After spending two years trying to make solar energy a more viable energy source, researchers at the University of California at Merced have recently made a breakthrough. Roland Winston, a professor at UC Merced, and Heather Poiry, a graduate student, have led a team of 30 different students over the past two years to create a machine that can use solar energy to power an air-conditioning unit. Their design, called an External Compound Parabolic Concentrator, or XCPC, is innovative because it does not have to follow the sun in order to collect solar energy.
Typically, systems that collect solar energy have to be able to follow the sun's path through the sky in order to be effective. This requires expensive equipment that has to be installed and maintained. However, the XCPC can remain entirely stationary, while still reaching efficiency levels of up to 50 percent at temperatures of up to 400 degrees Fahrenheit.
The system is also unique because it can collect both direct and indirect sunlight, making it efficient even on cloudy days. On overcast days, light is more scattered, making it harder to gather. However, the XCPC can amass the majority of that light and still produce a significant amount of energy.
The innovation that allows the XCPC to remain stationary and to work on cloudy days is called non-imaging optics. It was created by Winston in the 1960s. The developments of this field over the past decades allow for collector tubes that can gather direct and diffuse light without having to track the sun. It also has made available the higher concentrations of sunlight that can be collected and the higher efficiency levels. "Designs have gone through many iterations …and they have been optimized to date with the system that we have built at Castle," Poiry wrote in an email to The News-Letter.
The system concentrates sunlight into collector tubes, and the heat is then transformed into energy that currently is used to air-condition an area. The energy collected by the XCPC could have other potential uses as well, such as heating.
Aside from collector tubes, the XCPC also contains a reflector and piping. "Each reflector is roughly eight inches wide and six feet long. You can put these together in systems which can make large arrays of solar collectors," Poiry wrote. Poiry, who has spent her undergraduate and graduate careers at UC Merced, has been the lead engineer and project manager for this project since it started in 2009. She is in the process of getting her master's degree in mechanical engineering. A variety of other students, ranging from undergraduates to postdocs, also worked on the project.
The researchers tested the system by setting it up on a mobile trailer at Castle Airforce Base. 160 XCPCs were placed on the trailer and attached to a high-performance, double-effect air-conditioning unit that requires a significant energy source in order to function. They performed this test because many scientists and industry leaders were skeptical of their claims about the system's efficiency.
Among the benefits of the XCPC are its lower cost and high efficiency. The fact that it doesn't require all the equipment of tracking systems means that it can be set up in a variety of places. It could become a very cost-effective way to decrease fuel consumption and greenhouse gas emissions. In particular, Poiry would like the system she helped create to be used by food processing industries in the San Joaquin Valley. These businesses usually burn coal and oil for heat, generating significant pollution as well as greenhouse gas emissions. Using solar energy instead would significantly help the air quality in the area.
