"Darn if I can find it now."

Really? Did you read any of the links I provided?

Once again, first read if you even need to be bothered, because the rules changed, again:

https://kinectsolar.com/ira-safe-harbor/

Read for what they qualify for already, without any shenanigans. Otherwise, you seem to be describing downpayment and/or progress payment. However, articles refer to take title/ownership for products or components (not ordinarily in inventory, but specific and direct for that project) or have begun work of a significant nature (project owner has some risk in the project). That means specific benchmarks, not generic progress.

The contractor should be able to provide evidence that the contract meets grandfathered or safe harbor, as well. But that might not matter, since the 30% continues to be available, with qualifications.