Powerwalls in the UK

[Timd92277]

Im debating if a powerwall is worth the money in the UK
I currently have solar panels so maybe a good idea
Would 5 solar panels fully charge a m3 standard range ever night?
Has anybody got them installed in the UK if so what’s the whole process like ?

 

[MarkJ]

Im debating if a powerwall is worth the money in the UK
I currently have solar panels so maybe a good idea
Would 5 solar panels fully charge a m3 standard range ever night?
Has anybody got them installed in the UK if so what’s the whole process like ?

The Powerwall will have quite a long payback, probably over 15yrs, but if you have the cash spare would be a good idea.
However, using it to charge an EV overnight isn't its best use since it only stores 13.5kWh and I think your car's battery is about 50kWh.
What would be a good idea is something like Octopus Go tariff as electricity is 5p per kWh for 4 hours overnight and is long enough to add about 30kWh to your car (good for about 100 miles) and charge your PW from grid so your house uses the PW during the day.
This way all your energy is at the off peak rate.
Mark

 

[Timd92277]

The Powerwall will have quite a long payback, probably over 15yrs, but if you have the cash spare would be a good idea.
However, using it to charge an EV overnight isn't its best use since it only stores 13.5kWh and I think your car's battery is about 50kWh.
What would be a good idea is something like Octopus Go tariff as electricity is 5p per kWh for 4 hours overnight and is long enough to add about 30kWh to your car (good for about 100 miles) and charge your PW from grid so your house uses the PW during the day.
This way all your energy is at the off peak rate.
Mark

Many thanks for the reply!

 

[JohnRatsey]

I have 15 panels and the annual production is about 4000kWh ie an average daily output of about 11kWh but this varies between around 1kWh on a murky winter day and 30kWh on a very clear summer day. If you have only 5 panels then your output will be around 1/3rd of these numbers (depending on panel rated output).

I bought a Powerwall because only about 1/4 of my solar production was getting used at home due to a mis-match between production and demand. Even so, the big daily differences in generation mean that only 1/2 of the production gets used on the premises. However, charging the Powerwall using cheaper night-time electricity (I was on Economy 7 but have just switched to the Octopus Go) means that much more of the household consumption will use cheap power. The major constraint now is the default 16A limit for generation (see here for more info) which gets applied to Powerwalls even though they are not intended (at the moment) to export to the grid and means that the battery can't meet loads exceeding about 3.68kW. However, such demand spikes tend to be fairly short and often solar generation is available.

A further factor in calculations is the battery's efficiency. Tesla says 90% but power is used to keep the battery working even if it's not doing anything and the difference between power in and power out over a year suggests an overall efficiency of about 85%. This equates to 6kWh of solar or off-peak charging giving 5kWh out and effectively means that the cost of using Octopus Go electricity stored in the battery is 6p/kWh.

If your annual household demand (excluding vehicle charging) is, say, 4000kWh and 1000kWh is provided by direct from solar then, assuming that 2500kWh could be stored cheap electricity the battery could provide an annual saving of possibly 10p/kWh (current electricity tariff - 6p) x 2500 = £250. By itself that will give a very long payback period well beyond the guaranteed working life of the battery. If combined with storing solar genertion then the sums will improve as they also would if daytime electricity tariffs increase (at the same time I wonder how long Octopus can keep the 5p/kWh tariff as demand due to night-time charging increases).

 

[MarkJ]

"The major constraint now is the default 16A limit for generation (see here for more info) which gets applied to Powerwalls even though they are not intended (at the moment) to export to the grid and means that the battery can't meet loads exceeding about 3.68kW."

I pretty much agree with all your other points but would add that my single PW in the UK can and does output at 5kW continuous. So either yours has been incorrectly installed or is a limitation of your distribution network.

 

[JohnRatsey]

I pretty much agree with all your other points but would add that my single PW in the UK can and does output at 5kW continuous. So either yours has been incorrectly installed or is a limitation of your distribution network.

Did your installer obtain permission from the District Network Operator to exceed the 16A limit? If so, what was the cost of the process?

 

[MarkJ]

Did your installer obtain permission from the District Network Operator to exceed the 16A limit? If so, what was the cost of the process?

I'm sorry, this was all behind the scenes and not discussed with me or charged extra for. I just thought it was standard. From what other UK PW owners have said I think they all get 5kW as standard.

 

[fren]

great for UK , in france after 2,5 years i m still waiting ... installed pannels and since 8 month a wind turbine
in winter /wind / nosun ... one day i produced 27Kw ( 5kw wind turbine compared with 2,6kw pannels )
planning 2 pw2 , but sooo difficult to charge , in summer i can produce 10 to 15kw with sun / day maximum, in winter .. cross fingers 1kw some cloudy days max if no wind

 

[sashton]

I'm sorry, this was all behind the scenes and not discussed with me or charged extra for. I just thought it was standard. From what other UK PW owners have said I think they all get 5kW as standard.

