All is not well in the PW SE multi verse

[Pocster]

14 minutes ago, Radian said:

 

I think I get what you're saying. PW must know when there's free PV to slurp on, and when there isn't, in order for it to be compatible with the off-peak energy scheme it's associated with. Pretty fundamental to the whole idea behind it all. But of course it will never see (or expect to see) PV in the off-peak window.

 

Therefore when it does charge in the off-peak window, the resulting load must be hidden from SE and here we go around the explanation merry-go-round once again. I'm pretty certain You or your installer is going to have to do some nifty CT lacing to fix it. It may be that they did something along these lines but either got the current direction the wrong way around, or only did it for one battery system (or all the other combinatorial fails that are possible).

This installer didn’t install the PW so assume CT clamps etc. in that are “ as is “ . Would you like to place a guess on what will happen when both go to charge off peak from the grid ??

[Radian]

6 minutes ago, pocster said:

. Would you like to place a guess on what will happen when both go to charge off peak from the grid ??

 

Hard to say without knowing for sure the location of the CTs but if the SE CT is just sat next to the PW CT on the incomer (topologically speaking) then neither should baulk at the other taking 3kW+ as it might just be you needing to electric shower in the middle of the night. Like you sometimes need to 🙈 However, the fun & games might start, as I think you've seen, when one or other reaches capacity and switches to 'provider' mode. In principle it should know you're in the off-peak window and avoid any discharge so might have instead a 'standby' mode before switching to 'provider' mode at the end of the window. Don't know.

[Pocster]

1 minute ago, Radian said:

 

Hard to say without knowing for sure the location of the CTs but if the SE CT is just sat next to the PW CT on the incomer (topologically speaking) then neither should baulk at the other taking 3kW+ as it might just be you needing to electric shower in the middle of the night. Like you sometimes need to 🙈 However, the fun & games might start, as I think you've seen, when one or other reaches capacity and switches to 'provider' mode. In principle it should know you're in the off-peak window and avoid any discharge so might have instead a 'standby' mode before switching to 'provider' mode at the end of the window. Don't know.

I did think this ! . Not about showering in the night ; that’s a given ! . What happens when either is 100% full ? - does it act differently/ change modes .

Fun and games in the multi verse !

[MikeSharp01]

6 hours ago, RobLe said:

You don't need to worry about the voltages - the PW and SE will do all of that complicated stuff with their power electronics and control algorithms.  All you need to know is that the PW is trying to minimise the power flow through its CT; it will put out whatever current at whatever voltage is required to achieve this.

 

Imagine that you sublet a room in your house, where you had a single power feed in, and there was a PW battery, and a kettle which somebody turned on and off, maybe even a bit of PV.  The PW battery would effectively power the kettle.  You might not even know that they had done this, inside their sublet room.  Then imagine you fitted an SE battery to your whole house - this would work too, but nothing it does will affect the PW operation.

I am still unclear what you are saying here adding the SE without installing some sort of interventions is not going to work?

[SteamyTea]

Found the correct schematic for it.

 

[RobLe]

It's not my house, so I don't know for sure how it's installed...  a piccy of the CTs would help - I think they will be on the same wire, and I would be willing to bet money that it is actually installed like (e) below.  That is, each batt connects to the house consumer unit or a henley block next to the consumer unit.  Then each batt CT connects to the tail (the order of the CTs here makes no difference).  And wiring it like this is the cause of the issue, even though each battery may be individually wired as it's install manual - I'm guessing they haven't considered anybody would be ambitious enough to have 2 batteries.

 

In contrast, I think that (d) will fix the issue completely.  I'm not changing my mind, it's the same schematic as (c) I did a while back, and also the blurb I wrote some time back.  It is clear to me, although I'm having trouble convincing the internet!

[RobLe]

5 hours ago, MikeSharp01 said:

I am still unclear what you are saying here adding the SE without installing some sort of interventions is not going to work?

