Wrong, payoff time will be shorter. Why: During the next few years energy suppliers will "force" people, who feed energy to the grid into flexible pricing, so the reward for producing will be less and less ( current flexible prices https://markt.apg.at/en/transparency/cross-border-exchange/d... ) and the incentive for having a battery is getting stronger. For my situation that means almost zero energy costs from March to October. Even in December and January it covers 30-50% of the total energy demand (heat pump).