I don't know where the number was pulled from, but the original plan was to have 75MW power production capacity, and storage capacity of 530 MWh. Which is not too bad considering that Finland has about 14 GW peak energy consumption, and hydroelectric capacity peaks at about 1.2 GW. It is also not a game changer alone, but it would help to collect wind energy during the night times and also even out the morning and 5-to-7 PM peaks in power usage.
The plant has been planned for a couple of years now, and it was even already cancelled at the end of 2023 due to costs from high interest rates, but looks like it is back on due to a new operator chiming in.
Real Users never use the Help key.