All is not well in the PW SE multi verse

[Pocster]

24 minutes ago, MikeSharp01 said:

Firstly can I admire and respect your wish to give this setup a try. It feels relatively obvious that unless they were designed to, or can by use of their settings be made to, work symbiotically that they will work parasitically - everything tends to chaos. Both the PW & SE assumes that they are "the only battery in the village" and behaves accordingly. Which does what to which probably comes down to the sensitivity of the respective front end - IE what they think they see happening on the wires and a fractional difference in interpretation will be enough to upset the applecart. As I see it you will need some pretty tricky control electronics, perhaps a sort of rules based MQTT broker like device (function of not form of) to get these two talking to one another and their respective PV arrays nicely - have a word with @Radian cos he seems to be the master of this sort of stuff!

I did have reservations they wouldn’t play nice . Installer said they would though it’s the 1st install he’s done like this . Indeed I can’t find anyone else via googling who has . I’m confident I can sort this ; if not via SE options then a plan B is the arrangement of CT clamps .

Ultimately SE batteries are easier to come by than PW - so it’s only a matter of time before a PW owner considers a non Tesla battery to extended their storage .

[Pocster]

@Radian perhaps you’ll know !

How much faster does DC charge over AC ?

How do you compute the max kWh a DC battery can draw ( charge ) ?

[Radian]

3 minutes ago, pocster said:

How much faster does DC charge over AC ?

 

How long is a piece of string? Batteries can only charge from DC anyway, so an AC charger has to rectify the supply to DC anyway. Then it's just a question of the designed current limit.

 

6 minutes ago, pocster said:

How do you compute the max kWh a DC battery can draw ( charge ) ?

 

kWh is a measure of capacity. You already know that from the 'big print' in the brochure i.e. you bought a 10kWh battery. Do you mean how much power it takes when charging? The brochure probably tells you how long it takes to fill up from AC so divide that out. Again, for example, if they said it would take 10h to fill a 10kWh battery then it would be charging at 1kW, or 4.166A @ 240VAC. But I'm pretty sure you know all this already - so is there something else you're asking?

[Pocster]

6 minutes ago, Radian said:

 

How long is a piece of string? Batteries can only charge from DC anyway, so an AC charger has to rectify the supply to DC anyway. Then it's just a question of the designed current limit.

 

 

kWh is a measure of capacity. You already know that from the 'big print' in the brochure i.e. you bought a 10kWh battery. Do you mean how much power it takes when charging? The brochure probably tells you how long it takes to fill up from AC so divide that out. Again, for example, if they said it would take 10h to fill a 10kWh battery then it would be charging at 1kW, or 4.166A @ 240VAC. But I'm pretty sure you know all this already - so is there something else you're asking?

I actually can’t find the rate at which it charges from AC …

PW max charge rate is 3.68kwh . SE …???? . That’s what I’m trying to fathom . Though appreciate all batteries are DC . 
Of course though I may be asking the wrong question !

I’m trying too see that in my 4 hour off peak window ( and assuming they can’t charge simultaneously from the grid ) if there’s a preference to let one charge before the other …

Edited July 31, 2022 by pocster

[ProDave]

I am late to this thread, but will pose a dumb question.

 

You have a Power Wall and a Solar EDGE system?  BOTH of these are some form pf battery storage?  Is that correct?

 

Now to me TWO battery storage systems in the same house seems a recipe for disaster, as neither was specifically designed to work with other storage systems, so I am not surprised you ave conflicts.

 

for the benefit of readers like me can you explain what the two systems do and are supposed to achieve? and what makes you think they can work together without conflict?

[Radian]

18 minutes ago, pocster said:

PW max charge rate is 3.68kwh

 

Tesla Q&A:

Quote

Why is my Powerwall not charging from the grid at 5 kW?
The most efficient charging rate for the Powerwall is 3.3 kW. It will therefore charge at that rate when charging from the grid. If there is a compelling economic reason to charge faster, the system might decide to charge up to maximum capacity.

Makes it sound very condescending! It might if there's a compelling reason to. Huff.

[Pocster]

8 minutes ago, Radian said:

 

Tesla Q&A:

Makes it sound very condescending! It might if there's a compelling reason to. Huff.

Sorry I said 3.68kw from memory ( also because inverter is 3.68 max ). But yes it's 3.3kw. 

[SteamyTea]

Is that a mean 3.3 kW charge rate?

I doubt if the top 10% is charged that fast.

[Pocster]

28 minutes ago, ProDave said:

I am late to this thread, but will pose a dumb question.

 

You have a Power Wall and a Solar EDGE system?  BOTH of these are some form pf battery storage?  Is that correct?

 

Now to me TWO battery storage systems in the same house seems a recipe for disaster, as neither was specifically designed to work with other storage systems, so I am not surprised you ave conflicts.

