This appears to be the position of the IRS as of today. There is no set time frame. However, the 2022 form 5695
has a line to rollover the excess credit from 2021. If precedent is any indication the rollover should be available through 2034 when the program expires.
The IRS hasn’t announced new rules on this yet, but in the past the federal solar tax credit could be carried over for as many years as the incentive was active. The Residential Clean Energy Credit is active until 2034, so if you install in 2022, you’ll likely have plenty of time to use it over several tax years.
