Powerwall2 - over voltage problem

[Jetrangermike]

Hi,
A few months ago, we installed a Powerwall2 with 6.5Kw of Solar with enphase microinverters.

Under low load from the house conditions, the system as a whole operates as predicted. However, when we have a high (> 4Kw) load from the house the Powerwall seems to be tripping the Over voltage (> 255V in Australia) setting on the microinverters. This is happening pretty much every day when our inefficient hot water system cuts in and draws just under 4Kw, but also happens if we need to turn on the airconditioning during the day.

I've been doing some investigation and have raised the issue with the installer (they are being helpful, but it's pretty clear they aren't sure what is going on). Via the Powerwall2 API I can see that just prior to the hot water system kicking in the voltage as the solar is charging the Powerwall is about 247-248V, but as soon as the hot water system kicks in the voltage jumps to around 255-256V (hence the microinverters start shutting down with an over voltage error).

Has anybody had this problem? Any suggestions for solutions? Is there any way of reducing the Powerwall starts discharging at?

Any help would be greatly appreciated!

 

[power.saver]

When the PW is connected to the utility grid, it follows the grid voltage. It only sets the voltage when the grid is down.

If this is happening while you are connected to the grid, you may have a wiring problem with your water heater. You could try turning off the PW and just have solar feeding the grid. Use a volt meter and check the line voltage. Then turn on your water heater and see if the voltage rises. If so, it's not the PW causing the problem.

Do you have single phase or 3 phase power?

 

[Jetrangermike]

Thanks power.saver - it is a good thought in terms of turning off the PW and seeing what happens to the voltage.

Whilst on-grid, with the heavy load from the house I could see the voltage was hitting about 255V (as seen on the PW gateway API), with the PW supplying just under 5Kw to the house and the solar delivering about 3.5kw at the time. So, then I went out and flicked the switch on the powerwall - and then relooked at the PW gateway API and hey presto the voltage had dropped to about 246-247V. With the grid supplying the power that the PW was before I turned it off.

To answer your other question - we have 3-phase power to the house with the PW and Solar only setup on 1 phase. The hot water system has been changed to run off of the same phase as the PW and Solar, because I thought that this could have been causing the problem, but this hasn't made any difference.

BTW, I simplified the scenario slightly by just talking about the hot water system, we also have the issue when we run the air-conditioner (which is 3 phase) and sometimes if we have a lot of load from the house such as clothes dryers and other things adding up to a heavy load.

Given that it seems to be the PW that is driving up the voltage, I'll go back to the installer/Tesla to see if we can do some more diagnosis.

 

[power.saver]

Those are interesting results. I would have your installer look very carefully at the phase connections, especially between the PW and your utility feed. If there is too much resistance it could cause the voltage to rise, especially if there is a significant imbalance in the loads on each of the 3 phases.

 

[PBBear]

I've been doing some investigation and have raised the issue with the installer (they are being helpful, but it's pretty clear they aren't sure what is going on). Via the Powerwall2 API I can see that just prior to the hot water system kicking in the voltage as the solar is charging the Powerwall is about 247-248V,

Where are you based - which state? city, regional or rural?

Your first problem is that your normal grid voltage is too high. In Australia, the grid is supposed to be supplying at 230V, reduced from 240V almost 20 years ago - see When voltage varies - Electrical connection. If your normal grid voltage is sitting at 247-248, it would be worth contacting your electricity supplier and reporting it, and asking them to dial it down to 230V at the transformer. After that, the increase when the hot water kicks in shouldn't go over the threshold.

Your situation is odd - usually the voltage *drops* as the load increases. FWIW, my grid in Sydney is still stubbornly at 240V bobbling around up to 243V - but on really hot days when clearly all the neighbours are running the aircon hard, the grid pulls down to under 230V, then recovers when the aircons are turned off. I would normally expect your grid voltage, if anything, to drop when the hot water switches in , not raise.

