Powerwalls - I just don't get it.

[phil4]

Two things confuse me.

Firstly, it's early days, but it keeps charging to 100% overnight, despite a sunny day ahead. I figure this is part of it "learning", which is fine. Except I don't think I'm helping it. As I'm using the spare sun (there's lots as it's full) to charge the cars. But of course the PW sees this as house load, and so surely is going to keep thinking I need 100% charge each day. The obvious alternative is charge off peak... great, but then surely that stops me from solar charging in the future? which doesn't make any sense.

Secondly, I can't see what the difference is between Time of Use and Self-Powered modes if Grid charging is turned off. Neither mode can charge, so surely they behave exactly the same? (Nb. I'm not permitted export, so no option on that, it's off).

Anyone with a PW any ideas on the above?

TIA

 

[WannabeOwner]

I fiddle with mine in my own way, using the API and some String and Chewing gum, so I may not be offering good advice, nor the correct terminology.

Firstly, yes it definitely takes some time for the out-of-the-box to adjust and predict better. I am not aware that there is anything that tells you what it is thinking, so nothing to give you confidence / confirmation-bias. Whereas I think Givenergy? has a nice graph of yesterday's prediction vs. today's actual, which I thought was very impressive.

I use ""self powered" in Summer, and I set the LIMIT at the start of Off Peak (which might be 0% if I prediction is that there is enough stored from yesterday's Solar to last until tomorrow PV starts generating AND "tomorrow" prediction is 100% sunshine. Or I set x% charge limit during Off Peak for whatever extra is needed in addition to tomorrow's PV prediction)

Clearly that is what Tesla prediction is supposed to do for you ... my route is attempting to take into account what EV mileage / charging I know I will need later in the week.

That mode only charges at 3.5kw (I think) max. So there is a serious limit on trying to get the Powerwall full during Off Peak (but with PV unlikely you will need much, if any, off-peak charging during "summer")

In Winter I used "time-based" and set the Off Peak time period (have to set the same one for Weekday and separately for Weekend from memory). That will fill my PowerWalls at 10kW - so no difficulty getting them full in 4 hours (but if there is another heavy user, e.g. car charnging, the PowerWalls drop back to 3.5kW so might not fill up)

I use API to charge the cars (based on prediction) - so if the car needs some, and the PV is definitely going to fill the PowerWall today, then "charge the car"

You could just use e.g. a Zappi which in effect is: when PowerWall is full (i.e. Export is detected) then "charge the car"

 

[ACarneiro]

Self powered mode will NEVER use power from the grid at any time of the day (as long as there is charge left on the batteries).
ToU with grid charging turned off may use grid electricity at off-peak times.

 

[MadScientist]

I dont think it's suprising that the PW is charging to 100% if you are teaching it to expect massive loads during the day with car charging.

I'm getting my PW in a months time and I'll be using ToU mode as I have a relatively small solar array. As you imply, the latter mode makes no sense with 'self powered mode' enabled.

 

[WannabeOwner]

Self powered mode will NEVER use power from the grid at any time of the day (as long as there is charge left on the batteries).

Mine stops discharging when it drops to the LIMIT (unless there is a power cut and then it keeps going down to zero). If I set the LIMIT above current percentage it will charge (from grid) to that level.

At least I think that's how it works!

 

[ACarneiro]

Mine stops discharging when it drops to the LIMIT (unless there is a power cut and then it keeps going down to zero). If I set the LIMIT above current percentage it will charge (from grid) to that level.

At least I think that's how it works!

Well, yes.
My statement was assuming you weren’t fiddling with the backup reserve, which is a completely separate setting.
Indeed the battery will never drop to less than the set backup reserve and will charge from grid if you set the reserve to higher than the stored energy at that time.

 

[phil4]

I dont think it's suprising that the PW is charging to 100% if you are teaching it to expect massive loads during the day with car charging.

the car charging is from Solar excess, which is something I've always done, as is notionally free. It's a hard habit to break that one.

 

[ACarneiro]

the car charging is from Solar excess, which is something I've always done, as is notionally free. It's a hard habit to break that one.

Yes, this is a current limitation with the PW AI.
I believe there are rumours of a “Drive on sunshine” setting “coming soon” which will supposedly charge the PWs from solar and then dump any excess into the car rather than exporting to grid.
I am actually looking forward to seeing what that one will bring.

 

[Mrklaw]

if you could clamp the car or just somehow tell it whatever is going into the car (especially with a tesla but not only) is excess solar, then it can discount it frmo any charge calculations. Its an odd one and you'd think would be a core use case to have considered. A charger like zappi designed to suck up as much excess as possible will look like a permanent load with no solar excess to play with, wherease actually its a flexible load and you'd likely be happy for that to start off charging the battery.

Givenergy does have a nice visible solar predictio but its leaning on solarcast for that (which is fine). It doesn't yet have a way to use that to set the charge limit for the next day - coming soon apparantly.

 

[Dilly]

As others have said, set self powered for summer and time of use for late autumn to early spring.
if you have an off peak period, make that super off peak, and peak for the rest, in settings.
set reserve that suits in case of a power cut.