If the PW and SE are wired in series, as (d) above, I think that they both will work.  When the sun shines, PW will gobble it up assuming PW=B1 in (d).  It's not a voltage thing, it's just where it's CT is positioned that matters.  When the kettle is on, the PW will provide.  When there is too much sun, the PW will be full and stop taking power.... then the SE will fill up.  If the PW were to fully empty, then the SE would get a chance to power something. 

 

It might not be quite as above, as the PW can also be controlled by Tesla(?) - I think Tesla might tell it to power the grid sometimes and pay you for it - eg via Octopus "Tesla Tariff".   This could screw up if so, as SE will immediately thwart that behaviour, absorbing that power.  You might be better off with SE on the inner loop, so PW can discharge into the grid if you want that to actually work(don't bother if you don't want this!).  You'll also need to make sure any night battery charging times are synchronised between PW and SE.  Eg if PW charges in the middle of the night from the grid, but SE isn't programmed to do that, then SE will charge PW, which is inefficient.

 

By and large though I think d) is good.. 

[Radian]

7 hours ago, RobLe said:

You'll also need to make sure any night battery charging times are synchronised between PW and SE.

...But this is the issue we're trying to overcome in this thread. There appears to be insufficient control provided by SE and PW to do such synchronising hence the reverse routing trick through the CTs to mask the systems from each other.

[RobLe]

On 28/07/2022 at 18:45, pocster said:

 

PW charges off SE ( correct I think )

Then greedy SE steals it back - around the loop we go .

 

@Radian:

Agree syncing charging is part of the issue, but it alone wouldn't be terrible.  The dominant thing is an underconstrained system,  where it is completely valid for PW to charge SE and the other way around.  Hence the horrific up/down spikes in power in the top graph above from the op. 

[ProDave]

1 hour ago, Radian said:

...But this is the issue we're trying to overcome in this thread. There appears to be insufficient control provided by SE and PW to do such synchronising hence the reverse routing trick through the CTs to mask the systems from each other.

This just puts me off an "off the shelf" battery storage system.  There is too much "we know what it is doing" from the manufacturer and not enough control and information for the user.

 

As a very minimum I would like 2 user inputs "Inhibit charging" and "inhibit discharging" so you could at least have some control over what it does and when.

[Radian]

24 minutes ago, RobLe said:

Agree syncing charging is part of the issue, but it alone wouldn't be terrible.

 

Pocster and I both think it is. And it is the key constraint we require.

 

22 minutes ago, RobLe said:

Hence the horrific up/down spikes in power in the top graph above from the op. 

 

Sure, it's pretty gruesome. The CTs tell the two systems the quantity and direction of power flow between house and grid. If one system sees  the other drawing power from the grid but can't distinguish it from Pocster putting on the kettle, it will jump in and supply it.

 

That constraint can be met by nulling the drain from the opposing system. You appear to have looked at it from the perspective of only one system and put the other system on the other side of the CT to hide it. Fine, but once again, this is a symmetrical problem and can only be resolved by having each system nulled from the other.

 

We're spinning our wheels dreadfully here. Assuming that you're not just trolling, what is it about mutually nulling the systems to each other that you won't go along with?

 

[RobLe]

5 minutes ago, Radian said:

 

Pocster and I both think it is. And it is the key constraint we require.

 

 

Sure, it's pretty gruesome. The CTs tell the two systems the quantity and direction of power flow between house and grid. If one system sees  the other drawing power from the grid but can't distinguish it from Pocster putting on the kettle, it will jump in and supply it.

 

That constraint can be met by nulling the drain from the opposing system. You appear to have looked at it from the perspective of only one system and put the other system on the other side of the CT to hide it. Fine, but once again, this is a symmetrical problem and can only be resolved by having each system nulled from the other.

 

We're spinning our wheels dreadfully here. Assuming that you're not just trolling, what is it about mutually nulling the systems to each other that you won't go along with?

