Credit is applicable to future bills within the same 12 month billing cycle, remaining credit at the end of the 12 months is deposited into your account at the avoided cost rate. (solar-estimate.org)
You can carry credit forward for future bills or have the money transferred to your account. (solar-estimate.org)
No renters insurance requires a deposit for that very reason — there's no real risk if you don't pay future bills because that would result in you not having coverage. (effectivecoverage.com)