Turlough Hill was first conceived by Dermot O'Riordan, Deputy Chief Engineer in the ESB's Civil Engineering Department. In 1964, ESB engineers visited several locations in the Wicklow Mountains, digging trial pits and boreholes, looking for suitable sites for a pumped-storage station. A shortlist of three proposals was drawn up by O'Riordan: an artificial upper reservoir at the summit of Tonduff mountain with an artificial lower reservoir in the Glencree valley; an upper reservoir using Lough Ouler, a natural corrie lake near the summit of Tonelagee mountain, with an artificial lower reservoir in the Glenmacnass valley; and an artificial upper reservoir at Turlough Hill with Lough Nahanagan as lower reservoir.