User experience of Tesla Powerwall 11 - Energy cost savings and best energy plan to support battery charging?

  • 27 June 2020
  • 2 replies
User experience of Tesla Powerwall 11 - Energy cost savings and best energy plan to support battery charging?
Userlevel 1

I had a Powerwall 11 installed on 21st May with back up Gateway. My specification was to be able to have a self-powered home. I.e. I didn’t want to buy any grid electricity at all, or at least reduce my dependency on Grid supplied energy.

My solar array is some 6 years old and performs very well but the inverter is grid connected such that if there is a grid power failure/outage I have no power in the home – so not even the gas boiler will work! The Tesla back up gate way keeps the house energised even if the grid is down. Solar power continues and or the Powerwall depending on the time of day.

The installation was straight forward and was completed in 2 days. Things to look out for if considering a Tesla installation. Get at least three quotes and make sure any installer is Tesla accredited – Tesla won’t allow non accredited installers near their kit. The gateway needs to be connected to the internet - ideally three different ways. It comes with a SIM for remote monitoring by Tesla support but they require it also to be connected by a direct ether net connection and WI-FI.

The concern is that if your router is changed and the connection is not hard wired then you will not be able to use the APP to control the system. The Tesla APP allows you to monitor in real time how much energy is being produced and where it is being used or exported – very simple and straight forward – ok for smart phones as well as android tablets.

The result is that from 21st May 2020, I have only spent £0.02 per day on grid electricity plus of course the all-important daily standing charge.

BUT – on a poor day with low light the one Powerwall installation can become almost exhausted. I have set the back-up limit at 5% (in case of a grid outage) after which the gateway will allow grid energy through to power the home.

Now for the complicate bit – do I stay on my one tariff rate day and night – or switch to say economy 7?

Staying as I am, will mean paying more for charging the battery off peak, assuming that on most days I will have sufficient power in the battery to power the house during the day and evening? BUT switching to economy 7 and being caught out on occasions of poor light in the day may result in having to use grid power at an expensive time.

Experience to date suggests that our present profile of power usage allows the solar/battery combination to get us through the most trying days until late evening and as there has been so much sunlight through until charging can take place from the solar array.

I want to stick with OVO – been with them for 6 or so years and I have never experienced a more cooperative and supportive utility provider in 60 years of desperate struggles – so my instinct at this time is I will switch to economy 7 at the end of my current contract and tweak our usage through the winter such as to only use off peak power from the grid.

Hope all this helps someone and if anyone needs further info please let me know.

2 replies

Userlevel 7

Thanks for posting, @Stargazer8t6 


I’m tagging some time of use / Powerwall experts to get their thoughts on your eco-7 dilemma @Transparent @JohnR @speedfix @Pete632 @NickinHP @Gibbsy :)

I’ve had a Powerwall with the older, non-backup gateway (not available then even if I wanted it) for over two years. During the summer half of the year the solar generation is usually enough to meet the overall household demand with some carry-over from sunny days to supply the murky days. However, there’s still about 0.5 kWh drawn drom the mains as the battery output never exactly balances the household demand (plus occasional load spikes which exceed the battery output).

The winter half of the year is a different story: There tends to be more electricity demand (lighting and heating pump being two examples) and the shorter daylight hours means reduced opportunity to directly supply the household load from solar power. Off-peak charging lets the battery stock up with cheaper electricity and thus helps to justify the overall investment. I first tried an E7 tariff but then moved to a much cheaper (5p/kWh) tariff (not from Ovo) which is only for 4 hours each night and aimed at EV charging. The 4 hours is just about enough to charge an empty Powerwall although that situation rarely happens - it’s more about putting enough charge into the battery so that it + solar generation can get through the next 24 hours.

However, I would add that the off-peak charging is managed by Tesla’s software which only considers the historical power flows (household demand and solar generation) without any consideration of the weather forecast. Consequently, it can be caught out when a very cloudy day follows several sunny days or vice versa. A user with a backup gateway can reduce this problem by adjusting the backup % to suit the expected solar generation.