Tesla Powerwall 2 economics- any real data?

[mikemillar]

I’m looking at the economics of installing a single Powerwall 2. Battery backup in our house has never been an economic proposition. With PW2 it’s looking better, but still not quite worth it. We have normal on grid dual rate supply (I charge our Model S at night and it costs £250/year-12000 miles). We also have the standard 4kW solar panel installation which generates 3500kWh per year - south of England.

I’m looking for real-world UK figures for the difficult to assess variables, particularly solar input to the PW2. After several hours of spreadsheet calcs and playing with the variables, some of which are difficult to assess, I come out with a probable loss of about £100 per year over a 15 year useful life – that’s the life I’ve seen mentioned on the internet. The Tesla website gives the current price of PW2 as £7800 for an easy installation.

The most difficult variable to assess is the quantity of solar that would actually be available to charge the PW2. We use a very consistent 8.8kWh per day of peak rate electricity so the 13.5kW PW2 would easily supply all our peak rate demand. It would get it from either solar (free) or night low rate charging (about 5.5p/kWh). My best estimate from my existing solar data on real solar surplus over demand is 35% solar and 65% Low rate. In summer, on many days (but not all), there’s more than enough to fully charge (replace the 8.8kWh usage). In December/January there’s never nearly enough. Has anyone worked out actual real world figures for solar input?

Other variables that affect the numbers are:
Rate of electricity inflation, rate of interest (£7800 in the building society or equity investments)
Daily peak rate demand.
Any night low rate supplied by remaining PW2 charge – very marginal effect.
Useful life of PW2, and a few other variables like out of warranty costs.

I don’t see charging the Tesla from the PW2 as viable. There would only be sufficient surplus on some summer days after supplying the house peak rate demand, and it wouldn’t amount to much of the Tesla’s charge demand (typically say 30kWh for my usual 50 mile usage. And doing that instead of feeding the house peak rate demand is economic madness.

Any thoughts and real numbers on this would be most useful. I do have more detail about my calculations should anyone be interested, but this post is long enough already!

 

[The stag]

I’m looking at the economics of installing a single Powerwall 2. Battery backup in our house has never been an economic proposition. With PW2 it’s looking better, but still not quite worth it. We have normal on grid dual rate supply (I charge our Model S at night and it costs £250/year-12000 miles). We also have the standard 4kW solar panel installation which generates 3500kWh per year - south of England.

I’m looking for real-world UK figures for the difficult to assess variables, particularly solar input to the PW2. After several hours of spreadsheet calcs and playing with the variables, some of which are difficult to assess, I come out with a probable loss of about £100 per year over a 15 year useful life – that’s the life I’ve seen mentioned on the internet. The Tesla website gives the current price of PW2 as £7800 for an easy installation.

The most difficult variable to assess is the quantity of solar that would actually be available to charge the PW2. We use a very consistent 8.8kWh per day of peak rate electricity so the 13.5kW PW2 would easily supply all our peak rate demand. It would get it from either solar (free) or night low rate charging (about 5.5p/kWh). My best estimate from my existing solar data on real solar surplus over demand is 35% solar and 65% Low rate. In summer, on many days (but not all), there’s more than enough to fully charge (replace the 8.8kWh usage). In December/January there’s never nearly enough. Has anyone worked out actual real world figures for solar input?

Other variables that affect the numbers are:
Rate of electricity inflation, rate of interest (£7800 in the building society or equity investments)
Daily peak rate demand.
Any night low rate supplied by remaining PW2 charge – very marginal effect.
Useful life of PW2, and a few other variables like out of warranty costs.

I don’t see charging the Tesla from the PW2 as viable. There would only be sufficient surplus on some summer days after supplying the house peak rate demand, and it wouldn’t amount to much of the Tesla’s charge demand (typically say 30kWh for my usual 50 mile usage. And doing that instead of feeding the house peak rate demand is economic madness.

Any thoughts and real numbers on this would be most useful. I do have more detail about my calculations should anyone be interested, but this post is long enough already!

