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yes, devices to measure solar irradiation are called pyranometers. 

There are two types of pyranometers

1) blackbody pyranometers ( they use the thermoelectric effect to produce electricity when heated ) 

   they usually cost between 1000- 5000 $ and are the most accurate 

2) silicon based pyranometers (they use a silicon-based photodiode )

    they are much cheaper! For example  http://www.apogeeinstruments.co.uk/pyranometer/ ~ 150 $

If you want to know how much radiation energy you have for your solar panels, the cheap silicon based pyranometers might even give you more useful data, since the spectral response of silicon-based pyranometers closely matches the spectral response of silicon-based solar panels.

Finally, here's a cool 20 $  DIY project:

Measuring Sunlight at Earth's Surface: Build Your Own Pyranometer

http://www.instesre.org/construction/pyranometer/pyranometer.htm