A steam explosion in a superheated hot water tank can be lethal, a system that provides adequate solar hot water in winter really needs redundant safety devices to operate safely in summer. At least a couple of PTR valves (in case one fails) as well as whatever you're using to dissipate excess heat - imagine a bird cr*ps on the PV powering the fan while you're away, you need something foolproof as a backup.

   Here in Oz, latitude 37*, I have a solar HWS with a 330l tank and 2 panels each a bit over 1 sq metre - in summer I cover one of the panels, otherwise the PTR valve opens and wastes hundreds of litres of 80C+ water on a sunny day (serious drought here and we're on tank water).

   2.  I have a vague recollection of a TV show years (decades) ago where a cattle station in Australia was using 80C bore water to generate electricity, using the phase change in freon to run some sort of turbine, so you'd think you could do something useful with a 60C temperature difference.