I agree, but with a caveat. In 2002, I tried to get a job with a solar contractor in NM based on the fact that I had years of experience working in the building trades and knew how to turn a wrench from a stint working with an auto mechanic. An employee there told me that they would be doing me a disservice to hire me without any specific solar training and recommended that I look at the RE Program an San Juan College, which specializes in PV system design and installation (pretty much all battery-based at that time). The nice thing about having some book learning—including a heavy-dose of the NEC (Mike Holt's curriculum)—is that then when you get you on the job training you're in a better position to tell the good practices from the bad. If you're working for an experienced installer who has a long history of doing things the wrong way—perhaps using unlisted equipment or not using fall protection or not flashing roof penetrations—that's not the best legacy to continue forward. But I agree, that on the job training is the only way to get the book learning to sink in.