Recent Odd Charging Behaviour In Time Based Mode

[mw963]

FWIW, I started a thread here:

Powerwall Overnight Charging Rate

We've had a Powerwall 2 for just over two years, and for the first eighteen months (until March 2023) we had five hours per night of cheap rate electricity on the Octopus "Go Faster" tariff. Throughout that period - when using Time Based Control - our Powerwall would charge at a rate of 3.7...

teslamotorsclub.com

to ask about the fact that my TBC charging rate had gone from 3.7 kW to 5.0 kW at the end of Feb 2023. Initially someone at Tesla thought it was to do with grid codes, but when I made contact again I was informed that it was a global (well, maybe just Britain?) decision, and that it had been decided to make use of the full 5 kW rate, and they confirmed that the decision had been taken at the time I'd noticed it.

Which now seems to be a load of balls in view of xWren's experiences. I assumed it had more to do with the fact that Octopus had abandoned their Go Faster tariffs and moved everyone onto plain Go, with one hour less of cheap rate each night.

I continue to be utterly fed up that a piece of kit that I own is not under my control; I do believe in fairness that TBC has been improved somewhat, for example when we've had a couple of sunny days this winter the battery has still charged up to 100% the following night, rather than assuming that we're in the midst of a heat wave as used to happen, and thus failing to charge fully the next night, leaving an incompletely charged battery to cope with a sunless day. But I still - thanks to not sleeping well - check what's going on during the night, and use a combination of switching modes and storm reserve back up to make the system do what I want it to do, not what oh-so-clever Musk thinks it should do. We still desperately need a third "mode", that of "TBC with owner determined "charge to x% tonight" option". It would be so easy to implement, and like xWren if I'd known about the lack of control I'd have never chosen Tesla.

That said, a nieghbour has Solar Edge and for TBC it is utterly useless and doing things which are costing her money.

 

[BGbreeder]

I would be really interested to learn of the behind the curtain aspects of this, and how much is the Tesla programming, and how much is local throttling of the charge current due to infrastructure limitations. Do you know the kVA capacity of your local transformer, and how many other customers share it?

All the best,

BG

 

[JohnRatsey]

I continue to be utterly fed up that a piece of kit that I own is not under my control; I do believe in fairness that TBC has been improved somewhat, for example when we've had a couple of sunny days this winter the battery has still charged up to 100% the following night, rather than assuming that we're in the midst of a heat wave as used to happen, and thus failing to charge fully the next night, leaving an incompletely charged battery to cope with a sunless day. But I still - thanks to not sleeping well - check what's going on during the night, and use a combination of switching modes and storm reserve back up to make the system do what I want it to do, not what oh-so-clever Musk thinks it should do. We still desperately need a third "mode", that of "TBC with owner determined "charge to x% tonight" option". It would be so easy to implement, and like xWren if I'd known about the lack of control I'd have never chosen Tesla.

I too would like on option to set a maximum charge level. One workaround is to shorten the period of cheap electricity in the app. There would be a bit of trial and error but looking at my historic data suggests that one hour at 5kW charge rate increases the battery charge level by 30%.

 

[mw963]

I have no idea BGbreeder. Initially Tesla said I must have requested a change to the grid code to 99, but this was nonsense. I got the impression that the adviser was clutching at straws and didn't really know what she was talking about. Then a few months later they said it was a change in policy affecting everyone. Which is nonsense from the experience of others in other threads on here.
We share a transformer on a 11 kV line with one other house. We were only allowed 14 solar panels (4 kW limit) when we had them installed. Nothing has changed as far as the electricity distribution is concerned round here, we are very very rural.
Wish I could tell you something more useful.....

 

[mw963]

@ JohnRatsey - I set the storm contol to 10% less than the current battery level when we go to bed, with TBC. As I almost always wake up at a convenient moment during cheap rates I then change to self powered and set the storm control to say 70% if I don't want it to charge fully, or if in the shoulder months I find it's stopped charging I whack the storm level up to 100%, and then reduce it the next time I wake up once we're back on peak rate.

I bought the Raspberry Pi, took out the sub for a ReCaptcha work around, but it was totally beyond me to do what xWren has done to outwit Tesla. And it sounds as though his system is giving him problems now so I'm probably better off sticking to my amateur workaround.

Why do Tesla have to be so damned stubborn about control?

 

[BGbreeder]

I have no idea BGbreeder. Initially Tesla said I must have requested a change to the grid code to 99, but this was nonsense. I got the impression that the adviser was clutching at straws and didn't really know what she was talking about. Then a few months later they said it was a change in policy affecting everyone. Which is nonsense from the experience of others in other threads on here.
We share a transformer on a 11 kV line with one other house. We were only allowed 14 solar panels (4 kW limit) when we had them installed. Nothing has changed as far as the electricity distribution is concerned round here, we are very very rural.
Wish I could tell you something more useful.....

That seems useful to me, and it would be consistent with your local infrastructure not being in a condition to be supportive of higher charge or discharge rates. (Transformer/wire/substation) From an armchair a long way away, it doesn't sound readily fixable, but perhaps the utility (Octopus?) might place a higher value on your battery/solar in the future.

