PowerWall Cold Start without Grid Power

[miimura]

If you have more than one Powerwall, you could turn off the breaker to one of them when the whole system reaches 5% and preserve the energy in that one. Then you can let the other(s) run until they shut down. When there is sufficient solar insolation, turn on the breaker for the one with the reserve energy and hope everything starts up again. You could also turn off the breaker(s) that go to your loads so that the solar has time to start generating before you put any significant load on the micro-grid. It would also be useful to verify that there is still AC voltage at the breaker terminals from the Powerwall when it the breaker is in the OFF position.

This would be an interesting variation on the cold start test.

 

[fresnoboy]

The problem with this approach is the house load ends up having to be supported by the residual PW2 reserve, which may or may not be adequate for lasting enough until the solar kicks in. Even then, it could be a cloudy day and not enough power being generated to support the house load.

This is why it would have been nice if the PW2 was a DC supply, and could be used with hybrid inverters designed to support this specific use case.

There are ways to control generator turn on and off separate from sensing voltage from the mains line, but would require greater integration work for the gateway and the ATS or genset..

An alternative model would be for the solar inverters to be on the "line side" of the ATS, but the PWs located at the load breakers. When line goes down, the genset starts, and then the PW's and the loads are supported by the genset and begin to charge. When the PW's reach a different threshold (and are able to support the house loads which it can measure) and when the sun should be out, the gateway switches the ATS back to line, (still isolating the grid at the gateway), shutting down the generator and tries to start the inverters. If the inverters put out enough power to handle load and charge the PW, great. If the PW hits the low water mark again, it turns the inverters off and switches the ATS back to generator and so on.

This would allow the PW to be charged by the genset and run the genset at an efficient speed, and support the house until the it hits low water mark and starts the genset again.

But doing this needs interfacing between the gateway and the ATS.

Thx
mike

 

[miimura]

The problem with this approach is the house load ends up having to be supported by the residual PW2 reserve, which may or may not be adequate for lasting enough until the solar kicks in. Even then, it could be a cloudy day and not enough power being generated to support the house load.

This is why it would have been nice if the PW2 was a DC supply, and could be used with hybrid inverters designed to support this specific use case.

There are ways to control generator turn on and off separate from sensing voltage from the mains line, but would require greater integration work for the gateway and the ATS or genset..

An alternative model would be for the solar inverters to be on the "line side" of the ATS, but the PWs located at the load breakers. When line goes down, the genset starts, and then the PW's and the loads are supported by the genset and begin to charge. When the PW's reach a different threshold (and are able to support the house loads which it can measure) and when the sun should be out, the gateway switches the ATS back to line, (still isolating the grid at the gateway), shutting down the generator and tries to start the inverters. If the inverters put out enough power to handle load and charge the PW, great. If the PW hits the low water mark again, it turns the inverters off and switches the ATS back to generator and so on.

This would allow the PW to be charged by the genset and run the genset at an efficient speed, and support the house until the it hits low water mark and starts the genset again.

But doing this needs interfacing between the gateway and the ATS.

Thx
mike

As I said before in the Generator thread, the current Powerwall 2.0 design will never work well with generators. They need to add an independent generator input that only powers a battery charger. It is important that this input be frequency independent of the rest of the house and Powerwall inverter because most generators are not stable enough (in frequency and voltage) to be used with inverters that are designed to be grid tied. All the hybrid battery inverters I've seen implement generators the way I describe.

 

[fresnoboy]

As I said before in the Generator thread, the current Powerwall 2.0 design will never work well with generators. They need to add an independent generator input that only powers a battery charger. It is important that this input be frequency independent of the rest of the house and Powerwall inverter because most generators are not stable enough (in frequency and voltage) to be used with inverters that are designed to be grid tied. All the hybrid battery inverters I've seen implement generators the way I describe.

Well, if you connected it the way I outlined in my note, you never have the generator on at the same time the solar inverters are connected. You don't actually want that to happen, because the solar could generate enough power to backfeed the generator and fry it. In my scheme, the generator only feeds the PW's and the house load. The generator needs to be off when solar kicks in.

