Re: hot water. In VIC, legally whole tank must reach at least 60 degrees at least once a week, or if element is part way up tank, 60 degrees every day. Required to kill legionella. If you shower in mornings, and have good insolation, then apricus evac tube with electric boost part way up tank works fine. Switched our boost off mid Nov, prob not required until end April. I was told Dux are crap. Siddons heat pump systems apparently good. As for solar PV. One of my clients bought a system that has six monthly PM (preventative maintenance) written into the contact and the installer has to be paid to clean it twice a year or warranty void