Considering getting a Powerwall

[SimonT]

I recently switched to self-powered too.
I’ve noticed that while on balanced, our grid draw was about 500 watts per day, while on self-powered it’s risen to almost 1000 watts per day. Most of that is overnight.
Have you seen anything similar?

I have only used the self powered option. I think using time based might be worthwhile in the winter if you have a cheap offpeak and can charge it overnight. I'm finding that in half decent sunshine our PW is usually 100% charged any time between 1300 and 1500.

 

[gangzoom]

I recently switched to self-powered too.
I’ve noticed that while on balanced, our grid draw was about 500 watts per day, while on self-powered it’s risen to almost 1000 watts per day. Most of that is overnight.
Have you seen anything similar?

Been on 'self powered' just over a day. No noticable change in back ground energy usage.

Overall grid consumption is falling off a cliff for us. Yes not doing many miles in the EV helps, but the PW can charge the car overnight fine at 4KW. If I could get to 6pm daily with 100% SOC on the PW that would be enough to cover 20-25 miles a day of driving.

Very seriously now considering adding more solar PV + another PW to the house extension we are still planning.

Between October to March solar is next to useless, but for the rest of the year looking great. Plus another PW will allow additional E7 load shifting during winter months.

The big issue as always is cost, also keen on getting an heat pump to help heat the new rooms in the extension with the added benefit of using that as AC in the summer. All these costs add up very quickly .

But than again additional mortgage borrowing has never been cheaper, 1.75% 5 year fixed, versus inflation of 2%, its almost rude not too take up such an offer if it allows additional value to be added to the house???

Given we already have the wiring for a PW, and doing major electrical work am hoping additional labour/install cost will no be massive compared to all the other build costs. If I can get the hardware needed for a budget of £10-15k might be able to justify the additional cost. Need to do some more Tesla based man maths I feel

 

[ACarneiro]

Can a second Powerwall just “bolt on” to the first one?
Are the maximum rates of charge and discharge then cumulative?

 

[gangzoom]

Can a second Powerwall just “bolt on” to the first one?
Are the maximum rates of charge and discharge then cumulative?

I believe so, and yes charge/discharge rates are cumulative but the grid supplier still has to sign everything off.

As for how good PWs are, yesterday we used just 0.1kWh of grid electricity, and for the whole week we are at sub 20kWh despite also charging an electric car (am a key worker so still doing 10-15 mile daily commute). So about £3 bill last week including standing charge as we are also on E7!!!

This weeks weather is also looks fab, sub £20 electricity bill is looking good this month. May even hit sub £15/month at some point this year including EV charging costs .

 

[ACarneiro]

Well, I think I may just have to go down that route although I suspect that with two EV chargers already, the DNO may kick up a stink about adding a Powerwall to the mix (all three charging during E7 period in the night would make for a 96A continuous draw for a few hours and they may well not be happy about that, even on a 100A fuse).

 

[kuruma]

I recently switched to self-powered too.
our grid draw was about 500 watts per day, while on self-powered it’s risen to almost 1000 watts per day. Have you seen anything similar?

nope. We have 0-0.3 kWh of grid draw a day. Here's April so far. I switched to self-powered on the 6th.

 

[kuruma]

Hi Kuruma - how many KW of PV do you have?

3.6kW... standard semi-detached install of 12 panels. South facing though.

 

[Dilly]

Can a second Powerwall just “bolt on” to the first one?
Are the maximum rates of charge and discharge then cumulative?

Yes it’s cumulative. Yes they can literally and physically bolt on.
Around 1 pm, our two were taking in 10Kw from our PV.
In addition, two Can discharge at 10Kw but it doesn’t stop there.
If you have PV that can also add to your draw.
It’s an unlikely scenario, but in theory I could charge 2 cars and run the immersion diverter (13Kw) whilst running two ovens and a hob (7Kw) using 10Kw from PV and 10Kw from the Powerwalls without risk to my mains feed as it’s effectively dormant.

 

[ACarneiro]

Yes it’s cumulative. Yes they can literally and physically bolt on.
Around 1 pm, our two were taking in 10Kw from our PV.
In addition, two Can discharge at 10Kw but it doesn’t stop there.
If you have PV that can also add to your draw.
It’s an unlikely scenario, but in theory I could charge 2 cars and run the immersion diverter (13Kw) whilst running two ovens and a hob (7Kw) using 10Kw from PV and 10Kw from the Powerwalls without risk to my mains feed as it’s effectively dormant.

That’s really helpful, thank you!
Out of interest, when you’re load shifting, what’s the rate of charge that you get on the Two Powerwalls from the mains? My 100A fuse will just about take two cars charging (64A) and a Powerwall at another 32A or so...

 

[gangzoom]

That’s really helpful, thank you!
Out of interest, when you’re load shifting, what’s the rate of charge that you get on the Two Powerwalls from the mains? My 100A fuse will just about take two cars charging (64A) and a Powerwall at another 32A or so...

Do you mean charging both EVs and PW at the same time? Or charging two EVs with the PW?

Our PW will only charge at 4KW sustained - might even by 3.6KW, and at discharge/sorting our demand the software just does it all.

