I decided upfront that I will go for neither a heat pump (heat exchanger) nor resistive heating. I was advised that I would need a 7kW heat pump or a resistive heater of 25+kW. I find both totally impractical for very occasional residential use. Even with all the novelty of a new pool, I find that the kids hardly use it more frequently than once a week. Hence any chilling, if required, can be done by the evaporative enhancement of the fountain above. Reality: even on our hottest days this past summer when the ambient temperature rose to 44deg C (110+deg F), nobody complained of the pool water being unpleasantly hot. On hot summer days the pool got used only at night. Hence, no chilling is required anyway. Cross that one out :-) Fountain will be purely decorative.

Any electrical heating in the winter has to be switched on for several days, continuously, to make any perceptible comfort difference to our warm-water-lover swimmers. I.e. one will have to spend all that electricity, week long, in order to cater for a possible one-hour dip by the the kids on a week-end, maybe. Ain't gonna happen. Scratch out any electrical heater. So "free" solar heating is the only practical way to follow. We have to use the pool circulation pump most of the daylight hours to filter the water anyway. Do it when the Sun is up and you get your solar heating for near-free.