Agreed on the EU7000is sizing. You just need to run for an hour or two at a time to bring the PowerWalls up off the bottom of their SOC. Does anyone know of a similarly sized inverter generator that runs on NG or LP? The Honda is gasoline and keeping fresh gas on hand when you only drive EVs is problematic.
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PowerWall 2 Interface with a Generator
- Thread starter shs1
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- Powerwall Tesla Energy
Kohler has a whole set of NG/LP generators starting at 8KW. There are a of industrial generators in the 20-30KW range.
If the PW was DC, it could be integrated with some hybrid inverters that have generator inputs, and this would all be much easier. But Tesla likes building things all by themselves.
If the PW was DC, it could be integrated with some hybrid inverters that have generator inputs, and this would all be much easier. But Tesla likes building things all by themselves.
All Tesla really has to do is add an independent AC input to the PowerWall with a battery charger. That will completely and easily solve the problem. However, I don't think they feel that people who need a generator for extended outages are worth pursuing. Of course, I could be wrong. BTW, how much would you pay for such an optional feature?
That would be a simple solution. I don't have a dollar value in mind - but having something like that even at extra cost (hopefully set up so you can charge multiple Powerwalls from one generator,) would probably convince me to get off the fence and buy a pair this year instead of hesitating and thinking and looking at the (more expensive, harder to integrate, but more flexible) alternatives.
Higher end gensets don't do that. I am looking at used gensets from cellsites that are available at a fraction of list price and generally very well maintained. These are all most 1800 RPM and locked to that speed, and the engine power adjusts based on demand to spin the generator end at a constant speed for constant voltage output. They can be very very stable voltage sources and generally pretty clean.
The smaller gas units are very different, and have further problems due to how they handle grounding. You don't really want to try and hook them up to house wiring in any way - you could have a bad day.
I agree the better way would having the grid and generator connections to an inverter - that's what the hybrid inverters do.
Charging from the genset during an outage would be very very useful, as gensets are not efficient at low % of utilization. You get soot caking on the exhaust because the genset doesn't get hot enough. If you had days of clouds or some other issue affecting charging, the genset can charge the PW at Nx5KW, which is great for a modest side genset, and then it shuts off and lets the powerwall dribble the energy out as needed.
Does the TEG have any wires that connect to a transfer switch inhibit input (some of the fancier ones have those)?
Is dhu1 ok? I haven't seen him reply lately...
Also, just to toss in two cents (and again, apologies if I've missed a post, or a dozen): in the "how to do it" category -- if one can get the signal from powerwall that it's below X% charged, then disconnecting the Solar inverter outputs/PW inputs and reconnecting them to the generator does the task, I think, assuming both are well-behaved 240V AC. However, from experience with SMA, I would underline the point about having very high quality power out of your generator. Also, there may be any level of sophistication internal to the Powerwall that undermines this: if it tries to understand your solar system at all, this will confuse it to no end.
I am actually a little dumbfounded that the PW can't charge off of the grid, though this same approach would do that too.
I am actually a little dumbfounded that the PW can't charge off of the grid, though this same approach would do that too.
I recently discovered the PowerWall support page has some generator information that I don't recall being discussed here.
Generator Integration | Tesla
1. Powerwall can be used with a generator and external Automatic Transfer Switch.
2. Powerwall will be used first and charge with solar. If the Powerwall overloads or runs out of battery, the ATS and generator will kick in.
3. The Powerwall cannot charge from the generator and will remain idle, unable to charge from solar, until the grid returns.
Generator Integration | Tesla
1. Powerwall can be used with a generator and external Automatic Transfer Switch.
2. Powerwall will be used first and charge with solar. If the Powerwall overloads or runs out of battery, the ATS and generator will kick in.
3. The Powerwall cannot charge from the generator and will remain idle, unable to charge from solar, until the grid returns.
Which is in line with what we've seen upthread, and vastly inferior to other products if you get into that regime. (Of course, the lower price point means you can buy more capacity for the money which reduces the odds of getting to that point...)
What I thought was very interesting, though, was the repeated "cannot currently, stay tuned for updates" on that page, though. Out kinda sounds like Tesla has a future plan that involves better integration with non solar local charging options.
I'm guessing they are worried to allow generator charging of the powerwall due to the potentially "dirty" power possibly damaging the batteries?
