Homeowner Blog

Power Cut? Not My Problem... Tesla Powerwall's Solar Panel Backup

Erica Charles · 01 Mar 2019

The long-awaited Powerwall 2 backup capability is ‘on the water’, with the first wave of deliveries expected in April.  There’s a two stage roll-out, based on the type of earthing system required. Stage 2 will be in August.

If you are familiar with the Powerwall system, you will know that the system consists of the Powerwall unit itself, which houses the battery and the inverter, along with a ‘gateway’ which provides remote connectivity.

The original gateway, ‘GW 1’, was a plastic fronted box providing remote connectivity to the system.

From April this will be upgraded to a new gateway, GW 2, a stylish frosted glass-fronted ‘mini’ version of Powerwall 2, measuring 380mm wide x 580mm tall x 127mm deep, and weighing 9.8kg.  It is IP55 rated, so suitable for outdoors, and can be padlocked to stop any unwanted access.

The main purpose of the gateway upgrade is to enable ‘backup’ capability so that the homeowner can still power their home in a power cut.

So confident is Tesla that all customers will want the new backup enabled system, that they are actually expecting to discontinue GW 1 altogether, even though GW 1 offers a lower cost entry point into the Powerwall 2 system.

Tesla has certainly done its research. According to the company, in the nine month period 18/6/18 – 18/2/19 there were 93,965 unique power cut incidents in the UK, typically lasting between 15 mins and 4 hours and impacting 2 million customers. Anyone with a solar panel backup system in place would be smiling now....

[Apparently there are 22,200  online searches for "Schadenfreude" every month in the UK.  I wonder if Mr Musk has checked that stat out ....]


What do we mean by backup functionality?


[And should we spell it ‘backup’ or ‘back-up’? Wiktionary says as follows, in case you are wondering: “Back-up is an alternative spelling of backup. Both spellings are used as either a noun or an adjective. The verb back up is always spelled as two words and never with a hyphen.”     I sort of prefer the hyphened version so we’ll go with that from now on….]

Back-up means two things:

  1. firstly the homeowner can still power some or all of their appliances in a power cut;

  2. secondly, the solar system will continue to work in a power cut, as long as there is a load and / or battery capacity to ‘soak’ up the electricity generated (and as long as the system is ‘single phase’, as most domestic systems are – see below).


What happens in a power cut?

Powerwall 2 can be installed to back up the whole house, or it can be installed such that it backs up only certain loads. Even with ‘whole house’ back-up, certain large loads (such as a car charger) can be excluded.

The user can specify a reserve percentage (e.g. 30%) and the system will always keep that percentage of the 13.5kWh storage capacity in reserve for a power cut.  This setting can be changed via the Tesla app (anything from 0% to 100% can be specified).

If the grid goes down and the loads in the house exceed 5kW, (or if they exceed 3.68kW for a system set on the lower 3.68kW power output at commissioning), the battery will shut down. The system will spend the next hour sending reminders to the customer to turn off high power loads so that the total load falls below 5kW and the battery can re-start. After this the battery will need a manual reset to re-boot.


In practical terms….

If you reserve 30% of your battery (4kWh), then you should be able to watch TV, use your laptop and keep the lights and freezer working for almost four hours, whilst enjoying a few cups of coffee in the process.

You should probably wait until the power comes on before using an electric dryer, and if you want to ensure you can continue to cook up a storm in the kitchen, and you’re not into serving your guests raw vegetables, it’s probably best to install two Powerwalls. 

Typical loads are as follows:


  • fridge / freezer: 500W;
  • kettle: 3000W;
  • oven: 3650W;
  • induction hob: 1500W;

Office and entertainment

  • laptop: 50W;
  • TV: 80W;


  • average lighting load 500W (2500W all lights blazing for a typical 4 – 5 bed house (LED));

Laundry / dishwasher

  • dishwasher: 1250W;
  • washing machine: 500W;
  • electric clothes dryer: 4000W.

Solar system will continue to function in a power outage

Not only will a back-up enabled system keep the lights on, it will also keep the solar system functioning. The system will continue to function whilst there is either a load or sufficient spare battery capacity to soak up the solar electricity it produces.

If there is insufficient load or battery capacity to soak up the solar, the system will automatically power down the solar.  However it should be noted that for this to work effectively don’t connect more than 7kWp of solar to a system with a single Powerwall set at 5kW output. If the Powerwall is set at 3.68kW (due to DNO constraints), don’t connect more than 5kWp.

If you want more solar, you need more Powerwalls, or you need to connect the solar 'upstream' of the gateway so that the solar disconnects in a power cut…..

3-Phase connections

Most households run on a single phase connection (230V). If you have a 3 phase connection (400V), there are limitations to the system:

  • There is no ‘3-phase’ version of Powerwall 2 and so the batteries cannot power individual 3-phase loads (e.g. motors).
  • Even if you install a Powerwall 2 on each phase, the back-up functionality will only allow loads to work on one of the phases when the grid goes down. You can select which phase will work during the commissioning process.
  • If you have a 3 Phase solar inverter connected, the solar will not function in a power cut. If you have a single phase solar system connected to the same single phase of a 3 phase supply as the back-up Powerwall 2, then, subject to the size constraints above, it will work in a power cut.

Other functionality

Tesla has also taken the opportunity to improve other functionality e.g. metering accuracy has improved, as has connectivity.



There are a couple of ways to configure the system. For sample schematics, download our updated Powerwall 2 guide.



Download Updated Tesla Powerwall 2 Guide



Download now


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Topics: Battery storage, Solar PV, Tesla Powerwall