Confusing results with Powerwall 2

[ROXiDE]

Earlier this year we had a 10kWh solar system installed along with a Powerwall 2. After the install was complete, we had our smart meter installed. Recently, we received a huge electricity bill on top of the amount we'd already paid. It turns out that the initial amount was an estimate and our smart meter finally uploaded our usage to the power company.

I'm a tad confused!

According to our electricity company portal (we can log in and see what our smart meter has reported to them), we used 20kWh of electricity from the grid, yet the Tesla app states we only used 1kWh on Saturday (for example). Every day is pretty much the same. The power company states we used 10-20kWh from the grid, whilst the Tesla app reports 0.3 - 1kWh for the exact same period. We've only just been able to access the power company portal in the last week due to their being an issue at their end with that hence this discovery only just being made.

I've managed to pinpoint usage from the grid being from around midnight to 3-4am. I believe this is the electric hot water system. Each morning our Powerwall has anywhere between 30-60% (this morning was higher), charge left, so I don't understand why the hot water service draws from the grid and not the PW2. The peak draw our hot water system does is 4kWh, so it's not like it's beyond the PW2's capabilities to supply it. The highest I've sen it go is around 1.7 to 1.9kWh. Interestingly, the amounts we export match exactly on both the Tesla app and the power company portal.

I'm currently in a roundabout with the power company (is the smart meter wrong, or showing what's being used from the PW2 in off-peak times as being grid usage in error, or is it wired wrong?), the installers (has our system been wired incorrectly so the PW2 doesn't recognize our hot water system), and Tesla (they've checked our battery remotely and stated it's working fine, but are they able to check if it's powering off peak services like our hot water remotely?).

To give you an idea, we live in South Australia. Apparently, we do have some of the highest electricity prices in the world (40c/kWh), but our bill since the PW2 was installed in March of this year, was nearly $3000.00 (yes, three thousand), dollars. We live in a small, 3 bedroom house that was rebuilt with the most energy efficient appliances just prior to the install of our solar / battery system. Personally, I can't see that a hot water service could use so much electricity in that time and I believe there's an issue with the calibration of the smart meter and how our PW2 is set up (it seems to be ignoring the hot water service). I've been told that our hot water system is on the same circuit as the rest of the house, so is it an issue between peak and non peak times / charges that's not being recognized

I have our PW2 set to Self-Powered with a backup level of 15%.

Honestly, it's been a circus trying to work this out. Has anyone experienced an issue like this before?

 

[Visitant]

Are you on 3 phase power? If so, it's possible that the CT clamps are configured incorrectly. We had this issue when the PW2 was installed and the installer tried 2 more times before getting the configuration correct! (In South Australia too, by the way).

 

[neroden]

A full wiring diagram would be helpful to figure out what's going on. How is the Powerwall connected to the household loads?

The ultimate layout would be to have the grid *only* feed the Powerwall, with the Powerwall feeding the rest of the house -- this would be pretty much foolproof. But I suspect that's not the design. If the Powerwall is sort of "in parallel", there may be some situation where there's a draw from the house but the Powerwall isn't recognizing this and isn't discharging. You could probably prove this if it's the case.

I have no idea how your "smart meter" is set up. I'm lucky enough to have good old fashioned "stupid meters" here in the US, but here even "smart meters" basically just record electricity flow "across the meter" and send it to the power company -- do you know if yours is doing anything fancier than that?

Does the meter have a live, site-readable measurement? How about the Powerwall, and the hot water heater? You could stay up late and watch the meter to see if it's ticking forward, see if the hot water heater is actually on, and see if the Powerwall is actually operating at that time.

If the hot water heater is running and the Powerwall is not discharging, since it's supposed to, you either have an installer issue or a PW2 configuration issue, and *the installer owes you money*.

If it is discharging, or if the hot water isn't drawing power, but the meter is still moving forward, then you have a defective meter issue and the utiilty company owes you money.

But it looks likely to be a misinstalled or misconfigured Powerwall, because Google is showing me other reports of the self-powered option not working right:

Tesla

 

[ROXiDE]

Are you on 3 phase power? If so, it's possible that the CT clamps are configured incorrectly. We had this issue when the PW2 was installed and the installer tried 2 more times before getting the configuration correct! (In South Australia too, by the way).

We're on single phase. I was able to verify that recently due to a high grid voltage issue that caused our inverter to shut down. That's been resolved via SA Power Networks now though.

 

[ROXiDE]

A full wiring diagram would be helpful to figure out what's going on. How is the Powerwall connected to the household loads?

The ultimate layout would be to have the grid *only* feed the Powerwall, with the Powerwall feeding the rest of the house -- this would be pretty much foolproof. But I suspect that's not the design. If the Powerwall is sort of "in parallel", there may be some situation where there's a draw from the house but the Powerwall isn't recognizing this and isn't discharging. You could probably prove this if it's the case.