 

[The stag]

Hi Mike have plenty of data on my powerwall 2 I have a solar system of 8 kw and a power wall 2 system is it cost effective well mine is I am approx 93% off the grid and also have FIT payments for generation and FIT payments for electricity going up the grid I charge my car from my solar system and still have plenty for charging powerwall 2 I also have a solar I boost which also does all of my hot water from end of March until October savings Fit payments are approximately about £300 per annum my electricity bill for last year was £100 so already £200 pounds better off let’s look at previous electricity bills my electricity bill used to be approx £1400 my cost for petrol in my car was £4000 per annum now my electricity cost for my car is close to zero so a saving of £4000 per annum the total cost of my solar and powerwall 2 system was £12,000 so after about 3/4 years I will be in the clear pretty good payback in my opinion and that doesn’t include the savings on my hot water from my gas through the summer which I have estimated at about £400 per annum ok I haven’t included the cost of my car in this but after 3/ 4 years my car will be getting cheaper and cheaper so for me it’s worth it you have to oversize solar system for it to be cost effective my powerwall 2 was only about £6000 one of the first installed in the uk over the long term it’s a no brainier when you have an electric car aswell

 

[mikemillar]

Many thanks, Stag - very useful info. However, I think if you have an 8kW solar system that would make quite a difference. How may kW does your solar generate in a year? And at the lower price of £6000 (including installation?) it becomes economic sense. Putting in 93% solar input and £6000 purchase price to my spreadsheet gives a lifetime profit of nearly £200 per year, which would be well worth it. Damn - missed the boat!

When we had the 4kW solar installed (2014) I understood that that was the maximum to benefit from the domestic FIT rates. Also from memory of being stationed at Lossiemouth in the 1970's there was a lot of very clear, if rather windy weather. However, it hardly got dark in winter - The chaps down the back of our Shackleton never saw daylight in the winter!! However, you must have a rather low solar generation in December/January. Do you have any other source, like a wind turbine or waterwheel? I can't imagine that you can really get enough solar in the depths of winter to supply most of your requirements, although maybe they are rather lower than ours- we use 2 immersion heaters on low rate electricity and have 3 deep freezes (trying to be self sufficient!) With Tesla Model S, annual peak 3200kW, Low 9000kW. Annual bill £1000, Solar FIT payments £600 per annum. Solar will pay for itself in about 12-14 years.

I've just read that if/when one has a smart meter installed they read your real solar Export rather than assuming 50% and pay you on the real quantity exported. I only export 25%. I gather you can refuse to have a Smart meter - I certainly shall!

 

[The stag]

Many thanks, Stag - very useful info. However, I think if you have an 8kW solar system that would make quite a difference. How may kW does your solar generate in a year? And at the lower price of £6000 (including installation?) it becomes economic sense. Putting in 93% solar input and £6000 purchase price to my spreadsheet gives a lifetime profit of nearly £200 per year, which would be well worth it. Damn - missed the boat!

When we had the 4kW solar installed (2014) I understood that that was the maximum to benefit from the domestic FIT rates. Also from memory of being stationed at Lossiemouth in the 1970's there was a lot of very clear, if rather windy weather. However, it hardly got dark in winter - The chaps down the back of our Shackleton never saw daylight in the winter!! However, you must have a rather low solar generation in December/January. Do you have any other source, like a wind turbine or waterwheel? I can't imagine that you can really get enough solar in the depths of winter to supply most of your requirements, although maybe they are rather lower than ours- we use 2 immersion heaters on low rate electricity and have 3 deep freezes (trying to be self sufficient!) With Tesla Model S, annual peak 3200kW, Low 9000kW. Annual bill £1000, Solar FIT payments £600 per annum. Solar will pay for itself in about 12-14 years.

I've just read that if/when one has a smart meter installed they read your real solar Export rather than assuming 50% and pay you on the real quantity exported. I only export 25%. I gather you can refuse to have a Smart meter - I certainly shall!

 

[The stag]

Hi again Mike I export as little as possible up the grid and charge my car when I am producing over 6kw you can turn the amperage back on your model s and it doesn’t demand it from your powerwall thus taking full advantage of your solar generation when my model 3 arrives for my wife I will also be able to charge off my solar aswell thus taking full advantage of my system my powerwall can power my house for approximately 2 days under essential electrical items ie heating fridge freezer etc all my lighting in my house is LED which demands very little washing machines and tumble dryers are the worst the need lots of power I am just waiting for the new hardware for my powerwall 2 so that I can power my house when the grid goes down this will be amazing in the winter so I can charge powerwall 2 on the eco seven tariff approximately 4p / 6p per kWh through the night and power the house during the day only in winter when solar generation is low but my data is quite interesting ie from middle of November until middle of February is the only time when solar generation is fairly low today I managed to charge my powerwall to 80% which is great for the beginning of February I produce approximately close to 7500 kWh per annum my house uses approximately 4000 kWh per annum I am still exporting about 1500 kWh to the grid and taking approximately 900 kWh from the grid per annum hope this helps

