID-19 delayed research efforts, all the teams had substantially finished their work by July 2021 and submitted final reports by the end of the year. A full report on the teams’ activities can be found here. The proposals receiving grants represented a good mix of technical risk and reward, employing several refrigeration technologies.
- Vapor Compression Driven by Solar PV: Two teams tested concepts using vapor compression refrigeration. Purdue’s Herrick Labs tested a vapor compression unit that could be used to make ice while using compressor heat for crop drying. Solar Cooling Engineering built an icemaker using multiple efficient DC compressors, with an innovative, flexible design to minimize cost and promote local sourcing and construction.
- Solar Thermal Sorption: Two prototypes employed sorption refrigeration powered by solar thermal energy. Imperial College London built an icemaker by adapting a conventional diffusion-absorption refrigeration unit to be driven by hot water from an advanced solar collector. Xergy Corporation tested a prototype sorption refrigerator employing an innovative hydrogen/metal hydride working pair.
- Biomass-powered Thermal Sorption: Two teams explored the use of sorption refrigeration using biomass as an energy source. New Leaf Dynamic Technologies built a large, 1000-kg/day icemaker employing fuelwood as the primary energy source. Purdue University’s Herrick Labs experimented with working pairs that could be used in a refrigerator powered by a cookstove.
- Sky-radiant Cooling: Arup Engineering explored the concept of using sky radiant cooling for refrigeration and evaluated several potential barriers to the technology.
Takeaways
The primary objective of the Chill Challenge was to identify potentially viable technologies and several teams have demonstrated prototypes that merit further evaluation and development. While other research efforts were less successful, they include a few “interesting failures” that identified barriers or limits to the proposed innovations. More broadly, the initiative has brought into focus key elements that have to be considered in any potential off-grid refrigeration solution.
Based on the work done to date, an affordable refrigerator, as defined by the initiative’s parameters, remains an elusive goal. The existing market for off-grid refrigerators has been dominated by vapor compression units driven by solar PV, with an increasing interest in thermoelectric (Peltier) fridges. However, meeting the Chill Challenge target of providing refrigeration over two “dark days” without solar input is a particularly difficult challenge for any solar-powered process. Solar-powered units should become more affordable as the off-grid market expands, and significant drops in the cost of battery storage could make the dark day challenge easier to meet. Some alternative technologies, such as an intermittent sorption system driven by biomass, also offer potential and merit further investigation.
For affordable icemakers, the outlook is more promising. There are a greater number of viable technology options, such as the thermal sorption process demonstrated by New Leaf Dynamics’ icemaker. Furthermore, icemakers using solar energy, whether solar PV or thermal, can employ ice storage, rather than batteries to provide dark day coverage. Larger designs also typically operate at higher efficiencies than smaller fridges and may incorporate other technologies, such as evaporative cooling or sky radiant cooling, to improve overall COP. Perhaps more important than technology, icemakers may prove easier to finance and deploy than refrigerators to meet the needs of off-grid communities.
EWB’s Chill Challenge has provided an opportunity to explore innovative technologies, but significant work remains to make refrigeration affordable for the millions of people who will rely on off-grid power. The challenge, though difficult, also offers tremendous commercial opportunities to the innovators and entrepreneurs who succeed in addressing it.