Solar Concentrator Shows Promise for Bringing Electricity to Remote Villages

May 12, 2008
This computer graphic shows the solar concentrator with a bracket for mounting the Stirling engine at right
This computer graphic shows the solar concentrator with a bracket for mounting the Stirling engine at right

Fifteen percent of Arizona's electricity will come from renewable resources by 2025 under guidelines set in 2006 by the Arizona Corporation Commission. Currently, about 1 percent of the state's electricity is produced from solar, wind and other renewable sources.

To help move the state toward this goal, an engineering design team at The University of Arizona decided to build a low-cost solar concentrator that could be used in Arizona, while also being simple, robust and inexpensive enough to bring low-cost electricity to off-grid areas in developing countries.

The team displayed the results of their year-long project earlier this month at Engineering Design Day 2008, and won the $750 Raytheon Best Engineering Analysis Award for their efforts. Engineering Design Day is an annual event on the UA campus in which senior design teams display their projects and compete for cash prizes. The projects are judged by practicing engineers.

The solar concentrator project was funded by SunRISE Solar Engineering, LLC, which is working on a cost-effective approach to generating solar power.

Stirling Engine is Key

SunRise Solar is developing a version of the Stirling engine that uses solar heat for fuel. The engine will spin a generator and produce electricity. The senior design team’s part of the project is to build a concentrator that tracks the sun with a 16-foot-diameter, parabolic dish, which focuses sunlight on the Stirling engine.

Stirling engines depend on a temperature differential to alternately heat and cool a gas sealed inside the engine. As the gas expands and contracts, it drives the engine's piston or pistons, which spin a crankshaft, turning heat energy into mechanical energy.

The students focused on using appropriate technology to produce a rugged, low-cost design. They started with a discarded satellite TV dish, stripped off its microwave coating, and polished it to make a solar concentrator. Then they designed an inexpensive metal frame and a drive mechanism built around a surplus automobile axle.

"The axle only turns about 15 degrees an hour to follow the sun, so you can use one that might not be suitable for a car, but works just fine in this application," said Scott Lilley, an optical engineering senior.

Cutting Costs

"We're keeping the cost down to around $5,000," added Andrea Gains-Germain, a senior in mechanical engineering and a UA honors student. She noted that when the concentrator prototype is finished it will be about 24 feet wide and 20 feet tall, making it somewhat large and costly for individual use. "It's really designed to provide power for a small building or several homes in a village."

"It's a very site insensitive design," added Joseph Pursley, a mechanical engineering senior. "It's designed so you can take it across rough terrain and set up in a site that doesn't have to be graded or have a concrete base."

While the other students have job and internship commitments for the summer, Lilley will be working with SunRISE Solar Engineering to complete the prototype based on the team's design.

The design team included Lilley, Pursley, Gains-Germain, and Eric Vonder Reith. All the students are in mechanical engineering, except for Lilley, who is graduating in optical science and engineering.