Heat from the lights is the main reason in the UK. All that heat gotta go somewhere. Very easy to do an IR scan from a helicopter, scan 5000 houses in an hour, and the hot house is glaring white on the screen.
No matter what you do, all that heat gotta be dumped somewhere. Unless you have a large watercooling setup, which takes even more power, and I'm not sure if a domestic water supply can even remove 100kw of low grade heat. A heater on full is about 3kw, and a powerful oven on full is about 5kw.
180KW generator is about 3meters by 1.5 meter by 1.5m, and weights about 3 tons. Costs about $30-40,000 possibly including home delivery. Not too difficult to install if you have the money and a plausible reason.
BUT 180KW maybe not needed. Incandescent lights are about 10% efficient, and LED lights are around 2x to 4x more efficient, so power usage falls to around 40-90KW. A lot less heat to get rid of, and a much smaller generator needed.
If they were running it off the mains, that's still the same as having around 15-40 electric heaters running on full 18 hours a day. No wonder the electric company was suspicious, and if they didn't have water cooling, maybe the heat plume from the cave was detected via IR. Probably detectable via satellite