Circular reasoning (Rolfe's solar energy system)

[johnb80]

Indeed, John, quite confusing. I would still like to use my battery during the day and export the solar though, so figuring out how to do that is the next step.

I can sort of do that by running my DIY system to run the house and by setting the Growatt system to send everything to the grid. I'm not sure how I could do it with only the one system.

In other news I got back from my road trip last night on 5% battery, so I'm all set to plug in tonight for the half-price charge. I doubt if I'll gain £2 on it, but why not! (I would have charged last night, but today I only had to collect the cat from the cattery a mile away so it was no chore to leave it till tonight. So long as it's done for me to do another 100 miles on Wednesday.)

Aye, I'm charging both EV's tonight but I'm playing the Octopus game, I'm using scheduled times for the 6 hours. I have my suspicions of where Octopus are trying to go with this and I'm not playing

I am probably going to change over to Tomato tomorrow when Ive had confirmation about my off peak / peak ratio being ok with them. Looking at the prices I will make a considerable saving circa £310 per year which is not an insignificant amount and will help towards this governments measures against pensioners.

 

[SimonS]

Sorry if I made it sound worse than it is.

Charging your battery overnight at cheap rate is fine.
Using the battery to run the house during the day and topping it up from solar is fine.
Exporting the excess solar during the day is fine.
Exporting from your battery to the grid during saving sessions is fine (usually happens during the winter).
Exporting the remaining contents of the battery in the evening probably won't cause a problem (as John says) but just be aware that Octopus are within their right to ask you to account for where that power came from.

 

[Rolfe]

I can sort of do that by running my DIY system to run the house and by setting the Growatt system to send everything to the grid. I'm not sure how I could do it with only the one system.


Aye, I'm charging both EV's tonight but I'm playing the Octopus game, I'm using scheduled times for the 6 hours. I have my suspicions of where Octopus are trying to go with this and I'm not playing

I am probably going to change over to Tomato tomorrow when Ive had confirmation about my off peak / peak ratio being ok with them. Looking at the prices I will make a considerable saving circa £310 per year which is not an insignificant amount and will help towards this governments measures against pensioners.

Well, let us know how you get on. I would have thought that Tomato know perfectly well that there are customers whose objective is to use no peak-rate energy at all and who generally achieve that ain.

 

[Rolfe]

Sorry if I made it sound worse than it is.

Charging your battery overnight at cheap rate is fine.
Using the battery to run the house during the day and topping it up from solar is fine.
Exporting the excess solar during the day is fine.
Exporting from your battery to the grid during saving sessions is fine (usually happens during the winter).
Exporting the remaining contents of the battery in the evening probably won't cause a problem (as John says) but just be aware that Octopus are within their right to ask you to account for where that power came from.

Using my battery to run the house during the day so that I can export the solar is what I want to do but can't see how.

There is an "eco" setting that says, "This setting will use your battery or solar to power your home's electric demand." It seems to me that's no use because turning it off would cause the house to run on grid electricity exclusively. What good is that at all? I want a setting that powers the house from the battery alone, not from the solar.

There is a "timed discharge" setting that says, "This mode will trigger your battery to cover your home's electric demand only at the times you specify." I don't quite get that. It sounds to me as if that means again that outwith the specified times the house will run on solar or grid. It doesn't seem to be a way of stopping it taking the solar. Again, I'm not sure what the utility of this setting is.

Nothing else that seems relevant. Why would this be? Why wouldn't they configure the appliances so that you could run purely on battery if you wanted to?

 

[johnb80]

but just be aware that Octopus are within their right to ask you to account for where that power came from.

No apologies I'm grateful for you highlighting this T&C.

It would be absolutely impossible to tell where the energy in the battery came from. Consider:-
1) Operation with a PV system through the day which charges the battery and feeds the house with a small load. End of the day excess exported to the grid. Battery charged off peak.

2) Operation through the day with little / no solar PV but also out all day so little / no house load. Excess energy exported to the grid and battery charged off peak.

3) Operation through the day, lots of load, cars charging, tumble dryer running, heatpumps on. Solar providing a lot of energy. Evening, battery export to grid and charge again off peak.

How on earth can you, I or Octopus tell where the energy in the batteries came from? you simply cant, or I cant see how you can.

IMHO it's just a slippery clause that they can refuse to pay but in my mind the onus is on them to -prove it came from a non renewable source. If you charge from the grid supplied by Octopus theyre 100% green / renewable so you should be paid because you meet the criteria. I do think it's ok to charge off peak at 7p and sell back to them at 15p or more and I'm not convinced they can refuse to pay. I've been wrong before though but I would stand my ground on this one.

