Exactly, that's my whole point. Once renewables become a large majority of overall power production, it will be essential that we have adequate storage to account for the variability of renewables. Thus, the original idea that started this comment thread that once we get tons of renewables that energy will be free or negative (e.g. "road transport becomes nearly free") doesn't make any sense. Wholesale prices only go negative for a relatively small percentage of the time currently due to lack of storage and government subsidies.