I have no idea how your "smart meter" is set up. I'm lucky enough to have good old fashioned "stupid meters" here in the US, but here even "smart meters" basically just record electricity flow "across the meter" and send it to the power company -- do you know if yours is doing anything fancier than that?

Does the meter have a live, site-readable measurement? How about the Powerwall, and the hot water heater? You could stay up late and watch the meter to see if it's ticking forward, see if the hot water heater is actually on, and see if the Powerwall is actually operating at that time.

If the hot water heater is running and the Powerwall is not discharging, since it's supposed to, you either have an installer issue or a PW2 configuration issue, and *the installer owes you money*.

If it is discharging, or if the hot water isn't drawing power, but the meter is still moving forward, then you have a defective meter issue and the utiilty company owes you money.

But it looks likely to be a misinstalled or misconfigured Powerwall, because Google is showing me other reports of the self-powered option not working right:

Tesla

Thank you for your helpful reply!

I'll check tonight and see if I can interpret the meter whilst the hot water is heating (I've been working night shift so it's been a bit tricky to manually check). Speaking with the people who own the electricity network here in South Australia (SA Power Networks), they actually admitted that they've had a reasonable amount of issue with new smart meters either incorrectly reporting usage, or vastly exaggerating it, hence me being unsure if this issue relates to the new meter, the PW2 or both.

As for grid feed only type setup, our PW2 doesn't appear to get any power from the grid. It charges via our solar only.

 

[ROXiDE]

Here's an example from yesterday showing the same time-period.





Here's the usage over a couple of days showing grid use early in the morning.

 

[BJReplay]

Probably incorrect CT placement. If you have hot water, you may have originally had two dumb (basic / dial) meters - one for house load and one for controlled load hot water. If these have been replaced with one smart meter and a time switch, it is possible that there are two active cables from your meter to your switchboard - one for the house, and one for hot water (they won't have rewired when they replaced the meter), and the CT clamp for the powerwall is around the house load meter, not the hot water. If so, the installer needs to come out and install a second CT clamp around the hot water (assuming you do want to discharge your powerwall into the hot water).

But if you do, you'll drain your powerwall pretty quickly into the hot water load. Your load on Saturday was much more than the capacity of your powerwall.

If I were you, I'd concentrate on ensuring that you are on the correct tariff, and your hot water is being charged at off peak rates. $3000 for a quarter seems like you are paying peak rates for the hot water heating; I would have thought it should be a lot less. My guess is that the retailer has stuffed up (or the network - not putting you on the right tariff), and you'll get this resolved quickly by talking to the retailer and saying "I don't want to involve the ombudsman, but unless you can sort it out quickly, I guess I will have to"

 

[ROXiDE]

Probably incorrect CT placement. If you have hot water, you may have originally had two dumb (basic / dial) meters - one for house load and one for controlled load hot water. If these have been replaced with one smart meter and a time switch, it is possible that there are two active cables from your meter to your switchboard - one for the house, and one for hot water (they won't have rewired when they replaced the meter), and the CT clamp for the powerwall is around the house load meter, not the hot water. If so, the installer needs to come out and install a second CT clamp around the hot water (assuming you do want to discharge your powerwall into the hot water).

But if you do, you'll drain your powerwall pretty quickly into the hot water load. Your load on Saturday was much more than the capacity of your powerwall.

If I were you, I'd concentrate on ensuring that you are on the correct tariff, and your hot water is being charged at off peak rates. $3000 for a quarter seems like you are paying peak rates for the hot water heating; I would have thought it should be a lot less. My guess is that the retailer has stuffed up (or the network - not putting you on the right tariff), and you'll get this resolved quickly by talking to the retailer and saying "I don't want to involve the ombudsman, but unless you can sort it out quickly, I guess I will have to"

Thanks for your reply. It'll help me a lot when speaking with the installers!

I should have shown the solar amount for Saturday. It was around 35Wh (we were home and had reverse cycle AC on, hence the small export amount). The house happily runs off of that, so we generally end up with a fully charged Powerwall that really only see's minimal draw prior to us going to bed, so although we did use 19kWh, that was easily covered by solar generation. Having said that, these results will be seasonal and I do understand that things wouldn't be the same in Winter. I'd be more than happy to switch the hot water service over to the Powerwall though. Generally, each morning (this time of year), we have more than 50-60% charge left in it.

EDIT: today we exported 30kWh. That's around the average amount for a weekday, in good conditions. I make sure to have any washing etc done during the day. That way it doesn't impact on the battery come evening time. I was hoping that any extra electricity the hot water unit would require from the grid would be covered by our FiT (currently 18.5 cents).

 

[neroden]

Probably incorrect CT placement. If you have hot water, you may have originally had two dumb (basic / dial) meters - one for house load and one for controlled load hot water. If these have been replaced with one smart meter and a time switch, it is possible that there are two active cables from your meter to your switchboard - one for the house, and one for hot water (they won't have rewired when they replaced the meter), and the CT clamp for the powerwall is around the house load meter, not the hot water. If so, the installer needs to come out and install a second CT clamp around the hot water (assuming you do want to discharge your powerwall into the hot water).

