It's now two years since we've had our Tesla Powerwall 2 installed. We can now
take a look at all the data and understand the value that these types of system bring.
Was it worth it or did we make a big mistake?
Hi John here. In this video I will take you through how we have set up our Powerwall 2 and how
that differs depending on the time of year. I will talk you through the cost to purchase and install
then round up with the performance and stats for two years of ownership with our Tesla Powerwall
2 here in the UK. Let me talk you through our setup and how we manage our Powerwall throughout
the year as this will give you some context to hang the performance and saving information onto.
I have 1 Tesla Powerwall 2 which can store up to 13.5kWh of energy when fully charged.
We have a detached 4 bedroom house built in 2001 there's the two of us living here, me and my wife.
We're both retired which means we're at home for most of the days. We have 2 electric cars
a Tesla Model 3 and a Hyundai Kona. We also have a glass studio which has 3 electric kilns.
Our typical daily house usage is about 20kWh per day.
Here's a schematic of our system. You might want to pause that if you want to look at
it in a bit more detail. Also there's a copy down below in the description to my dropbox.
We have 6.3kW of solar PV array which will charge the Powerwall battery when the panels
are generating. If the solar panels are generating at their peak output then the
Powerwall can be charged from 0% to 100% in just over two hours. That's fine in the summer months
but what happens in the winter when there's less sunshine. We'll cover that in a minute.
We have a myenergi zappi car charger which can divert excess solar to charge the cars.
We also have a myenergi eddi which heats our hot water from excess solar.
The priority order for using this excess solar is; house, Tesla Powerwall, eddi and then zappi.
How we configure the Powerwall differs depending on the time of year.
We swap between two modes Self-Powered
and Time-Based Control. So let's have a look at those both those modes in a bit more detail.
Self-Powered mode stores any solar energy not used during the day to power the how home at night.
This stored energy will then be used when your home needs more power than solar can provide.
When you have enough solar energy to offset all consumption of your home and your Powerwall is
fully charged the excess energy will then be diverted to heat up water and charge up cars.
Finally after that any excess over the top will be exported to the grid.
Similarly if you are consuming more than is available from your solar and Powerwall you'll
import energy from the grid. Self-Power mode increases the amount of solar energy that powers
your home and is the best way to reduce your carbon footprint and be more energy independent.
In the summer months we use the Powerwall in Self-Powered mode and this mode targets
the storage of excess solar energy during the day which it then uses to power the house from sundown
through to sunrise the following day. This means we can be 100% Self-Powered from solar and battery
if there is sufficient solar activity during the day. Typically we need a minimum of 20kWh
of solar generation each day to be 100% Self-Powered on a rolling daily basis.
This is easy to achieve with our solar setup provided the sun plays its part.
Then there's the Time-Based Control. Now our electricity prices vary every 30 minutes
during the day. Our energy supplier is Octopus Energy and we're on their Agile tariff. The
key difference with this Agile tariff is that it tracks the half hour wholesale electricity rates.
The rates are published daily for the following 24-hour period. This means
that the cost of each unit of electricity changes every 30 minutes. It's a bit like
whack-a-mole for pricing and does actually make it a bit tricky to do price comparisons as a result.
The Agile tariff has a peak time period between 4pm and 7pm every day. There's a variable off-peak
time slot which is typically in the early hours of the morning from midnight through to around 7am.
We've been on the Agile tariff since July and it has certainly saved us
money on our electricity bill. Before that we were on the Octopus Go tariff
which is a fixed unit rate. It still has an off-peak period in this case four hours
overnight and the rest of the time during the day it is at a higher fixed unit rate.
Time-Based Control is also referred to as Load Shifting helps us to maximise savings by smartly
charging and discharging. And there's actually two variants of the Time-Based Control mode
which is Balanced and Cost Saving. In Balance setting its goal is to balance sustainability
and cost savings to reduce your peak usage while maintaining a high self-powered score.
What this means in terms of behaviour of your Powerwall it will charge from excess solar during
off-peak the Powerwall will discharge during all periods minimising exports during off-peak.
