Using google translate, it shows they are planning on upgrading the reservoir to 1 million cubic meters, which is about 264 million gallons from ~58 and that it will fill 3 times a year naturally, 4 times with pumps. 1/3 will be used to just keep the river flowing down the mountain, 1/3 for snowmaking and 1/3 for electrical generation.

Some extremely back of the napkin math (using ChatGPT) shows that if 1.33 million cubic meters of water per year were used at 1000psi (this is a huge assumption) to generate electricity, at the standard 80% efficiency you could do 2,030 MWh per year. A random search for the average price of electricity in Switzerland shows 0.154 euros per kWh, so it seems like this could potentially generate 312,620 euros (at consumer rates...) worth of electricity per year. Given that the idea of pumped hydro is to pump when electricity is cheap and then generate at peak demands...I'm not quite sure how to do that math!