That simply is a transfer switch that is built in.
"Transfer switch" refers to a specific kind of switch that transfers load between two sources. There is only one source (the panels) and one load (the grid) on a grid-tied inverter, so what you're saying does not make sense.
There are more complicated solar setups that do involve transfer switches, but they are not applicable to the balcony solar use case and remain uncommon even for hardwired rooftop solar.
And indeed these are uncommon, mostly because they tend to be more serious devices. Victron and formerly Xantrex make nice ones, but the inverter alone probably costs more than a complete balcony solar installation.
For the solar balcony and more common rooftop solar setups there is only a simple disconnect, but both a transfer switch and a disconnect are the same thing: a (usually beefy) relay, but the transfer switch variety switches your house between the inverter and the grid whereas the disconnect just physically disconnects the inverters output. The downside of that setup is that if there is no grid but you do have solar that you still have no power.
Most of these wouldn't be able to power anything but the smallest installations anyway (300 W or so, typically), and don't have a battery to store any excess (as if there would be any...).
As soon as you add a battery it makes good sense to use the transfer switch: you can disconnect from the grid but the inverter can keep running to power your house and if you're lucky the solar will replenish it fast enough during the day that you can hold over for a while.
The big rooftop inverter that I have has a built in transfer switch but I'm not using it right now simply because I don't have a good way to route the wiring to and from the inverter. It is stuck in my garage with the main distribution panel on the other side of the house. In my old house in Canada that was all designed from scratch and there we had the house entirely off-grid with the transfer switch hooked to a genset if the power was out for longer than the battery could sustain us (48 KWh so that usually was good for a couple of days).
> the transfer switch variety switches your house between the inverter and the grid whereas the disconnect just physically disconnects the inverters output
> That simply is a transfer switch that is built in.
Then in this comment:
> but both a transfer switch and a disconnect are the same thing
These statements are false, and the fact that the second one was written even after being corrected once makes me think they still do not understand.
This user appears to blast paragraphs upon paragraphs of irrelevant noise at anyone who responds to them so that either the comment has internal conflicts (as you noticed) or any criticism seems nitpicky.
The units likely have "protected outlets" too that likely use an internal transfer relay to disconnect from the grid side, but at 15/20A it doesn't have to be terribly beefy.
I have a similar situation here but at much higher power levels, a single underground cable from my garage to the house carrying 16A tri-phase and a whole raft of consumers in the garage itself. There too there is the potential for overload with both consumers and producers on the same cable. The solution there was to have a secondary distribution panel, breakers on both sides of the cables, for the consumers and for the inverter guaranteeing that none of the wiring in the panel or to the house or the consumers ever exceeds its rating.
This was by far the most cost effective solution, saved adding another ground cable and relieves the main distribution panel of a lot of current going in and out of the garage.
Just curious - are you exporting power or zero export with a current monitor upstream of the main panel? Also same question regarding off-grid operation and a transfer switch ahead of the main panel.
I don't know what tri-phase breakers cost in NL but the second panel and feed-in breaker sound like the straightforward solution in the US too. Our wires cost considerably more, and we don't even have RCD in the breakers you'd use for that.
Hehe, ok. I think that's your insurance company calling on the other line.
> are you exporting power
Exporting 12 MWh / year or thereabouts.
> or zero export with a current monitor upstream of the main panel?
There is a current monitor (a Shelly tri-phase one), right now it is still economically viable to do so (though the utility companies are trying what they can to dissuade you by changing the deal through politics). If it is no longer then I will just install a battery and disconnect from the grid for the summer months.
And I'm not using a transfer switch because I don't have a battery to stabilize the system.
Well, technically those breakers are a manual transfer switch, only it is broken up into two halves and I can just disconnect the mains feed and run in island mode but I would still need to install a battery and a charger. House mains breaker off, solar on would be the house running entirely off the local stuff, I just don't trust that inverter without a battery behind it to be able to react quickly enough to load changes and by default it is set up to disconnect if the grid goes off, so you'd have to manually override that. The main issue with it being two halves is that you can not guarantee that the house net is in-sync with the grid at the moment you make the switch and that's a bad idea with a system this powerful, so I'd definitely get a proper automated one if I intended to do this for real, otherwise you might cause a load spike which could trip breakers and annoy the neighbors.
Right now I can't switch that on or off under load anyway because the large inverter would simply disconnect as well.
Tri phase breaker of the right amperage was about 150 bucks.
If I were to do this I would probably get a complete set from Victron, their stuff is amazingly well engineered, but if these open source people are going to make an inverter/charger combo then I might go for that and add a another manufacturers automated transfer switch.
An inverter is, complexity wise, not that much harder than a large switching power supply, there is some more instrumentation and some more rules but it isn't super difficult. It is much harder to make one that is commercially viable because those guys all cut corners to stay competitive. Ironically a proper case is probably the hardest part, there are also some larger inductors that might be tricky to source. And if you were to design one you should probably make the low voltage stuff (UI, CPU) on a completely separate board from the line voltage stuff and go for tri-phase right away because it is so much cleaner. Bonus points for modularity of the output stage.
(then again maybe someday I'll hit some wall with off the shelf MPPTs and find myself wanting to go down that rabbit hole lolol. but honestly AC coupling seems cleaner in terms of things like fault protection on longer runs - fault on a stiff mains circuit -> breaker will trip. Fault on a circuit where the current/power is intrinsically limited to what the solar panels can supply -> ???)
I asked about the transfer switch / monitoring because I've looked at the same problem here, first with a generator now with solar. Incoming power service is on the complete opposite side of the house from where I really want the power handling gear. The manual two breaker thing is practical (for a generator at least), but not code compliant here (no positive lockout).
I would think Victron would have an option for a remote transfer (/disconnect) switch, but I haven't really looked into it yet. It would still have to get the grid phase timing somehow to line them up before connecting, so something more than merely a dumb contactor.
Same in my house.
> It would still have to get the grid phase timing somehow to line them up before connecting, so something more than merely a dumb contactor.
Then you'll want a synchronous one. They match phase before making the switch, which is one reason why it's nice if you use one tied to your inverter, which already has the capability to steer its phase to match the grid.
But really an independent transfer switch wouldn't actually fully solve the problem - power at the main incoming service panel would still have to blip off-on for the downstream Victron to see the grid loss, disconnect from grid with the external transfer switch, disable anti-islanding, and then re-close the relay to backfeed up its own AC-IN. And even that would be a bit dodgy relative to proper certification for anti-islanding.
What one really needs for this topology is to move both the contactor and the current sense normally in the Victron, to the location of the incoming service panel. Which is why I was wondering aloud if they had a solution to do this, and coordinate with the inverter to maintain export rules, phase matching, etc.
I'm guessing the common answer is just run two sets of wires, as with generators.