Also, not entirely sure how the powerwall would necessarily know the difference from grid power if the ATS was installed "before" the powerwall. Perhaps it could detect grounding or neutral issues. There is some lengthy discussion on here about charging teslas with generator power and I know some have gotten it to work. Same batteries I would assume it is the same issue....
The big upside here is in the ability of the powerwalls to shift or smooth peak demand. In my example I use about 2,900 kwh per month. Assuming enough powerwalls to smooth demand I could run the whole house on a 5,000 watt generator (assuming no solar) vs a 20kw generator if I had to be able to handle all starting loads at once. The difference in fuel usage would be massive!
If you account for solar you could presumably get a portable 2,000 - 3,500 watt inverter generator to charge the powerwall as needed in a longer outage and you are essentially off the grid!
I'm hopeful the solution will come soon!
Also, not entirely sure how the powerwall would necessarily know the difference from grid power if the ATS was installed "before" the powerwall. Perhaps it could detect grounding or neutral issues. There is some lengthy discussion on here about charging teslas with generator power and I know some have gotten it to work. Same batteries I would assume it is the same issue....
The big upside here is in the ability of the powerwalls to shift or smooth peak demand. In my example I use about 2,900 kwh per month. Assuming enough powerwalls to smooth demand I could run the whole house on a 5,000 watt generator (assuming no solar) vs a 20kw generator if I had to be able to handle all starting loads at once. The difference in fuel usage would be massive!
If you account for solar you could presumably get a portable 2,000 - 3,500 watt inverter generator to charge the powerwall as needed in a longer outage and you are essentially off the grid!
I'm hopeful the solution will come soon!
Steve1081,
I think the problem is this: if we assume the generator power is perfect, so no dirty power issues, then if the generator is swapped in for the grid, the PW won't know and will operate as usual: which means it will only charge off the solar (no sun, no charge). it's conceivable that the PW will try to backfeed to the generator, which could prove problematic: ideally that's largely resolved by having the generator turn off as the PW approaches some charge level at which it tries to contribute (the ideal algorithm would involve short-term predictions of use and sunshine, I think).
If we swap the generator in for the PV, with the grid down, the PW might not know, and will charge, and will power the house to it's normal degree possible. The solar will not contribute anything, and some gymnastics will be necessary to shut the generator down when the PW is 100% (or whatever) charged.
Ideally something involving both would happen, so that the generator only ran when the grid was down AND the PW needed charging (AND predicted solar output was inadequate to the task of charging + keeping up with demand). Which could in principle be done with a combination of those two wiring configurations and a little logic (really not much). It still wouldn't be exactly optimal: there are times when the solar could contribute but was disallowed, I think, and also the PW output capacity would limit house consumption. The final point could in principle be resolved by more PW's, and since we're essentially talking about an off-grid(able) house, hopefully loads have been minimized before any of this.
I think the problem is this: if we assume the generator power is perfect, so no dirty power issues, then if the generator is swapped in for the grid, the PW won't know and will operate as usual: which means it will only charge off the solar (no sun, no charge). it's conceivable that the PW will try to backfeed to the generator, which could prove problematic: ideally that's largely resolved by having the generator turn off as the PW approaches some charge level at which it tries to contribute (the ideal algorithm would involve short-term predictions of use and sunshine, I think).
If we swap the generator in for the PV, with the grid down, the PW might not know, and will charge, and will power the house to it's normal degree possible. The solar will not contribute anything, and some gymnastics will be necessary to shut the generator down when the PW is 100% (or whatever) charged.
Ideally something involving both would happen, so that the generator only ran when the grid was down AND the PW needed charging (AND predicted solar output was inadequate to the task of charging + keeping up with demand). Which could in principle be done with a combination of those two wiring configurations and a little logic (really not much). It still wouldn't be exactly optimal: there are times when the solar could contribute but was disallowed, I think, and also the PW output capacity would limit house consumption. The final point could in principle be resolved by more PW's, and since we're essentially talking about an off-grid(able) house, hopefully loads have been minimized before any of this.
All of this complication could be avoided if they would just add another input to the PowerWalls that directly charges the batteries. If you avoid the interaction of the AC waveform from the generator and the AC waveform of the PowerWall and solar running off-grid, you vastly simplify everything.
um, not at all sure about that. Li Ion batteries require sophisticated charge control. I'm not quite sure what you're suggesting: i.e., if it's a "48V" battery bank, why don't they add an input so you can drop 52V DC (or whatever) across it and charge that puppy up? Is that what you're suggesting?
