[kkfx]

Victron (to cite an NL vendor) actually can perfectly operate in LAN only via MQTT and ModBUS also offering a (bad) WebUI locally for settings pretty anything, including a display for the said WebUI in a framebuffer with an embedded mini-keyboard. It's up to the installer decide to go with their cloud offer or not.

The sole remark I have against them (beside the not so good software quality it's the impossibility for individual owners to do offline updates, we can upgrade via VRM portal but not downloading fw and flash it locally even if the needed device is on sale, because they offer fw files only to registered vendors.

Fronius (to remain in the EU) have a local WebUI witch need a connection only for fw updates, even if differently from Victron it's not a Debian based system with sources available but a closed source one, they unfortunately offer only a very limited REST API and a very slow ModBUS but still anything con be do locally.

I'm not sure, since I haven't any myself by SMA (Germany) and Enphase (USA) seems to been able to operate offline as well.

Stated that, yes, you are damn very right in saying most installers have no competence, thankfully where I live self-installation is allowed (at least so far), but that's simply demand better UIs and training for them perhaps avoiding the current state of the industry with an immense amount of CRAP at OEM level, with most "state of art" systems not at all designed to be used in good ways (see below) and absurdly high prices to the customer at a level it's not interesting installing p.v... 4 years ago I paid my system 11.500€ for 5kWp/8kWh LFP, the smallest offer to have it designed and built by someone else was ~30.000€ the most expensive ~50.000€ and all the 6 offers I tried shows some unpleasant issues and incompetence.

About OEMs just observe how ABSURD is that there is no damn DC-to-DC direct car charger. Most EVs now have 400V batteries, the same of stationary batteries, with equal BMS comms. Why the hell not sell an MPPT-to-CSS combo direct solution? Ok, we do not ONLY charge from the Sun, than it's perfectly possible have a compo charging station with DC for p.v. and AC for the grid, switching from one to another as needed. It's ~30% energy lost in double conversion.

Why no DC-to-DC high power appliance who still run DC internally (A/C, hot-water heat-pump heaters etc)?

Why not a modern standard protocol for integration of anything instead of building walled gardens?

Long story short OEMs have choose the cloud model partially because most installers are electricians able to use desktop holding the mouse with one hand and clicking with the other, but also because they have no intention to made user-interesting solution in an open market...

[ansgri]

I'm not a pro in these systems (yet, I hope), but my understanding is that, beside lack of demand, HVDC is a safety nightmare compared to AC, and inverters are getting more efficient each year. So, even given the choice, I'd keep AC home-wide distribution and set up inverters in key places, with exactly the highest required voltage.

[kkfx]

Well, yes DC is unsafe because if you get electrocuted instead of being "pushed out" you get "attached" to the conductors, but if you have a p.v. inverter at home you already have a 400V DC line from the module to the inverter, how different can be having the same to the garage? The same to an exterior heat-pump unit (where the DC compressor it's typically located) witch is also insulated by the mere fact you drive it via a remote?

Aside I'm not much an expert as well but, from DC to AC we are pretty efficient, around 98% of energy get converted. But the other way round it's pretty inefficient, meaning a loss around 30%. So while your p.v. it's pretty efficient in generating AC, your car it's pretty inefficient generating DC from AC to recharge. You heat pump would gain as well.

To be clear I do not advocate DC for any DC home appliance like washing machines or dishwashers, just for energy intensive appliances like big heat pumps and car chargers. Not more.

[ansgri]

Valid points, though for safety I thought less about shock and more about fire: the DC arc is much more stable, thus the switches, breakers and relays have to be more robust. The rated DC voltage of magnetic relays is about 1/10 of AC.

[kkfx]

Well... I'm ready to pay 10-time the price of an AC breaker to recharge regularly DC-to-DC and since that's the very same link than stationary 400V LFP batteries being able to use the car battery as a home one when I'm at home.

Try to imaging how well you could run if you have a small battery, as an expensive UPS for the home when you are not there (ventilation, homeservers, fridge(s)/freezer(s) etc) and when you are at home, thanks to a let's say 70kWh battery you can also run your heating in winter in case of a blackout...

In the end it's the very same power circuit, why not? 300€ extras in breakers to run my heat pumps more efficiently? No issue, they'll pay back countless more.