No basis - no deduction. Although an entirely different situation, I believe the net metering ends up in the same boat.
Case law has held that most consumer "points", rewards etc.... are not taxable income, therefore there is no basis to deduct.
In the case of the net metering, the taxpayer also does not recognize income by producing more energy than he/she produces but receives a credit instead. It sounds like the only options are: use it, lose it, or give it away.
If the taxpayer had an option to receive cash, the excess electricity produced could generate taxable income and a 1099. In that case the taxpayer would have a basis to deduct.
So it appears to me without a basis there is no deduction.