This is already the third post on the Tesla powerwall series and especially how it is (mis)presented in the mainstream media. This misinformation is not only limited to the mainstream media, it is also strong in social media. The subject of this post is a facebook post by the owners of the Tesla home battery mentioned in previous two posts.
It starts informative with a description of their powerwall (translated from Dutch):
Our home battery is a lithium ion battery with a usable capacity of 6.4 kWh (slightly less than our average daily consumption). We decided NOT to go for the #offgrid option, so when the grid voltage is lost, our battery will also not be able to power us. The battery can deliver 2 kW continuous power, with a peak power of 3.3 kW.
The capacity of their powerwall is indeed somewhat lower than their average consumption. I understood from a previous post that their annual consumption is around 3,200 kWh, meaning around 8.77 kW per day. On average of course, their consumption will be lower in summer (when production is high) and in higher in winter (when production is low).
Not sure whether all this 6.4 kWh is really usable and how long it stays that way (this battery is currently brand new, but lithium ion batteries degrade after a while). But that aside.
It becomes a bit trickier in the next sentence when it comes to the limitations of the powerwall (translated from Dutch):
With a load of 2 kW, the battery is depleted after 3 hours.
Followed by the justification that this is not much of a restriction for them (translated from Dutch, my emphasis):
But our home has a nominal consumption of about 150 watt, so even in winter a fully loaded battery gets us easily through the night (even if we make a kettle of tea in the evening).
They lost me with that sentence. What they basically say is that the powerwall has limitations, but that these don’t apply to them because their home has a low nominal consumption and to prove that, they claim that they get through the night on a fully loaded powerwall, even in winter.
First it was not really clear what they meant with “nominal consumption” (which is much lower than their average consumption). From the context of that last statement, my guess is that they mean “their electricity consumption during the night” and then, yes, they will easily get through the night on a fully loaded 6.4 kWh battery.
Even in winter.
Even after they made a kettle of tea in the evening.
To be honest, I am not really impressed: of course, a fully loaded battery gets you easily through the night. That is not a big deal.
People tend to sleep at night, so electricity consumption is low anyway. Getting through the night starting from a (nearly) fully loaded battery is not something to brag about, it is a rather meaningless feat. If they don’t get through the night on a fully loaded battery, then there would be something seriously wrong with their system…
What does this actually prove anyway? Their example looks like a non sequitur to me. Sure, their powerwall has more than enough juice to come through the night, but this doesn’t prove anything for the performance during the day when consumption is high.
As far as I know, capacity problems during the night were never an issue with the home battery, so the example that was given is meaningless for what they want to prove.