No, I'm suggesting that Tesla should offer the option of a second AC input which would be connected to a proper internal battery charger for the PowerWall pack. It doesn't even have to be that smart because they could limit it to only charging below 70% SOC and they would not even have to do charge tapering.
So I've been following this thread closely because I'm working on a project to charge my powerwall in the event of a grid outage if the percentage goes below x% and to stop charging at y% where X and y are arbitrary values that can adjusted.
I wrote a program which runs on a raspberry pi connected to the gateway wifi to pull state of charge from the powerwall API. Once the powerwall goes below x% my program starts my generator using a relay. I was going to get my generator wired into my switchboard with the active wire going through the solar energy clamp.
Theoretically, when the generator starts, the powerwall will think it is solar, let it take over the loads and charge using the excess. Once the powerwall has charged to y% my program kills the generator and resets, ready to start it up again if the powerwall drops below x%
Only thing I am unsure of is, will the generator be clean enough so the powerwall will charge (it is a alternator directly connected to a Honda IGX390) and will there be any excess for the powerwall to charge on anyway?
I wrote a program which runs on a raspberry pi connected to the gateway wifi to pull state of charge from the powerwall API. Once the powerwall goes below x% my program starts my generator using a relay. I was going to get my generator wired into my switchboard with the active wire going through the solar energy clamp.
Theoretically, when the generator starts, the powerwall will think it is solar, let it take over the loads and charge using the excess. Once the powerwall has charged to y% my program kills the generator and resets, ready to start it up again if the powerwall drops below x%
Only thing I am unsure of is, will the generator be clean enough so the powerwall will charge (it is a alternator directly connected to a Honda IGX390) and will there be any excess for the powerwall to charge on anyway?
I think there's a pretty good chance you'll kill your generator this way.
Grid connected Solar inverter systems require an AC flow to them to operate, and are required to match the frequency and phasing of that flow.
I have yet to find a home generator that is capable of that, though I suspect some of the inverter driven models can be if you can sort out how the sync cables work on them.
As it is, if I followed your system design correctly, you're going to be connecting your generator to a live AC line that the Powerwall's inverter is dictating a phase timing for, and if the generator isn't perfectly in sync it'll be fighting that phase, just like if you plug your generator into the grid.
Yinn
Active Member
I think the problem is a chicken and egg conundrum based on how I understand it. Someone please jump in and correct me if I'm wrong.
Option 1. Install the Generator ATS before the Powerwall. When the grid cuts out, the ATS is the first to detect this and would kick on the generator. This is how the powerwall would be able to still charge and be tricked into thinking the grid is still functioning. The problem here is if it has too much energy, it would tried to discharge and potentially backeed the generator. There wouldn't be anything to indicate to the generator to shut off until it runs out of fuel.
Option 2. Install the generator ATS after the Powerwall, which is what is recommended I think. The Powerwall would be the first to detect an outage and disconnect itself from the grid. It would continue powering the house and charging from solar. The generator ATS wouldn't actually detect a grid failure until the powerwall runs out of juice because the local grid created by the powerwall is still functioning. Once the powerwall is done, the ATS of the generator then detects an outage and kicks the generator on. But since it has disconnected itself from the powerwall, it can no longer charge it up.
In both situations, the in-line disconnect seems to be problem. By putting either one in front, you eventually exclude it from the new local grid you create. The disconnect and resulting new local grid needs to be inclusive of both the battery backup as well as the generator. The software/hardware needs to be able to simulateanously monitor state of charge and disconnect the generator when it is no longer needed. Which is where @technerdx6000 is trying to go...
I think it's possible as long as the powerwall is prevented from simulateanously providing power while the generator is running. The SMA Sunny Island does the same and is integrated. It allows a genset to be started to charge the batteries, when it hits a low state of charge and disconnects the generator upon full state to allow the local grid to run off of batteries only.
My understanding:
The grid provides a stable reference voltage and frequency, and the Powerwall inverters can operate in grid-tie mode by matching this reference. Likewise the grid-tie inverters on a PV system.
