That page is way out of date and in general not accurate (thus all the warnings on the table). If you have the space, it's cheapest to do gravity storage with w

That page is way out of date and in general not accurate (thus all the warnings on the table). If you have the space, it's cheapest to do gravity storage with water reservoirs, however you need specific geography for that to happen. If you need to build such a reservoir without assisting geography it would be prohibitively expensive. The only other real option is batteries.