I thought renewables were cheaper than coal. How is this possible?

This is one of those in general vs in particular things.

In general, yes coal is way more expensive versus renewable energy. In this particular instance, they’re just expanding the site, all of the really expensive stuff like logistics and transportation are already paid.

This is the same reason just keeping old nuclear plants running is cheaper than building a new one. Each industry has expensive parts and cheap parts. If you’re doing something that only expands the cheap parts then you’ll be able to beat out competitors.