Powerwall / battery storage: can you share how you use it with UK energy tariffs?

[squarepeg77]

Hi,
With the VAT rate now nil on battery storage, I think a home battery may make now (almost!) sense for our household.
I’m leaning towards the Powerwall. I was considering the Givenergy AlO, but after spending some time on the Givenergy forums I’m concerned by their long-standing SOC / BMS issues.

We have 4kW of PV, a Zappi, an Eddi and an air source heat pump.

My first goal is to maximise self-consumption of solar and minimise overall electricity costs, while being kind to the grid.
As we are current on FITs payments for solar, I haven’t yet done the maths to work out whether switching to an Octopus export tariff to replace the deemed export is worth the risk. We have about 11 years left on FITs.

In summer, I think we’ll have plenty of solar to live off self-consumption.

In winter, the ASHP will often use more than one Powerwall can provide just charging once per day.

We are currently on the Octopus Agile tariff as this is cheapest for our current energy usage; the heat pump needs to run at various times through the day. We can avoid too much draw during the peak evening period on Agile.

I’m interested to learn from other Powerwall owners how you use the self consumption and time of use tariffs, in conjunction with plans like Agile, Go, Intelligent etc.

Do you use self-consumption mode in summer and time of use mode in winter, or does time of use work satisfactorily all year round?

How do you prioritise Powerwall and car charging?

I have a decent Home Assistant setup and am not averse to some automation, but a bit unsure what Fleet API will mean for third party access and so don’t know if I can rely on clever automations to nudge Powerwall behaviour long term.

Thank you.

 

[Dilly]

I have 2 Powerwalls, 41 panels, 2 Zappi’s, an Eddi and 2 EV’s.
I use time based over winter Oct-Apr and self powered the rest of the year. The cut-offs for switching are a bit variable depending on the weather.
I’m on Octopus Go, though I know others who use IO though it can be a bit of a faff.
I generate 8MWh Solar, draw 2MWh grid, export 1.2MWh and use just 60kWh peak rate grid power annually.
I had my main fuse upgraded to 100amp. The Zappi’s should load balance but I tend to let the Powerwalls draw what they like (10kWh max) and charge the EV’s alternate nights.

The powerwall’s AI (if it has any) can be challenging. Two good Solar days means that if the third is dire they may not charge as much as you’d like. Upping the reserve usually cures that.

I’m on FIT with 16 years left and don’t export enough to make switching worthwhile.

 

[Mark_T]

I’m on Octopus Go, though I know others who use IO though it can be a bit of a faff.

I've got 2xPW2 and 4kWp of solar and use IO, no 'faff' at all since they added the Zappi as a supported EVSE integration.

Fully automated using HA to protect the PW2 when charging outside the 23:30-05:30 low rate period.

Running happily with an 80A main fuse and the limiter set on the Zappi accordingly. Not actually had the limit cause any issues so far though (gas heating).

Generally stay on time-base all year as out Solar PV is relatively modest.

I have a decent Home Assistant setup and am not averse to some automation, but a bit unsure what Fleet API will mean for third party access and so don’t know if I can rely on clever automations to nudge Powerwall behaviour long term.

I take your point, but even without Fleet API Tesla have a habit of making unexpected changes that break things, but so far at least the community have quickly found solutions.

 

[phil4]

2xPW2 5.3kWp Solar, 2xEVs and a zappi.
All in IOG.

Of late, charge PW2 fully overnight at 7.5p, powers the house during the day. All solar exported at 15p.

IO usually sticks to 23:30-05:30 so very bonus slots. Those that do I just alter the PW schedule and it drains a little less.

Avg unit cost is ~7.5p over a month, with export at 15p reducing the bill further.

