How to count sun hours with solar panels

Any silicon solar panel/cell is probably within 5% (linear) of solar insolation if you "short" the output (typically a low resistance resistor and logging volt meter) measuring the Isc (short circuit current).

There are a lot of DC Amp*Hour meters out there these days--The first is this one (US source--I am sure you can find many other sources in your country):

http://www.rc-electronics-usa.com/ammeters/dc-amp-meter.html

Connect the meter's shunt side across a solar panel, and connect the external power source (for meter power).

Say you have a panel that is rated for 3 amps Isc (short circuit current). That rating is typically at 1,000 Watts per square meter (full noon time sun).

If the meter reads 15 AH at the end of the day, then:

15 AH per day / 3 Amps (Isc @ 1,000 W/sqm) = 5.0 "hours of sun" per day (or 5,000 WH per square meter per day)

Or, you can put a low Ohm resistor across the output of the solar panel (keep the maximum voltage low--less than 0.2 volts) and use some sort of logging millivolt meter (scale shunt resistor to meter's range--Keep voltage low, you want to measure Isc, the higher the voltage, the less accurate the readings will probably be).

You can also find weather stations (for home use) with their own solar insulation meter too.

http://www.davisnet.com/weather/products/weather_product.asp?pnum=06450

The DYI solar panel solar insulation is not perfect--But should be close enough for most people trying to do some quick and dirty measurements.

The right weather station can be nice--Would include internet access and software.

-Bill