I don't know enough about storage costs to calculate them well, although several recent low-priced PV power-purchase agreements have included storage components, including the one we're talking about here. I look forward to seeing your calculations!
I don't know the calculation either, and have been trying to get hard numbers on various potential large scale storage such as https://en.wikipedia.org/wiki/Thermal_energy_storage and Lithium ion, as well as some sort of learning curve for costs. So far I've found a pretty compelling and well backed case for solar, but the storage component is always hand waved.
Well, sure, storage costs depend in part on how long you have to store the energy, and how often. But surely someone has computed some kind of curve about how much storage is needed for PV to displace increasingly large percentages of peaker and baseload generation, assuming no demand response or other stabilization measures like rolling blackouts?
I hope you aren't making the assumption that storage = batteries, then arguing because weeks and months of batteries would be needed, it's impossibly expensive.
