Hi, that's a difficult challenge. I like the deposit idea best, but it still poses the risk you describe.
I have a couple thoughts. You had mentioned the reason you can't charge too high is because it would be unfair to those who use less. But are you able to set higher nightly rates according to your market demand? I imagine you're already rate-optimized there. But to my thinking, I would set the rates you're able to, to compensate if possible, even if that means those who use less ultimately pay more. To protect yourself. And perhaps if you do it that way you'd even be able to lower your electricity deposit. This would still leave you at risk. But potentially it would reduce the probability that someone exceeds your deposit AND the increased rate together.
Second thought is whether you have any ability to improve energy efficiency in the unit, like lights with sensors & timers, or new HVAC etc. But that of course is a large upfront cost in hopes to provide ROI while still leaving you at risk. Last thought is whether to require credit pard payment info, and inform them you will bill them offline and provide them an invoice, as a replacement of the electricity deposit. But that is not ideal for guests and would take more work on your part. IDK. Good luck.
