How does the itc tax credit work for retired workers?

[DoninGA]

Are you referring to an Investment Tax Credit?  What type of credit, Corporate or Personal?  The Solar tax credit?

[gregdebhaz-]

solar tax credit

[Opus 17 · Accepted solution]

No different than anyone else.  If you install solar equipment on your personal residence, you can take a credit of up to 30% of the cost.  Because it is a non-refundable credit, it reduces your tax, maybe even to zero, but is not refunded if you owe no tax.  

If you have income, such as a pension, annuity, investment dividends and gains, and so on, then the credit will reduce your tax.  If your income is too low to owe tax then you won't have tax for the credit to reduce.