Fiddling with 2 off matte black domestic flat radiator panels heating a 7,000 litre swim spa. ESP8266 running DS18B20 1-wire sensors switching on a small pump when solar output exceeds spa temperature by 1 deg C

Temperature data streaming from Raspberry Pi connected to 3 probes in my hotbin (hot composting).

Electrical & onsite parameters for solar panel located in COEP.