In Cost-Saving setting the Powerwall's goal is to maximise savings which means your Self-Powered
score may be slightly lower. In terms of behaviour the Powerwill charge from excess solar during
off-peak. It would discharge during peak and discharge in other periods to make room for solar
based on energy forecast and historic usage patterns. In the winter months we use the
Powerwall in Cost Saving mode. This mode ensures that it can supply the house's needs during the
peak time slot of 4pm to 7pm at other times it'll favour the grid and then use the cheap off-peak
times in the early hours to charge up the battery. This means we are using cheaper stored electricity
to run the house during the peak rates when it when when electricity is more expensive.
It was worth explaining those two different approaches to using the Powerwall
as they have an impact on our overall cost savings and the Powerwall's performance.
E.g. we save more money in the summer because we are self-powered for more of the time and we save
less money in the winter when we will have to draw from the grid to supplement the lower levels of
solar production here in the UK. Cost then. Let's talk about costs. Cost to buy and install
the Tesla Powerwall 2 with Gateway 1 was £6,808 back in December 2018. The amortised costs of
the Powerwall is worked out by dividing its guaranteed lifetime, in this case 10 years,
into the total purchase cos. So £6,808 divided by 120 months (10 years) equals £57/month.
Which means it's costing me £57/month for the Powerwall over the 10 years.
But how much am I saving each month by having the Powerwall. For the cost breakdown there's a
lot of factors to consider. I found it actually very difficult to work out exactly to the penny
how much the Powerwall has saved. Why is this? Well in short there's been just too many variables
during the two years we've owned the Powerwall. We've swapped energy suppliers. We've had 2
totally different electric tariffs which have been very different in their approaches. A fixed
unit rate tariff where we pay a fixed amount for a unit of electricity to a variable rate
which tracks the wholesale electricity rates and the rates change every 30 minutes.
We had additional solar panels fitted. So yeah sort of lots of changes in pricing,
in configuration, in suppliers, and it doesn't end there. Unfortunately because we also swap between
Self-Powered mode and Cost Saving mode which makes the Powerwall behave very differently.
In Self-Powered mode it tries its damdest not to import from the grid. To actively import from the
grid during the cheat rate in Cost Saving mode. So completely different approach and behaviour.
So I have actually found it difficult to split out how much electricity
the Powerwall has taken from the grid versus how much it has taken from our solar panels.
And as I said we've also added a second PV solar array into the mix in year two
and this means obviously the Powerwall is taking more excess solar as well. So unless I'm missing
a trick here and anyone knows different. And if you do please comment down below.
I found it almost impossible to boil all these changes and variables down to concrete figures.
I will give you some cost saving figures and my rationale behind them in a bit so
keep watching and stay tuned for that.
So let's just talk about what's happened in terms of how the Powerwall has performed over those two
years, then that will lead us into the costs. If I look at the Tesla mobile app and choose Lifetime.
This is what it shows me. These figures are from the 11th of December 2020,
a couple of days past the two-year anniversary but they're close enough. For Self-Powered our home
has been Self-Powered for 56% of the time over the lifetime of the Powerwall. 30% of that came from
our solar panels and 26% of that came from the Powerwall. The remaining 44% would have come from
the grid. Scrolling down shows our solar offset against our house usage. Again over the lifetime
of the installation 55% percent of our energy uses has been supplied by solar and you can see the
totals in the bottom there. 11,655kWh of solar generated against a house usage of 21,221kWh.
If I go into the Energy Usage option and choose Lifetime it shows me the following.
Home usage ,again the same 21,221kWh, solar 11,655kWh of generated.
From the Powerwall we've had 6,168kWh. To the Powerwall 6,897kWh and this figure incidentally
isn't shown in the data that you're looking at. However, I record this daily from the Tesla app
and just summarise it into a total. So that's where that figures come from. From the grid we've
pulled 11,980kWh and sent to the grid 1,544 kWh of surplus solar generation that we couldn't use.
