I want to claim a federal and state solar tax rebate but don't have enough liability right now. Can I change my W-4? Up, down or is there another way?

Please read this entire discussion on a similar credit:

https://ttlc.intuit.com/questions/4114325-i-purchased-a-17-nissan-leaf-how-do-i-maximize-the-tax-cre...

Bottom line: You need to generate additional taxable income, not change your W4 withholding. But be aware that Congress is looking at 2017 tax law changes.

An unused Federal solar credit can be carried forward to the next tax year.