 

[Rolfe]

My thoughts were running along the same lines as yours, John. First, I'm doing your option 1. The battery is being kept at 100% all day from the solar (whether I like it or not). So at least some of that is green energy. And as you say, all that Octopus supplies is supposed to be green, so even though some of what's in the battery did come from the grid between 2 am and 5.30 am, it's still green, right? I would have thought that the objection would be a different one, that you're simply churning power for profit.

I'm going to go on doing it for now anyway. Wide-eyed innocence on the part of a new user is the position I'd take. I'm fairly sure they'd only ask you to stop doing it, not demand repayment for previous sessions anyway.

I would rather power the house from the battery during the day and export the solar as it comes, and if I did that then the battery might not have all that much left in it by 11.30 anyway, especially in winter. But I can't see how to do that. So in effect, they're getting what I would have exported during the day (plus a bit more, admittedly) after 11.30 instead. Maybe they'd even prefer that? I'm giving them power at the start of the cheap period when a lot of people plug in, so maybe it's welcome?

 

[Rolfe]

Back on the 16th April when you were starting to plan this install I posted some advice as follows:

On Forums/Facebook you will see with monotonous regularity people ask why their charger 'stole' all the electricity out of their battery. Having the charger on its own consumer unit means the Grid CT clamp can be placed between the two consumer units so that a house battery system (if fitted) will not see any current drawn by the charger and you will avoid the house battery being drained.

It seems that the message was not passed on to the installer or they ignored it.

I have discussed this at some length with my installer, and I'm fine with the way it's operating at the moment. While the Zappi does have access to the battery, this can be prevented very easily, and there are times when it is actually advantageous to let it happen.

If I want to pre-heat (or even pre-cool) my car before leaving home, and it's plugged in to the Zappi, it will take the power from the battery rather than from the mains at peak prices. I can spare 1 kwh from the house battery to warm the car if I'm going out, and if I can't it's easy enough to stop the battery discharging for the ten minutes it will take to do that. (Though, really, what difference would it make, if the battery runs down it will simply take power from the grid possibly at peak prices, so it's swings and roundabouts.)

If I am charging the car directly from the solar (which I was doing for three months, but have stopped doing now) and the sunshine is intermittent, it's very useful to have the battery supply power to tide the charger over when clouds come over. This gives an uninterrupted charge, and the battery simply recharges from the solar once the cloud has passed. (Often it recharges from solar that wouldn't even be available otherwise because of the 5 kw limit on the inverter which only comes into play when the battery is at 100%.)

To guard against the Zappi swiping the entire battery if the sun fails to come out again, my installer suggested setting a discharge limit on the battery for the duration of the charge. I hit on 93%, which seemed to be enough to tide the Zappi over most intermittent cloudy periods. Sometimes the charge would be cut at 93% but start again if the sun reappeared, sometimes that was that for the day. I only had to remember to remove the limit on the battery before the house load came calling later. It worked very well, though as I said I'm not charging the car from the solar now that I have the export tariff.

Yes one does have to remember to protect the battery when the car is charging, but that is normally achieved by setting the battery so that it's doing other things during the off-peak period when the car will normally be charging. If the car is going to charge outwith the off-peak period some intervention is required - this evening I forgot, I'm still new at this, and lost 10% of the battery before I remembered - but it's simple.

So I'm fine with it the way it is. As my installer said, different people find slightly different ways of working that suit them, and this suits me.

 

[johnb80]

Back on the 16th April when you were starting to plan this install I posted some advice as follows:

On Forums/Facebook you will see with monotonous regularity people ask why their charger 'stole' all the electricity out of their battery. Having the charger on its own consumer unit means the Grid CT clamp can be placed between the two consumer units so that a house battery system (if fitted) will not see any current drawn by the charger and you will avoid the house battery being drained.

It seems that the message was not passed on to the installer or they ignored it.

You’re not alone in giving this advice, unfortunately it’s fallen on deaf ears and Rolfe is happy with the bodge/workaround.?

 

[Robf]

With a type 1 Zappi and solar panels (no battery, it was a previous house) I gave up charging the car directly from the panels and just charged it overnight during the cheap time. The spare electricity during the day being used to heat water. If I go ahead and install at current house I would charge house battery, then the water whilst charging the car overnight, much simpler.

 

[johnb80]

With a type 1 Zappi and solar panels (no battery, it was a previous house) I gave up charging the car directly from the panels and just charged it overnight during the cheap time. The spare electricity during the day being used to heat water. If I go ahead and install at current house I would charge house battery, then the water whilst charging the car overnight, much simpler.