The round-trip efficiency for the Powerwall over these 2 years is 89%. Tesla's technical
specs stayed at 90% round-trip efficiency at 25 degrees Celsius for a 3.3kW charge and discharge
of power at the beginning of the unit's life. So I'm actually really pleased with our performance
as our Powerwall is installed outside which means it needs to work harder to maintain the
temperature inside on those cold mornings and allow it to take advantage of any early solar
generation in the winter months. What has that 26% of electricity supplied from the Powerwall saved
us in our electric bills over the past two years. As I mentioned earlier about all the changes and
variables over those two years it's therefore a tricky question to give a definitive answer to.
So what I've done I've taken an average unit cost for our electricity over the two years to
calculate this saving. The figure will be sort of their or thereabouts. I've not included any
VAT or any Standing Charge in these particular figures as we would have been paying those anyway.
So 26% of our overall home usage works out at, if we take our overall house usage of 21,221kWh
26% of that is 5,517kWh. So 5,517kWh x our average unit rate of 16p per unit comes out at £882.72p.
£882.72 divided by 2 years (maths error, see video description) comes out at £18.39p saving per month. If you recall
the Powerwall was costing us £57/month over the 10 years. Which means that the Powerwall
is costing us £57 - £18.39 = £38.61/month over the two years that we've had it so far.
However, that's not entirely accurate as a picture going forwards in terms of forecasting because
as I said earlier we've added additional solar panels 12 months into ownership of the Powerwall
which means the savings going forward will actually be more as that additional solar panel
reduces our grid import and will improve our overall self-power percentage. However,
it gives you an idea of the costs and the savings. Have we had any issues or problems with
the Powerwall? Well just 2 actually. 3 days after the Powerwall was commissioned it stopped working
and was offline for 3 days. Tesla fixed the problem remotely and it's been working flawlessly
ever since. I guess that initial problem was down to installation or configuration setup.
The other issue we've had is not a fault of the Powerwall per se. I noticed a phantom
draw on the grid once we've had smart meters installed back in July 2019.
After 18 months of investigation this turned out to be an incompatibility issue between this
particular brand and model of smart meter and the Powerwall. I've done a separate playlist of that
particular problem and resolution if you want to learn more about that up here. All in all it's
actually been faultless in terms of its operation apart from those initial 3 day outage. Do I have
any regrets? Well just one really. We had the choice of having a Gateway 2 which provides
backup facility in the event of a power outage. Over the 2 years that we've had the Powerwall
installed we've had 1 power outage during the daytime which lasted just a couple of hours.
So the lack of power outages in our area was the main reason for not choosing the backup
Gateway 2 as an option. Plus it added another £1,300 pounds on top of the price back in 2018.
The backup facility does give you the ability to have a sort of
workaround to be able to manually charge the Powerwall by setting a backup percentage in the
battery in case of a power outage. With the Gateway 1 we have no manual control
we can't override when and by how much to charge the battery it relies purely on its algorithm
which looks at historic usage patterns for solar generation solar excess house usage and so on.
In the winter when we are in Cost-Saving mode it can sometimes get it wrong
as it doesn't have any weather forecast built in. Now I've already explained this in a lot
more detail in another video which again I'll link up here if you're interested rather than
going back through it again here. I guess it's a minor point and I'd say it's about
95% accurate you know. It gets it right most of the time it's just a little foible I guess.
So was it worth it for me? Yes in short. Yes it was. Does it make financial sense? Over the
long term yes I believe it does. The Powerwall will still be working past its 10 year warranty.
Tesla guarantees that the battery will maintain at least 70% of its capacity to hold a charge
during that 10 year period. Solar panels keep going for 25 years plus which means all things
being equal we will still be saving past the 10 years that I have calculated to in this video.
So it's certainly not a short term payback, however over the longer term I firmly believe
it will pay for itself. Not only that we've reduced our reliance on the grid by 26%.
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Thank you for watching. If you've got any questions then drop them down below.
And I will see you on the next video. All right, cheers for now. Bye.