Can a Solar Cell Store Its Own Power?

Researchers at Ohio State University have invented a device that looks like a solar cell but has the ability to store the power it generates. The patent-pending device is the world’s first solar battery. On October 3, 2014, the researchers reported in the journal – Nature Communication – that they have succeeded in combining a solar cell and a battery into a single hybrid device.

The innovation is a special solar panel in the form of a mesh that allows entry of air into the battery. Another unique process allows electrons to be transferred between the solar panel and the electrodes of the battery. Light and oxygen entering the device enable chemical reactions to charge the battery.

According to Yiying Wu, Professor of chemistry and biochemistry at the Ohio State University, they will license the new solar battery to industry. Wu expects that the solar battery will tame the costs of renewable energy.

A solar panel is typically used to capture light for converting it to electricity, which is then stored in a cheap battery for later use. By integrating the two functions into a single device, installation becomes simpler and costs go down. The new solar battery may typically bring down the costs by about 25 percent.

The invention also has another advantage. The long interconnections between solar panels and its battery introduce ohmic resistance that reduces the solar energy efficiency because of heat generation when charging. Typically, about 20 percent of the electricity generated by the solar cells is wasted as heat when charging the battery. With the new design, nearly all the electricity generated reaches the battery.

Wu and his students have also developed a high-efficiency battery for use with their solar cells. An earlier designed battery, invented by Wu and his research team, won them the 2014 clean energy prize of $100,000 from the US Department of Energy. The researchers have created a technology spinoff – KAir Energy Systems, LLC – to develop the battery.

The high-efficiency battery is air-powered, meaning it breathes in air when discharging and breathes out when charging. The battery discharges by the chemical reaction of potassium and oxygen. The researchers faced a formidable challenge when trying to combine a solar panel with the KAir type of battery. Typical solar cells are solid panels of semiconductor material and this would prevent air from entering the battery.

Wu and his research team had to redesign the solar panel to make it permeable. They did this by using titanium gauze, a flexible fabric. They grew vertical rods of titanium dioxide on the fabric, similar to blades of grass growing on soil. The rods capture sunlight, while air passes freely through them and the gauze.

Normally, interconnecting a solar cell and a battery requires four electrodes – two on the solar panel and two on the battery. The hybrid design of the researchers has reduced the number of electrodes required to three.

The mesh in the solar panel forms the first electrode. Under this, a thin sheet of porous carbon forms the second electrode, while a lithium plate forms the third. Layers of electrolyte sandwiched between the electrodes forms the battery to store electricity.