 

[JohnRatsey]

On a 3 phase system voltage drops in one or two phases due to high loading can cause a voltage increase in the remaining phase. See here for an explanation. The utility may need to rebalance the local distribution system.

 

[Jetrangermike]

Thanks for the replies ... we are near Mt Barker in the Adelaide Hills. We have logged a job with SA Power Networks, typically they need about 3 months to go from running their data loggers through to actually changing the tap settings on the local transformer. Looking at the grid voltage at non-sunny times it is typically down to about 239-240V - so who knows whether they will will want to change it by much.

In terms of the unbalance between the 3-phases, I know my installer did do some testing at one stage and the voltages across the 3-phases were pretty even, if anything the phase with the hot-water system and the PW/Solar etc. was 1 or 2V lower than the others at the time of testing. And if it was an imbalance as described, wouldn't turning off the PW make the problem worse, not better? ie. the voltage only increases when the PW is discharging.

I could understand if the hot-water system was on a different phase to the PW why it could cause an imbalance across phases, but in my case it's running on the same phase, and given the PW output is just matching the remaining load from the house, there shouldn't be any power being drawn (or exported) to the grid.

Thanks for the help - i'll go back to the installer and chase them up about the issue.

 

[PBBear]

Via the Powerwall2 API I can see that just prior to the hot water system kicking in the voltage as the solar is charging the Powerwall is about 247-248V, but as soon as the hot water system kicks in the voltage jumps to around 255-256V (hence the microinverters start shutting down with an over voltage error).

I'd be getting the HWS and the circuit between switchboard and HWS checked by an experienced sparky. Mains voltage should not change when the HWS kicks in. If it is kicking up, that could indicate your wiring to the HWS is constricted/corroded/degraded and has significantly increased resistance. May have always been like that, but you'd normally never know until installing an accurate power monitoring system (which just happens to have a battery attached to it).

 

[ROXiDE]

Thanks for the replies ... we are near Mt Barker in the Adelaide Hills. We have logged a job with SA Power Networks, typically they need about 3 months to go from running their data loggers through to actually changing the tap settings on the local transformer. Looking at the grid voltage at non-sunny times it is typically down to about 239-240V - so who knows whether they will will want to change it by much.

I'm not that far from you and have had huge issues with grid voltage. To the point of electrical devices, LED lights and appliances blowing up. We've been pressuring SAPN for the last year to sort it and finally, they're proceeding with some major works here that they say will be done by the end of April. The highest grid voltage recorded here was 291. Yes that's correct. 291! We're only on single phase.

We've had three rounds of poly-logging on both our sub-board and the grid and also had onsite single tests performed by their techs. We've had tap settings changed and been shifted to a different phase, but the problem still exists.

SAPN constantly blamed the huge influx of solar systems but we were seeing huge grid voltages at night time, or very early in the morning as well.

We're running a 10kW solar system and 1 x Powerwall2. Being that the Powerwall shuts itself off when grid voltage exceeds 260, we haven't had a huge amount of use out of it since its install 11 months ago. It's been mostly switched off to avoid damaging it.

 

[Jetrangermike]

After many months of going back and forth with the installer and Tesla - we are still no closer to resolving the issue.

So far, we've eliminated it being a grid voltage issue (albeit on a bad day the grid voltage can get to the high 240s), but what is happening as soon as the Powerwall starts discharging rapidly (ie. 4Kw or higher) the voltage in the house immediately (within a few seconds) jumps by about 8V. Tesla are able to plot the voltage throughout the day and you can clearly see on their plots the correlation between the voltage jump and the discharging of the Powerwall.

Tesla tried to blame the installation and the resistance in the wires, so the Installers electrician came out and ran a heap of tests and sent back to Tesla, which showed that the installation is fine.

The turnaround for Telsa support is terrible! ie. if I don't keep chasing them, weeks pass by with zero response from them.

I am over it - if they can't provide some sort of resolution, my next step has to be to go to consumer affairs. Anybody had any experience with this?