 

for the benefit of readers like me can you explain what the two systems do and are supposed to achieve? and what makes you think they can work together without conflict?

Yes 2 systems, 2 batteries.

 

The installer ( I asked many questions ) said they could work together and can charge from grid simultaneously . I have that in writing.

I went on a holiday recently and explicitly asked the rep in resort if it was "adults only" . They said yes. It wasn't so after the holiday got half my money back.

My point being I have nothing to fear if these 2 systems don't work (though I'm sure they will in the way I want ).

 

I see PW as the dominant device here. You have very little control over it. I give it the off peak charge window and it decides whether to charge and how much. It takes into account apparently your consumption, how much PV you generated (just the day before?, or week?, or month? no idea ) also *allegedly* it takes into estimated account PV production tomorrow.

SE is dumb. This makes life simpler. It will charge/discharge at set times/days/months - which I can define.

The MAIN objective is in winter. 13kw storage in PW is not enough to last the day (even with some negiigle PV). So I need more storage so I can fill my boots with just off grid electricity.

Don't want to spend 10k on 3 phase and then ££££ on another PW - oh and maybe rewire my house !!!

So a 'simple' battery that sits (how I view it) between PV and the inverter is what I need.

When PW is <1% it drains from the SE . This is what I want.

If load > 5kwh (max output for PW sustained) it will pull from SE and any PV.. This is what I want.

 

What I don't want is SE stealing from PW then PW stealing from SE.

This I think I have stopped.

 

So now; it's just a case can both systems charge from the grid simultaneously .Not one charges, other steals from it. Otherwise essentially only 1 will be charging in my 4 hour window.

 

TBH @ProDave I treat this 'problem' just like building an underground house from zero knowledge. Just give it a go and learn. Doesn't mean I won't fail or f up. Those are guaranteed .

Installer will sort this if I can't otherwise I start claims court. They are still in comms with me even though been paid. I also recall they did say that another customer was having an SE added to their PW - so they in theory will experience the same issues. 

Edited July 31, 2022 by pocster

[SteamyTea]

Have we seen a wiring diagram of all the bits yet.

 

Does it really matter if the PW takes from the SE, as long are fully charged during the cheap time windows i.e. 4 night hours or a good PV day.

It is the average price you pay for the kWh overall that is important, not which way the electrons and ions move about.

Have you added up all your import bills and divided it by your total usage?

[Pocster]

6 minutes ago, SteamyTea said:

Have we seen a wiring diagram of all the bits yet.

 

Does it really matter if the PW takes from the SE, as long are fully charged during the cheap time windows i.e. 4 night hours or a good PV day.

It is the average price you pay for the kWh overall that is important, not which way the electrons and ions move about.

Have you added up all your import bills and divided it by your total usage?

Yes it matters . I only have 4 hours . That’s the total time a depleted PW needs to charge . If one takes from the other - you are simply shifting the load not charging simultaneously ( so do not fill both batteries and equally charge/ discharge cycle reduces battery life span ) .

Import bill this month is zero 😁

[Radian]

It seems simple enough. Both battery systems would obviously like to do 'the right thing' (for normal single battery installations) and deliver any load your house imposes in preference to imports from the grid, whenever they are able to. To cooperate in the way you require, both must be able to be told not to do so in your off-peak window. If you cannot instruct them to obey this then there will always be a competition between them.

[SteamyTea]

4 minutes ago, pocster said:

only have 4 hours

Plus some PV time.

 

I don't think they charge sequentially though, the electrons may go on a seemingly tortured route, but I suspect at night, both get charged up.

You will be loosing a bit of efficiency, but as that is shared across the whole system, probably not that bad.

9 minutes ago, pocster said:

Import bill this month is zero

That kind of shows it is doing its thing.

But to put it into perspective, I have no storage, other than the water cylinder, and have imported 100 kWh this last 30 days. 30 of them at the eye watering 35p/kWh day rate so £10.50 and 70 at 20p/kWh night rate, so £14.

Plus the standing charge at about £15.

So about a tenner a week, with no investment.

[ProDave]

It seems to me you are designing a system to power the entire house from just PV and the 4 hour cheap rate at night.? You don't want to use ANY peak rate (outside the 4 hour window) electricity?

 

And to do this your installer has specified 2 different systems, one of which has little or no programability in how and when it charges or discharges?

 

I will read this with interest to see if it ever works the way you want it to.

 

Oh and you are basing this on a particular tariff from one supplier available at the moment without knowing how long this tariff will last and if something similar will always be available.

 

I keep having thoughts of more PV and battery storage, but each time those thoughts drift to HOW will it work and how much control will I have on when it charges and discharges, and the conclusion I draw each time is it probably needs to be a DIY designed and built system.

