They don't need to build anymore, they just import it.
I lived 30km away from Alsace, and despite us having a significant amount of solar on all of our buildings, as did most of the local community/neighborhood, it was well understood that a significant amount of Baden-Wuttenberg's energy (the 'greenest-centric' Stat of Germany) needs were just bought from France.
I don't have the figures in front of me, but I was there in 2012-13 during the transition, and I lived in an old 7 bedroom old Chateau style home that had its top floor being renovated, which was exposed to the cold winter.
We lived on the bottom floor and mainly relied on wood heat from the backofen in the center of the home to heat the rest, and when we didn't/forget to keep it goin I could literately see my breath while I laid in bed as I lived the furthest away from the source, and as someone born and raised in SoCal it was incredibly terrifying at first.
Before I wised up and figured out the heating method I often made my bed before having a shower and going to bed and I stuck a 2L glassflasch with hot water from those instant water heater kettle's. But it wasn't long before I summoned the inner pyro in me I had suppressed since my early teens.