More  Tester Circuits

Solar Insolation Meter (June 1, 2017)
designed by David A. Johnson, P.E.

You don’t need a fancy and expensive meter to measure the sun’s intensity.  With some inexpensive parts you can build your own meter.  I used a 1ma meter movement and a single solar cell I got on eBay with an area of about one square inch.  I calibrated the meter on a very clear bright summer day when the sun was directly overhead.  I pointed the solar cell for the maximum deflection on the meter and then adjusted the 100 ohm variable resistor R2 for a full scale reading. 

The meter is great for spot checking expected sun power at specific roof angles, times of the day and even overcast conditions.  I was amazed when I expected a low power reading on a cloudy day but measured about 60% intensity.  I have also shown below the circuit needed for a typical 100uA meter movement.