I’ve had a Solar PV array on the roof since around 2010. Earlier this month I had a Tesla Powerwall2 battery fitted. This is a 14kW battery that saves excess solar generation to run the house later in the day.
The first few days have been interesting. Even this time of year it’s clear a sunny day is enough to charge it to about 30% (About 4.5 kW). You can see this from yesterday’s graph.
– White is mains power usage
– Yellow is Solar PV generation
– Green is Powerwall charge/discharge
The mains draw drops to zero as the Solar PV starts to generate and takes over powering the house. Excess solar generation now charges the Powerwall (the green under the line. Generation maxes at about 2.5 kW (on a 3.8 kW array). I was surprised a December sun can do this.
Around 15:30 the sun goes and the Powerwall then discharges to run the house until between 20:00 and 21:00 when it begins what looks like a graceful decline in output.
You can also see when we get home about 4pm and put the kettle on! Other spike are, I think, a mix of kettle, washing machine, and the fridge & freezer.
The result is that even in December the battery can lift self-powering from about 10% Solar only to 43% solar/battery combined. Sunny days only, however. Today with rain/cloud, and sun it will be less, but still something. I’m really looking forward to seeing what happens in the summer months and hoping we will go off-grid for long periods.
In other news, the installers did struggle with configuring the control unit – a separate unit to the battery that manages the power flow etc. This need a firmware upgrade to get it working, provided remotely by Tesla, and it then was clear that the WiFi module is faulty. At the moment it is directly connect via UTP to a Wifi network extender I happened to have spare. So it IS all working but I am waiting a replacement unit.
None of this is the fault of the installers, who have worked above and beyond, and I’m putting this down to being a very early adopter in the UK. So far I’m very happy and slightly obsessed with the whole thing.