[werk_ag]

My being frustrated is not with you or the weather station, but with my inability to sufficiently comprehend the system to manipulate it to make it do something (I am admittedly over my head because I've never undertaken this sort of hands on project with something I knew so little about).

I also haven't interpreted the expression, as something directed to me or to the project, perhaps just some impatience to get results, something I can very well understand, as sometimes I suffer from the same problem.

I will try to give some simple figures that may help to understand to what we are dealing:

Supposing that R2 have a value of 4900 Ohm, the gain of the OP is around 3, this mean that by each mV on the input the output will be 3 mV.

So, if the pyranometer (or any interference) presents a voltage of just 0.33mV in the OP input, that is enough to produce 1mV at the OP output, which by turn will produce a reading of more than 1W/m2.

I think this figures will illustrate how easy is having some spurious readings. Cutting the readings below an acceptable threshold will be almost always necessary.

I'm aware that there are better designs than a simple non-inverting circuit for the OP, but they can't also give 100% insurance against spurious readings.