Applying is generally free. Approval beyond 16A or below is simply a notification process to the DNO but above 16A approval is required before commissioning. Grid reinforcement can be expensive but running unauthorised over spec kit can render your insurance void.
It is simple to tell if your installer has followed the process as it results in a completed DNO connection agreement which should be signed by your installer (or you) and kept for your records.

 

[Solar1920]

Did your installer obtain permission from the District Network Operator to exceed the 16A limit? If so, what was the cost of the process?

Hi John, you can still get full utilisation of your PW even if your export is limited to 16A.
I’ve a setup similar to yours 4K plus 1 x PW and my DNO application was refused, but my installer has setup the system so exporting is limited.
When the PW is still accepting charge, all solar can be utilised to charge it and for house use all solar is available for the house use if needed plus 5kW from the PW, but when the PW is full, all solar and 5kW PW is still available for the house but if I start exporting solar this is limited to 3.68kW and if the unused solar being exported exceeds 3.68kW the solar gets clipped. Therefore I get to use the full output of my PV system for internal use and I still get to use the full 5kW of the PW day or night. Only exporting is affected.
So if your setup is really annoying you there are ways around it.

 

[JohnRatsey]

Hi John, you can still get full utilisation of your PW even if your export is limited to 16A.
I’ve a setup similar to yours 4K plus 1 x PW and my DNO application was refused, but my installer has setup the system so exporting is limited.
When the PW is still accepting charge, all solar can be utilised to charge it and for house use all solar is available for the house use if needed plus 5kW from the PW, but when the PW is full, all solar and 5kW PW is still available for the house but if I start exporting solar this is limited to 3.68kW and if the unused solar being exported exceeds 3.68kW the solar gets clipped. Therefore I get to use the full output of my PV system for internal use and I still get to use the full 5kW of the PW day or night. Only exporting is affected.
So if your setup is really annoying you there are ways around it.

Thanks. Very useful insight. However, my solar generation appears to be capped at the 16A limit (~3.68kW) irrespective of whether or not the battery is charging. To me, this makes sense as the inverter (Solar Edge) isn't aware of the battery.

The battery, on the other hand, is aware of different power flows. I'll have to pluck up the courage to investigate the battery configuration (but not while I've got the ongoing issue of erratic charging from solar). Better still, while I'm in correspondence with Tesla I'll ask about this limit.

When did you get your battery? I'm wondering if an option was added after mine was installed in March 2018 and a setting selected would be carried through any software updates. It is clearly capped at the 16A limit and any household demand exceeding that + current solar generation has to come from the mains supply.

 

[Solar1920]

Thanks. Very useful insight. However, my solar generation appears to be capped at the 16A limit (~3.68kW) irrespective of whether or not the battery is charging. To me, this makes sense as the inverter (Solar Edge) isn't aware of the battery.

The battery, on the other hand, is aware of different power flows. I'll have to pluck up the courage to investigate the battery configuration (but not while I've got the ongoing issue of erratic charging from solar). Better still, while I'm in correspondence with Tesla I'll ask about this limit.

When did you get your battery? I'm wondering if an option was added after mine was installed in March 2018 and a setting selected would be carried through any software updates. It is clearly capped at the 16A limit and any household demand exceeding that + current solar generation has to come from the mains supply.

Mine was installed in July 2019. I also have a SolarEdge inverter, I would need to check to be sure but I believe that the setup with mine uses a modbus meter, this communicates back to the inverter and the inverter then knows if any exporting exceeds 3.68kW and clips the solar. It doesn’t know about any battery, the PW is not involved in the export limitation.
I understand the PW can be limited to 3.68kW in the setup configuration, so it sounds like both your PW and inverter are set at a fixed limit.

 

[JohnRatsey]

Tesla support have replied quickly regarding my query on the power limit.

Your current grid code is the G83 which means that the battery is allowed to charge and discharge at max. 3.8kWh.


The only option you have is to ask your DNO to get an upgrade to the G59 grid code that allows the battery to charge and discharge at 5kWh. It is something that you have to request and they can approve it or not.



If we don’t get their approval, and written statement, we are not allowed to change it from our side.

It looks like your installation has a bit more intelligence with the inverter sensing the export power whereas mine just looks at the inverter output. However, the solar was installed first before a battery was considered. I'm not so worried about the cap on the inverter output as it's only a few days per year when the sky is clear enough for the cap to show up on output graph.