The cost of solar photo-voltaic panels has been decreasing exponentially since they were first invented, as illustrated in the chart below.
Solar electricity is the logical source of power for sunny, rural communities that are not connected to other power systems. As these panels continue to decrease in price, more and more communities will be able to access electricity. The next question is what to do with it. The classic conundrum with solar energy is that it is only available when the sun in shining — how can one keep this energy around in order to use it during the cold, dark night?
One solution is the battery. It stores electricity from the solar panels, and can provide that electricity for use later. Batteries have some problems: they’re expensive, they aren’t easily transported, they’re potentially hazardous/toxic, and they don’t last very long. These problems mean that batteries may not be the best solution for rural, decentralized energy storage.
Before the technical considerations of the electricity storage, it is ultimately important to think about what human problems can be solved through access to electricity. One important use of electricity is refrigeration. According to a 2015 report from the University of Nottingham:
“Only about 10% of perishable foods are refrigerated worldwide, yet refrigeration is the best technology, with no associated risks, to ensure food safety and prolong the shelf life of perishable food. For example, milk can last for up to two weeks at 0 degrees C but just a few hours at 30 degrees C. More than 50% of global food loss and waste is comprised of commodities that can benefit from refrigeration.”
Refrigeration allows communities to save food (produce from harvest, as well as meat from livestock) and improve their food security. Refrigeration also allows farmers to store their crop to sell it at different times, increasing their earnings. The graph below from the University of Nottingham report illustrates how refrigeration is expected to extend the shelf life of different horticulture products:
The graph below from gapminder.com shows the positive relationship between the amount of electricity generated per person in a country, and the number of calories available for each person each day. This correlation does not imply that simply generating electricity will lead to more calories available, however, it is reasonable that having access to refrigeration will extend a community’s food supply.
The question is: How might electricity from solar panels be used/stored to maximize usefulness to a rural community, while minimizing its cost and negative impact? Can this energy be used to keep food from spoiling?
Solar Ice is a better solution!
The Solar Ice team aims to provide a method of refrigeration to rural communities who would otherwise have no means for extending their food security. The solar ice solution is paired with simple small-scale electrification, which can be extended to provide electricity for other needs.
The solar ice project uses solar panels to run a freezer during the day (when the sun is out). Making this ice is a form of energy storage! (keeping things cold with ice instead of keeping things cold with an electric refrigerator). The freezer is very well insulated, so the ice will last through the night. Families can then fetch units of ice for family cooling needs, or store food communally within the solar ice facility.
The solar ice solution also avoids another common pitfall in solar electricity production: inefficiencies from DC to AC conversion. Most appliances that we are used to require AC power. Solar panels produce DC power. Energy is wasted when converting from DC power to AC power — therefore it would be best if we could use the DC power straight from the solar panels. The solar ice facility will use a freezer which can be run directly form the solar panels, therefore removing the need for additional conversion components, and increasing the overall efficiency of the system.
The team anticipates that the efficiency of the system can be improved even further if the solar ice system is paired with an aquaponics system. The thermal sink of the pond will help increase the efficiency of the freezer. We hope to design a joint system that maximizes electrical efficiency, and also provides a sustainable source of food.
The solar ice team will also investigate the solar ice facility’s feasibility in promoting the production and consumption of Real Foods in our local community.
There are many possible models (business models, community models, etc) that the solar ice facility could be integrated with in order to ensure the facility’s sustainability. Some of the models that we have investigated are listed below:
Communal Responsibility; Communal Refrigeration Space
Under this model, the solar ice facility will be owned by the whole community. The community may decide as a group how to maintain the facility (they may elect a group to oversee its operation). Because the whole community owns the facility together, they all are entitled to use the refrigerator for food storage. We predict this model would run into a number of problems: With the responsibility diffused across the community, it may happen that no one feels strongly about maintaining the facility. Additionally, because everyone is entitled to use the space, quarrels may arise if too many people want to use it at once. We’re looking for a model that motivates a group to take ownership of the facility and feel empowered by their ownership of it.
Single Responsibility: Selling Blocks of Ice
Under this model, an individual or small group (family or business) has ownership of the facility. They use the facility to produce blocks of ice that they can sell to community members for their smaller refrigeration needs. This model provides a revenue stream for the owners to offset the cost of the system over time, and creates a sense of ownership that will lead to the small group caring about the maintenance of the system. We believe this model does well to empower the small group and solve refrigeration issues; but it also runs into some problems: If families do not have the resources to buy ice for their personal needs, they won’t be helped by the system. The goal is to empower everyone in the community, and this model disproportionately empowers those who already have the resources to buy ice. Additionally, this model requires that individuals who buy ice have their own way to use/store their ice, which is another barrier for the most marginalized.
Single Responsibility: Selling Space in Refrigeration
Under this model, the facility is operated by an individual or small group like above. Instead of selling blocks of ice, however, they sell or rent space in the refrigerator for individuals to store their food in. This model could work well in specific situations: a small/localized community, or in a marketplace. If this model was used in a spread-out community, then it wouldn’t make much sense for families who live far away from the refrigerator to store their food far away. This model makes more sense in a marketplace: if someone rented out refrigeration space in the market, then people who sell food in the market could store their food while they’re not selling in order to extend the amount they can sell. The marketplace model doesn’t address the need of individual families storing their own food, but it still positively affects everyone associated with the market.
The grocery store model specifically pairs the solar ice facility with a food-producing aquaponics system. This combination increases the efficiency of the solar ice facility (as discussed in Solar Ice Prototype), and also provides a sustainable source of food. This system can be run as a business, with food being grown, stored and sold from the facility itself. This model removes the need for costly transportation and extends the life of the food that is produced.
The solar ice team is investigating how a solar ice facility could benefit a communities:
Exploring viability in the developing countries: Ghana, Uganda, Haiti, and Baja Mexico.
We are also interested in exploring how a solar ice + aquaponics facility could be viable to implement in our own communities.
We are building a prototype of this technology on Cal Poly’s Student Experimental Farm. Check out our design and progress!
What is the real problem for people without refrigeration?
How will refrigeration help improve their lives?
OUR PROJECT VIDEO :
(pictured from right to left)