Even pumped hydro is pretty small for seasonal storage.
Probably the only economical approach will be some sort of factobattery[1], which can be thought of as a flow battery which operates "once through" to avoid round-trip losses. Instead of outputting electricity, the beneficiated material itself is the economic output.
This eliminates the entire chemistry-to-electricity side of the process, which may require dissimilar equipment under some approaches.
When I try to model out an all-renewable grid I think of it this way: capital cost is the sum of generation capital cost + storage capital cost + transmission capital cost.
In the winter you get less energy from your solar panels, one answer to that is build enough storage to shift energy from summer to winter, another is to build an excess of solar panels. In the latter case you need less storage but you have an excess of cheap energy in the summer you can do something with (e.g. factobattery, desalinating water, making e-Fuels, e-Fertilizers, etc.)
To realize that benefit you need additional investment in transmission (with an option of locating sinks close to sources to minimize transmission cost) Also the capital cost of any facility that you run 50% of the time is effectively doubled.
I have yet to seen a cost analysis of a 100% renewable + storage system as it needs a detailed analysis. One problem is that you occasionally have the bad luck of an extended patch of unfavorable weather. It's going to cost more to build a system that runs out of juice once every 20 years compared to one that runs out of juice every year. Advocates of renewable + storage systems claim to be a lot cheaper than AP-1000, my back of the envelope calculation is that that renewables + storage might be a little cheaper than AP-1000 under favorable assumptions, but I haven't done detailed enough modelling to have much confidence in that and I haven't seen anyone else do it.
Distributed energy resources eliminate a large portion of the transmission cost, leaving only the distribution grid in an idealized/future-state scenario (as I assume you’re talking about). In the summer, you lower the solar output so as not to overload the s distribution grid.
Also, batteries come in several long-term flavors. Thermal sand batteries are able to provide many months of energy storage today. A mid-term future will surely include even longer term storage as we develop improved storage technology. LiPo batteries are a bridge storage solution.
Or burn some of the gas you save by using solar and batteries. You can burn it in the gas plants you already have. And store it in the gas storage you already have.
And just keep rolling out more and more renewables with the money you've saved.
Once you get to a low carbon electricity, it makes more sense to electrify other things (transport, heating, industry) than to worry about the last few percent of carbon in the electricity mix.
This is the kind of economy wide tradeoff that carbon pricing makes explicit.
I agree that accurate carbon pricing would be great. However it's so politically infeasible (and widely known to be so) that fossil fuel companies have been caught faking support as a foot-dragging strategy.[1]
In the inevitable absence of carbon pricing, such "bridge solutions" get enshrined as special case regulations, resulting in zombie solutions that hang on far beyond their expiration dates. We see this today, where European biofuel zombie regulations are directly causing the clear-cutting of Canadian old growth forests... in the name of "the environment." [2]
Carbon pricing is widely and successfully used around the world. The US federal level is a notable outlier in this regard and leads to people having distorted views on the topic.
Exxon is an international group with obviously aligned profit motives, so I trust their actions far better reflect the real (as in realpolitik) international situation over a self-admittedly biased website (PMI = Partnership for Market Implementation[1]).
I see the UK has four entries on this dashboard, but nevertheless they're still cutting down forests in Canada and the USA for "green" biomass, and for their trouble quadrupling the (fully accounted) carbon emissions. Whatever this dashboard actually measures, it's clearly no guarantee against perverse non-market "green" incentives.
Anyway, just pointing out a few of the pitfalls and tripwires on the path to good climate policy. I think we agree in the broad strokes. Cheers
Probably the only economical approach will be some sort of factobattery[1], which can be thought of as a flow battery which operates "once through" to avoid round-trip losses. Instead of outputting electricity, the beneficiated material itself is the economic output.
This eliminates the entire chemistry-to-electricity side of the process, which may require dissimilar equipment under some approaches.
[1] https://www.moderndescartes.com/essays/factobattery/