I don't disagree that the most elegant solution is to use a hybrid inverter, or add a generator input to a PW and turn it into a hybrid inverter. But if you are going to do a kludge, there are better kludges than the one Tesla has implemented so far.

thx
mike

 

[miimura]

Well, if you connected it the way I outlined in my note, you never have the generator on at the same time the solar inverters are connected. You don't actually want that to happen, because the solar could generate enough power to backfeed the generator and fry it. In my scheme, the generator only feeds the PW's and the house load. The generator needs to be off when solar kicks in.

I don't disagree that the most elegant solution is to use a hybrid inverter, or add a generator input to a PW and turn it into a hybrid inverter. But if you are going to do a kludge, there are better kludges than the one Tesla has implemented so far.

thx
mike

You're assuming the grid interactive inverter in the Powerwall can tolerate a typical alternator based generator waveform. Tesla's guidance so far indicates that it cannot. In theory they could give guidance regarding inverter generators, but they have not done that yet.

 

[LV_Solar]

Existing Solaredge Solare user, very happy with their system and planning on AC coupling a battery (PW2 or other).

With a recent update to the Solaredge firmware, the inverters support AC coupling and you can define the production based on frequency shift from the battery inverter (in this case a PW2). So the PW2 says hey I'm at 70% full you should slow down the production by changing the frequency to 60.1hz and the Solaredge is already set to know that 60.1 means lets say 80% of production and that 60.2 means 60%, 60.3 means 40%, and 60.5hz means no solar production (because the batteries ont the PW2 are full). All that is configurable.

What I am messing around with is this very issue, what happens when the PW2 is run to exhaustion. I know that there is a reset you can do on it to wake the PW2 back up, but it can aparently also wake because it recieved power via connected solar panels. So why not use your generator or whatever power source to feed the DC "solar" input? The solar input should already be ready to take varied wattage and voltage just like solar panels getting different sunlight levels. You could probably plug an AC to DC power supply into your generator to convert 110v AC to 50v DC and avoid all these issues of making sure the frequecies are stable, backfeeding into the grid, confusing the ATS, etc.

Love to hear other folks thoughts about this.

David

 

[miimura]

What I am messing around with is this very issue, what happens when the PW2 is run to exhaustion. I know that there is a reset you can do on it to wake the PW2 back up, but it can aparently also wake because it recieved power via connected solar panels. So why not use your generator or whatever power source to feed the DC "solar" input? The solar input should already be ready to take varied wattage and voltage just like solar panels getting different sunlight levels. You could probably plug an AC to DC power supply into your generator to convert 110v AC to 50v DC and avoid all these issues of making sure the frequecies are stable, backfeeding into the grid, confusing the ATS, etc.

Love to hear other folks thoughts about this.

David

The way I'm reading your post, it comes across as a little backwards. The solar inverter and Powerwall(s) are AC coupled. Applying DC power to the panel side of the solar inverter doesn't really do anything because it needs the AC waveform to synchronize to. Really what you need to do is bootstrap the AC side and simulate the grid so that the Powerwalls wake up. If you had an inverter generator, you could turn off the main breaker (to ensure no back-feeding the grid) and inject the generator power into the main panel outside the Tesla Gateway. As long as your generator can power all your loads, or you turn off the ones it can't, then the house should start up, the Powerwall(s) and solar inverters should wake up and then you can disconnect and turn off your generator. You just have to be careful that the solar doesn't back-feed the generator before the Powerwall(s) can start absorbing the solar production.

