If the systems of a starship or installation aren't really used then the equipment isn't all that taxed. In other words it's build to last various extreme conditions so if it's not used the parts don't broken down that fast. Take life support for example, if there is no one breathing on the ship the Co2 scrubbers and fans don't do anything, they only need to work when people are aboard.
Further to the above we are never told what fuel the ship used. It may have been some form of radioactive fusion reactor the fuel for which could have lasted for thousands of years.
That last thing said has to be part of the deal. It takes power to generate heat and to move air through CO2 scrubbers, lithium hydroxide canisters, etc.
--ProfessorTrek 07:30, February 4, 2012 (UTC)
It can best be explained by Picards complement on the skill of the ships designers and builders.