The power of water
The mountain may be used as a power plant or, to be more precise: a giant battery
This battery is constantly charged, transferring the surplus of generated renewable energy into kinetic energy, stored in a volume of water. This buffered energy can be tapped at times our power grid is in need of additional resources. This principle is not new (see the plan Lievense), but an artificial mountain puts it into a slightly different perspective.
Arthur Meerloo made a wonderful presentation of how this might look like! Okay, there may be some unpracticial elements in this approach. But it’s great inspiration for sure!