I got my tubes in March and the boiler has been totally switched off ever since. It's amazing how much energy is there for the taking.
I have 2M^2 of Ritter tubes and 220 litre hot tank. There have only been a few days when there wasn't ample hot water. We are 2 adults and 1 child.
The cloudless days have been capturing too much, and the system has been saturating by 2PM. We have been deliberately running it off steaming into paddling pools and stuff. I have the tank set at 70C. If I had TMV installed I might run it hotter, but I also have some plastic pipework from the tank so it's sensible to leave it there.
I'd expect to run without any additional water heating for about 8 months of the year at the rate it's going now. A sucession of cool cloudy days will see the tank unspectacularly hot, but so far I haven't experienced that.
For anyone interested, I also got 2.2KWP of PV just over 3 weeks ago, and have already generated 250KWH, 2/3 of which has gone back into the grid. My electricity meter runs backwards..