Yiying Wu, Professor of chemistry and biochemistry at the Ohio State University, Ohio State, and his team has combined a solar cell and a battery to form a single device. A novel solar panel on top of the battery captures energy from sunlight. The battery is able to source 20% of its energy from sunlight. Although the design is pending a patent, the researchers have published their findings in the Journal of the American Chemical Society.

Tests conducted by the researchers show that their solar flow battery produces the same output as a lithium-iodine battery does, even when the solar flow battery had a lower charge. They charged and discharged both batteries 25 times. Each time, they discharged the batteries until the terminal voltage fell to 3.3 volts. Conventional lithium-iodine batteries have high energy densities, approximately twice that of lithium-ion batteries. Hence, lithium-iodine batteries have the potential to fulfill the needs of long-driving-ranged electric vehicles.

In the experiments, lithium-iodine batteries had to be charged up to 3.6 volts, before they could be discharged down to 3.3 volts. Comparatively, solar flow batteries produced the same energy output with a charge of only up to 2.9 volts, as the solar panel made up the difference in their terminal voltage. That represents an energy saving of nearly 20 percent.

The team has made two changes to their earlier design from 2014. The solar panel, which was a mesh earlier, is now a solid sheet. Additionally, they now use a water-based electrolyte within their battery. With water circulating within the battery, the team has assigned the new design to an emerging class called the aqueous flow batteries. Yiying Wu claims their solar battery with aqueous flow is the first of its kind.

The water-based solar battery is compatible with the current battery technology and is easy to maintain. The environmentally friendly technology can be very easily integrated with existing technology.

According to Wu, the design of the solar flow battery is adaptable and can be applied to grid-scale solar energy conversion and storage. In the future, electric vehicles might also benefit from the electrolytic fuels used in the solar flow batteries.

In the earlier design, Wu and his team had designed the solar panel with a titanium mesh, which passed air to the battery. The new design using water based electrolyte does not require air to function, and hence, the solar panel is now a solid sheet.

The solar panel has a red dye so that it can tune in to a specific range of wavelengths of solar light to capture and convert to electrons. The team calls their solar panel dye-sensitized and the electrons it produces serve to supplement the energy stored within the lithium-iodine battery.

The electrolyte within the battery helps to absorb the electrons produced by the solar panel. A typical electrolyte is actually part solvent and part salt. Earlier, the researchers had used the organic solvent dimethyl sulphoxide to dissolve the salt lithium perchlorate. They have now changed over to lithium iodide salt dissolved in water, as this is more eco-friendly and offers higher energy storage capacity at lower cost.