Modern pumped hydro gets about 80% round-trip efficiency, perhaps 75% for older plants get 75%. Interestingly, grid scale batteries seem to get something close

Modern pumped hydro gets about 80% round-trip efficiency, perhaps 75% for older plants get 75%. Interestingly, grid scale batteries seem to get something close to that, 80-85 percent - I would have expected more. Transmission losses for 1000km are something like 2%-3%. So halfway around the globe isn't efficient, but 1000km might as well be considered "local" and transferring across the whole EU would be more efficient than local storage.