Depending on your tariff, it’s better to export all solar generated and charge ev and hot water on off peak. 15p export, 7p import with IOG.

 

[Robf]

Depending on your tariff, it’s better to export all solar generated and charge ev and hot water on off peak. 15p export, 7p import with IOG.

Agree, but at that time I was on the FIT scheme, so was paid for 50% of electricity generated from the panels regardless of export, so it was better to heat the water. This will apply to all those still on the FIT scheme.

 

[Rolfe]

You’re not alone in giving this advice, unfortunately it’s fallen on deaf ears and Rolfe is happy with the bodge/workaround.?

That's entirely uncalled-for. It didn't fall on deaf ears in the slightest. I gave it full consideration and decided I preferred the system as it was installed, for the reasons given. (Last night also realised an additional reason.)

Different people operate in slightly different ways, and this way suits me. Now that I understand the way it works there is zero chance of my home battery being drained by the car - unless I want it to.

 

[Rolfe]

Depending on your tariff, it’s better to export all solar generated and charge ev and hot water on off peak. 15p export, 7p import with IOG.

Dragging this back to the point that's exercising my mind at the moment, what you describe is exactly what I want to do, but I can't see how to do it. Everything in my system is forming an orderly queue to use the solar generation rather than let me export it, and it's difficult to impossible to stop this happening.

1. The house always uses solar if there is any to be had, and I don't think I can prevent it. Only if its demand exceeds the available solar will it call on the battery.
2. The battery is incapable of seeing solar and not grabbing it, if it's not fully charged. In the morning, as soon as the solar generation exceeds what the house wants, it recharges. If the house takes anything from the battery during the day, as soon as the load has ended, the battery takes more solar to recharge. The net result is that it stays at 100% until the solar fades in the evening.
3. I have set a schedule on the Eddi to heat the water up to temperature finishing just before 5.30 am. That's often enough for the day - I don't need it permanently scalding hot. (If I do, I can always boost it.) But the damn Eddi insists on ALSO heating the water periodically all day any time it's turned on. The only way to stop it is by turning it off altogether. Which prevents the scheduled boost. I find myself having to remember to turn the Eddi off the minute I wake up (by which time it's already grabbed some sunshine on sunny summer mornings) and turn it on again after sunset. Every bloody day. It's a complete pain, and a recipe for waking up to lukewarm water if I forget to turn it back on.
4. If I get home on a sunny afternoon and want to schedule a charge for the car overnight, I can't just plug the Zappi in and leave it to start the charge on schedule. Oh no. If the sun is shining it'll have that! I've taken to going back out to the garage after dusk to plug the car in. Someone mentioned a way of doing this from my phone rather than actually having to go outside, but it's still a right royal pain in the neck.

This was all fine and dandy when I didn't have an export tariff. I imagine it's all fine and dandy if you have a FIT. But it's not fine and dandy if you're trying to do what John describes above. Why is this so bloody difficult?

 

[johnb80]

That's entirely uncalled-for. It didn't fall on deaf ears in the slightest. I gave it full consideration and decided I preferred the system as it was installed, for the reasons given. (Last night also realised an additional reason.)

Aye of course

Different people operate in slightly different ways, and this way suits me. Now that I understand the way it works there is zero chance of my home battery being drained by the car - unless I want it to.

Thats good then.

Dragging this back to the point that's exercising my mind at the moment, what you describe is exactly what I want to do, but I can't see how to do it. Everything in my system is forming an orderly queue to use the solar generation rather than let me export it, and it's difficult to impossible to stop this happening.

1. The house always uses solar if there is any to be had, and I don't think I can prevent it. Only if its demand exceeds the available solar will it call on the battery.

2. The battery is incapable of seeing solar and not grabbing it, if it's not fully charged. In the morning, as soon as the solar generation exceeds what the house wants, it recharges. If the house takes anything from the battery during the day, as soon as the load has ended, the battery takes more solar to recharge. The net result is that it stays at 100% until the solar fades in the evening.

On many inverters there are different modes of operation, on Growatt for example, theres 'grid first' mode which does exactly what youre talking about. In this mode the battery doesn't get charged, any energy above the house load is exported.

3. I have set a schedule on the Eddi to heat the water up to temperature finishing just before 5.30 am. That's often enough for the day - I don't need it permanently scalding hot. (If I do, I can always boost it.) But the damn Eddi insists on ALSO heating the water periodically all day any time it's turned on. The only way to stop it is by turning it off altogether. Which prevents the scheduled boost. I find myself having to remember to turn the Eddi off the minute I wake up (by which time it's already grabbed some sunshine on sunny summer mornings) and turn it on again after sunset. Every bloody day. It's a complete pain, and a recipe for waking up to lukewarm water if I forget to turn it back on.