 

[simon_rb]

Friend of mine has an AIO and I have 2x PW. More customisation with the AIO however you are correct with the BMS issues. Also, PW literally draw nothing from the grid when in use. Prior to the most recent PW update, I would draw 0.00kW from the grid if I had enough solar and battery. (Recent update seems to draw 10Wh a day on average which is around 300Wh a month at peak rate) However the AIO will draw around 200 - 500Wh a day, same scenario. Don't regret the PW's at all.

Getting 2 is an advantage as you get 10kW's charge/discharge and even below 0 degrees outside (batteries are is our garage) they still charge/discharge at full rate. With the 10kW, it gives you the option to top the car up at full 7kW and still have 3kW for the house (if no solar generation). Before we have put a couple of ours charge in the morning from the PW, then we'll drive off and the PW's will charge back up from solar.. driving on future sunshine

I use the IO Go, I usually just charge in the off-peak window and so do the PW's in the winter, like @Dilly says; we have two Zappi's and they load share. In the summer we we can run on self power mode and usually have enough solar for house and cars.

Hope this helps! Good luck

 

[Mark_T]

I use the IO Go, I usually just charge in the off-peak window

... as long as you are not actively preventing IOG from charging outside that window then all is good...

For me, IOG very frequently prefers to charge up to 08:30 or later in the morning rather than between 00:30-0300, but that works as I don't need the car earlier than that and HA takes care of the PW.

 

[simon_rb]

... as long as you are not actively preventing IOG from charging outside that window then all is good...

For me, IOG very frequently prefers to charge up to 08:30 or later in the morning rather than between 00:30-0300, but that works as I don't need the car earlier than that and HA takes care of the PW.

I disable the smart charging so I can charge via Solar during the day. If I keep it on Smart Charging, it will always charge at full rate, drawing from the battery/grid (Zappi integration). I do fortnightly let it do its thing for 24 hours to satisfy the T&C's. For that 24 hours, I'll adjust the PW settings so it doesn't interfere too much.

 

[ACarneiro]

Current Octopus outgoing tariff means I export all my solar and I suspect in the summer I will also be buying at 7.5p during the night and then selling from batteries at 15 during the day.
Will be interesting to see how much credit I will be able to accrue per day over the summer.
I'm thinking I may well offset most of my winter bills with summer production (assuming the export rate stays as it is after teh 12 month fixed term comes to an end)

 

[Mark_T]

Current Octopus outgoing tariff means I export all my solar and I suspect in the summer I will also be buying at 7.5p during the night and then selling from batteries at 15 during the day.

Exactly, unless your Solar PV is old enough to benefit from a FiT payment there is more to be made from exporting the excess than you save by charging the EV with it...

 

[squarepeg77]

Thanks for all the replies! I'll have a good look at Intelligent Octopus.

Two Powerwalls certainly seems to be common! Not sure I can justify a second PW - total cost would then be in excess of 10 years of our current electricity bill... maybe I need some different man maths

A few follow-on questions:
- Is the "protecting the Powerwall" automation in Home Assistant just setting the backup reserve to the current Powerwall charge percentage?

- what is the minimum solar surplus needed for Powerwall to start to charge? I'm wondering how much of the "shoulder" solar that PW can mop up

- those of you with Zappi chargers: I think I need another CT to monitor the Powerwall, right? And how do you prioritise Powerwall and Zappi? Assuming you try and charge car with solar surplus and Eco+ at some point.

- Are there any unexpected gotchas from the Powerwall? Intrusive fan noise or anything? I'm thinking of those things that you might not know when purchasing and are stunned to find out afterwards (e.g. wipers )

 

[simon_rb]

Thanks for all the replies! I'll have a good look at Intelligent Octopus.

Two Powerwalls certainly seems to be common! Not sure I can justify a second PW - total cost would then be in excess of 10 years of our current electricity bill... maybe I need some different man maths

A few follow-on questions:
- Is the "protecting the Powerwall" automation in Home Assistant just setting the backup reserve to the current Powerwall charge percentage?

