Should we choose a Fronius inverter for best cloud-free PV monitoring interfaces?

Who’s been through this process, selecting a PV inverter & system best suited to cloud-free monitoring? Can you advise me if I should insist on a particular inverter, or connect an add-on box (EmonCMS or other)?

We’re looking to install solar PV on our roof and maybe an air source heat pump too. I’ve collected plans, thoughts, questions on my own web site here:

Solar PV & Heat Pump – Julian Foad [1]

My particular passion is to be “cloud-free”. That’s when I found you, the open energy monitor community. Hurray!

In other words, I shun connecting anything through “the cloud” a.k.a. somebody else’s computer system. That’s because then “they” control the connection and can change or take that away at any time. I’ve become passionate about this and started blogging a bit:

A Freedom-Respecting Smart Home — julian [1]

But the installers who gave quotes know little about monitoring. That’s when I started my own research.

The main “smart” device in the system seems to be the Inverter. (Probably a hybrid inverter, controlling the battery charging too.)

In my research I found Fronius Inverters as the only company that makes a deliberate effort to provide “local” APIs. From my (recent) understanding there is a “Modbus Sunspec” standard API for controlling and monitoring devices like these. Fronius provide that Modbus API, as do other manufacturers, but more than merely providing the API, they document it openly on their web site, seeming to be serious about people using it rather than hiding it away as an installers-only option. See their “open interfaces” page:

That gives me a nice warm feeling that it would be in my interest (personal and supporting my values) to use them.

So right now my dilemma is: some local installers say they could get a Fronius inverter for me but it’s harder to source (lead time, price) and they’re unfamiliar with it, and it looks like it requires a particular battery system (“BYD”) which in turn is likely more expensive and harder to source. One installer goes with Sunsynk inverters and advises I find myself “one of the many available ‘buddy’ boxes that you can add on to provide monitoring”. So that brought me here, as I prefer open over commercial alternatives.

I want to get this right from the outset. I want to support companies like Fronius that support cloud-free operation. But I’m not sure I understand everything well enough to be sure it would work out properly, especially if I ask a naive installer to do something they’re not familiar with. Should I try to find an installer who knows this stuff; are there any?

Or, whom should I consult?

Thanks in advance,
– Julian Foad

[1] These links are to my own web sites
My POSSE copy of this message

[Edited by Mod so URLs work]