He is running beyond the scale of that Tesla's controller unit can really handle:
> Tesla soon worked out that the system was being overloaded due to having too many Powerwalls connected at once ... The gateway is being overloaded, reaching 100 per cent CPU and RAM usage. There’s too much info when they are all online.
He is doing something very uncommon among customers, and Tesla apparently doesn't even try to make it work:
> But while Tesla claims it can do off-grid 10-Powerwall setups, there are only a handful around the world – most are backed up by grid electricity, papering over any outages. ... “At the beginning there were actually only three 10-Powerwall installs in the world that were off-grid,”
They also apparently have poor support for off grid firmware updates, possibly related to the lack of CPU and memory to both keep the lights on and upgrade at once:
> “During these upgrade cycles, the system goes into this chaotic state that takes between four and eight hours, turning off and on 50 times,”