- what is the minimum solar surplus needed for Powerwall to start to charge? I'm wondering how much of the "shoulder" solar that PW can mop up

- those of you with Zappi chargers: I think I need another CT to monitor the Powerwall, right? And how do you prioritise Powerwall and Zappi? Assuming you try and charge car with solar surplus and Eco+ at some point.

- Are there any unexpected gotchas from the Powerwall? Intrusive fan noise or anything? I'm thinking of those things that you might not know when purchasing and are stunned to find out afterwards (e.g. wipers )

I don't use HA for my PW; however setting the backup reserve to current percentage will "pause the battery" at a guess.

Minimum Solar capture is.. less than 100 watts I believe.. It's not like the car where you need 1400 watts. Ours capture every watt and doesn't export anything to the grid (unless I want it to)

Zappi CT clamp for the battery is correct. Then it will show in the app and you can set how the Zappi behaves with the battery (not from the app though; settings are on the charger itself)

You'll be happy to know I have no issues with the wipers on my PW

 

[Js1977]

- those of you with Zappi chargers: I think I need another CT to monitor the Powerwall, right? And how do you prioritise Powerwall and Zappi? Assuming you try and charge car with solar surplus and Eco+ at some point.

- Are there any unexpected gotchas from the Powerwall? Intrusive fan noise or anything? I'm thinking of those things that you might not know when purchasing and are stunned to find out afterwards (e.g. wipers )

It's up to you if you want to lark about with HA but If you want the sure thing, talk to your installer as to see if you can have the charger on a separate circuit so that the powerwall does not see it or ask about an external CT clamp for the powerwall (its not your average cheap CT clamp).

 

[simon_rb]

It's up to you if you want to lark about with HA but If you want the sure thing, talk to your installer as to see if you can have the charger on a separate circuit so that the powerwall does not see it or ask about an external CT clamp for the powerwall (its not your average cheap CT clamp).

I've had no issues with my Zappi being on the Powerwall circuit. It gives me options to charge from the PW if I'd like to. It's only an issue if you get extra IO charging slots. I get enough charge from the standard 23:30 - 05:30 so it hasn't been an issue for me. Also, if there is a power cut, my Zappi's will stop charging. Think it has something to do with were the CT clamp is so if there is an outage and you're charging, the Zappi will stop charging until the grid returns. This is the behaviour I was hoping for and seemed to inherit by accident

 

[Js1977]

I've had no issues with my Zappi being on the Powerwall circuit. It gives me options to charge from the PW if I'd like to. It's only an issue if you get extra IO charging slots. I get enough charge from the standard 23:30 - 05:30 so it hasn't been an issue for me. Also, if there is a power cut, my Zappi's will stop charging. Think it has something to do with were the CT clamp is so if there is an outage and you're charging, the Zappi will stop charging until the grid returns. This is the behaviour I was hoping for and seemed to inherit by accident

Yes, its fine if you dont actually use IO

 

[Mrklaw]

was: Intelligent octopus, set the battery to charge to 25/50/75/100 depending on season (would be just about to set it to 75%) and maximise solar self consumption.

now : Intellignet gives you access to Octopus SEG at 15p for export, and 7.5p import. So the more efficient route would be - charge battery to 100% every night, use the overnight as much as possible and home stays on battery - maximise solar export as its worth more than the electric in your battery. If your battery automatically charges from solar first you coudl also force discharge a chunk before 11:30 when the cycle starts again.

4kwp solar so maybe 4000kwh generated? on FIT deemed export thats 2000kwh at 5p (ish) - £100 a year. If you give up deemed export and move to SEG, that could be 4000kwh * 15p or £600 per year. Note: you can keep generation FIT and just give up deemed to move to SEG - you don’t lose the whole thing.

In theory thats £50pm effective credit whihc would pretty much cover my electric bill

 

[ACarneiro]

- Are there any unexpected gotchas from the Powerwall?

