Solar-Flow Battery Achieves 20% Conversion of Energy From Sun

By Allison Proffitt 

July 17, 2020 | Solar cell researchers have created a highly efficient and long-lasting solar-flow battery, which is a way to generate, store, and redeliver renewable electricity from the sun. The solar-flow battery achieved a new record efficiency of 20% conversion of energy from the sun.

The work was published this week in Nature Materials (DOI:10.1038/s41563-020-0720-x). The Song Jin lab in the UW–Madison chemistry department led the research in collaboration with researchers at Utah State University, King Abdullah University of Science and Technology in Saudi Arabia, the City University of Hong Kong, University of New South Wales and the University of Sydney.

Solar flow batteries are likely years away from commercialization, but the model is attractive as a low-cost, compact, and promising solution to rapid electrification of rural areas. Combining photovoltaic cells with electrolyte energy storage, could provide reliable electricity generation and storage for lighting, cell phones, or other fundamental uses for homes in remote areas. However, obtaining high energy conversion performance and long device lifetime simultaneously in these systems has been challenging, the authors write.

For this battery, the researchers used high-efficiency halide perovskite, a popular material for photovoltaic cells, combined with silicon, which stabilizes the device so it can withstand the chemicals in a flow battery. Numerical analysis methods enable the rational design of both components, achieving an optimal voltage match.

The result: a high-performance and stable solar flow battery that maintained a high efficiency over hundreds of hours and hundreds of charge-discharge cycles while retaining most of its capacity and exhibiting a lifespan that was several times longer than earlier devices.

The solar-to-output electricity efficiency was 20.1%—the best yet for solar flow batteries—and that efficiency is available both during the day and from storage in the evening.

This is the Jin lab’s third iteration on the general design marrying a solar cell with a liquid battery. The lab published its first prototype in 2016 in Angewandte Chemie International Edition (DOI: 10.1002/anie.201606986). The team combined silicon photovoltaic cells that convert sunlight into electricity with a “redox flow battery,” or RFB, which stores energy in a tank of liquid electrolyte. The first version achieved 1.7% efficiency.

In 2018, the team published an update in Chem (DOI: 10.1016/j.chempr.2018.08.023). The new battery returned more than 14% of the incoming solar energy as electricity.

Now, in the third version, the Jin lab achieved a new record efficiency of 20%—besting most commercially available silicon solar cells used today.

The design is still a long way from commercialization, but this improvement offers a clear path forward. “The conceptual design strategy… suggests general future optimization approaches for integrated solar energy conversion and storage systems,” the authors write in the paper. They will continue to increase the size and scale of the batteries improve robustness.