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I was just talking to a relation about this, and he said Tesla's guy said he needs two Powerwalls to replace a generator in the event of power interruption.

Is that true, or a sales guy thing? I'm not sure and haven't investigated.

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It depends on your relation's power usage, I'd imagine. I believe the spec is 5.5kW max output, which is probably insufficient if you've got any sort of large load. My well pump is rated for 30A @ 220V, so startup would likely overwhelm a single powerwall, and I think my air conditioners have similar startup needs (and I've got multiple units); we managed to trip the overcurrent protection on our 35 kW whole house generator during one of our early outages (it's unfortunately not connected to the well pump, overcurrent was just from using multiple heat pumps and washing/drying clothes; dryer heat is from propane. We had a nearly 3 day outage our first winter.

However, at my previous house, I didn't have any substantial electric loads, other than an electric water heater in an underused ADU, so 5.5kW would have been likely been fine, and our typical energy use was around 1kW, so we would have had several hours for service to be restored, which fit within the experienced outages.

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