They want to capture power that is now being wasted for lack of storage. The simplest example is a big hydroelectric dam. The water goes over the dam 24/7. Suppose between 10 p.m. and 6 a.m., only 10% of the power is used. (I made up the numbers but you get the idea.) So the question is, can you find massive storage at an affordable price? Batteries are expensive, but if there is large-scale adoption of plug-in hybrids, there is a potential there that might be exploited.
Hydro is an obvious example but the same principle holds for a nuclear, coal, or natural gas fired system. It doesn't simply shut down and go cold at night. The operators can throttle back somewhat and save a bit on fuel but the system still is live around the clock, and a lot is wasted. Cheap storage is worth exploring.
“Cheap storage is worth exploring.”
How about hydro-electric storage ?
http://www.rise.org.au/info/Tech/hydro/pumped.html