 

[Musterion]

The last time I called Tesla Powerwall North America support for an urgent problem, they could not solve my problem and told me that they didn’t have enough coverage for anyone knowledgeable to help me in less than one day, so they asked me to call back at night when the Australian support team wakes up and comes on line. I wish you good luck — apparently any improvement in Australian support you stir up is going to help me directly!

 

[Dave EV]

So far, we've eliminated it being a grid voltage issue (albeit on a bad day the grid voltage can get to the high 240s), but what is happening as soon as the Powerwall starts discharging rapidly (ie. 4Kw or higher) the voltage in the house immediately (within a few seconds) jumps by about 8V. Tesla are able to plot the voltage throughout the day and you can clearly see on their plots the correlation between the voltage jump and the discharging of the Powerwall.

Tesla tried to blame the installation and the resistance in the wires, so the Installers electrician came out and ran a heap of tests and sent back to Tesla, which showed that the installation is fine.

This is really curious - I'm at a loss as to what would allow the Powerwall to only boost the house voltage +8V without also discharging significantly to the grid. Really would want to get a oscilloscope on the mains when the issue occurs.

Honestly, my first assumption would be some sort of install or grid issue as well.

What tests were run and what were the results?

 

[Dan123]

It seems like the voltage increases when the Powerwall supplies power. Maybe there is something wrong with the cable between the grid and your meter, or with the meter itself.

Or maybe the CT monitor is not working correctly, and the Powerwall thinks that it needs to supply more power than is needed.

 

[D123]

Hi, I have exactly the same setup, and exactly the same problem. 3 phase PW2 and single phase solar. Measured voltage by gateway2 goes >250 with 3 phase aircon on (and PW has limited output 3-4kW). Switch battery off and gateway reports no Voltage rise. Baseline Grid voltage around 245.

Did you have any joy?

 

[ctslc]

I've seen this sort of thing happen to a solar inverter connected via a rather long cable to the utility connection: When the inverter produced more power, the voltage at the inverter went up, and the system tripped out on over voltage. In that case, the problem was obvious: Excess resistance on the lead between the solar inverter and the connection to the utility - in this case, due to a failing splice.

In this case, the voltage rise depended on where the largest load was: If it had been on the same sub-panel as the inverter, there would never have been an overvoltage condition - but if the "nearby" load was low and was, instead, more distant (e.g. at the connection to the utility at the end of the long interconnect) then the inverter would trip on overvoltage - hence the condition where different loads of the same magnitude would cause very different results.

I would expect a similar thing to be happening in your case: The more current is required to provide, the greater the I*R loss in the wiring.

At first, it seems counterintuitive that a higher load can cause a higher voltage, but a lossy circuit (wire sized too small, excessively long run, losses due to loosening connecting screws, an inferior circuit breaker that is getting warm - or some combination of these) that may be conducting the bulk of current can certainly do this. Presumably, when the load is being fed back into the grid, this may not happen, but higher loads in the house may cause current to flow from the inverters along a slightly different path with higher overall resistance. Since it sounds like you may 3 phase, a terrible phase imbalance can contribute to excess loss.

The only way that the problem will be properly identified - and how I identified it - is that, on the verge of this happening (e.g. a high enough load to cause a voltage rise, but not enough to result in a trip-out) there are accurate, simultaneous measurements of voltages (and possibly current) on all of the conductors (including neutral) at the inverter(s), the main electrical bus, and at the highest loads - and the remedy will likely be shortening a circuit's run and/or using heavier conductors.

I later talked to an electrician that had been involved in the original wiring (that is, the ones that hadn't properly tightened the clamp that caused the problem - which ended up burning up a chunk of wiring and making a mess when the junction box was flooded with corrosive, hydrogen chloride gas) but I could not seem to explain the problem as he, too, presumed that a higher load would always result in a lower voltage due to I*R drop.

CT