I have had the system since 2009 - each credit bal goes into an grid account that I have with my utility - I will bank credits till June - in June/July the air conditioner season will start - and my bank credits will be used against that usage on a retail basis - and be gone by Sept (if the past is predictive of this summer). If I was able to bank all year after 12 months, my utility would pay me at their wholesale credit of 37 cents per kwh Note to bank all year - I would need another 29 panels and my spouse would be very UNHAPPY for using up all the property for panels - currently they are on my roof GLA