In Saudi Arabia and the United States, researchers have harnessed the abilities of a battery and a solar cell in a single device called "solar flow battery". This device is capable of soaking up sunlight and efficiently storing it as chemical energy for subsequent on-demand use.
This image shows a new integrated solar flow battery with a 14.1 percent efficiency. (Credit: David Tenenbaum, UW-Madison)
This latest breakthrough could make electricity more readily available in the world’s remote regions. The results of the study have been reported in the journal
Although sunlight has become increasingly appealing as an abundant and clean energy source, it has one apparent limitation-- some days are much sunnier than others, and there is only so much sunlight in a day. Therefore, one way to keep solar energy practical is to make sure that once sunlight is transformed into electrical energy, it should be stored efficiently. While two devices are generally required for this—that is, a battery and a solar cell—the solar flow battery is specifically made to function like both.
Compared with separated solar energy conversion and electrochemical energy storage devices, combining the functions of separated devices into a single, integrated device could be a more efficient, scalable, compact, and cost-effective approach to utilizing solar energy," states Song Jin, a professor of chemistry at the University of Wisconsin-Madison. Along with his team, Jin developed the novel device in association with Jr-Hau He, a professor of electrical engineering at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia.
There are three different modes in the solar flow battery. In case energy is required immediately, the solar flow battery can behave like a solar cell and instantly transform sunlight into electricity. If not, the device can harness the solar energy during the day time and store it as chemical energy. This chemical can later be delivered as electricity when the sky grows cloudy or night falls. If required, the device can also be charged by electrical energy similar to a standard battery. The most recent solar flow battery model designed by the team is capable of storing and delivering electricity from solar energy in a more efficient way when compared to other integrated devices that are presently available.
According to Jin, the novel solar flow battery could help in overcoming the restrictions of the electrical grid by offering an alternative source of energy when conventional electrical systems malfunction and making electricity more readily accessible to people residing in rural regions.
These integrated solar flow batteries will be especially suitable as distributed and stand-alone solar energy conversion and storage systems in remote locations and enable practical off-grid electrification," states Jin.
While it is still too costly to develop current solar flow batteries for real-world markets, cheaper solar cell materials, simpler designs, and technological developments could help in reducing the costs in the future, says Jin. And while the existing model is relatively efficient, the researchers intend to enhance its design even more. Some of the voltage of the existing device is still going to waste, which means that the researchers may have to tweak the photoelectrode materials and redox species that operate together to transform solar energy input into electrical output. However, Jin thinks that solar flow batteries may soon become practical with more research.
We believe we could eventually get to 25% efficiency using emerging solar materials and new electrochemistry," Jin says. "At this efficiency range, without using the expensive solar cells, it should be quite competitive with other renewable energy technologies. Then I think commercialization could be possible."