(Also, Amazon is where most people get their solar equipment these days and you would be amazed how much of it is not UL certified either.)

Grid-connected is an entirely different ball game. You will not see any open source projects there, or at least not any that anyone will want to use.

Let's think about why not. Anything grid-connected, you REALLY want a licensed electrician to plan and install. And competent electricians will NOT go anywhere near a piece of equipment that is not UL certified. A company producing equipment is NOT going to go through the expense of getting UL certified and then just release their design, PCB, and schematics for free.

And I want to be clear that I am a strong proponent of open source hardware, there are just certain situations where the incentives in reality just don't line up. This is one of them.

I got solar installed by the local power company and while it's well done and was a great deal regarding the price, the inverter stats are locked behind a really terrible app. At least there isn't a subscription cost but I wouldn't be surprised if they add one someday.

Would gladly pay more for fully open and serviceable replacement.

This project isn't being marketd to people who call up a company to white-glove the whole-home installation end-to-end. This is for DIYers who have enough knowledge to tinker with self-designed solar projects but not the EE degree required to engineer some of the more specialized equipment themselves.

I'll give a good example: I use solar to power a ham radio station for a weekend in the summer. However, nearly ALL of the equipment you can buy for the production and storage of solar power emits some degree of radio-frequency interference, which is bad when your whole goal is to power a very sensitive radio.

When it comes to charge controllers in particular, there are exactly two companies that claim to make RFI-quiet MPPT controllers. One has mixed reviews (some people say they work great, some say they are not any better than anything else), and one is very good but also very expensive for what you get. So, more open design and community feedback from people like me might get the cost of a reliable RFI-free charge controller down to where it should be.