And yet it is a miracle that Voyager 2 managed to send anything back at all, for its main radio system failed soon after launch, and its back-up system proved to be faulty.
The Post reported that a malfunction in Mir's attitude-control system also occurred in March, causing it to list until an alternate back-up system was activated.
This means that if energy is required on a constant basis then the system needs to be backed-up by conventional sources of power 73% of the time, and there are days when the back-up system is required for more than 90% of the time (In Germany, the industry association insists that renewables uptime averages 10%).