Sammi Mulhern // Mustang News

Located in the far reaches of Cal Poly’s agriculture fields, the Student Experimental Farm is home to interesting and innovative ideas. In the summer of 2016, an idea blossomed in the farm that may one day reach across the globe.

Three seniors started working with two Cal Poly professors to design and create an affordable solar-powered freezer to be implemented in developing countries that might not have access to power.

Sammi Mulhern / Mustang News

Physics associate professor Peter Schwartz was working on solar-powered cookers when he started collaborating with physics lecturer Nathan Heston. Instead of turning solar energy into heat, Heston wanted to turn it into ice.

After living in Ghana from 2010 to 2014, Heston noticed there were no ways to preserve fresh food in the country. The problem specifically arose near Lake Volta, where fishermen needed a way to store fish for the weekly market.

“As an engineer or a physicist or a scientist, you can choose different world problems to work on,” Heston said. “I’m passionate about trying to make the world more sustainable, and that means
less waste.”

The team hopes to be done with the design for the solar-powered freezer by the end of 2017. Once it is finished, the product can be sold to Burro, a company that manufactures and sells products specifically designed for the developing world.

The problem with mass producing freezers lies in affordability. Normal refrigerators run on alternating current (AC) power, but because solar energy is direct current (DC) energy, the solar-powered freezer must run on DC power. DC power is normally stored in things like batteries, but batteries do not last long enough to power a freezer. The team wants to convert this DC energy into ice that can last multiple days, even when the sun isn’t out.

Sammi Mulhern / Mustang News

“I see our work here as trying to develop a tool that helps people in developing countries to do their jobs and make their countries better,” Heston said. “We need to move to things like solar power because it’s a sustainable solution.”

To achieve this goal, a DC compressor must be used to convert the energy into ice instead of the typical AC compressor. DC compressors take gaseous energy and convert it to a liquid. A heat dissipator then removes the heat from the freezer. The compressed liquid that results from the heat being removed expands into metal bars in the freezer, causing it to eventually freeze.

DC compressors typically have brushes that break down refrigerant gas. However, the brushes in standard DC compressors create sparks that inhibit the breakdown from gas to liquid. This means a special DC compressor must be used for the solar-powered freezer. These compressors are currently expensive, but as they become more popular, the price drops.

According to Heston, the current cost of a solar-powered freezer is approximately $500. To be able to sell it to Burro, the price needs to be approximately $200.

“I’ve always been interested in green energy,” mechanical engineering senior Luke Holmes said. “This worked out perfectly as my senior project and fits my heating, ventilating, air-conditioning and refrigerating concentration.”

Holmes is working with two other mechanical engineering students, Tyler Batchelder and Jonathon Lo, to fulfill their senior project requirements.

For now, the team has to wait until the price of special DC compressors drop. In the meantime, the group aims for a smaller prototype that a few families or fisherman could share. The team doesn’t have a set location for installation of the first finished solar-powered freezer, but they are looking at a few African countries.

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