We need to find a way to store massive amounts of electrical energy. That’s the single biggest obstacle to getting a large fraction of our electricity from solar power.
– Michael Aziz, Harvard University Professor of Energy Technologies
Solar panels and photovoltaic systems keep getting cheaper, as higher volumes, more investment and constant research drive down costs. However, storing the abundant solar energy generated during daylight hours so that it can be used at night requires much greater efficiency. The batteries used for energy storage have a long way to go before households can economically go off-grid and power companies supply continuous energy from renewable sources.
Deep cycle batteries
The batteries used for storing energy from alternative renewable energy sources are called “deep cycle” because they can survive long periods of being repeatedly and deeply
discharged to almost their entire capacity. The market for battery-storage solutions is growing in line with the increase in solar installations. Photovoltaic systems are typically paired with battery packs.
Lead acid batteries
The first technology used for storing solar energy for future use was lead acid batteries. They are fairly affordable but not highly efficient and are most suited to low-intensity applications.
Lithium ion batteries
Lithium ion batteries are more efficient than lead acid batteries at saving electricity produced by rooftop photovoltaic panels during the day for use at night. They are more expensive but provide more cycles in their lifetime, meaning that they last longer. Suitable for domestic and industrial use, these batteries employ the same technology as cell phone batteries and those used in electric cars.
Flow batteries have been in use since the 1980s. They consist of tanks filled with vanadium ions, and the hours of energy they deliver depend on the amount of vanadium in the storage tank. But vanadium is expensive. Professor Aziz of Harvard University is therefore leading a team of scientists to research alternatives. They are using organic molecules called quinones, found in plants, to reversibly store energy in a water-based solution at room temperature. This promising application, mimicking photosynthesis, is still in the experimental phase.
Another innovation still being developed is to convert solar energy into hydrogen through water electrolysis. A solar panel generates electrical current, which is used to split water molecules into oxygen and hydrogen. The idea is that the hydrogen would then be stored to generate electricity when required later