Solar power is much more expensive if the power must adhere to some number of 9's of reliability.

Often data centers need to run at three nines of availability (ie: 99.9) and at that level of availability the price of solar power is many multiples of conventional power due to the cost of batteries and over provisioning.

Hydro is cheaper, if you have access to it. That (and cooling) is why many data centers are built next to rivers like The Dalles.

But your point otherwise stands; solar + battery is cheaper than any fossil fuel form of power.