 

[mikemillar]

I got a measly 2kWh today, although I got 9kWh on 3rd Feb - best yet this year. - just enough to charge a PW2 in my house! I have lots of LED's too but my baseline consumption is about the same as your total 4000kWh per annum (24 hours a day), and that doesn't include kettles, cooking, washing machine, dishwasher etc (no tumble drier - I believe they are very power hungry). in addition I power 2 immersion heaters, although I get some help from the solar using power diverters. was able to turn off the immersion heaters for 2 months this exceptionally hot and sunny summer, but that's unusual. Also in winter I run a single storage heater in my workshop. All that plus the Tesla (4500kWh) adds up to a total of 12000kW per annum.

I think you've got a very good balance of solar input over your annual requirement. It suggests that one needs an 8KW solar installation to power 4000kWh house demand, plus Tesla. My economics would only work with a much bigger array and probably more than one power wall, which would blow my economic model. Now if only I could use the Model S battery to power the house...... I wonder if we'll ever see that option. I suspect it would need rather more than an over the air software update!

I think the problem with charging my Tesla from solar that if the sun goes in it would drag peak rate power from the grid my grid input, without a Powerwall. - not a problem in your case which is no problem with your setup. How could I get round that (without a Powerwall)? I wish I could divert surplus solar to the Tesla too. Do you have a power diverter to the wall charging point? I'm not clear how the Powerwall gets surplus solar - is there power diverter in the circuit or is it directly wired to the solar output. If so, how do yo feed surplus solar to the grid?

Many thanks for the info. It's most useful to be able to compare figures with you.

 

[The stag]

I got a measly 2kWh today, although I got 9kWh on 3rd Feb - best yet this year. - just enough to charge a PW2 in my house! I have lots of LED's too but my baseline consumption is about the same as your total 4000kWh per annum (24 hours a day), and that doesn't include kettles, cooking, washing machine, dishwasher etc (no tumble drier - I believe they are very power hungry). in addition I power 2 immersion heaters, although I get some help from the solar using power diverters. was able to turn off the immersion heaters for 2 months this exceptionally hot and sunny summer, but that's unusual. Also in winter I run a single storage heater in my workshop. All that plus the Tesla (4500kWh) adds up to a total of 12000kW per annum.

I think you've got a very good balance of solar input over your annual requirement. It suggests that one needs an 8KW solar installation to power 4000kWh house demand, plus Tesla. My economics would only work with a much bigger array and probably more than one power wall, which would blow my economic model. Now if only I could use the Model S battery to power the house...... I wonder if we'll ever see that option. I suspect it would need rather more than an over the air software update!

I think the problem with charging my Tesla from solar that if the sun goes in it would drag peak rate power from the grid my grid input, without a Powerwall. - not a problem in your case which is no problem with your setup. How could I get round that (without a Powerwall)? I wish I could divert surplus solar to the Tesla too. Do you have a power diverter to the wall charging point? I'm not clear how the Powerwall gets surplus solar - is there power diverter in the circuit or is it directly wired to the solar output. If so, how do yo feed surplus solar to the grid?

Many thanks for the info. It's most useful to be able to compare figures with you.

 

[The stag]

Hi again Mike my powerwall needs about 13 kWh to fully charge it leaving about 1.2 kWh as spare capacity my solar charges the battery first until it is full then any surplus switches to my solar I boost which has a power inverter connected to my Emerson heater in my hot water tank once it heats the water up any excess goes up the grid that’s the point when I plug in my car and charge it at about 14 amps thus only drawing about 5kw so that the powerwall doesn’t start discharging in the height of the summer I can produce about in excess of 60 kWh I produce too much solar at the moment but when my model 3 arrives I will be taking full advantage of solar generation next time you are in Scotland pop in for a coffee and I can explain and show you my set up was an absolute nightmare to get approval for my very large system lots of red tape and stupid laws it all boils down to what the grid can handle in my case it was approximately 7.2 kW because I am at the end of the supply but my main point being I don’t want to export it I want to store it and use it when I would like to use it I will probably add another powerwall this year depending on money as they are quite expensive now but all in all Tesla were amazing and the installer I have personally known for over 20 years and knows more about electricity than the power companies and specialises in electronics and control systems so for him it was very straightforward never had one problem but I do believe the installer is the key especially when he knows more than Tesla . When Tesla came to inspect the install they were impressed as he had added certain redundancies in the event of future issues

