Molten batteries pack more power

Batteries aren't just a problem for your iPhone or laptop. They're a huge problem in smart grids and getting solar or wind energy to market. (Picture by Patrick Gillooly for the MIT News Office.)

If electricity can't be used immediately it must be stored. Lithium batteries are expensive. Metal batteries don't hold enough power.

Transforming electricity into hydrogen, then back into water is possible, but the energy costs of the transformation are high.

How big a problem is this? Presidio, Texas, a border town of under 5,000 people in the Rio Grande Valley, recently had a 4 megawatt battery installed by Electric Transmission Texas to improve service. It cost $25 million and was bigger than a house.

The Big Ol' Battery (BOB) is dwarfed by Fairbanks' Battery Energy Storage System (BESS), installed by ABB Group in 2003. BESS can hold a charge of 26 Megawatts for up to 15 minutes and is used to back up the local grid.

The two batteries are quite different. BOB uses sodium and sulfur. BESS is nickel-cadmium.

But what Don Sadoway of MIT has discovered is that if your metal is molten, it can hold a lot more power in a lot less space. Sadoway says his battery costs less than lithium, and holds a charge for a longer period of time. A battery the size of a shipping container would carry 1 megawatt for several hours.

The design is relatively simple. Melted magnesium at the top, melted antimony at the bottom, and a salt composed of both elements in the middle. The salt breaks down as the battery is charged, then rebuilds as electrons are discharged.

Sadoway, who recently turned 60, said his inspiration was the way aluminum is coaxed from bauxite by being melted using electricity. For his birthday he's getting a symposium in his honor this June. Sadoway is a University of Toronto alumnus. (Go True Blue.)

While the Sadoway battery is impressive, it really illustrates how far research must travel to make a smart grid a reality.

Renewable power is not reliable -- clouds obscure the sun, and sometimes the wind doesn't blow. Power demand also fluctuates. Better, more powerful, and cheaper batteries are needed to match supply with demand.

Sadoway's battery is one small step down a long, long road. It's an interesting technique, but it's probably not our final answer.

This post was originally published on Smartplanet.com