[rob74]

I guess that with "throughout the country" you mean the US? There, building gigantic new pumped storage systems might work, e.g. somewhere on a mesa in a desert with few people living nearby (OTOH you need some source of water for pumped storage too, so a desert location is not really ideal), but in more populated locations (i.e. Europe) such a project would face opposition and interminable delays caused by all the NIMBYs living next to it.

Besides that: pumped storage is good for regulating short-term fluctuations (between day and night), not so sure about storing surplus renewable energy produced in summer to use it during winter, as the article proposes?