sure cab123 - i posted a ino sketch for a flow heat metre here
it does multiple flows meter at the same time but if you only need to plug one in if you like it will work fine …( depending on esp you use you might have to comment out the reference to the second one )
how is your evacuated solar tubes set up. with relief valve, with out relief valve, or open system. the only reason i ask if it with out relief valve you probably have to buy a metal flow meter sensor that handles 2Mpa instead of the more common 1.2 Mpa . when i set up my systems i set them up either as open or with relief valve… though alot of installs are done with out relief valve and the pressure in side there can get pretty high during a power outage or pump failure. the hall effect flow sensors are easily found on ebay amazon or aliexpress when ordering try to buy rated for 100c but lower is fine too if you have the sensor on the cold side…