Beacon Power

There are essentially two markets when it comes to utility-grade energy storage. On one end are storage devices that can store several hours or even weeks of electricity. These "bulk storage" devices are designed to make power generation resources, particularly wind or solar power, available when it's needed.

At the other end is the market for "grid stabilization," which is like the short-term, random access memory that a PC uses.

Beacon Power makes a flywheel that is designed for grid stabilization. It delivers 1 megawatt of electricity but only for 15 minutes. That's enough to maintain a steady frequency and to smooth out differences in grid demand and supply. The company says that a 1-megawatt device like this one will be deployed on the grid by the end of the year.