1m2 of pv wont create any where near the same heat input as 1m2 of thermal.Is it though?
What's a rough kWh/year/£?
Edit; I reckon PV sits at around 1.6kWh/year/£ for a new DIY install.
In my opinion, PV is simpler. But that's just personal preference plumbing Vs electrics.
A 30 tube panel for about £783 & a bit of plumbing / pump & a cheap controller.
You need the tank already so not an additional cost.
Googling suggest that thermal can collect 90% of available energy compared to PV's 20% (?) or what ever the current spec is.
thermal 1851 watts for £783
PV at 42p per watt would be about the same cost per watt but would cover 4 or 5 times the area.
Reducing how much you can fit & increasing install costs.