A little late to the game...this should have been considered BEFORE the artificial boom in wind farms.
I believe Kalifornia has already dealt with this issue...IIRC, companies are required to post a bond to pay for removal, before the turbines are built.
How do they jackhammer and remove the concrete blocks under the Turbines that are stories deep and acres in size. They essentially took arable land out of commission for Millenia. The same goes for the solar farms, as they pour concrete pads to place solar farms on, and when all is said and done, it will just be torn up driveway type of massive mess within a single generation.