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PowerWall 2 Interface with a Generator

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I'm glad I found this very timely discussion. We are finalizing plans for a middle-sized remote home with 7kW on a solar carport, and a Powerwall 2 to permit us to weather frequent and sometimes lengthy grid outrages. But the location (with a high forested horizon and frequent clouds) limits solar production during the winter months when outages occur. So I'm curious about how to integrate a 7,500-Watt (LP) Standby Generator with Automatic Transfer Switch. The unit will run at 50% output, well within the charging capacity of a single PW2.

I understand that partial solution is being piloted with ten folks, but the other half of my "want" is for the propane-powered generator to recharge the Powerwall 2. Is anyone else pursuing that capability with Tesla?
 
The ability to charge the PW from the generator was something I fully expected when I agreed to purchase the PW, not to mention, simply being able to use the generator at all in the system! I would settle for a system that would automatically fire up the generator if the load exceeds the PW's discharge capacity and/or the battery level approaches zero and wait for solar to recharge the batteries. Although, as I typed that last sentence, it seemed pretty silly since competitive system will do it. It is a dilemma.
 
One of the things that is really inefficient is running the generator overnight with minimal load, just to keep the fridge and a few other light loads running. That is why the ability to use the generator for shorter periods of time with the PWs as a load makes so much sense. It is hard to believe that this capability will not happen at some point. The question then is how much will I need to spend to redo the configuration of grid/solar/generator/house interconnect, and will the PW I have now (paid for, but not installed) support it?
 
I'm glad I found this very timely discussion. We are finalizing plans for a middle-sized remote home with 7kW on a solar carport, and a Powerwall 2 to permit us to weather frequent and sometimes lengthy grid outrages. But the location (with a high forested horizon and frequent clouds) limits solar production during the winter months when outages occur. So I'm curious about how to integrate a 7,500-Watt (LP) Standby Generator with Automatic Transfer Switch. The unit will run at 50% output, well within the charging capacity of a single PW2.

I understand that partial solution is being piloted with ten folks, but the other half of my "want" is for the propane-powered generator to recharge the Powerwall 2. Is anyone else pursuing that capability with Tesla?
Per my advisor, the generator will NOT charge the powerwall. That was something they were pretty clear about.
 
Per my advisor, the generator will NOT charge the powerwall. That was something they were pretty clear about.

Really? What's the point then? You might as well skip the powerwall and run on the genset entirely.

A fronius or Storedge system will do all this already - you just have to use DC batteries and not a powerwall.

It's like Tesla is going out of it's way to not solve this problem. If they had kept producing the DC version, it could have plugged into these other systems like an LG battery.

You have to wonder who is running product engineering for the Powerwall.
 
Presumably if Generator could charge the Powerwall you could size the generator for the power needed averaged over 24 hours, rather than peak power, and then run the generator 24/7 during power outage and have the Powerwall handle peak loads.

But I've no idea if that actually represents a practical reduction in generator size, such that it would save money?

We have a generator socket on the outside of the house, in case the grid goes down for a prolonged period (10 second outage happens quite often, but being down for hours happens maybe once a year (scheduled) and once a decade we have a storm which takes parts of this area out for anything up to a week). My generator is small and we limp along with essentials only, but with a powerwall I could perhaps use occasional higher-power devices. We have Solar too (not had a generator-event since that was installed), but my understanding is that my Solar will also work on the Generator (in UK power is needed for Solar to work so it doesn't back-feed the grid - when linesmen may be working on it :eek: - and as such my generator solution has a change-over switch which isolated the grid).
 
Really? What's the point then? You might as well skip the powerwall and run on the genset entirely.

<snip>

You have to wonder who is running product engineering for the Powerwall.

fresnoboy, there are NEM eligibility requirements from the utility....for example, to become and remain an NEM customer, a non-renewable source is not allowed...Sounds like Tesla is trying to respect those requirements...

Net Energy Metering Program | San Diego Gas & Electric
 
I'm glad I found this very timely discussion. We are finalizing plans for a middle-sized remote home with 7kW on a solar carport, and a Powerwall 2 to permit us to weather frequent and sometimes lengthy grid outrages. But the location (with a high forested horizon and frequent clouds) limits solar production during the winter months when outages occur. So I'm curious about how to integrate a 7,500-Watt (LP) Standby Generator with Automatic Transfer Switch. The unit will run at 50% output, well within the charging capacity of a single PW2.

I understand that partial solution is being piloted with ten folks, but the other half of my "want" is for the propane-powered generator to recharge the Powerwall 2. Is anyone else pursuing that capability with Tesla?
If I was in this situation and had a hard deadline to get the system installed, I would plan for a different system that is designed for generator use. Hybrid inverters from Schneider and Outback power can handle generators elegantly, but they need 48VDC nominal battery packs. I have not checked, but the LG battery solution may be good for this application. When your deadline comes, at least you will have a good solution ready to go if Tesla doesn't work out.
 
fresnoboy, there are NEM eligibility requirements from the utility....for example, to become and remain an NEM customer, a non-renewable source is not allowed...Sounds like Tesla is trying to respect those requirements...

Net Energy Metering Program | San Diego Gas & Electric

This makes no sense to me. The only time the genset is turned on is when the AC power is down, and therefore there is no issue with the generator sending power to the grid in that circumstance. Are you saying the utility would be worried about people running their diesel genset and generating power at a huge price premium to the grid price by disconnecting from the live grid, and charging the battery with genset power and selling it back to the grid after the genset transfer switch is back in the grid position? That's just silly.