"13.1.6 Supply Grid – Exp Threshold This is the amount of export that must be exceeded before eddi starts diverting power to the heater loads. Once diverting starts all the surplus power, less the Export Margin (see below) will be diverted to the heater load."
Set this figure above what your maximum export value is and EDDI will do what youre wanting.

4. If I get home on a sunny afternoon and want to schedule a charge for the car overnight, I can't just plug the Zappi in and leave it to start the charge on schedule. Oh no. If the sun is shining it'll have that! I've taken to going back out to the garage after dusk to plug the car in. Someone mentioned a way of doing this from my phone rather than actually having to go outside, but it's still a right royal pain in the neck.

"Export Margin This sets a minimum level of export power which is maintained when zappi is charging in ECO or ECO+ modes. Export Margin would normally be set to 0W (zero Watts) so that all available surplus will be used to charge the vehicle. In some cases, it may be desirable to always set a minimum export level set. An instance of this would be when using zappi with a hybrid PV/battery system."
As above, this time for Zappi

This was all fine and dandy when I didn't have an export tariff. I imagine it's all fine and dandy if you have a FIT. But it's not fine and dandy if you're trying to do what John describes above. Why is this so bloody difficult?

It isnt difficult, you just need to understand the system you have and the interactions of all of the equipment.

 

[GaryMG4]

Rolfe's journey has been quite an eye opener, it all sounds so simple, sell solar, power house from battery that is charged up on cheap overnight electricity, use some solar if battery is unable to cover house use. In practice it seems quite complicated to get it to work that way.
When we moved here we had solar on FiT and I was happy that income from FiT covered our electricity bill, 8 years on FiT no longer covers electricity, I get an EV and happily charge using the granny from solar/grid because any solar reduces the cap rate I pay to charge the car. Now I've added Octopus Go to the equation I try to only charge from solar if my excess is above around 1.7kW otherwise the net cost is more than Go's 8.5p.
I originally thought, get a Zappi, that way I can syphon off any excess between 1.4 and around 3.3 kW (the max my 4kW is likely to produce) but there's a limited number of days where my excess exceeds what the Granny can consume. An Eddi would be good but I have an oil combi boiler so no immersion heater. So my circular reasoning comes back to do I need a battery, but by the sounds of it that's not simple either.

 

[johnb80]

Rolfe's journey has been quite an eye opener, it all sounds so simple, sell solar, power house from battery that is charged up on cheap overnight electricity, use some solar if battery is unable to cover house use. In practice it seems quite complicated to get it to work that way.

It actually isn't, all very doable with the right equipment.

When we moved here we had solar on FiT and I was happy that income from FiT covered our electricity bill, 8 years on FiT no longer covers electricity, I get an EV and happily charge using the granny from solar/grid because any solar reduces the cap rate I pay to charge the car. Now I've added Octopus Go to the equation I try to only charge from solar if my excess is above around 1.7kW otherwise the net cost is more than Go's 8.5p.

Have a look at Tomato Energy, 5p kWh for 6 hrs, 13p for 4 hours during the rest of the day, the balance art 23p. There's no restriction on car/charger compatibility either.

I originally thought, get a Zappi, that way I can syphon off any excess between 1.4 and around 3.3 kW (the max my 4kW is likely to produce) but there's a limited number of days where my excess exceeds what the Granny can consume.

It can certainly do that, there seems to be a good number of them on the secondhand market too.

An Eddi would be good but I have an oil combi boiler so no immersion heater. So my circular reasoning comes back to do I need a battery, but by the sounds of it that's not simple either.

Well, it is really simple. Use an AC coupled battery so its independent of your FIT system. Your FIT payments wont be affected. It will sit on your mains, charge up off peak and from solar, supplying the house when demand exceeds you current inverter or when solar PV isnt generating. Loads of systems out there that can do this or build your own if you fancy a bit of DIY.

 

[GaryMG4]

It actually isn't, all very doable with the right equipment.

Have a look at Tomato Energy, 5p kWh for 6 hrs, 13p for 4 hours during the rest of the day, the balance art 23p. Theres no restrictions on car/charger compatibility either.

It can certainly do that, there seems to be a good number of them on the secondhand market too.

Well, it is really simple. Use an AC coupled battery so it's independent of your FIT system. Your FIT payments wont be affected. It will sit on your mains, charge up off peak and from solar, supplying the house when demand exceeds you current inverter or when solar PV isn't generating. Loads of systems out there that can do this or build your own if you fancy a bit of DIY.

