Monday, September 29, 2008

Storing Renewable Energy

Discover Magazine has a cool piece abou thte Vanadium battery-- a massive, rechargable battery that will-in theory-- make alternative energy generated by wind and solar dispatchable.

One of the knocks on this kind of alternative generation has always been that sunshine and wind are unpredictable so the ability to store massive amounts of energy greatly enhances long term feasibility.

According to Discover:

"A traditional battery, such as the familiar AA dry cell, holds electrolytes in its own sealed container. But the vanadium battery is a flow system—that is, liquid electrolytes are pumped from external tanks into the stack, where the electricity-generating redox reaction takes place. Want to store more power? Use bigger tanks. The bigger the tanks, the more energy-rich electrolytes they can store.

The downside is that flow batteries tend to be big. It takes a flow battery the size of a refrigerator, incorporating a 160-gallon tank of electrolytes, to store 20,000 kilowatt-hours of electricity, enough to power a full-size HDTV for about three days. This is because the energy density in the liquid electrolytes is relatively low compared with that of the chemicals in lithium-ion batteries. (Energy density is a measure of the amount of energy that can be extracted from a given volume or mass of a battery.) For this reason, flow batteries are unlikely to be found in mobile applications, like laptops or electric cars. In those cases the battery of choice remains lithium-ion, which has an energy density five times that of vanadium."

The Element That Could Change the World [Discover Magazine]