The question is: is it efficient enough during the cold season? Cyprus, situated in the middle of the Mediterranean heat reservoir and with plenty of daylight during the off season seems to be well situated.
As for the need: I’m from up north, our houses are built to keep heat inside as that is most positive for our energy consumption. In the south, houses try to limit the need for cooling. The effect of which became very clear to me when I went to the Mediterranean in November. Heating? Yea please.
As with all heating relying on water for energy transport, absolutely when building new buildings, but will cost an arm if you add it in a remodeling.
As for solar capture in Sweden, there are a few places that try to store heat in sandpits, among others a high school in Stockholm. And on that subject the Finns must be mentioned😊 Will be interesting to follow!