So I ran across an interesting study recently on utility level power storage;
http://re100.eng.anu.edu.au/global/
The upshot of the article was that there are hundreds of potential locations for pumped hydro electric storage throughout the West and East of the United States- not so much in the middle. Total capacity of all these theoretical sites is something on the order of 200 times the projected requirement if the entire country went to renewable wind and solar power generation.
Obviously, not all of these potential sites will be suitable; some are too far from water, others already have infrastructure in the basin, etc, etc. But there are plenty of places to choose from.
Why does this matter? Because sufficient utility level energy storage is the ONLY fundamental obstacle to a complete change to renewable energy in America, home of the highest energy consuming public on Earth.
PHES is clean, renewable, non toxic, reversible, compatible with other users such as irrigation and recreation, and a fully proven workhorse technology already in use in hundreds of locations worldwide.
It's dead simple; use energy to be stored to pump water uphill and store it in a reservoir. When energy is needed, let it drive generators as it falls back down. Round trip is about 70% efficient, sometimes better. Energy storage lasts as long as the water stays in the reservoir.