The owners corporation is responsible to pay its electricity account and you are a member of that OC so you are liable in proportion to your unit entitlements. I’m afraid this one is just bad luck for you. Similarly, if the OC has some expensive maintenance required and has not accumulated sufficient in its sinking fund you will be up for that too, even though most of the accumulated wear and tear may have taken place over the past decade or more. Ideally an OC anticipates such things in a sinking fund plan and has sufficient reserves for some unanticipated contingencies. This way the cost of one-off expenses is spread across multiple years and past, present and future owners.
What seems odd is that each year I would have expected the OC would have passed a budget that included an amount for electricity and each year someone (treasurer, EC members, manager, ordinary owners) should have noticed that nothing was spent on electricity yet the lights were still on.