Whole House Solar System - Comments Please

[German_EE]

I'm sitting in a room with someone who has lots of ideas about solar power but neither of us are experts in the subject. After much discussion we have decided on the following and I would appreciate some comments:

Solar cells on the roof charge a battery bank, maybe 24V truck batteries or maybe a Tesla unit. At night the batteries are topped up using an incoming 230V single phase line which is also used if it's cloudy.

The battery bank feeds a 100A 230V inverter, this powers all of the house 24/7

If the battery bank is charged then the solar cells heat the hot water tank

If there is hot water AND it's Winter then the solar power is used to pre-heat the water in the under-floor heating which uses a gas boiler.

If there is hot water AND it's NOT Winter then the surplus solar power is used to heat the hot tub.

Note that selling solar power back to the electricity company is not an option in this case as it's not financially viable. My job is to design and build all of the control circuits for this including a flashy front panel showing what's going on although the 100A inverter will be a commercial unit. After construction everything will of course be inspected and tested by the local power company before connection to the mains.

Thoughts? Comments?

[awallin]

How much do you need/want to build the controller for this yourself?
Aren't there hydrid inverters out there from the big brands (ABB, Fronius, etc.) that do what you want?

With the panels and good sun-light the payback time is 10 years or longer - over here in northern europe at least.
If you add to that a li-ion battery pack for 10 keur that will make the break-even time even longer?
So I guess you need to decide if you want to do it because of economy or because of the environment, or as a hobby/project - or a bit of everything...