If one has an EV with a 200 mile range, and one is going to do 300 miles, then to do that 200 miles will take 4 to 5 hours, so 3 kW is an extra 10 kW hours plus it would mean power not used for cab heater, it does depend on how power hungry the car is of course, but when one knows one has a long trip ahead it can extend the range by quite a bit. And running at a fixed output it can run very efficiently.
OK with larger cars may need to be 5 kW, but point is not being big enough to drive the car with, but simply a range extender, and also a method of recharging when no recharging point can be found, same idea of have a spare gallon of petrol.
1978–79 was when I remember the
Winter of discontent that's over 40 years ago, however as a result I will not entertain heat pumps, and I have a back up battery which can be charged from the solar panels.
I don't think it will get that bad again, but we have seen loss of power in some areas for a day or two, I remember one petrol station had a moped with the wheel rubbing on the wheel of the petrol pump to deliver petrol, and others were using hand cranked pumps, which have now long gone, so really today no electric means no petrol as well.
Even seen shops stop trading during a power cut as they could not work the tills, so likely could not buy candles even if in stock.