the solar energy credit is not going to affect you AGI, so either I am not following your concern or you are not thinking about this correctly.
IRMAA is generally based on Line 11 of your tax return; the tax credits come into play much further down the form than that.
this is an excellent website to assess the IRMAA impact -
https://thefinancebuff.com/medicare-irmaa-income-brackets.html
