The Brultech/GEM now has an adapter board inside it ("ESP-Wifi") that speaks MQTT natively. You can reach out to their sales team to buy one to retrofit to older GEM's (which is what I did).
Their module was done for easier GEM/HA integration, but a HE driver wouldn't be difficult... you could also use [RELEASE] Simple MQTT Client Driver, which is what I'm using to pull in my GEM data.
NB: It's on my todo list to cutover from my Python/rPi/MQTT driver to use the native GEM MQTT support.
I'd still need the MQTT Broker (as we all do). Some of the python code, to bridge my Solar data to PVOutput.org would be needed in my env also
