In Africa we've built small home/lab/datacenter power systems that charge a battery bank off utility mains plus on-site generation. It's basically a gigantic U

In Africa we've built small home/lab/datacenter power systems that charge a battery bank off utility mains plus on-site generation. It's basically a gigantic UPS that can automatically switch among a variety of power inputs. What's stopping someone from building something like that here in the U.S.? Charge batteries from solar, supplement with mains power, maybe even add a diesel generator for extreme emergencies, and use an automatic transfer switch to prevent backfeeding the utility mains (which is super dangerous to line workers and probably the reason for Florida's regulation). Not being a power systems guy myself, I don't see where the flaws in such a design are. Any EEs out there who care to comment?