I have also been thinking about a zero emissions way to prevent the Powerwall(s) from shutting down in the first place. The "dark load" of my house with all computers, DVRs and internet running is about 600W. Of course, I could shut down my server and some other stuff, but that's a good base number. I have chosen a list of components from Amazon that will take 12VDC from my EV's AUX battery and feed 600W of AC synchronized 240VAC through the solar CTs so the Powerwall(s) will see it as production. If my Powerwall(s) were getting low during an extended outage, I could turn off any non-essential loads and turn this rig on before going to bed and it would ensure that the Powerwall(s) would not drain and shut down while I was sleeping. My EV could run like this for at least 40 hours before needing recharging. Of course, I could also slowly charge the EV from 120V while the sun is shining during the day too.

 

[LV_Solar]

Miimura - You misunderstood, my thought is not to give DC voltage to the Solaredge Inverter, but give DC (From a generator or similar source) directly to the PW2. They are supposed to have the ability to act as the primarry solar inverter so they must have an input. Your solution of the generator and in effect a double transfer swqitch is complex and franly a bit dangerous for most folks - I want to eliminate that with the use of DC conversion. Generators revving up and down output, frequency sync, stopping to re-fuel are all no longer an issue. The PW2 is supposed to have a feature that automatically sees the solar, lets the power charge the battery and I **believe** re-start the unit at some point.

But lets keep this conversation going, I do not have a PW2 to play with at this point.

David

 

[mongo]

Miimura - You misunderstood, my thought is not to give DC voltage to the Solaredge Inverter, but give DC (From a generator or similar source) directly to the PW2. They are supposed to have the ability to act as the primarry solar inverter so they must have an input. Your solution of the generator and in effect a double transfer swqitch is complex and franly a bit dangerous for most folks - I want to eliminate that with the use of DC conversion. Generators revving up and down output, frequency sync, stopping to re-fuel are all no longer an issue. The PW2 is supposed to have a feature that automatically sees the solar, lets the power charge the battery and I **believe** re-start the unit at some point.

But lets keep this conversation going, I do not have a PW2 to play with at this point.

David

Original PW had a DC input version. PW2s in the US are only AC.

 

[miimura]

Miimura - You misunderstood, my thought is not to give DC voltage to the Solaredge Inverter, but give DC (From a generator or similar source) directly to the PW2. They are supposed to have the ability to act as the primarry solar inverter so they must have an input. Your solution of the generator and in effect a double transfer swqitch is complex and franly a bit dangerous for most folks - I want to eliminate that with the use of DC conversion. Generators revving up and down output, frequency sync, stopping to re-fuel are all no longer an issue. The PW2 is supposed to have a feature that automatically sees the solar, lets the power charge the battery and I **believe** re-start the unit at some point.

But lets keep this conversation going, I do not have a PW2 to play with at this point.

David

Even if you could find a way to charge the Powerwall 2 battery with DC, it won't address the issue of cold starting. The Powerwall 2 is NOT designed to be a "primary solar inverter". It is designed to act as a micro-grid master inverter during a utility outage. I cannot imagine how a Powerwall could "see" a solar inverter when the AC micro-grid is down. The solar inverter won't wake up until after it sees the AC grid waveform.

Anyway, none of this is addressing the fundamental ability of the Powerwall 2 to do a cold start when the utility grid is down and solar would be available. It's really a firmware and safety issue. By safety I mostly mean safety of battery pack to avoid being over-drained by trying to start up when there is no surplus energy to charge with.

 

[LV_Solar]

Ahh there is my misunderstanding. I had read a statement from Tesla mentioning they had all the technical expertice to do their own inverters, and thought they were using the PW2 as their own Solar Inverter (High voltage DC from panels or battery pack is reasonably similar to convert).

 

[miimura]

Ahh there is my misunderstanding. I had read a statement from Tesla mentioning they had all the technical expertice to do their own inverters, and thought they were using the PW2 as their own Solar Inverter (High voltage DC from panels or battery pack is reasonably similar to convert).

A Tesla Energy installation that includes solar and Powerwall will have conventional solar string inverters. If you have shading issues, they will probably use SolarEdge with optimizers. From what I've heard, they otherwise tend to use Delta inverters.

