Wind and solar energy generation creates challenges, since the Sun only shines by day, and sometimes the wind doesn't blow. Another variability is surges of demand on the grid. On a hot day when air conditioning is in use, utilities must have load-balancing strategies to meet peak demand. A water-based battery was developed that could provide a cheap way to store wind or solar energy generated when the Sun is shining and wind is blowing so it can be fed back into the electric grid and be redistributed when demand is high.
The prototype manganese-hydrogen battery generates a mere 20 milliwatt hours of electricity, which is on par with the energy levels of LED flashlights; however, the researchers can scale up the battery to an industrial-grade system that could charge and recharge up to 10,000 times, creating a grid-scale battery with a useful lifespan well in excess of a decade. Given the water-based battery's expected lifespan, it would cost a penny to store enough electricity to power a 100-watt lightbulb for 12 hours.
The battery uses a reversible electron exchange between water and manganese sulfate, a cheap, abundant industrial salt used to make dry cell batteries, fertilizers, paper, and other products. To mimic how a wind or solar source might feed power into the battery, the researchers attached a power source to the prototype. The electrons flowing in reacted with the manganese sulfate dissolved in the water to leave particles of manganese dioxide clinging to the electrodes. Excess electrons bubbled off as hydrogen gas, thus storing that energy for future use.
The prototype uses platinum as a catalyst to spur the crucial chemical reactions at the electrode that make the recharge process efficient, and the cost of that component would be prohibitive for large-scale deployment. Researchers are working on cheaper ways to coax the manganese sulfate and water to perform the reversible electron exchange. More than 10,000 recharges of the prototypes were conducted; it will be necessary to test the battery under actual electric grid storage conditions in order to truly assess its lifetime performance and cost.