That sounds about right.
500w running 12/12 uses 360kwh per month. About $20 a month in electric. Cops don't go knocking on doors when people use an extra $20 a month, and your electric company only reports crimes to the police. Other than that, there is absolutely no reason why the cops would even know that you're using an extra $20 a month.
Using electric is sort of like paying for your equipment with a credit card. It's something the cops collect AFTER they find out you're growing pot, they don't actually sit there and monitor everybody's electric no more than they pour over every single person's credit card statement. But they will collect that info if your friend who saw your plants gets arrested and decides to rat you out so he doesn't have to spend 30 days in jail.
It always amuses me when I see an average joe going out of his way to pay cash, for growing equipment, that he's going to keep and use in his house. That doesn't save you from getting caught, it just gives the cops one less piece of circumstantial evidence to collect if they start an investigation on you. If an informant says your growing pot (which is how most people get busted), the fact that you paid cash for your equipment isn't going to help you.
That's why I maintain that, if the cops are looking at either your electric bill or your credit card statement, you're already fucked. The only reason they have for looking at that shit is if somebody told them you're growing pot and they start an investigation on you.
Happy luck and good growing!!!!