The general tax rule is that all income is taxable unless specifically excluded under the tax laws. Since the iRS has not issued a ruling it would seem to be taxable and that's the conclusion "Green Accountancy" arrives at.
However The Clean- Coalition.Org takes a different view. and that is while the income is taxable, you get deductions for depreciation and maintenance on the generator.
https://www.clean-coalition.org/wp-content/uploads/2018/11/NEM-and-FIT-tax-treatment-analysis-28_jb-...
My opinion, which can be wrong, would be to not report the income which would be the result if you were under net energy metering (NEM). I'm basing this on the fact the iRS ruled credit card rebates are not taxable income.