 

[MorrisonHiker]

Our power went out in the blizzard yesterday. Besides the 63 Hz, the Powerwalls did great and powered the house over 20 hours. The storm moved on and I cleared all the snow off the panels but am having the cold start problem today. I called last night and asked if I needed to maintain 6 percent to get things running again. The rep told me that issue had been fixed. Unfortunately, I believed her and found out that when the Powerwalls hit 5 percent they shut off. I was able to get the inverters to synchronize and instantly was producing over 5 kW. I got busy clearing some other panels and noticed everything was off again. I got things going again and things ran fine for half an hour or so. I called and the rep today told me "the whole point of a grid-tied solar system is to shut off when there is no grid power". I didn't want to go there and explained the Powerwalls allow me to power my house when the grid is down. She put me on hold and things started working again..temporarily. I must've tried a dozen times today. I can get things going but then it shuts off after 5 to 30 minutes. I tried doing only one inverter at a time, tried different inverters, etc. but the problem keeps coming back.

I called again and the latest clueless rep told me it was due to clouds. I told her there wasn't a cloud in the sky and hasn't been any all morning. I explained the issue again and she claimed it was snow in the panels. I explained to her that I had removed snow from most of the panels earlier in the day and have been able to produce several kWh throughout the day. She tried claiming again it was clouds even though I mentioned the grid had been down for over 30 hours and read her the errors on the inverters.

The Powerwalls keep powering on randomly every hour or so. The inverters synch and it works for a while but now the Powerwalls have dropped to 2%. I'm generating 5 kW again but expect them to shut off within 30 minutes.

Any suggestions? ETA for grid power is two and a half days. Should I just turn the Powerwalls off to pervent then from draining more?

 

[MorrisonHiker]

Within seconds of posting the above message, the battery got up to 3% and then everything shut off again.

 

[MorrisonHiker]

Now 4% but it shut back down again.

When it is running, it showed the grid is out, the solar production, etc. but when it shuts down, nothing.

 

[miimura]

What was the frequency doing while it was going up and down? Back during my November outage, the solar came up for about 30 minutes after the first 5 minute sleep period, then the frequency went to 63Hz and shut off the solar.

 

[mongo]

Our power went out in the blizzard yesterday. Besides the 63 Hz, the Powerwalls did great and powered the house over 20 hours. The storm moved on and I cleared all the snow off the panels but am having the cold start problem today. I called last night and asked if I needed to maintain 6 percent to get things running again. The rep told me that issue had been fixed. Unfortunately, I believed her and found out that when the Powerwalls hit 5 percent they shut off. I was able to get the inverters to synchronize and instantly was producing over 5 kW. I got busy clearing some other panels and noticed everything was off again. I got things going again and things ran fine for half an hour or so. I called and the rep today told me "the whole point of a grid-tied solar system is to shut off when there is no grid power". I didn't want to go there and explained the Powerwalls allow me to power my house when the grid is down. She put me on hold and things started working again..temporarily. I must've tried a dozen times today. I can get things going but then it shuts off after 5 to 30 minutes. I tried doing only one inverter at a time, tried different inverters, etc. but the problem keeps coming back.

I called again and the latest clueless rep told me it was due to clouds. I told her there wasn't a cloud in the sky and hasn't been any all morning. I explained the issue again and she claimed it was snow in the panels. I explained to her that I had removed snow from most of the panels earlier in the day and have been able to produce several kWh throughout the day. She tried claiming again it was clouds even though I mentioned the grid had been down for over 30 hours and read her the errors on the inverters.

The Powerwalls keep powering on randomly every hour or so. The inverters synch and it works for a while but now the Powerwalls have dropped to 2%. I'm generating 5 kW again but expect them to shut off within 30 minutes.

Any suggestions? ETA for grid power is two and a half days. Should I just turn the Powerwalls off to pervent then from draining more?

Is your solar generation capacity more than your power wall can accept? I'm wondering if the powerwall is forcing the solar to back off/ disable and then an intermittent load (like fridge, freezer, or sump pump) kicks on and browns out the system. 63 Hz indicates the system was over generating. Do your inverters linearly reduce output vs frequency, or are they only on/off?

