Actually, this pumping water idea is considered in solar. During the day, energy is used also to pump water behind a dam. At night, when the solar output is nu

Actually, this pumping water idea is considered in solar. During the day, energy is used also to pump water behind a dam. At night, when the solar output is null, the water is released and produces power via normal hydro turbines. For example in Romania, which produces exces power [1] almost all the time, there is a plan to build a huge reservoir in mountains to use this power to pump water from the major rivers into it, thus building a reserve energy store.[2] [1] http://www.transelectrica.ro/widget/web/tel/sen-harta/-/harta_WAR_SENOperareHartaportlet http://www.transelectrica.ro/widget/web/tel/sen-harta/-/hart... [2] http://www.hidrotarnita.ro/en/despre-proiect/ http://www.hidrotarnita.ro/en/despre-proiect/