The numbers in the OP show that the RO equipment is by far the largest cost so you need to maximize its utilization. The energy is used to pump water through the RO at high pressure so another alternative would be to use solar to pump water uphill so you could run the RO at night. The design using batteries is easier to price.
There are energy companies like Quidnet that are commercializing geopressure storage, where water is pumped underground at pressure, then recovered and the energy extracted. This would be an ideal system to combine with solar and RO.
