I.d.k. why i thought that Euclid, and perhaps also others, were around Plato
There was an Euclid that was a pupil of Socrates. He was a friend(and classmate i guess) of Plato.
https://en.wikipedia.org/wiki/Euclid_of_Megara
And dont worry, it wasnt just you who was confused
"Editors and translators in the Middle Ages often confused him with Euclid of Alexandria when discussing the latter's Elements. "
Pretty much all houses in Greece have this and no, it is only good for the summer or sunny days. But still it is a no brainer, unlimited free hot water during the summer and limited free hot water during most days.
The tricky part is calculating whether it was sunny enough(during the winter) to produce enough hot water for your shower or if you need to turn on the electric water heater.
Some greeks pre-emptively turn on the electric heater for 15-30 mins, other more financially stressed greeks prefer to gamble.