Pumped hydro works by pumping water into a reservoir during low-demand, low-cost hours to be held until needed. When demand increases, the water is released, flows through a turbine and produces electricity. The energy storage capacity of a pumped hydro facility depends on the size of its two reservoirs, while the amount of power generated is linked to the size of the turbine. There are two types of pumped storage – Open Loop and Closed Loop.
Open-Loop Pumped Storage Hydropower are projects that are continuously connected to a natural body of water. TC Energy’s proposed project in Meafoed is an example of an open-loop pumped storage hydropower project.
Closed-Loop Pumped Storage Hydropower are projects that are are not continuously connected to a natural body of water. The proposed Marmora Hydroelectric Pumped Storage Project is an example of a closed-loop cycle design that would recirculate the same water between Marmora’s former open-pit mine and upper reservoir.
Image Source: https://www.ontario.ca/page/powering-ontarios-growth