> Thirdly, the best annual storage is pumped hydro.
I strongly dispute this. E-fuels like hydrogen would be much superior to PHES for annual storage.
I strongly dispute this. E-fuels like hydrogen would be much superior to PHES for annual storage.
Yes, hydrogen has low round trip efficiency. But it comes out cheaper than PHES. The "cost of inefficiency" is proportional to the number of charge/discharge cycles. For annual storage, efficiency is 365x less impactful than it is for diurnal storage. What matters for annual storage is capex of storage capacity.
Which is exactly why PHES wins the cost comparison for annual storage. Open air water storage is ridiculously cheap compared to hydrogen storage.
If you want something that may compete with hydrogen for annual storage, consider bulk thermal storage (using artificially injected heat, not naturally occurring heat). The thermal time constant of a very large object increases quadratically with radius, if everything is scaled proportionally, and can easily reach many years. This is why geothermal works at all -- there's plenty of heat stored in the near crust ready to be mined.
You're also comparing hypothetical costs to historical costs. Hypothetical costs put out by industry are usually out by about an order of magnitude.
There's a reason that PHES is the only one with historical costs.
These are not hypothetical costs. Construction of these caverns is state of the practice for natural gas storage. Vast volumes of gas are stored in these things, allowing steady production of natural gas and constrained pipeline capacity to serve seasonally unsteady consumption patterns.
The reason PHES is the only one with historical costs is that, historically, PHES has been used for diurnal storage, from the days when baseload plants were cheaper. There was never a market for long term storage via hydrogen (although some hydrogen storage has been constructed and used to help steady the hydrogen input to ammonia plants); why bother for the grid when just varying the use of fossil fuels would serve that function just as well?