Should I get rid of the existing solar water panel
I have solar thermal (and plenty of PV). Solar Thermal has been up since long before I had PV (they are evacuated tubes, rather than flat-panel, so most probably better in the shoulder months). That's for Domestic Hot Water, my Father in Law had some fitted at the same time (so 2nd source of data for me). I also have some flat panel solar thermal for the pool.
I think there are a couple of things to consider:
When they produce they always produce ... so that heat has to go somewhere. You can just rely on an expansion vessel to "expand" but I think that puts a lot of heat stress on the system. So really you need another place to dump the heat - e.g. a Pool
My Father in Law's system turns on his radiators in the situation. Not ideal in Summer, but in reality I don't think he's really aware of it - the radiator space probably loses the small amount of excess heat relatively easily.
The problem I have with them is maintenance. PV is fire-and-forget. If you get a leak / air into the Solar Thermal it needs sorting out. My evacuated tubes (and my Father in Law) have "just worked". My flat panels have been no end of trouble from day one. Leaks and air creeping in. I've given up on them ... and, for a pool, I think PV and a Heat Pump would be a MUCH better solution. Use the Grid to run the Heat Pump in early / late months, if you want to, and in mid Summer (when my pool Solar Thermal was working the pool was like a sauna ...) just use the PV for something else.
Diverting excess PV to an immersion heater is easy (albeit a lousy use of electricity), but nowadays people are increasingly likely to divert to EV
I reckon I get more "hot water" out of my Solar Thermal than I would by replacing them with PV (and using that to heat Hot Water) ... but ... the maintenance is a cost and annoyance. Also, how to know if Solar Thermal is working? working well? My control panel records the kWh (or similar) generated, and I read that manually (to a spreadsheet) each week. But we have immersion on a timer for "end of Off Peak" to make sure we have hot water in morning ... in Summer it doesn't do any work, in Winter the central heating would normally do that job ... but the rest of the time if the normal solution stops working the backup immersion solution just takes over and we have no idea something is bust ...
All these blinking things should come with the ability to alert "Something Wrong". Central Heating thermostat detects that the temperature is below SET, and send the signal for "Call for heat". An hour later the thermostat has fallen another degree - what does it do? Nothing! Just continue "call for heat". Utterly useless in this day and age ... so basically you come home to a freezing cold house (and maybe burst pipes) and only then are you able to start doing something about it.
If the Solar Thermal panels are working well maybe keep them. When they break I would replace them with PV. Would you be able to "just add some PV panels" at that time? And would you have the cost of putting up scaffolding? Can you find out how well they have been working, from existing home owner?
I'm thinking, taking all that into account, the solution would be "Solar Thermal on eBay" ... and go for the best optimised layout for PV instead
Somewhere on the internet will be a figure for annual production of kWh from Solar Thermal vs. PV and that might be significantly in Solar Thermal favour ... except for what happens when it is over producing in Summer.
