Duke researchers pursue new ways to store solar power

Although solar power has grown quickly in the United States and around the world, it still accounts for a very small portion of overall electricity production. One of the key challenges facing solar photovoltaic (PV) systems is that their output is intermittent, and the power they generate cannot be cheaply stored for use at a later time.

Researchers at Duke University are developing new technologies for energy storage by using innovative electrical systems that will lower the cost of storing electricity from sources such as solar PV. They approach the problem by developing integrated modules consisting of solar panels and batteries, which can easily be combined to generate small- or large-scale power and storage systems.

"This technology has the potential to bring down the costs of energy storage using a source like solar," says project leader Angel V. Peterchev, assistant professor in the departments of Psychiatry and Behavioral Sciences, Electrical and Computer Engineering, and Biomedical Engineering. "It's advantageous because it's modular, and could be scaled for use in homes, businesses and even for large centralized power plants."

The project is supported by Duke’s Energy Initiative, which has provided seed grants to encourage a variety of innovative energy research projects. The Energy Initiative is currently accepting applications for a new round of seed grants; the deadline is Friday, Jan. 30.

The modular approach tackles several downsides of existing solar systems that utilize storage. First, existing solar panels use electrical systems that are not perfectly compatible with other electrical components, leading to efficiency losses in the transfer of power from the solar panel to the battery or onto the grid. The Duke team’s modules are designed to be more compatible with one another, greatly reducing these efficiency losses.

Second, existing systems are often interlinked so that the failure of a single component can disrupt or disable the entire solar array operation. "With existing technologies, if one battery fails, the whole system can come down," says Peterchev. "Protecting against this issue adds substantial costs for existing systems."

The team uses an innovative power switching device called a "modular, multi-level, series-parallel converter," or M2SPC, invented by post-doctoral researcher Stefan M. Goetz from Peterchev’s lab. The M2SPC allows them to bypass malfunctioning equipment, preventing isolated failures from spreading throughout the larger system.

Finally, the team's approach is able to send power directly from a battery to the electrical grid without the need for conventional power converters. Converters, which use magnetics to convert power from direct current (DC) to alternating current (AC), are some of the costliest pieces of equipment for battery storage systems.

A variety of efforts are under way to create large-scale electricity storage systems that can store power when the sun is shining and send it to consumers when demand is highest. However, few large-scale storage projects have actually been deployed.

Peterchev and his team, which includes professors Jie Liu of the Trinity College of Arts and Sciences and Jeffrey Glass from the Pratt School of Engineering, hope their modular system can help lower the costs of solar systems and associated energy storage, allowing for more deployment of solar power and other renewable systems.