All the best,

BG

 

[xWren]

The random erratic behaviour when charging in Time-Based mode continues. Some nights are fine and others do things like this:

The mystery drop to 1.7kW as if it is in self-consumption mode, this time for 20 mins.

My internet was working fine, I happened to wake up and check during that 1.7kW period, so looking for new explanations. As long as it charges to the level I want in the 4 hours this behaviour doesn't matter, however this is a change and doesn't look like a deliberate well designed one. It is either an accident (the opposite of good design) or a sign that something has broken. So I still want to know why this is happening sometimes.

@BGbreeder the default UK 3.7kW limit on Powerwalls and 4kW on solar panels (which practically get limited in the inverter to 3.6kW) is historic more than infrastructure limited. Originally every installation had to apply for permission to export to the grid, so when solar first started to take off the governing body set somewhat arbitrary limits for what could be installed without the site inspection and load planning overheads. It isn't that the local grid can't cope, but done to cut the paperwork and a quick amendment to the existing protocol. Permission to export 5kW is just about paying an admin fee, and there is no concern from the grid about a house having a device the draws 5kW. However originally Tesla applied the 3.7kW export limit to charging too, unless you had the setting changed. Maybe this is what changed for @mw963, what Tesla support were groping to explain, or maybe the throttling has been removed for both by changing the setting (with or without permission from the grid).

 

[JohnRatsey]

That seems useful to me, and it would be consistent with your local infrastructure not being in a condition to be supportive of higher charge or discharge rates. (Transformer/wire/substation) From an armchair a long way away, it doesn't sound readily fixable, but perhaps the utility (Octopus?) might place a higher value on your battery/solar in the future.

All the best,

BG

It's more a case that the local distribution networks have been designed around a voltage drop between the nearest transformer and the users. If the power flow is reversed due to lots of solar generation then there might be unacceptable voltage rise at the users' end of the line. Usually the mains fuse for the consumers is 80 amps, which is around 18kW although few people draw that much power (but use an 8kW electric shower while there's something cooking in an electric oven and that's 12kW).

I've also noticed a significant increase in the number of houses with solar panels (which will all reach maximum generation at the same time).

 

[BGbreeder]

Engineering and design tradeoffs are always an interesting subject, at least for me.

 

[mw963]

The random erratic behaviour when charging in Time-Based mode continues. Some nights are fine and others do things like this:
View attachment 1015492
The mystery drop to 1.7kW as if it is in self-consumption mode, this time for 20 mins.

My internet was working fine, I happened to wake up and check during that 1.7kW period, so looking for new explanations. As long as it charges to the level I want in the 4 hours this behaviour doesn't matter, however this is a change and doesn't look like a deliberate well designed one. It is either an accident (the opposite of good design) or a sign that something has broken. So I still want to know why this is happening sometimes.

@BGbreeder the default UK 3.7kW limit on Powerwalls and 4kW on solar panels (which practically get limited in the inverter to 3.6kW) is historic more than infrastructure limited. Originally every installation had to apply for permission to export to the grid, so when solar first started to take off the governing body set somewhat arbitrary limits for what could be installed without the site inspection and load planning overheads. It isn't that the local grid can't cope, but done to cut the paperwork and a quick amendment to the existing protocol. Permission to export 5kW is just about paying an admin fee, and there is no concern from the grid about a house having a device the draws 5kW. However originally Tesla applied the 3.7kW export limit to charging too, unless you had the setting changed. Maybe this is what changed for @mw963, what Tesla support were groping to explain, or maybe the throttling has been removed for both by changing the setting (with or without permission from the grid).

You raise an interesting point re peak demand for a consumer during the short cheap rate period. In spite of my continued loathing of the fact that Tesla ultimately - and often dumbly - control my system, we have just ordered a second Powerwall, taking advantage of the drop in price and the removal of the VAT part of the bill. Although we can - just - get through a sunless winter's day on the previous night's battery charge, it does sometimes mean that the air to air heat pumps have to be left off if we're to do a roast in the evening. In other words use is carefully rationed. We could of course import some "expensive electrons" when needed, but it's become a matter of honour between me and Mrs mw963 to eke out the nightly charge the following day, without resort to "cheating" by importing at peak rate.


When we get the second battery, on current form, they would both be charging at 5 kW at night, giving a draw of 42 amps. With the immersion heater on (another 12 amps) and possibly the dishwasher and clothes washer and tumble dryer, I can see a max night draw of 78 amps, although it's unlikely that the white goods would all be drawing at full whack at the same time,, due to their various thermostatically controlled demands.

I happen to know we have a 100 amp fuse (the guy who changed our meter expressed surprise when I told him that was the rating he would find when he pulled out the module) so I assume that a second Powerwall won't be a problem, and it's possible that when the second one goes live to Tesla they might throttle us back to 3.7 kW charging per battery, in fact I might have another go at persuading them so to do.

Another incidental advantage of a second PW may be that instead of having to charge up to 100% each night in the winter it might be possible to charge the pair to only 80%, thus perhaps reducing wear and tear....? We would rarely need a full 27 kWh reserve for day time use, even with more generous use of our air to air heat pumps.