Hi.
Found this schematic when looking to build a solar insolation measuring sensor. Would it be reasonable to calibrate with a potentiometer in series as to show 1KW/m2 full scale at the maximum obtainable observation angle sampled for several sunny days ? Does it need to be a more complex circuit ?

 

It should work but the scale will probably be very non-linear. It will depend on the characteristic curve of the photo diodes and the full scale deflection voltage of the meter.