Even just a large water tank which you can choose when to add heat.

https://en.wikipedia.org/wiki/Seasonal_thermal_energy_storag...

You need something that's valuable, energy intensive, easy to stop and start, and cheap to build capacity for. Either or both of those last two tend to be the problem for most industrial processes (and also crypto mining).

There are may different energy storage systems.

https://en.wikipedia.org/wiki/Energy_storage

There have wildly different prices for unit of stored energy and wildly different storage times.

https://css.umich.edu/publications/factsheets/energy/us-grid...

It's not cost effective run aluminum smelting only during peak electricity production.

That's what batteries are for.

That is the trade off for renewables. Power is very expensive when needed and very cheap when not.

It’s still capped at £1/kWh, which is a lot but also a price I’ve seen maybe for a few slots on a couple days in the last three years.

The price was known ~1 day in advance so I had the choice to fill up the battery with cheaper (but still high) prices overnight and reduce the impact

Consumer pricing in the UK is regulated with a price cap (per kWh), so consumers can't be fleeced in an unexpected event.

Business energy users aren't protected, so they buy long-term contracts, hedge, or go-under in the event of an unforeseen energy-shortage.