Power supply Power in the mine
Decommissioned and abandoned mines are being turned into long-term energy storage solutions through methods such as pumped storage hydropower and underground gravity energy storage. Martin Morris speaks with Julian Hunt, research scholar, Energy, Climate and Environment Program, International Institute for Applied Systems Analysis; Rebecca Ellis, energy policy manager, International Hydropower Association; and Mark Swinnerton, founder and CEO of Green Gravity, to discuss the advantages and challenges of the various methods in play – and the benefits they can offer society at large.
ccording to the US Department of Energy, pumped storage hydropower (PSH) accounted for 93% of all utility-scale energy storage in the US in 2021. A form of hydroelectric energy storage, PSH is based on a configuration of two water reservoirs at different elevations, generating power as water moves down from one to the other – known as ‘discharge’ – while passing through a turbine. When the opposite holds true and water is being pumped back into the upper reservoir during the recharge phase, power will be required to complete the process. As a result, PSH can be viewed as tantamount to a giant battery, given it can store power and then release it when required. PSH can also be characterised as ‘open-loop’ or ‘closed-loop’. Open-loop PSH has an ongoing hydrologic connection to a natural body of water, while in the case of closed-loop PSH, reservoirs aren’t connected to any outside body of water.
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On the face of it, open-cycle hydropower plants are cheaper, because they can take advantage of the available natural topography and geology – only requiring a large upper reservoir and a smaller lower one connected to a river. Yet, as Julian Hunt, of the International Institute for Applied Systems Analysis (IIASA), is quick to point out, much will be determined by river flow and overall demand for the water. One potential water conflict resulting from open-cycle seasonal pumped hydropower storage plants (SPHS), for example is that most water is consumed during the summer – invariably for agricultural purposes. However, the SPHS would store water during the summer and release it during the winter when water demand is low. Closed-cycle plants, on the other hand, are more expensive, because they require large upper and lower reservoirs. “Their main benefit is that water is reused in the storage cycle and water conflicts are significantly reduced,” says Hunt.
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