Sun illumination logger with Arduino - eclipse oriented

Last week I found out that a good part of Europe will see a Solar eclipse during the morning of March 20th, 2015. In my location the Sun will be covered at about 72%, peaking at 10:30 local time.

So, why not build something to measure and log the decrease in solar radiation? If any, of course!

Ingredients:

• an Arduino board of your choice
• an SD card adapter (and an SD card itself)
• a solar panel (or other light-sensitive component)

Concept:
A solar panel produces an amount of current that is proportional to the incident light. With a shunt resistor that current is transformed into a voltage and measured by the Arduino analog-to-digital converter. Read data is saved to an SD card for further analysis.

To calibrate the I/V conversion the solar panel must be exposed to the maximum sunlight (~ Noon) with an orthogonal (90°) incident angle. Then the generated current is measured and an appropriate resistor is calculated so that a bit less than 5 Volts are produced.

That's it. Leave the acquisition system run for a few days in the chosen operating position (facing South or the Sun position at eclipse peak time, with enough tilt to achieve 90° angle of incidence.

An RTC (real-time clock) module would be advisable, so that each reading could be timestamped. Unfortunately I never bought one and nobody in my circles has a spare one to lend.

I need to calibrate the little solar panel. Then pictures and Arduino code will be posted (in due time before the Eclipse, in case you want to reproduce this experiment at home).