Most discussion of how using solar photovoltaic cells to account for most electricity generation has focused on the daily cycle of load versus the daily generation cycle. That cycle has been heavily analyzed, and there are a large number of companies working on local and neighborhood storage to support the daily cycle. But there is a much longer cycle that gets little attention and has a much larger impact on the cost of investment and on the efficient use of the solar generation. Simulations based on data from four major U.S. grid systems show that long-term storage needs will be large. This is but one of many scenarios that need to be explored.