[gizmo686]

What else would they need power for? Heating and cooling are the only appliances I can think of that would be necessary for habitability.

[evan_]

sump pump or well pump, which would also need quite a bit of power but not as much as HVAC

maybe just lighting if there are no windows or they have to keep the windows covered

[jstarfish]

The device they're asking the question from ;)

[jccooper]

Ventilation and/or lighting.