 

I am actively resisting a smart meter and time of use tariffs and would prefer finding a way to add more PV with that PV only being used via a battery system and only discharging when the existing PV is not generating but that is too much fred drift to discuss that here.

[Pocster]

5 minutes ago, SteamyTea said:

Plus some PV time.

 

I don't think they charge sequentially though, the electrons may go on a seemingly tortured route, but I suspect at night, both get charged up.

You will be loosing a bit of efficiency, but as that is shared across the whole system, probably not that bad.

That kind of shows it is doing its thing.

But to put it into perspective, I have no storage, other than the water cylinder, and have imported 100 kWh this last 30 days. 30 of them at the eye watering 35p/kWh day rate so £10.50 and 70 at 20p/kWh night rate, so £14.

Plus the standing charge at about £15.

So about a tenner a week, with no investment.

4 hours off peak is 00:30 to 04:30 so no pv 

Your consumption a bit less than mine 😁

[Pocster]

1 minute ago, ProDave said:

It seems to me you are designing a system to power the entire house from just PV and the 4 hour cheap rate at night.? You don't want to use ANY peak rate (outside the 4 hour window) electricity?

 

And to do this your installer has specified 2 different systems, one of which has little or no programability in how and when it charges or discharges?

 

I will read this with interest to see if it ever works the way you want it to.

 

I keep having thoughts of more PV and battery storage, but each time those thoughts drift to HOW will it work and how much control will I have on when it charges and discharges, and the conclusion I draw each time is it probably needs to be a DIY designed and built system.

Yes . Whole house off pv  and off grid.

PW was there long before current installer ( sorry probably should of made that clear ) so SE is an add on .

I’ll get it to work ! - 

[Radian]

7 minutes ago, SteamyTea said:

I don't think they charge sequentially though, the electrons may go on a seemingly tortured route, but I suspect at night, both get charged up.

 

As there's no communication between them both will just 'fill up' until they decide they've had enough. The Telsa seems to be the one with most unpredictable behaviour in this respect. However, once 'full' they will return to supplying the house loads - of which one load may be a battery still charging. Hence a window must be defined in which no generation takes place. But this means some import for the house's base load must be tolerated.

[Radian]

If you could cancel the load imposed by each battery system when charging from the other's CT (by routing their live wires in the opposite direction to the main incomer) then they will both only respond to the other house loads. But when current goes the other way, when generating, my head explodes. I mean, I haven't figured out what would happen yet!

[Pocster]

4 minutes ago, Radian said:

If you could cancel the load imposed by each battery system when charging from the other's CT (by routing their live wires in the opposite direction to the main incomer) then they will both only respond to the other house loads. But when current goes the other way, when generating, my head explodes. I mean, I haven't figured out what would happen yet!

Lol ! Bit of a head f isn’t it !

imagine the fun I have when SE says there’s 6kw of solar at 5am !

PW says house load at 4kwh when it isn’t . PW says PV at 3kwh when there’s no solar because it’s draining the SE . The list goes on 😁

[Pocster]

I’ve said it before I’ll say it again …..

 

If it was easy everyone would do it !

[Radian]

It seems OK, it's entirely symmetrical - the power delivered by the battery systems will be hidden to each other so they should always just 'see' their own imports/exports and everything else bar the other battery system. I think.

[SteamyTea]

10 minutes ago, Radian said:

both will just 'fill up' until they decide they've had enough.

 

11 minutes ago, Radian said:

of which one load may be a battery still charging

Yes, but I am not sure if that is an actual net loss (other that battery inefficiencies).

 

Rather that play about with relocating CT clamps, cannot a simple voltage sensing lock out be used.

I bought a clamp on relay to operate my kitchen extractor fan (never fitted it as window is arms length away). Could something like that just be fitted to one of the batteries to stop it discharging until necessary. Treat it like the fuel tap on a motorcycle, twist it when you are down to the last 2 litres.

[SteamyTea]

3 minutes ago, pocster said:

I’ve said it before I’ll say it again …..

 

If it was easy everyone would do it !

Unlike what I say

"If it worked, we would all be doing it"

[Pocster]

2 minutes ago, SteamyTea said:

Unlike what I say

"If it worked, we would all be doing it"

😁 they said the same about underground housing …..

[Radian]

30 minutes ago, SteamyTea said:

Yes, but I am not sure if that is an actual net loss (other that battery inefficiencies).

 

No, it's an unnecessary drain on the other battery. We want both to charge from the grid, not each other.

 

Here's a schematic of what I think might work:

 

 

Obviously the symbol for the batteries is a bit wrong for AC but it gives the idea. CT1 is owned by B1 and C2 by B2. Whatever current flows to or from Live by either battery is hidden from the other. Am I being silly or is it as simple as this?

Edited July 31, 2022 by Radian