When the grid is down, something needs to provide a stable reference voltage and frequency, and take care of ensuring that all times, power produced exactly equals power consumed, i.e. to balance this mini-grid. The Powerwall inverters can operate in standalone mode to do this, allowing any PV grid-tie inverters to sync to it and generate power. If the solar output is greater than can be handled, the Powerwalls shift their generation frequency outside of the PV grid-tie inverters' sync window to get the PV to shut down.
Now if you want to add a regular generator to this mini-grid, I don't think you can AC-couple the generator. I don't understand enough of the innards of a generator to know how a generator normally balances a mini-grid consisting of it plus loads. But I'm pretty sure however generator balancing works, it won't play well with Powerwalls. How is the load supposed to be divided between the generator and the Powerwalls, and how would that happen?
Perhaps a variant Powerwall could control a regular generator, turning the generator on and off, syncing its output to the generator, and controlling its own power output/consumption to ensure that the generator sees a constant load. The generator would need to provide a stable voltage and frequency reference, I'm not sure that many do; and if there is solar, there would need to be some side-channel way of shutting off the solar when production is too great. Alternatively, a special generator with a grid-tie inverter on it could work with a regular Powerwall, although there would still need to be some mechanism to control how much current the generator injects into the AC-grid.
Probably a better solution would be to DC-couple the generator to one of the Powerwalls. That would mean a special Powerwall that has a second AC-input that would be isolated from the AC mini-grid, and which would be used to charge the batteries only. That would make a DC mini-grid within that Powerwall consisting of the batteries, the Powerwall grid-tie inverter, and battery charger. Within various limits on power levels, a system with one of these generator-enabled Powerwalls could recharge other Powerwalls from the generator via the AC mini-grid.
Cheers, Wayne
The grid provides a stable reference voltage and frequency, and the Powerwall inverters can operate in grid-tie mode by matching this reference. Likewise the grid-tie inverters on a PV system.
When the grid is down, something needs to provide a stable reference voltage and frequency, and take care of ensuring that all times, power produced exactly equals power consumed, i.e. to balance this mini-grid. The Powerwall inverters can operate in standalone mode to do this, allowing any PV grid-tie inverters to sync to it and generate power. If the solar output is greater than can be handled, the Powerwalls shift their generation frequency outside of the PV grid-tie inverters' sync window to get the PV to shut down.
Now if you want to add a regular generator to this mini-grid, I don't think you can AC-couple the generator. I don't understand enough of the innards of a generator to know how a generator normally balances a mini-grid consisting of it plus loads. But I'm pretty sure however generator balancing works, it won't play well with Powerwalls. How is the load supposed to be divided between the generator and the Powerwalls, and how would that happen?
Perhaps a variant Powerwall could control a regular generator, turning the generator on and off, syncing its output to the generator, and controlling its own power output/consumption to ensure that the generator sees a constant load. The generator would need to provide a stable voltage and frequency reference, I'm not sure that many do; and if there is solar, there would need to be some side-channel way of shutting off the solar when production is too great. Alternatively, a special generator with a grid-tie inverter on it could work with a regular Powerwall, although there would still need to be some mechanism to control how much current the generator injects into the AC-grid.
Probably a better solution would be to DC-couple the generator to one of the Powerwalls. That would mean a special Powerwall that has a second AC-input that would be isolated from the AC mini-grid, and which would be used to charge the batteries only. That would make a DC mini-grid within that Powerwall consisting of the batteries, the Powerwall grid-tie inverter, and battery charger. Within various limits on power levels, a system with one of these generator-enabled Powerwalls could recharge other Powerwalls from the generator via the AC mini-grid.
Cheers, Wayne
Yup. DC coupling the generator is the normal approach, a separate line in that gets rectified down to charge the pack, possibly with an automatic start signal.
The problem is the existing Powerwall doesn't seem to have that circuitry. I'm also not sure how you handle multiple Powerwalls in that setup (wire generator to the input in both/all three?)
I understand what you guys are saying here which has made me rethink how I'm going to achieve this. What about if I use a bridge rectifier to change the generator output to DC. So then I'll have 240Vdc output. If I connect that to a grid-tie solar inverter, the inverter will think the generator is a solar string and will sync to the powerwall. The powerwall should recognise the inverter output as solar (if I thread the active wire through the solar clamp) and charge from it. Only issue here is how to govern the generator output at a constant amperage (ideally 15A which would provide 3.6kW).
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