If Michigan is to join 25 states requiring that more electricity come from renewable sources, the Legislature must sort out all kinds of issues -including the price tag. Compared with existing power from old, already-paid-for coal plants, renewable energy is more expensive. The House is considering capping residents' extra costs at no more than $3 a month, or $36 a year over 20 years, which could let power companies off the hook for meeting the renewable energy requirement, known as an RPS. Under legislation pending in the House, commercial customers would pay no more than $190 a year more, while the cap for industrial customers would be $2,250.