 

I think the mutual nulling you suggested will:

Make PW supply the same power the house uses, and at the same time

Make SE supply the same power the house uses

That's too much power, that's why I don't like it!  I think it will provide 2x the required power.  The cables are unlikely to fit through the CTs, as an aside.

 

I would love any/all schemes to be tried though, out of interest!  

 

[Pocster]

Patience guys ! . I’m driving my EV everywhere so I can flatten it 

[Radian]

1 hour ago, RobLe said:

I think the mutual nulling you suggested will:

Make PW supply the same power the house uses, and at the same time

Make SE supply the same power the house uses

That's too much power, that's why I don't like it!  I think it will provide 2x the required power. 

 

Whoa! The way you say it "too much power sounds" very bad but is, in fact, what's required here. It's not like the lights will be brighter!

What it really means is that both batteries can slurp free/cheap leccy together when available (good) and both can supply it in preference when not (also good).

 

[Dillsue]

13 minutes ago, Radian said:

What it really means is that both batteries can slurp free/cheap leccy together when available (good) and both can supply it in preference when not (also good).

 

As both batteries need to be configured to supply household load, which includes the other battery charging, are you saying run the AC connection cable for one battery through the other batteries CT?

[SteamyTea]

44 minutes ago, Radian said:

What it really means is that both batteries can slurp free/cheap leccy together when available (good) and both can supply it in preference when not (also good).

Ain't that what I said a while back?

 

Apart from the metering displays showing odd things, I suspect it is working fine.

What it does show is that battery storage is probably best left up to the DNOs and generation companies, they can put in, and monitor, systems that do as they are told.  Relying on last weeks double glazing salesman to make a claim about the viability of low voltage, mixed, domestic storage systems, is probably not a wise one.

[RobLe]

1 hour ago, Radian said:

 

Whoa! The way you say it "too much power sounds" very bad but is, in fact, what's required here. It's not like the lights will be brighter!

What it really means is that both batteries can slurp free/cheap leccy together when available (good) and both can supply it in preference when not (also good).

 

I think with the symmetric scheme where each batt has a CT with 2 wires through it in order to negate the other battery current flow, and a 2kW kettle turns on, then:

Batt1 will provide 2kW

Batt2 will provide 2kW

So yes, the kettle will be powered by the batteries.  But then the main tail will export 2kW, surely not wanted?  

[Dillsue]

13 minutes ago, RobLe said:

I think with the symmetric scheme where each batt has a CT with 2 wires through it in order to negate the other battery current flow, and a 2kW kettle turns on, then:

Batt1 will provide 2kW

Batt2 will provide 2kW

So yes, the kettle will be powered by the batteries.  But then the main tail will export 2kW, surely not wanted?  

Surely as they both see the grid demand intially rise then fall off as both batteries try to satisfy the demand, there wont be 2kw of surplus but both batteries could start to ocillate output?? If one battery is not quite as reactive to demand then the more reactive battery will supply all demand until its discharged??

[Radian]

1 hour ago, RobLe said:

I think with the symmetric scheme where each batt has a CT with 2 wires through it in order to negate the other battery current flow, and a 2kW kettle turns on, then:

Batt1 will provide 2kW

Batt2 will provide 2kW

So yes, the kettle will be powered by the batteries.  But then the main tail will export 2kW, surely not wanted?  

 

No. During peak hours both battery system's aim should be to provide power in preference to importing it. To do this they look at magnitude and direction of power through their respective CTs and modulate their output to keep it to zero. Power thus flows from both battery systems into the kettle load, possibly a little lopsidedly but not massively so. Roughly 1kW therefore flows into the kettle from each and nothing to the grid.

 

You're suggestion that both will deliver 2kW 'come what may' might be based on your thinking that each system can't see the other's contribution. Indeed they can't. All they can see is the same house load drawing on the grid so both raise their outputs to compensate. This is where differences in control loops might become apparent but as they both see the same power flow to or from the grid, they will not blindly raise their outputs and start exporting (or importing).

