He's pointed out that there's more energy produced during the artificially expensive peak hours. Supply and demand doesn't bear out their pricing energy higher during the day. If it did, the going rate during the day compared the decreased value at night suggests the 5 stored during the day should net him roughly double what it costs to use it at night. The utility isn't doing him any favors holding onto valuable energy during the day in lieu of him using having his own storage, just based on their own pricing.