I need to set up my solar system using the "SMA FLEXIBLE STORAGE SYSTEM with Battery-Backup Function" which is hybrid (but not adequately described for my version of the inverters).
My problem is that when on-grid it uses the grid neutral for the earth. When we disconnect, it disconnects both poles, so I need to use a local earth. The battery inverters will be chugging along anyway so I don't need a full "Automatic Transfer Switch", just something that detects a loss of power from the grid and automatically transfers the earth to local (and back again when it comes on). Any ideas?
@VickForcella I live in France so am juggling languages as I need to buy in France and explain the technical details to a local electrician too. That gets really difficult if I just stick to English.
If I didn't use the off-grid setup I'd need a mashup of the Battery Backup upthread and the flexible storage system (which needs circuit breakers, surge protectors and RCDs for each inverter as well as the grid earth).
@simonzerafa Sounds similar to molten salt which works for concentrated solar pointing at a tower. It works best at large scale thanks to lower surface area to volume ratio.
I'll just be using my batteries to store electricity as I'm not harvesting thermal energy.
@VickForcella@simonzerafa@davep honestly if they already have batteries I'm sure those will work, not discounting other interesting energy methods but that'd be a separate experiment probably :)
The main thing you want to watch for is that you don't accidentally become the neighbourhood's power grid backup by turning on your backup source before turning off the main grid connection, so in that sense for safety reasons I'd recommend an ATS, or some other way to make sure it doesn't flow back🤔
@simonzerafa@VickForcella@davep definitely! It's always good to talk with the local grid provider (usually that's not the utility company but a separate local-ish company) and see what the possibilities are, I also had to put my potential power feedback into a central database.
I don't think it's ever good to feed power back to the main grid if it's offline though hehe, but it seems the SMA power meter in the schematics would take care of the disconnection
@VickForcella@simonzerafa@davep looking at the schematics, it seems like the SMA system already is equipped with a sort of basic ATS? as long as you disconnect your mains phases I guess it should be fine. If your neutral/earth also gets disconnected, I think you should just be able to use a local one, just make sure it's dug in properly and has low enough resistance.
I'm by no means a wizard, or even certified though, I want to get certified at some point, but it's just a hobby right now.
@anthropy@VickForcella@simonzerafa I've got the SMA Home Manager which can be programmed to stop backing up to the grid. And if I'm using the grid as a generator, the inverter will be just switching it on when needed (my problem currently being trying to find a something that will use my DC relay signals to switch the grid on and off to the generator wiring of my master inverter).
@davep@VickForcella@simonzerafa is there any way to tell the SMA power meter to disconnect from the mains grid as a manual override of sorts?
You could use contactors, remote controlled (motorized) circuit breakers, or an ATS, but if your SMA power meter can do it then that might be enough, if you can bridge the gap with the batteries then having something (could even be manual) to turn on the local earthing then I think that should suffice. ---
@davep@VickForcella@simonzerafa An ATS would probably still be the easier, safer, more reliable option though, plus would give you redundancy on top of your SMA power meter for disconnecting the grid if something goes wrong.
But technically speaking you could make your own ATS of sorts by using things like remote controlled contactors and such, but since that's your own system you'd have to be sure that your control mechanisms are reliable, or at very least your fuses :P
@anthropy@VickForcella@simonzerafa Given the cost of SMA components, I would hazard a guess that the Home Manager is pretty reliable. This stuff is built to last 20 years.
@anthropy@VickForcella@simonzerafa I'm considering just using the grid live for the generator, so no risk of grid earthing. It's the Home Manager 2.0 that replaces the Energy Meter nowadays and as it's notionally an off-grid setup it won't be fulfilling that role.
I was thinking of putting it between the "generator" (grid live) and my inverter, but it would need to be between the grid live and the relay to ensure it has power (in which case it could also stop backing up to the grid).
I just need to find a 230V relay that is triggered by my (DC?) relay wires from the inverter so the grid generator can be switched on and off by the inverter.
@davep@VickForcella@simonzerafa hmm, I don't have doubts the SMA power meter will work, but I have less faith in (cheap) relays for high power scenarios. If you're never using more than 2kw per phase from the mains grid it may work (although still edgy for the whole home mains input), but using something like a remote controlled (magnetic or otherwise) contactor (which are usually 25-100 ish depending on quality/rating) could work similarly but more reliably I think. Again im just hobbyist tho
@davep@VickForcella@simonzerafa something like this should work: https://www.se.com/il/en/product/A9C22715/ict-16a-1no-1nc-230-240v-50hz-contactor/
Assuming 50hz, 230-240v, <16A, one normally-open and one normally-closed connection, this could work. I don't actually know how the remote control on this works, from what I could find it just works like a relay with a "control circuit" input/output, but it could also be that it uses Schneider Electric's proprietary UMAS or Modbus protocol. But this is the type of device I meant at least
@anthropy@VickForcella@simonzerafa Yeah, I've been looking at similar ones and it's not clear. Guess I'm going to need to check on the SMA forums. Thanks 🙏
@anthropy@VickForcella@simonzerafa Yeah, I'm currently learning about contactors but can't seem to see ones that are triggered by low voltage/current DC rather than AC. And the sheer number of types of contactors is rather bewildering.
@davep@VickForcella@simonzerafa yea that seems about right. It should all be simple but companies prefer to sell you their own end to end solutions it seems.
Perhaps you can contact an electronics/hardware store nearby by phone and just explain what you're looking for, if they give you the wrong advice you can always go back and get something else instead
@davep@VickForcella@simonzerafa I guess it makes sense they didn't specify it then, if it's not specific to any signal haha, that's good to know! Thanks, I will probably also use these at some point then, for similar reasons :)
I think it's really for for larger scale use (think grain silo sized) but once you heat up a bunch of sand to 500C in an insulated tank it stays hot for a while 😉
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