I'd note that "federal land" is federal-government-owned land, like national parks, national forests, national wildlife refuges, and so forth. It's not "all land in the US" or something like that. I'm not sure how many projects exist today on federal land, which I don't think are generally open to development, whether it's to sticking solar farms or whatever up.
thinks
Hmm. Maybe offshore wind. If I remember correctly, in the US, territorial waters are under state control up to something like a nautical mile or three out, and then the remainder of the territorial sea, which runs up to 12 nautical miles out, is under federal control.
kagis
It looks like it was the Submerged Lands Act of 1953 that set the line, and to three nautical miles. And there are exceptions for Texas and part of Florida, which managed to get ahold of slightly larger control.
https://www.bsee.gov/guidance-and-regulations/regulations/bsee-governing-statutes
The Submerged Lands Act (SLA) of 1953 grants individual States rights to the natural resources of submerged lands from the coastline to no more than 3 nautical miles (5.6 km) into the Atlantic, Pacific, the Arctic Oceans, and the Gulf of America. The only exceptions are Texas and the west coast of Florida, where State jurisdiction extends from the coastline to no more than 3 marine leagues (16.2 km) into the Gulf of America.
The SLA also reaffirmed the Federal claim to the lands of the Outer Continental Shelf (OCS), which consists of those submerged lands seaward of State jurisdiction. The SLA led to the passage of the Outer Continental Shelf Lands Act later in 1953 (OCSLA). The OCSLA and subsequent amendments, in later years, outlines the Federal responsibility over the submerged lands of the OCS.
EDIT: BLM land -- which is mostly fairly dry land in the West that isn't considered to be especially valuable -- is the one that the federal government permits the most free use of by individuals. Like, you can go do dispersed camping on BLM land wherever you want as long as you move every couple weeks, livestock can graze on it, stuff like that.
BLM land:
This page says that they do permit solar projects on some of their land, so I guess that could be significant:
https://www.blm.gov/programs/energy-and-minerals/renewable-energy/solar-energy
Across the 245 million acres of public land it manages, the BLM maintains more than 19 million acres as open for potential solar development, subject to a variance process. Solar energy development projects on BLM-managed public lands are authorized as rights-of-way under Title V of the Federal Land Policy and Management Act of 1976, as amended consistent with appropriate BLM land-use plans. Regulations at 43 CFR 2800 identify requirements for solar development application and permitting. Applications for solar energy uses on public land are subject to paying cost-recovery fees and all proposals are subject to review under the National Environmental Policy Act and other applicable laws and regulations.
EDIT2: The Ivanpah Solar Power Facility
which you may have seen an in-game rendition of if you've played Fallout: New Vegas, where it played a significant plot role, is apparently on public land administered by the BLM.