In our new home, I plan to split the hot water system into two:
This will ensure the majority of the hot water used is heated by the sun and that hot water is not stored unnecessarily for the lower use and occasional usage areas. For example, guest rooms and bathrooms may only be used a handful of times a year, so storing hot water in tank just doesn't make sense. The other main benefit this approach gives is independence from guest water usage. It means there will always be hot water available for us and our guests, resulting in a much better quality of life.
The plan is to use evacuated glass tubes (solar thermal collector) to provide solar water heating and to use a very well insulated hot water storage tank, which will be augmented by smart electric water heating, under the control of my contextual smart home. This will make it incredibly efficient as it will be using whole home context and thus make more intelligent decisions as to when to use electricity to heat the water in the tank.
Just like my current home, there will also be sensors on the hot water tank, to measure how much hot water is available.
The key to a great shower is decent water pressure. I don't want to be reliant on mains water pressure, so the hot water tank will be at a suitable height above the main ensuite ceiling. In addition, I will be using larger bore pipes, to reduce noise and ensure better flow.
All of the hot water systems will have sensors connected to my contextual smart home, to monitor performance and usage. Things like flow sensors can also provide useful context and occupancy information to things like my smart shower. My AC voltage detection sensor will allow it to track when things are in use too.