Researchers at Case Western Reserve University in Cleveland received a $3 million U.S. Department of Energy grant to study a promising type of battery that could allow electrical energy to be stored four times longer.

The “slurry electrode iron flow batteries” being developed by researchers at the university are rechargeable batteries that store its electrolyte, the material that provides energy, as liquid in external tanks.

According to the DoE’s Advanced Research Projects Agency, flow batteries dramatically increase power density and enable a smaller and less costly battery.

One of the main disadvantages of flow batteries in their current state is that the electrolytes used for them are rare and expensive. The researchers are currently working on a method that would use inexpensive iron as part of the process.

The adoption of flow batteries could allow renewable energy systems to make up a larger part of the nation’s energy grids.