> TFA makes it pretty clear that the energy source is geothermal.

Is it more likely that when this plant switches on, other people will just make do with that much less electricity, or that when this plant switches on, electricity production will go up?

Thats not the point. To design ,build and operate this plant you first need to use a lot of energy, tools and resources that are not carbon neutral. Before this plant is even operational it will be carbon negative.