I managed to reset the sensor on our HoneyWell immersion heater today, so any excess solar that we have which isn't going into the PW because it's full is going to heating the hot water (the PW reports this as grid export), so we are using every single last kWh of electricity the solar PVs generate

@ACarneiro I think you just need to get your PW(s) installed, it really is a fab bit of kit .

 

[ACarneiro]

Do you mean charging both EVs and PW at the same time? Or charging two EVs with the PW?

Our PW will only charge at 4KW sustained - might even by 3.6KW, and at discharge/sorting our demand the software just does it all.

I managed to reset the sensor on our HoneyWell immersion heater today, so any excess solar that we have which isn't going into the PW because it's full is going to heating the hot water (the PW reports this as grid export), so we are using every single last kWh of electricity the solar PVs generate

@ACarneiro I think you just need to get your PW(s) installed, it really is a fab bit of kit .

I meant charging both EVs and the Powerwall from the mains during cheap E7 time...
4kW seems very slow, will take nearly 8 hours to fully charge two PWs?

I’m really keen on having them but I have no solar yet so the whole shebang will cost me around £25k and I don’t have that much money available just yet.

 

[Dilly]

That’s really helpful, thank you!
Out of interest, when you’re load shifting, what’s the rate of charge that you get on the Two Powerwalls from the mains? My 100A fuse will just about take two cars charging (64A) and a Powerwall at another 32A or so...

Cars charge at 7KW & 3.6KW max. I’ve set an overriding limit of 90amps on the higher one So that limits the total draw to protect the main fuse. That’s more for winter use when I use cheap rate 4 hour period. Powerwall will draw what it thinks it needs, 3.6 PHEV will fully charge, 7 EV will charge what it can in the time given with the remaining power available. Not overly bothered with the EV, I can charge over several days if needed.
The Powerwalls are pretty clever. They expect some solar input to follow to fill up The next day and mostly get it right. Generally they start to draw 8-10KW and drop back to around 7KW when charging from the grid.
I just noticed that we had two power cuts on Sunday. Never noticed!
Currently, solar charging to 100% daytime. Heating water from them early morning (6KW). Leaves 50% usable power and 15% Minimum backup for long power cuts.

 

[gangzoom]

I meant charging both EVs and the Powerwall from the mains during cheap E7 time...
4kW seems very slow, will take nearly 8 hours to fully charge two PWs?

I’m really keen on having them but I have no solar yet so the whole shebang will cost me around £25k and I don’t have that much money available just yet.

Each PW will charge at 3.6KW sustained I believe, so two will draw around 30amps and fill up in around 4hrs. Two EVs + two PW will push a 100amp fuse but thats not a reason not to get them. The amount of electricity you will save on E7 versus full price will be massive if you are actually using that much juice daily!!

You 100% need solar to take advantage of PWs, when coupled together you really can start making use of solar generation potential.

Cost is always an issue, but for me I would rather spend £20k on additional solar + another PW than get another EV, or get a £30k one instead of a £50k one instead if it means getting another PW+solar. EVs you only use a few hours a day max, the PWs are ALWAYS doing something .

 

[ACarneiro]

Well, I commute 100 miles daily and my housemate probably does about 70 so we do use a lot of electricity.
Best start saving

Thanks for the information, nobody had been able to really answer these questions for me

 

[Dilly]

I meant charging both EVs and the Powerwall from the mains during cheap E7 time...
4kW seems very slow, will take nearly 8 hours to fully charge two PWs?

I’m really keen on having them but I have no solar yet so the whole shebang will cost me around £25k and I don’t have that much money available just yet.

If you’re on E7 you probably get a longer cheap rate than my four hours. Also, if you have no solar the Powerwall algorithm will take this into account and aim to fully charge within the allotted time.
It’s certainly worth having a discussion with an experienced installer and outline your requirements and intentions.

 

[roadcred]

anyone from surrey recommend an installer that they used for powerwall 2?

 

[markharro]

Subject to still having funding available at the end of this crisis we have plans to build a passive house next year with a pretty large PV array - probably about 12-14kw coupled with a powerwall. One thing that I cant really find info on and that is how we coordinate this with our DNO? We are in southeast Scotland so it is SP Energy Networks. I have made initial contact with them but the feedback is really too technical for me. I just wondered what the potential issues were/costs involved in getting consent to connect an array of this size to the grid? Thanks.

 

[kevuwk]

Subject to still having funding available at the end of this crisis we have plans to build a passive house next year with a pretty large PV array - probably about 12-14kw coupled with a powerwall. One thing that I cant really find info on and that is how we coordinate this with our DNO? We are in southeast Scotland so it is SP Energy Networks. I have made initial contact with them but the feedback is really too technical for me. I just wondered what the potential issues were/costs involved in getting consent to connect an array of this size to the grid? Thanks.

I would guess a minimum requirement would be to have a three-phase supply for an array of that size but you should probably work with an MCS certificate company and let them handle the DNO

 

[markharro]

Yes you're right of course - I am simply trying to do as much of my own research as possible atm to try to understand the big picture (and outline costs) at this stage. Is there much involved in installing a 3 phase supply?

 

[kevuwk]

Yes you're right of course - I am simply trying to do as much of my own research as possible atm to try to understand the big picture (and outline costs) at this stage. Is there much involved in installing a 3 phase supply?

https://www.ukpowernetworks.co.uk/electricity/upgrade-reduce-electricity/whats-involved