 

[MorrisonHiker]

Is your solar generation capacity more than your power wall can accept? I'm wondering if the powerwall is forcing the solar to back off/ disable and then an intermittent load (like fridge, freezer, or sump pump) kicks on and browns out the system. 63 Hz indicates the system was over generating. Do your inverters linearly reduce output vs frequency, or are they only on/off?

I thought about that so I tried turning on only one inverter at a time. I planned on turning on another inverter if I could make it to 6 precent but never made it that far. It didn't make any difference how many inverters I tried {1, to or 3} and the inverters have worked fine since July when they were installed. We have 3 inverters: 7.6 kW, 5.2 kW and 5.2 kW. There are Delta Solivia but I don't know the answer to your output vs frequency question. We currently have 3 Powerwalls and 51 325 Watt panels.

I didn't think about unplugging refrigerators. I did notice an issue when the laser printer was plugged in so I unplugged it and most other solidness are already unplugged. The 63 Hz issue was on Wednesday, when the power first went out. The UPS devices complained so I unplugged them out turned them off. Today when the power was on they were showing 60 Hz.

As I mentioned earlier, the phone support was horrible as I knew way more about solar and Powerwalls than the did {at least concerning what I'm seeing}. Tesla is sending someone to troubleshoot tomorrow. The system had worked great so far but this is the first extended grid outage. Now going on 32 hours and perhaps another 24+ hours to go. Oddly enough, my neighbors to the north and east of me all have power. It's just a group of 13 houses that are down in my neighborhood.

BTW, whenever it was working today, the max load was less than 2 kW. The max solar today was less than 6 kW. Normally the Powerwalls can handle 16+ kW without any problem.

 

[wwhitney]

This suggestion is a bit late, but in the morning you could try turning on just your smallest inverter and shutting off all your loads via the breakers (maybe you need to leave on a router to talk to the Powerwalls to check status). If that is stable, then I would suggest there is either a problematic load, or the Powerwalls are limiting their charge rate due to temperature and state of charge. You can check for the latter by turning on all the inverters with no loads to see if it holds; you can check for the former by doing a binary search on your load breakers.

Cheers, Wayne

 

[mongo]

I thought about that so I tried turning on only one inverter at a time. I planned on turning on another inverter if I could make it to 6 precent but never made it that far. It didn't make any difference how many inverters I tried {1, to or 3} and the inverters have worked fine since July when they were installed. We have 3 inverters: 7.6 kW, 5.2 kW and 5.2 kW. There are Delta Solivia but I don't know the answer to your output vs frequency question. We currently have 3 Powerwalls and 51 325 Watt panels.

I didn't think about unplugging refrigerators. I did notice an issue when the laser printer was plugged in so I unplugged it and most other solidness are already unplugged. The 63 Hz issue was on Wednesday, when the power first went out. The UPS devices complained so I unplugged them out turned them off. Today when the power was on they were showing 60 Hz.

As I mentioned earlier, the phone support was horrible as I knew way more about solar and Powerwalls than the did {at least concerning what I'm seeing}. Tesla is sending someone to troubleshoot tomorrow. The system had worked great so far but this is the first extended grid outage. Now going on 32 hours and perhaps another 24+ hours to go. Oddly enough, my neighbors to the north and east of me all have power. It's just a group of 13 houses that are down in my neighborhood.

BTW, whenever it was working today, the max load was less than 2 kW. The max solar today was less than 6 kW. Normally the Powerwalls can handle 16+ kW without any problem.

The laser printer has a big heater in the fuser, but if you weren't printing, it was off.

From the manual I found, those inverters do not do generation shedding, so if the PW shifts the frequency for any reason, they'll cut off (59.3-60.5 operational). Their displays will show what they are seeing. PW likely does not react instantaneously (esp going from discharge to charge), and the inverters trip out in ten cycles or less.