Researchers at the Ohio State University have reported that they have developed a device which combines a solar cell and a battery and achieves a 20% energy savings over traditional lithium-ion batteries.

In October 2014, the research team announced that it had developed solar cells that can also store energy. Their design comprised a lithium plate base, a thin sheet of carbon separating the layers of electrodes and a dye-sensitive titanium dioxide photoelectrode, which was kept inside a titanium gauze mesh. This used a conventional salt-solvent electrolyte and required air in order to work.

When the original battery failed to perform as well as they hoped, the researchers developed a new version which uses water instead of the conventional solvent and lithium iodide salt. This so-called “aqueous solar flow battery“ is topped with a single sheet, dye-sensitised solar panel.

In testing, when a standard lithium-ion battery was charged with 3.6 volts, it discharged 3.3 volts. To discharge the same 3.3 volts, the aqueous solar flow battery only needed to be charged with 2.9 volts. The remaining 0.4 volts were made up by the solar cells.

The team leader, Professor Yiying Wu, said that “The truly important innovation here is that we’ve successfully demonstrated aqueous flow inside our solar battery. It’s also totally compatible with current battery technology, very easy to integrate with existing technology, environmentally friendly and easy to maintain.”

The team’s ultimate goal is to boost the solar cell’s contribution to the battery well beyond the current 20% – ideally to 100%.