> Now you have built two energy systems and one of them has to be on standby and ready to be used only rarely. Cross your fingers and hope everything still works. You also have to maintain long term storage of gas, staff that knows how everything operates, etc.

Well yes, except that the backup system happens to be already built. There's definitely a maintenance cost associated with this, and long-term (beyond the lifetime of existing stations) this wouldn't make any sense. But in the short-term the costs associated with this are relatively low.