 

[Subevo]

Hi I phoned tesla for a powerwall quote recently .if I remember correctly it was £7500 plus installation which could cost up to £2000 but let's say at least £1000. That's expensive.real cost £8500-£9500 installed.
I have a 4 kw Pv system with individual inverters for each panel cost £8000 in 2015. Payback 10 years but maybe less.today produced 6.5kw.
I also have an immersun diverter for hot water.

Edf energy have a deal for a powervault 3 8.2kw battery for £5000 this includes a £2000 discount for grid services.
I'm due to get mine installed in a few weeks time.(tesla out of my reach)
They also do a 4.1kw battery for £3300.
Also I've never charged my tesla at home due to free public charging in Scotland.

 

[The stag]

Hi I phoned tesla for a powerwall quote recently .if I remember correctly it was £7500 plus installation which could cost up to £2000 but let's say at least £1000. That's expensive.real cost £8500-£9500 installed.
I have a 4 kw Pv system with individual inverters for each panel cost £8000 in 2015. Payback 10 years but maybe less.today produced 6.5kw.
I also have an immersun diverted for hot water.

Edf energy have a deal for a powervault 3 8.2kw battery for £5000 this includes a £2000 discount for grid services.
I'm due to get mine installed in a few weeks time.(tesla out of my reach)
They also do a 4.1kw battery for £3300.
Also I've never charged my tesla at home due to free public charging in Scotland.

 

[The stag]

Hi great info but yes free charging in Scotland is great at the moment but I would invest to future proof because as more car manufacturers come into the ev world you will struggle to charge when you want to due to the charge place scotland network being full albeit you will be able to get free charging at the moment I believe this will be charged in the not distant future as the market place is being disrupted by tesla and the other automakers rush to get their products to market yes there are other batteries in the market place but cheaper is not always the best when I look at a product I look at total life costs and not just purchase price the Tesla batteries are the highest energy density on the market place that’s why I chose them which will in turn give me a longer life also the chemistry they are using is way ahead of any competition at least 7 years all I will say if you can afford it go for the powerwall 2 you will have less battery degradation over the life of the cells don’t no much about other battery systems the questions you must ask do they have a thermal management system and software and hardware which can be upgraded over the air but battery cells is a subject I know more than most.

 

[The stag]

Hi I phoned tesla for a powerwall quote recently .if I remember correctly it was £7500 plus installation which could cost up to £2000 but let's say at least £1000. That's expensive.real cost £8500-£9500 installed.
I have a 4 kw Pv system with individual inverters for each panel cost £8000 in 2015. Payback 10 years but maybe less.today produced 6.5kw.
I also have an immersun diverter for hot water.

Edf energy have a deal for a powervault 3 8.2kw battery for £5000 this includes a £2000 discount for grid services.
I'm due to get mine installed in a few weeks time.(tesla out of my reach)
They also do a 4.1kw battery for £3300.
Also I've never charged my tesla at home due to free public charging in Scotland.

 

[The stag]

Had a look at EDF Powervault tech specs nothing of any great detail apart from they use a lithium polymer battery good luck with that tech it does have a cooling setup but no mention of a heating system for the battery pack not enough detail in the overall system again companies rushing products without really understanding batteries so that they do not loose market share it really makes me laugh no mention of their energy density which in my opinion is the key to any battery system what you have to remember tesla was originally a battery company in the beginning and have been building batteries alongside Panasonic for many many years let’s put things into perspective Tesla build more batteries than all of the other battery manufacturers put together they know what they are doing and they just bought a super capacitor company the other day called maxwell which have made some huge leaps on dry cells ie solid state lithium cells with nearly no cobalt in the chemistry what you have to think about is what is best for you and when everyone says they have batteries comparable energy density to tesla I say prove it and measure it they are no where near tesla at the moment and never will be.