Yeah, if the Powerwall can handle having two pairs of CT clamps.

Or rewire the hot water into the house feed so that the CT clamp is behind the point where they split. This is why an as-built wiring diagram would be helpful in understanding this.

If I were you, I'd concentrate on ensuring that you are on the correct tariff, and your hot water is being charged at off peak rates. $3000 for a quarter seems like you are paying peak rates for the hot water heating; I would have thought it should be a lot less. My guess is that the retailer has stuffed up (or the network - not putting you on the right tariff), and you'll get this resolved quickly by talking to the retailer and saying "I don't want to involve the ombudsman, but unless you can sort it out quickly, I guess I will have to"

 

[ROXiDE]

I've found out a bit more so I thought I'd post an update.

According to our installer, our PW2 is not connected to the hot water service. This is due to that being on a different circuit to allow for cheaper, off peak electricity prices. This would go some way to explaining the difference between the Tesla apps reported usage and our power suppliers reported usage however, things still don't add up even taking that into account.

Our electricity retailer has tried numerous times to get SA Power Networks to perform an on-site smart meter check (because really, our issues seemed to coincide with the installation of that), but due to forms being sent from our retailer to SAPN not being filled out exactly correct, SAPN keeps rejecting the request. Our power retailer is now organising to send one of their own techs out to check the meter. They themselves have stated that our usage seems to be quite incorrect and seem to think there's an issue with either how the meter was wired, or its calibration (a few days in August we apparently used 50kWh from the grid whilst we were away on holidays and the house was empty!). This will occur in the next 10-15 days so hopefully, we're getting closer to discovering what's actually going on.

Ultimately, this no longer appears to be an issue with our solar system or PW2 however, we won't know for sure until the smart meter has been thoroughly checked.

I'd really like to thank everyone above for their helpful suggestions. They all went a long way towards us being able to argue our case with retailers and also, gave me a better understanding of how PW2 systems work (CT clamps etc), when speaking with the installers. Considering we've been chasing this issue for a few months now it's looking like we're finally getting somewhere.

Thanks again all!

 

[neroden]

If it's legal, I'd guess that in your situation you want your hot water connected to the Powerwall & the solar. (And actually, you want it on a timer to run at midday, so that it's using the solar directly.) Even if it requires changing your rate plan.

Sounds like you should be at nearly 100% self-consumption; selling power to the grid and then buying it back to heat water is almost certainly worse than using it yourself to heat water. Unless you have an extremely high feed-in tarriff on your exported power.

 

[ROXiDE]

If it's legal, I'd guess that in your situation you want your hot water connected to the Powerwall & the solar. (And actually, you want it on a timer to run at midday, so that it's using the solar directly.) Even if it requires changing your rate plan.

Sounds like you should be at nearly 100% self-consumption; selling power to the grid and then buying it back to heat water is almost certainly worse than using it yourself to heat water. Unless you have an extremely high feed-in tarriff on your exported power.

According to the installers, that's not possible. I'm waiting for a call back from a different installer to verify that though.

I can see your point regarding having the HW service run during the day but during Winter (or any day that we encounter poor or overcast conditions), that would mean we would be paying 42c/kWh for peak use time to heat water, as opposed to 22c/kWh for off-peak at night. We get a FiT of 18.5c/kWh so that's pretty close to what we pay for off-peak usage. Having said that, I still believe the smart meter is incorrect and our hot water off peak use is exaggerated.

The installer also said something which did make sense to me though, being - if we use the PW2 to run our HW system, the PW2 would be pretty much drained by morning, meaning that any activities we do involving preparation of breakfast, PC use, cook-top use, ZIP-tap (a sink-mounted hot / cold water filter separate to our standard, domestic HW service), lights, music, coffee machine and even heating or cooling etc would all then be charged to us at the peak grid rate of 40c/kWh, unless we wait until solar starts generating, which is a timing issue due to us having to be up early for work / school drop-off. We generally see enough solar input to run basic house functions at around 07:30 - 08:00 in good times of the year. We're usually done and have left the house by then.

By having some charge left in the PW2, we do all (or the vast majority), of this for free, even though it means the HW system did cost us during the night (at 22c/kWh compared to 40c though). It also means I can set washing, dryers and dishwashers running as well if needed. I generally use the delay timers on these appliances so they only kick in around late morning to midday.

Once the day is done, we've achieved all of this via the PW2 or solar input and also have a fully re-charged battery for evening activities.

Having said that, I'm still thinking you are correct and it would be a viable option for us to connect the HW as you've suggested, but it would require some data on the way we currently use our system and how much that costs compared to your method. It'd be an interesting experiment!

Thanks for your input again. Greatly appreciated