Flow Batteries Could Back An Affordable Tesla Powerwall Rival


 – Oct 2, 2015


As renewable-energy use becomes more widespread, energy storage could become a major business.

Using stationary battery packs to store energy increases the effectiveness of wind and solar.

Tesla Motors hopes to exploit this potential market with packs that use the same lithium-ion cells as its electric cars.

Flow-cell battery prototype developed by Harvard University

Flow-cell battery prototype developed by Harvard University

But researchers at Harvard believe there is another configuration that could better suited to energy storage.

Professor Michael Aziz and his team are researching flow-cell batteries, believing they have certain properties that make them a better choice for this type of use, according to Gizmag.

In flow cells, a liquid electrolyte is circulated between two tanks, with a membrane in between. Particles passing through the membrane produce an electric charge–similar to the way electricity is generated in hydrogen fuel cells.

Flow-cell battery prototype developed by Harvard University

Flow-cell battery prototype developed by Harvard University

The capacity of a flow-cell battery can be adjusted by changing the size of the tanks, while power output can be changed by adjusting the area of the membrane.Researchers claim flow-cell batteries can remain idle for long periods of time without losing charge, and are not affected by extremes in temperature.

They claim a flow-cell energy-storage unit could prove cheaper than a comparable lithium-ion unit, too.

The design being tested at Harvard uses more readily-available materials than lithium-ion cells, which are also safer than those used in previous designs, researchers claim.

Certain previous flow cells used vanadium and bromine dissolved in acid as their electrolytes.

Since last year, researchers have been testing a flow cell that uses quinones instead of vanadium, and ferrocyanide instead of bromine.

NanoFlowcell Quant F prototype

NanoFlowcell Quant F prototype

The prototype battery uses a less-corrosive alkaline solution, allowing for lighter and less-expensive plastic tanks.Replacing the metal tanks used in other designs came at the cost of added electrical resistance, but this was reportedly accounted for by increasing voltage.

Researchers say their prototype cells exceed 99 percent efficiency, and could have a useful life of 1,900 cycles.

However, they appear to have lower energy density than lithium-ion cells.

In the lab, researchers have only achieved 19 watt-hours per liter, compared to 300 Wh per liter for a lithium-ion cell.

Nonetheless, the Harvard team believes its flow cells could be commercially viable for energy storage within three years.

NanoFlowcell Quantino concept

NanoFlowcell Quantino concept

That isn’t the only proposed application for flow cells, though.Germany’s nanoFlowcell AG has shown multiple concepts for flow-cell cars–including a 1,075-horsepower luxury coupe.

But while the company has gotten approval from German authorities to test its cars on public roads, it’s been light on details regarding production prospects.