You only need to hold this energy until the next peak period hits the grid. The Snowy Mountains Hydroelectric Scheme in Australia actually buys off-peak electri

You only need to hold this energy until the next peak period hits the grid. The Snowy Mountains Hydroelectric Scheme in Australia actually buys off-peak electricity to run the turbines in reverse & pump water back into reservoirs, and then generated electricity when demand is high: effectively time-shifting power generation & arbitraging the peak/off-peak price difference.