Ten teams working to drive down the cost of long duration storage are competing in a way, using federal grant support to make enough progress to earn a follow-on grant for pilot-scale production. Projects include a sulfur flow battery for full-week backup capability, and a more efficient means of converting electricity to hydrogen and back again.
Each project aims toward a goal of 5 cents/kWh for storage that can last for days, under the DAYS program of the U.S. Department of Energy’s Advanced Research Projects Agency (ARPA-E).
Here are highlights of the ten projects, spanning corporate, university and hybrid teams.
Sulfur flow batteries
Flow batteries use electricity to produce an electrolyte, which may be stored separately from the battery. The electrolyte is later “flowed” through the battery to generate electricity. As a result, long-duration storage using flow batteries requires only a large storage capacity for electrolyte.
Form Energy aims to achieve “full-week backup capability” with a sulfur flow battery “at a factor of 10 or greater cheaper” than lithium-ion batteries, said company co-founder Marco Ferrara in a video posted by global utility Enel. Form Energy may ultimately pilot its battery technology in a joint project with Enel.
“Aqueous sulfur flow batteries represent the lowest chemical cost among rechargeable batteries,” says Form Energy’s grant award notice, but have low efficiency. To improve efficiency, the firm is working on anode and cathode formulations, membranes and physical system designs.
A United Technologies project is focused on sulfur and manganese flow batteries, and has three project partners: Lawrence Berkeley National Laboratory, MIT, and Pennsylvania State University. The project aims to “overcome challenges of system control and unwanted crossover of active materials through the membrane.”
Electricity to hydrogen
A team at the University of Tennessee, Knoxville aims to improve the efficiency of the round-trip process of converting electricity to hydrogen and back again. The current process uses electricity to power an electrolyzer to convert water to hydrogen and oxygen, and then uses the hydrogen and oxygen in a fuel cell to produce electricity and water.
“It has long been a goal to make a regenerative fuel cell, a single device that functions as both a fuel cell and an electrolyzer,” said lead researcher Dr. Thomas Zawodzinski, as quoted in a university press release. “However, such devices have previously suffered from poor overall efficiency. The new project uses an alternative approach by changing one of the chemical reactions in the cell and bypassing the efficiency bottleneck.”