depending on the outside temperature, there’s a limit to what the heat pump can do, which an internal electric heater inside the water tank takes over to reach usable shower temperature.

That is also true for solar heaters when there is no sun. and there are not many places that have climates where heat pumps cant operate these days.

Also air source heat pumps can have a COP of 3.5 so or higher. so even with a lower efficiency from the PV you might get ahead. You also get gains from the high COP on cloudy days where you might need resistance heating on the thermal one

I dont think you can claim any of them is better without doing the math.

I think they heat a refrigerant and then use a heat exchanger to transfer that heat to the water.

I would love to see numbers on how they compare against solar panels+ air source heat pump. I guess the solar heater is cheaper, but I would guess photovoltaic+heat pump probably is more efficient all around and it useful for all your home, not just water.

while these news are great. it is good to remember than decreasing emissions is not enough.

if you see in a room that is filling fast with water and you are about to drown, would you be relieved if water simply started pouring a bit more slowly?

it will take decades for the atmosphere to get back to normal even if we halted new emissions