Here's an update. From what I was told today, my "mandatory" solar is because of the CCR (California Code Regulations) title 24 for 2016, which took effect on Jan 1, 2017. The requirement was for new constructions to be 30% more efficient and KB decided to use solar to meet this efficiency "requirement". Although, the only major requirements I could find for 2016 CCR title 24 is the requirement for high efficiency lighting such as LED bulbs. The 2019 CCR title 24 is where the law makes it a requirement to have solar on all new constructions for Jan 1, 2020. Regardless, the sales office did send me a Solar Addendum that did say solar was "mandatory" and we could either lease or buy.
Mety brings up a good question of why not lease instead and I'll have to do some research into that. We don't plan on moving until the kids graduate high school which with a newborn is at least another 20yrs so maybe buying is the right choice for us. I really wish we could have had the option to pick the solar ourselves like how we decided not to use any of their flooring options, but do planning on ripping everything out before we move in and installing our own flooring.