There are plenty of companies with hybrid inverters selling solutions with DC batteries attached to net metering systems in California. Call up an installer who sells these, and they will tell you its not a problem with NEM conditions.

Maybe Tesla is trying to get you to buy a bunch of powerwalls so you never have to use a generator, but with all the natural diasters happening that can cause multi-day outages, a genset is really the only practical way to make sure you have reliable power.

A combo system with one or two PW's would be ideal. Diesel generators are horribly inefficientunder about 15-20% of their max power rating. If you have a lot of HVAC power needs, you can easily end up with an oversized generator, so charging a powerwall during an extended outage and having the genset disconnected at night if the HVAC can be off would really help keep it in its sweet spot, and reduce a lot of emissions as well.

Like I said, I have no idea what product management at tesla is trying to do with the Powerwall. Maybe a new Powerwall 3 is coming with DC support that would plug into the hybrid inverters...
 
Doing my install today/tomorrow. Quite complicated since I have a lot of things going into my meter (generator transfer switch, EV charger, sprinkler system, etc..). My installer explained to me that the failover in case of power outage is to default to power wall, once that PW is depleted, then the generator kicks in. Once the power is restored via the grid, I would manually have to flip the switch to re-engage the PW--so not completely automatic
 
Doing my install today/tomorrow. Quite complicated since I have a lot of things going into my meter (generator transfer switch, EV charger, sprinkler system, etc..). My installer explained to me that the failover in case of power outage is to default to power wall, once that PW is depleted, then the generator kicks in. Once the power is restored via the grid, I would manually have to flip the switch to re-engage the PW--so not completely automatic

So the generator isn't actually interacting with the Powerwall, then? It sounds like this is just stages of backup - the generator doesn't come on until the PW is drained, and doesn't charge the PW, just carries the loads?
 
Like I said, I have no idea what product management at tesla is trying to do with the Powerwall. Maybe a new Powerwall 3 is coming with DC support that would plug into the hybrid inverters...
If Tesla wants to properly support a generator, they need to add an isolated battery charger to the PowerWall along with a dry contact output to start the generator. The generator should connect to the battery charger only and extend the runtime beyond what the solar + batteries or batteries only can provide. The only downside to this setup is that the peak output is still limited to what the PowerWall inverter(s) can handle.
 
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If Tesla wants to properly support a generator, they need to add an isolated battery charger to the PowerWall along with a dry contact output to start the generator. The generator should connect to the battery charger only and extend the runtime beyond what the solar + batteries or batteries only can provide. The only downside to this setup is that the peak output is still limited to what the PowerWall inverter(s) can handle.

The only other option real is to AC couple - to have the generator equipped with an inverter that works like the micro inverters for solar panels - finding the existing AC signal from the PW and adding to it - but then you'd still need to manage when the PW is charging from the generator.
 
So the generator isn't actually interacting with the Powerwall, then? It sounds like this is just stages of backup - the generator doesn't come on until the PW is drained, and doesn't charge the PW, just carries the loads?
That is correct. First half of power walls installed today (physical install plus moving lots of panels around). Tomorrow is hooking up the power wall to the panel+testing. One further update, they had an engineer out checking on everything...I spoke to him and he said that TOU update won't come out for a few more months
 
I don't understand this. If the powerwall is set to charge from the grid, it would seem it could take power from the generator as well. I assume they turn off the solar when the genset is running to avoid sending power back to the genset and frying it. But if that's true, then once the PW is drained, it can't be charged by the solar or by the genset, so it's down for the rest of the outage? That doesn't seem useful.

Or do they allow the solar to charge the PW while the genset is running and powering all the loads? That seems pretty hard to do too in an AC coupled system.

Would be really be interested to see how they wire all this up.
 
I don't understand this. If the powerwall is set to charge from the grid, it would seem it could take power from the generator as well. I assume they turn off the solar when the genset is running to avoid sending power back to the genset and frying it. But if that's true, then once the PW is drained, it can't be charged by the solar or by the genset, so it's down for the rest of the outage? That doesn't seem useful.

Or do they allow the solar to charge the PW while the genset is running and powering all the loads? That seems pretty hard to do too in an AC coupled system.

Would be really be interested to see how they wire all this up.

You can't simply connect the typical generator to an active AC line - if the voltage, frequency, *and* phase aren't a nearly exact match for the grid when connected, it'll fry the generator.

Most battery based inverter systems that allow generator inputs solve this by having a separate input for the generator that isn't connected to the grid at all, and rectifying the generator power to DC and then connecting it to the battery bus and inverting that back to AC to carry the loads.

The other option is to have a generator that can match the grid - generally by having a true sine inverter internally.
 
With an off grid house, the battery charger is just another power consumer. If the total load exceeds the generators ability to maintain voltage, the system trips off.

The solar inverter matches the frequency of the generator, just as it does with mains power. So at a fundamental level here there is nothing new. Generator output simply replaces main power as and AC source.

That said, controlling all this with the user making choices as to priorities becomes complicated. Tesla starting with simple rules (empty battery first, then run the generator) is understandable. A highly flexible system may take a couple years. I doubt that the current generation of inverters and chargers will allow a fully flexible system. There will probably be edge safety and performance issues that need to be solved with new hardware.

In particular, seamless transition between modes is complicated when a generator is put in the mix.