I've set up a few solar systems (and, I agree, it's a pretty ambiguous name). Generally speaking, they're devices that include an MPPT charger (which regulates the power coming from the solar panels), battery charger, and inverter (which produces mains AC), often with a bridge rectifier that also allows the system to accept input from the grid, and a second inverter to supply power back to the grid. It a lot of kit in a compact package, so it's unsurprising that they come with apps to allow them to be monitored and configured and, sometimes, support for automation in, say, Home Assistant.

And let me tell you: the majority of these things are fucking horrendous. I've lost count of the number of cheap Chinese units - with brands like LCERRZOPX and JRXYLNG, or provided whitebox so a fly-by-night European companies with a name like TotalCharge Voltacon Solutions can silkscreen their own logo on - which are guilty of every IoT sin imaginable: no local API or connectivity; plaintext communication to a data center in China; apps that force you to sign up and sends your credentials in clear text; apps that have not been updated since they were released in 2013 and crash constantly; no interface other than that fucking horrible app; and so on. This might seem like a minor thing, but if you're depending on these things to run your entire house, you need access to that information, but I have to plead with people not to buy them because they're €50 cheaper than the equivalent from a reputable brand. These devices are susceptible to anyone with a copy of Wireshark, let alone the manufacturers or Chinese government, and they're just waiting to be exploited.

Incidentally, if anyone is looking at buying something like this, I can't recommend Victron highly enough. Aside from their kit being high quality, you can access every feature using Bluetooth either from their own app, or a number of other apps that support their published protocols including, of course, Home Assistant.