The fee is only charged on certain days, I believe a total of 29 days this year, to dissuade people from visiting on those days that are considered to be the busiest.
They use surplus energy to pull up weights and lower them when energy is in demand, using the principle of a grandfather clock. They are using abandoned mine shafts because they are readily available for this purpose.
They’re making so much money with Fortnite they could pick up this project again silently and release a finished product to the fans that were let down.