There's no clear carryover limit; as DanaB27 notes, the language is "future tax years."
You can see that Form 5695 provides for carryforward from 2021 (line 12), and carryforward to 2023 (line 16), so it's clearly allowed for multiple years.
The Residential Clean Energy Credit -- which includes solar property -- has been extended to property placed in service through December 31, 2034, so you'll probably be able to use up the credit at some point.