 

[MrT3]

Whereas I think Givenergy? has a nice graph of yesterday's prediction vs. today's actual, which I thought was very impressive.

It relies on the owner setting up a Solcast account and linking the API. It also doesn’t use the data to alter charging, just there for the owner to see and make their own adjustment.

 

[phil4]

if you could clamp the car or just somehow tell it whatever is going into the car (especially with a tesla but not only) is excess solar, then it can discount it frmo any charge calculations. Its an odd one and you'd think would be a core use case to have considered. A charger like zappi designed to suck up as much excess as possible will look like a permanent load with no solar excess to play with, wherease actually its a flexible load and you'd likely be happy for that to start off charging the battery.

That's probably why it puzzles me so greatly, that they've not thought of this very situation. It's not like the cars they make aren't all EV's. And you're right, I've got the Zappi set so it only uses excess solar once the PW is fully charged, so it always gets first dibs.

 

[Mrklaw]

thining about it I would like givenergy to split out charger vs home load - at the moment it doesn't. I'm tryign to estimate eg how much we use in the house during each period of the day (overnight, off peak window, solar day) and optional spikes like if you wnat to do an extra load of washing/drying. I think I'm about 10kwh a day so even in winter a full charge and a tiny trickle of sun should manage, but no leeway to cook a chicken

but any solar charging of the car mucks up the reports so I have to pick through by hand quite a bit. I'd probably have to do some ready reckoning with the myenergi data combined with teh givenergy stuff but I can't be arsed really I think I have enough of a handle to be confident setting a 10% charge (basically don't charge) during summer, probably 50% in autumn at some point, and 100% in winter. I think I want another battery for funsies and to have some buffer just in case, but then I think I should have waited for the new all in one for 6kw charge/discharge and a nice 13.5kwh usable which would have been just right. Not 3kw charge/discharge so can only charge up 12kwh in an octopus window etc..

 

[phil4]

thining about it I would like givenergy to split out charger vs home load - at the moment it doesn't. I'm tryign to estimate eg how much we use in the house during each period of the day (overnight, off peak window, solar day) and optional spikes like if you wnat to do an extra load of washing/drying. I think I'm about 10kwh a day so even in winter a full charge and a tiny trickle of sun should manage, but no leeway to cook a chicken

but any solar charging of the car mucks up the reports so I have to pick through by hand quite a bit. I'd probably have to do some ready reckoning with the myenergi data combined with teh givenergy stuff but I can't be arsed really I think I have enough of a handle to be confident setting a 10% charge (basically don't charge) during summer, probably 50% in autumn at some point, and 100% in winter. I think I want another battery for funsies and to have some buffer just in case, but then I think I should have waited for the new all in one for 6kw charge/discharge and a nice 13.5kwh usable which would have been just right. Not 3kw charge/discharge so can only charge up 12kwh in an octopus window etc..

MyEnergi should record both, at least it does for me.

If I click the home icon (pink at the top of the spokes), I get the home use excluding any charging via the zappi.

If I click the charging blue icon, it tells me the charging amount.

So using those two I can split the use.

 

[Mrklaw]

ah you're right it does split them out because it knows load and what its used. Good one.

 

[phil4]

ah you're right it does split them out because it knows load and what its used. Good one.

Like you, I was struggling to figure it out, prior to getting powerwalls... wondering if I was going too small or too large. Was trying to find days I didn't charge etc... but then hit that pink home one... and bam... my answer was there in front of me.

So looks like we've both walked the same path.

 

[Mrklaw]

Like you, I was struggling to figure it out, prior to getting powerwalls... wondering if I was going too small or too large. Was trying to find days I didn't charge etc... but then hit that pink home one... and bam... my answer was there in front of me.

So looks like we've both walked the same path.

just had a dig

so device usage for last week shows 112.7 home, 42.2 zappi. Total 154.9.
Then on the consumed/exported tab it has 137 consumed and 17.8 imported - which adds up to 154.8, close enough. So that should be my split of solar/grid. Cool. Now just need to do that regularly and start logging.


(still wish myenergi let you choose a custom period, not just a single day. Givenergy lets you pick eg a week/month from a year ago which would be really helpful if you havne't been logging recently)

 

[Tonybvi]

I have had my Powerwall for the best part of 6 months and just leave it alone. The only settings I have input are reserve level and off peak charge times and tariff. Even when away I just leave it on ToU. Recently during 6 weeks away in the motorhome, so cars still topping up occasionally, it simply input 0.2kwh every night which, at 4.5p/kWh is as good as nothing leaving the battery to run the low domestic requirements. I charge 2 cars overnight on scheduled charging and on really sunny days plug one of the cars in using the granny charger. Powerwall sees charging as house load but it seems to have learnt spectacularly well in the 6 months I have had it. Biggest cost now is the damned electricity fixed daily rate.

 

[Dilly]

Biggest cost now is the damned electricity fixed daily rate.

It sure is! My bill for June will be about £12.50. Of that, £2.50 or less is electricity.

 

[PITA]

Being 3-Phase... I divide my standing charge by three.

Makes it seem cheaper that way