sisyphean or gravity-assist

One of the sad ironies of electrical infrastructure is that the places, like Germany, with the highest utilisation rates of renewable energy also have the highest incidence of air pollution, due to fact when there’s not enough wind or sunshine, there’s only recourse to burning coal or natural gas and no large-scale means to store excess production for use when it’s needed.
The impediments lie in not only not being able to save energy for a later time, unpredictable vectors like the Sun and the wind can easily over-burden a distributed grid whose output has to be spent, along those wires, in one way or another. There are some methods to harness this abundance, however, like the sluices that store potential energy (please don’t mind my bad German)—or project in the state of Utah called the Sisyphus Train, where excess aggregate of electricity is used to power a locomotive to the summit of a hill, and there it rests like the accursed boastful king’s eternal task to roll a boulder uphill. This labour is not futile or in vain as when needed the turbine rolls back downhill, generating electricity during its descent.