No.
They’re seamless and work as intended for me. Quiet and reliable so far (within the constraints of the Tesla Vision-like AI control that Tesla seem so annoyingly fond of).
You’ll need to be aware of IO if that’s the tariff you’re on but I’m hoping (against hope) as the Powerwall fleet grows and Tesla opens their APIs that Octopus will eventually integrate their Intelligent tariff with the Powerwall ecosystem.

 

[ringi]

Can get 2 to 3 times the capacity with Fogstar batteries on a 3rd party inveter for the cost of a PW. Could be much better option if have heatpump and wish to move all electricity usage to ofpeak.

 

[squarepeg77]

was: Intelligent octopus, set the battery to charge to 25/50/75/100 depending on season (would be just about to set it to 75%) and maximise solar self consumption.

now : Intellignet gives you access to Octopus SEG at 15p for export, and 7.5p import. So the more efficient route would be - charge battery to 100% every night, use the overnight as much as possible and home stays on battery - maximise solar export as its worth more than the electric in your battery. If your battery automatically charges from solar first you coudl also force discharge a chunk before 11:30 when the cycle starts again.

4kwp solar so maybe 4000kwh generated? on FIT deemed export thats 2000kwh at 5p (ish) - £100 a year. If you give up deemed export and move to SEG, that could be 4000kwh * 15p or £600 per year. Note: you can keep generation FIT and just give up deemed to move to SEG - you don’t lose the whole thing.

In theory thats £50pm effective credit whihc would pretty much cover my electric bill

Thanks, that is certainly an interesting option!

We’re getting between 3500-3800kWh per year; relatively old panels and some shading, so maybe £540 at 15p/kWh export.

We’ll be getting a little over 7p/kWh deemed this year, I think. So in the region of £125.

If we didn’t self-consume any solar, we’d need to buy more from the grid, perhaps 1750-2000kWh (pre-battery stats), so at 7.5p/kWh that would cost another £130 (say).

So £540 - £125 - £130 = £285 net.

I’m not sure yet about giving up a guaranteed index-linked payment, for the next 12 years or so, for Octopus Fixed Export at 15p. I don’t suppose there’s any guarantees beyond a 12 month contract about how long that might be around? With Agile rates already below 15p/kWh for much of the day, I’m not sure how sustainable that price will be?

 

[Dilly]

Thanks, that is certainly an interesting option!

We’re getting between 3500-3800kWh per year; relatively old panels and some shading, so maybe £540 at 15p/kWh export.

We’ll be getting a little over 7p/kWh deemed this year, I think. So in the region of £125.

If we didn’t self-consume any solar, we’d need to buy more from the grid, perhaps 1750-2000kWh (pre-battery stats), so at 7.5p/kWh that would cost another £130 (say).

So £540 - £125 - £130 = £285 net.

I’m not sure yet about giving up a guaranteed index-linked payment, for the next 12 years or so, for Octopus Fixed Export at 15p. I don’t suppose there’s any guarantees beyond a 12 month contract about how long that might be around? With Agile rates already below 15p/kWh for much of the day, I’m not sure how sustainable that price will be?

Tricky one! There is talk about deemed export being dropped to be replaced by SEG or similar. I believe some suppliers have already implemented it. Not sure though. Nor am I sure what deal will follow. I haven’t been contacted by Octopus about it.

Difficult to know whether to sit tight. I assume your FIT rate is pretty good though!

 

[squarepeg77]

Can get 2 to 3 times the capacity with Fogstar batteries on a 3rd party inveter for the cost of a PW. Could be much better option if have heatpump and wish to move all electricity usage to ofpeak.

I take your point that cheaper alternatives are available.

However I don’t know if the differential is quite that big… I’m seeing 15kWh Fogstar for £3000, 30kWh for £6000, with an inverter and installation to add on. (And I don’t know much about other inverters!)

Powerwalls can be installed for less than £8000 now.

It would be nice to run heat pump entirely on off-peak electricity…