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PowerWall 2 Interface with a Generator
- Thread starter shs1
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- Powerwall Tesla Energy
Is it possible to install PowerWall(s) without the Tesla Gateway?
I'm thinking of a design topology where there's another gateway-device (GD) (non-Tesla) that does the job of connecting/disconnecting from the grid. The PW(s) would be mounted behind the GD. Solar back-feed would also be part of this micro-grid.
The idea is to use the PW as the "backup generator", but somehow still keep it charging from solar.
Thoughts?
I'm thinking of a design topology where there's another gateway-device (GD) (non-Tesla) that does the job of connecting/disconnecting from the grid. The PW(s) would be mounted behind the GD. Solar back-feed would also be part of this micro-grid.
The idea is to use the PW as the "backup generator", but somehow still keep it charging from solar.
Thoughts?
I don't think so, but what you are describing already happens with the Tesla Energy Gateway. The grid can go down and the combination of Solar and Powerwall(s) keeps your house going. (As long your net daily Solar can keep up with your net daily usage.)
Yes, but I'm proposing the idea of using thing else that may already have TOU, and other, capabilities. Separation of responsibilities (and vendors) may be good here.
However, if the TBUG/TEG is the other half of the PowerWall "brains" and PW can't even do self-consumption without it, then oh well.
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I'm pretty sure the Tesla Energy Gateway (non Backup version) would still be requirement to talk to the Powerwalls, but if you have a separate transfer switch you wouldn't need the relay provided in the Backup Gateway. Not sure how you'd be able integrate the Tesla Energy Gateway with whatever other control system you'd provide.
Cheers, Wayne
Cheers, Wayne
I think you still need a transfer switch. The TEG seems to just break the circuit, not switch it to something else.
DHU1 and others, I realized I am missing something significant in my understanding of how this all works.
In the normal situation without a powerwall, when the grid goes down, the transfer switch will detect that, initiate a generator start, and when the genset's voltage hits the required level, the transfer switch contacts flip from the grid to the genset.
In the case of a grid outage with a powerwall, from what I understand, the TEG will disconnect the grid from the house (presumably with a generator, this would be the connection to the transfer switch) to make sure no backfeeding happens, and the powerwall supplies power to the loads.
So what happens with the generator in how Tesla has designed it when the powerwall is functioning? if the grid goes down, the transfer switch would have normally started the genset, unless some sort of inhibit signal is sent to the switch. And if the powerwall exhausts its capacity and goes offline, presumably the TEG would reconnect the house to the transfer switch, but does it then start the genset too?
How does all this work in your setup? Presumably the genset is not running when the PW is providing power? How does that not happen with how they wired it?
thx
mike
In the normal situation without a powerwall, when the grid goes down, the transfer switch will detect that, initiate a generator start, and when the genset's voltage hits the required level, the transfer switch contacts flip from the grid to the genset.
In the case of a grid outage with a powerwall, from what I understand, the TEG will disconnect the grid from the house (presumably with a generator, this would be the connection to the transfer switch) to make sure no backfeeding happens, and the powerwall supplies power to the loads.
So what happens with the generator in how Tesla has designed it when the powerwall is functioning? if the grid goes down, the transfer switch would have normally started the genset, unless some sort of inhibit signal is sent to the switch. And if the powerwall exhausts its capacity and goes offline, presumably the TEG would reconnect the house to the transfer switch, but does it then start the genset too?
How does all this work in your setup? Presumably the genset is not running when the PW is providing power? How does that not happen with how they wired it?
thx
mike
There's a post up thread about an install, but not real integration - that one is apparently set up so when the grid goes the house relies on just the Powerwalls and solar - and if that gets drained then the generator comes on to carry the house, but doesn't run the solar or charge the Powerwall as I understood it.
yes, thats what I think was described, but I am having trouble understanding how the automatic transfer switch avoid turning the genset on when the PW kicks in. It's just looking at voltage from the grid, and would have no way of knowing if the TEG has disconnected the loads.
So in this installation, how is starting the genset upon grid failure avoided?
The installation instructions for the Generac generator I looked at has a 120V circuit that charges the battery. When that circuit loses power it triggers the startup of the generator and activation of the automatic transfer switch. If you moved that circuit inside the Tesla Gateway, then the generator would not start until the PowerWalls shut down.
If I were doing it, the transfer switch that started the generator wouldn't be connected to monitor grid voltage - instead it'd be connected to something on the Powerwall side of that transfer switch. That way, it'll see the "grid" providing power when the grid is live, or when the Powerwall is live but the grid is out, and it'll only trip the generator after the Powerwall gives up.
That isn't what I want, though. What I want is the ability to manually start the generator while the Powerwall is still working and use the generator to recharge the Powerwall when solar isn't keeping up (or even have the option to have the Powerwall call for the generator when the grid is out and the Powerwall gets down to twenty percent...)
I suspect the problem is making sure there is no-backfeed of Solar to the generator as well as keeping all of the frequencies matched.
I would think that you would have to shut the Powerwall down, start the generator, and then turn the Powerwall back on so that it can match the generator's frequency.
If you handle everything on the AC side, matching frequency will be a pain, yes. There are inverter Generators that are designed to link to others and match waveform - I'm not sure of what communications they perform on their link cables, and whether you can just hook one of those into the Powerwall grid and it'll sync itself.
My solar microinverters and for that matter any grid tie solar inverter has the circuitry to do this correctly.
Competitors that offer this function, like the Xantrex battery inverter series, mostly seem to handle it by converting everything to battery voltage DC and matching the various sources there.
Sunny Island may help also.
http://files.sma.de/dl/5610/TechNDIGIN-HUS123112.pdf
And: http://files.sma.de/dl/15216/SI4548-6048-US-BE-en-21W.pdf
http://files.sma.de/dl/5610/TechNDIGIN-HUS123112.pdf
And: http://files.sma.de/dl/15216/SI4548-6048-US-BE-en-21W.pdf
I think the fundamental problem that Tesla has with generators is that most of them are traditional mechanically phase locked devices. When the load changes the ICE engine changes speed and therefore the frequency is not stable. It's very hard to be grid interactive with that kind of generator. As mentioned above, an inverter generator can avoid this problem, but I've never seen a whole-home sized generator that used an inverter. Something like a Honda EU7000is is the largest I've seen for an inverter generator. All the Off-Grid setups I have seen that integrate with a generator simply put a battery charger on the generator input and the inverter keeps going about its business without worrying about synchronizing to the generator. SMA Sunny Island and Outback Power's various products do that.
That matches my understanding of what's out there too.
I'd argue that in the proposed paradigm, as a backup for solar in a system with functional Powerwalls, you won't generally need more power than the EU7000is you mentioned - you don't need to match peak loads or have a big reserve to spin up motors, because the Powerwalls will cover that. The generator just has to fit into the net with the Powerwalls and exceed the average daily usage on days the solar isn't enough.
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