I plan to investigate Tomato once the new rates are published, a battery once I return from holiday. I'm still not convinced that a Zappi offers any significant benefit over a granny especially if I have a battery. There do seem to be a number of s/h Zappis on eBay, I wonder why?

 

[Rolfe]

Rolfe's journey has been quite an eye opener, it all sounds so simple, sell solar, power house from battery that is charged up on cheap overnight electricity, use some solar if battery is unable to cover house use. In practice it seems quite complicated to get it to work that way.
When we moved here we had solar on FiT and I was happy that income from FiT covered our electricity bill, 8 years on FiT no longer covers electricity, I get an EV and happily charge using the granny from solar/grid because any solar reduces the cap rate I pay to charge the car. Now I've added Octopus Go to the equation I try to only charge from solar if my excess is above around 1.7kW otherwise the net cost is more than Go's 8.5p.
I originally thought, get a Zappi, that way I can syphon off any excess between 1.4 and around 3.3 kW (the max my 4kW is likely to produce) but there's a limited number of days where my excess exceeds what the Granny can consume. An Eddi would be good but I have an oil combi boiler so no immersion heater. So my circular reasoning comes back to do I need a battery, but by the sounds of it that's not simple either.

It's quite a learning curve, because the different parts of the system interact in ways you don't necessarily anticipate until you see them doing it. It's easy to say "it's simple!" when you're sitting at the top of the learning curve with everything at your fingertips. But it really isn't beyond the wit of woman. Or indeed man.

The complication I'm discovering at the moment is that everything seems to have been designed assuming the household is on a feed-in tariff. Perhaps that was the case initially, but the variable import/export tariffs have surely been around long enough for the manufacturers to have added capability for handling these to their systems. Apparently not, though. As a result every damn appliance is queuing up to use the solar, when I want them to leave it alone and let me export it.

The house itself isn't really an issue, unless Octopus gets sticky. Whatever the house grabs for itself during the day it's not taking from the battery, and whatever the battery recovers during the day is still in there. So by exporting what's left in the battery at 11.30 I'm in effect exporting the solar I couldn't persuade the house not to use when the sun was shining. If it did it my way then the battery would be much more depleted by 11.30, with little left to export. So it's swings and roundabouts.

The Zappi is a pain, but not a large one. Simple solution, don't plug the thing in until dusk.

The Eddi is the real annoyance. I like it, because it's getting my water hotter than the central heating boiler achieves, and given the price I pay for kerosene it's probably cheaper. (Though considering that the kerosene is not getting the water particularly hot, that may be debatable.) The issue is that it's determined to keep the water scalding hot all day, when this really isn't needed. That's genuine loss, because it's pumping heat in there that's just going to dissipate through the insulation on the tank. It's such a nuisance to have to keep remembering to turn it off in the morning and on again in the evening that I might just go back to using the central heating to heat the water once it gets cold enough that I'm running it every day.

 

[Rolfe]

On many inverters there are different modes of operation, on Growatt for example, theres 'grid first' mode which does exactly what youre talking about. In this mode the battery doesn't get charged, any energy above the house load is exported.

"13.1.6 Supply Grid – Exp Threshold This is the amount of export that must be exceeded before eddi starts diverting power to the heater loads. Once diverting starts all the surplus power, less the Export Margin (see below) will be diverted to the heater load."
Set this figure above what your maximum export value is and EDDI will do what youre wanting.

"Export Margin This sets a minimum level of export power which is maintained when zappi is charging in ECO or ECO+ modes. Export Margin would normally be set to 0W (zero Watts) so that all available surplus will be used to charge the vehicle. In some cases, it may be desirable to always set a minimum export level set. An instance of this would be when using zappi with a hybrid PV/battery system."
As above, this time for Zappi

It isnt difficult, you just need to understand the system you have and the interactions of all of the equipment.

Oooh, I didn't see this post at first. Lots of good information, thank you. If I can get the Eddi to do that, then that's my main issue solved. Ditto the Zappi, although that wasn't such an issue. I don't know where to find these controls, but I will try to find the way to do it as soon as I can.

 

[johnb80]

I plan to investigate Tomato once the new rates are published, a battery once I return from holiday.

I suspect new rates will be higher on all fronts ?

I'm still not convinced that a Zappi offers any significant benefit over a granny especially if I have a battery.

Apart from:-
Charging up to 7.2kW
Variable charging rate to match solar excess
Compatible with IOG
I agree, no advantage at all.

There do seem to be a number of s/h Zappis on eBay, I wonder why?

I have several, some are removed when a new car includes a new charger, I have bought some with stuck relays and some people sell when they move house.