I am familiar with the concept and have previously argued that the effect of the extension is that Tesla will likely hold off on planned price reductions that I expected them to implement when the ITC was expected to fall from 26% to 22%. And while we could discuss the impact of the change on pricing and the elasticity of demand in the solar market, the problem is this is not an economics issue any longer - it is a contract issue. Tesla and a customer had an agreement to do a job for a certain amount. The change in the ITC does not change the terms of the contract, particularly since Tesla is clear in the contracts that the customer is responsible for claiming the ITC and Tesla is not involved, nor is it responsible, should the customer fail to qualify (beyond its standard representations that the system being installed is an eligible solar system.)
Whether or not Tesla has ways to get out of the contract may be a question for lawyers, but simply adding more into the permitting bucket, just in response to the ITC, is not acceptable. (And I do note that this assumes that is actually what happened, and it is not that there are other legitimate reasons the cost went up.)
Certainly if the situation was reversed, the friend would ask, because in the reverse case the friend is made monetarily worse off while Tesla is unchanged, but that still doesn't mean Tesla would be obligated to make a change. In any event, had Tesla been upfront about the change, it might have gone better with the customer than what apparently happened.
Agreed 100% that it's a contract and customer service issue. And to be totally fair if I was in his position I'd make the same complaint to Tesla. That said, if suddenly a bunch of people can pay more net because of a subsidy (like the extension of the ITC) you can be assured they'll be the first to raise prices exactly that amount (existing contract concerns notwithstanding of course).
And I disagree with the statement that every penny is lining corporations' pockets. Certainly, companies are aware of these incentives, and they absolutely capture some of the incentive for themselves (which is as expected.) But to suggest every penny is lining their pockets implies that we would have anywhere near such a large solar market without these incentives. I think there is a reasonable discussion to be had over whether the phase-out of the ITC should have been lengthened or is perfectly matched to the pace of innovation (and cost reductions) in the marketplace, but I disagree with the overall characterization of the subsidy.
You're disagreeing with fundamental principles of economics. Every penny is lining corporations' pockets, which incentives more companies and expands the market, but none of it is going to directly reduce the out of pocket cost to customers.
As a thought exercise: what would happen to the marketplace if the exact same subsidy was not paid to the consumer but instead paid directly to the companies providing the solar products and services?
The correct answer is "nothing" which should be indicative as to the true nature of supply side subsidies.