[njb311]

Yes, I wasn’t suggesting that this solution was more efficient, but that solutions that are more efficient than what they replace are what we should be focusing on. It’s fine to say that resistive is 100% efficient, but my point was that a 10kW instant electric heater is not enough to meet the demands of many households (and falls well short of a gas boiler output) and you can’t just say install a 20kW electric heater because typically household supply is not built for that. And so if you heat a tank of water (a typical immersion heater is 3kW) then all of a sudden you have heat loss and you are nowhere near 100% efficient.

[SigmundA]

Again the discussion being resistive versus microwave, restive should be better even in an instant water heater, again microwave has no advantage that I see.

And when talking about efficiency you must specify context. In this case heating water via electricity, not losses of storing the heated water which is a separate issue based on tank vs instant regardless of heating method.