 

1 hour ago, Dillsue said:

Surely as they both see the grid demand intially rise then fall off as both batteries try to satisfy the demand, there wont be 2kw of surplus but both batteries could start to ocillate output?? If one battery is not quite as reactive to demand then the more reactive battery will supply all demand until its discharged??

 

AC battery systems already seem to manage this scenario. I agree we have no reason to guess the exact share that would result but it's a secondary objective to evenly share the local energy store. The primary objective is to stop the two systems stealing each others charge and careful CT threading can achieve this.

[Pocster]

It’s all getting to complicated all this talk . So I’ll just stick with 

[Pocster]

Tomorrow night could be the day !

EV sufficiently low . PV generation for tomorrow looks low .

So ! Late in the afternoon empty PW into EV . Keep going then PW will pull from SE and drag that down .

Then set SE to charge at off peak ….

then wait !!

[Dillsue]

4 hours ago, pocster said:

Tomorrow night could be the day !

EV sufficiently low . PV generation for tomorrow looks low .

So ! Late in the afternoon empty PW into EV . Keep going then PW will pull from SE and drag that down .

Then set SE to charge at off peak ….

then wait !!

If the SE battery is DC coupled, the PW doesnt know if the SE inverter output is from PV or battery?? If SE sees the EV charging demand wont it start to power that load? Because PW assumes SE output is PV wont PW reduce output to let the SE "PV" fulfil the EV charging demand, so SE will discharge before PW???

[Pocster]

31 minutes ago, Dillsue said:

If the SE battery is DC coupled, the PW doesnt know if the SE inverter output is from PV or battery?? If SE sees the EV charging demand wont it start to power that load? Because PW assumes SE output is PV wont PW reduce output to let the SE "PV" fulfil the EV charging demand, so SE will discharge before PW???

No idea !

First thing is PW and SE charge from grid simultaneously ( no EV charging ) . I’m emptying my PW and SE deliberately into my EV to force them to charge from the grid .

I would assume EV charging is simply seen as a load to PW and SE like everything else …..

[MikeSharp01]

8 hours ago, SteamyTea said:

Relying on last weeks double glazing salesman to make a claim about the viability of low voltage, mixed, domestic storage systems, is probably not a wise one.

The whole discussion sounds more like a lesson in the dark arts at Hogwarts than a gathering of double glazing sales people. Still it has definitely raised the tone somewhat as even @pocster has been somewhat restrained (perhaps evolving into some sort of scientist) - and now he is brining a third battery to the party (in the EV) - this should be fun. 

 

PS I still think this will only work if the two sub-systems (PW and SE) can talk to one another and decide what to do when the overall system (the house incl charge point) is put under load and/or when PV / cheap leccy is available. I worry that the nulling idea, simple as it sounds - and the best ideas are the simplest, will come down to the resolution of their respective ADCs and associated response times - I can't put my finger on it but something about +ve feedback is ringing alarm bells in my head but it might just be the beer.

[Radian]

16 minutes ago, Dillsue said:

If the SE battery is DC coupled, the PW doesnt know if the SE inverter output is from PV or battery??

 

That is how I understand it.

 

17 minutes ago, Dillsue said:

If SE sees the EV charging demand wont it start to power that load?

 

Yes, the SE CT will show imported grid current so it's SE's duty to raise it's output voltage enough to zero the grid current while still meeting the EV's demand.

 

21 minutes ago, Dillsue said:

Because PW assumes SE output is PV wont PW reduce output to let the SE "PV" fulfil the EV charging demand, so SE will discharge before PW???

 

I believe that PW is expecting to be paired with PV but I don't know if it uses 1 ro 2 CT's to determine when PV is providing the power. Interestingly, if the SE live is threaded in with the PW grid CT (as I showed in my schematic) SE generation will 'look' like grid power so PW ought to step in to minimise it. How this settles out is difficult to predict but it could be that they both end up sharing the duty.