 

[The stag]

Hi I phoned tesla for a powerwall quote recently .if I remember correctly it was £7500 plus installation which could cost up to £2000 but let's say at least £1000. That's expensive.real cost £8500-£9500 installed.
I have a 4 kw Pv system with individual inverters for each panel cost £8000 in 2015. Payback 10 years but maybe less.today produced 6.5kw.
I also have an immersun diverter for hot water.

Edf energy have a deal for a powervault 3 8.2kw battery for £5000 this includes a £2000 discount for grid services.
I'm due to get mine installed in a few weeks time.(tesla out of my reach)
They also do a 4.1kw battery for £3300.
Also I've never charged my tesla at home due to free public charging in Scotland.

 

[The stag]

Maybe I am wrong but you said the Powervault was £5000 for 8.2 kWh = £609 per kWh
Powerwall 2 let’s say £7000 to buy instal is less than £900 so let’s say in total £8000 for 13.5kwh =£592 per kWh my goodness the powerwall is cheaper how much is the Powervault to install will be the same as tesla approximately please add all your calculations as it could be misleading you also said something about grid services ? What is this? having run solar pv with a powerwall 2 for 2 years now you need a battery larger than 13kwh for the payback to be worth it and you need a solar pv system double the size on what everyone tells you because you believe them trust me I have done every calculation known to man on this subject and have all of the data to prove it I was still 5% out on my calculations thankfully I wasn’t 50% out or it would take to long for payback.

 

[The stag]

I got a measly 2kWh today, although I got 9kWh on 3rd Feb - best yet this year. - just enough to charge a PW2 in my house! I have lots of LED's too but my baseline consumption is about the same as your total 4000kWh per annum (24 hours a day), and that doesn't include kettles, cooking, washing machine, dishwasher etc (no tumble drier - I believe they are very power hungry). in addition I power 2 immersion heaters, although I get some help from the solar using power diverters. was able to turn off the immersion heaters for 2 months this exceptionally hot and sunny summer, but that's unusual. Also in winter I run a single storage heater in my workshop. All that plus the Tesla (4500kWh) adds up to a total of 12000kW per annum.

I think you've got a very good balance of solar input over your annual requirement. It suggests that one needs an 8KW solar installation to power 4000kWh house demand, plus Tesla. My economics would only work with a much bigger array and probably more than one power wall, which would blow my economic model. Now if only I could use the Model S battery to power the house...... I wonder if we'll ever see that option. I suspect it would need rather more than an over the air software update!

I think the problem with charging my Tesla from solar that if the sun goes in it would drag peak rate power from the grid my grid input, without a Powerwall. - not a problem in your case which is no problem with your setup. How could I get round that (without a Powerwall)? I wish I could divert surplus solar to the Tesla too. Do you have a power diverter to the wall charging point? I'm not clear how the Powerwall gets surplus solar - is there power diverter in the circuit or is it directly wired to the solar output. If so, how do yo feed surplus solar to the grid?

Many thanks for the info. It's most useful to be able to compare figures with you.

 

[The stag]

Hi Mike you can use your model s to power your house it’s actually very straight forward unfortunately tesla will invalidate your warranty on your car but I know exactly how to do it but would recommend just to get a powerwall 2 instead less hassle

 

[Subevo]

Hi I know the powervault is more expensive per kWH.
I wanted to support a uk company .
There is no additional installation cost.
10 year warranty
Grid services mean my battery is connected to other batteries and if excessive electricity is produced overnight then the excess is dumped into my battery for me to use.downside is batteries won't last as long as they are constantly working.

There was a good comparison done on the subject of powervault 3 vs powerwall 2
Powervault 3 vs Tesla Powerwall 2: It's All In The Chemistry

 

[Fly.guy]

We have 3.4kW of PV and had our PW2 installed in mid Oct 2018. We are on the Green Energy Tide tariff at 5p overnight, 25p peak and 15p mid-rate. These costs haven't changed in the last year.

I have therefore plotted the first 3 full months of life with the PW2 and compare them to the same three months the year before.

Overall we have saved £42.06 over those 3 months despite using more electricity (more driving). I would expect savings to get better over the summer as the PV picks up again. However assuming that these savings extrapolate to the year thats £168pa which given the £6300 that the system costs represents an annual return of 2.7%