The Battery Is Ready to Power the World

I've read a fair number of articles about stationary batteries providing services to the grid. Frequently, the authors describe the batteries capability in MW or GW, units of power. This will tell you how quickly energy is added to the grid -- and commonly used to describe continuous energy sources such as gas-fired and coal-fired plants.

However, I never (or rarely) see the energy storage capacity of these batteries mentioned (kilowatt-hours or kWh). Such information is important to figure out if the battery installations will last more than an hour supplying to a grid that is suffering extreme lulls in wind generation.

Anyway, knowing this information would help also in the context of the significant demands the electric vehicles will make on our grids (a typical EV requires about 10 kWh, daily, to serve a driver's 10,000 mile-a-year habit).