Thermal panels are different to PV in that instead of converting the sun’s energy into electricity, it converts it solely into hot water which is stored in a cylinder. We had thermal panels installed back in 2007. At the time we had just moved in and the old combi boiler that came with the property was actually struggling to cope with a largish house and family.
There seemed to be quite a few solar thermal salespeople around back then (always attracted by government grants) some of which were obvious cowboys. They seemed to be the “new double glazing salesman.”
But we found a reputable local company and we got a whole system with new condensing boiler and unvented cylinder that was designed for solar thermal. This seemed to work so well that the water was usually too hot for the safety regulations, so that we had a mixer tap on the cylinder installed. This allowed it to store water that was too hot, but the mixer at the cylinder reduced it to a legal level at the tap.
As years went by (2022) we decided to have a heat pump installed. We needed a new cylinder anyway and one that would have accommodated both ASHP and thermal solar would have cost a lot more. In the we decided it made sense not to go to the expense of accommodating the old thermal system. This decision was partly due to the difficulty in finding a local service engineer, the parts are becoming impossible to find and we now use much less hot water as the children had left home. So basically we were making more hot water than we could use, so a lot of that solar energy was going to waste.
In hindsight PV would probably have been better to begin with. Although thermal is very efficient compared to PV, it only becomes worthwhile if you use a lot of the hot water. Very often the water would heat up fully in a few hours, so on a sunny day the rest of the sun is not used unless you decided to shower for a couple of hours. Unlike electricity, you can’t sell hot water back to the grid. PV panels have become much more efficient over the years and the energy is more versatile. So for example if you need to heat water on a sunny morning, once that water is hot the electricity can then be used for something else, stored in a battery or sold to the grid.