Yes, you are right-- we need enough solar+battery for when the sun goes down. I understand it is abou 6x, and you cite 8x.
so a 1GW datacenter would take 6-8GW of solar. it is less than $1/W to installed, so $6-8Billion which is alot until you calculate what the servers will cost, and also the investment that is going into this sector, and that this may be the easiest way for these guys to get the power they need. (and no new long distance power lines if co-located)