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Powerwalls in the UK
- Thread starter Timd92277
- Start date
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
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).
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).
"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.
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?
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.
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
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
Member
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.
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.
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.
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.
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.
That's not implausible. It's a heavy beast and needs two people to get it in place plus some minor items (cables, isolator ... ) to connect it then add on the overheads that a DNO will add to the basic costs. A smaller company would probably have lower overheads.
Having your DNO install the Powerwall, I didn't know they did that. Ours was done by a local installer. Practically it took 3 guys to get the heavy Powerwall on a pallet off the van, and then 2 stayed to lift it onto the wall mount and do the wiring and get the Gateway configured. I paid £550 + VAT in April 2021 for the labour and £75 delivery, rest was parts.
This seems to be something new that the DNO have started charging for.
We ordered our Powerwall in August 2020 with a delivery date of November the same year. There was no discussion about any cost for DNO approval which would be required for our additional solar as well as utilising the full 5kW of the Powerwall. November came and went, additional solar was installed but the Powewall was pushed back into Jan/March/July/November 2021.
In the meantime our installer 'lost' our DNO application and had to re-apply. They then contacted us to ask for £750 to pay for the DNO to design and then come onsite to check our installation. We were given permission for the full export of our solar but the Powerwall wasn't allowed to export.
I queried what this design cost was for and how they would be able to check onsite if the export limit was set, didn't get a response. Powerwall was installed in November 2021 but appears to be limited to the 16A discharge limit.
I've got a few things that I need to discuss with the installer having had the system in for a couple of months. This will be one of them, the other is whether we require an earth rod to be installed.
Hope this helps.
Ah DNO approval fees... I may have misunderstood the post from @NikoV6. I have to wonder if having permission to export at 5kWh rather than the standard 3.8kWh (that does not need special approval) is worth £750. I guess the main use would be to enable the Powerwall to supply more house load during a grid outage, but then would also not last as long.
I had one installer offer to configure the Powerwall to the higher rate without telling the DNO, not the supplier that I went with. I was asking about getting 5kWh from the Powerwall, and they said DNO approval was a pain and so not to worry they could just configure it anyway. Not going to comment on that further.
I had one installer offer to configure the Powerwall to the higher rate without telling the DNO, not the supplier that I went with. I was asking about getting 5kWh from the Powerwall, and they said DNO approval was a pain and so not to worry they could just configure it anyway. Not going to comment on that further.
The discharge limit should only apply when on-grid. When the system islands itself, it should discharge to its full limit of 5kW continuous, 7.5kW peak (10sec?) per Powerwall. The strange thing is that the system should be allowed to supply all house load up to 5kW without exporting battery energy. I think that would be worth the £750 one time fee.
Could the Powerwall be designed to do what you suggest @miimura? I believe that the current concern is that switchover to island mode is never clean and so 5kW could be briefly exported onto the grid in an outage during. I have had some outages now, and it isn't instantaneous, so I guess it could export during that. You would need a number of neighbouring properties with Powerwalls for this to be an actual issue for the grid, but they have set the default acceptable without approval to be 3.8kW and anything more requires full assessment.
I so rarely exceed 3.8kW domestic load and draw on the grid at peak rate (some pre-battery usage and power saving habits helping out) it would take a long time to re-coup the £750 fee.
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