You need to have a panel tester that is known as an amp meter.
How to test solar panel amp output.
You want to choose a voltage range capable of displaying the maximum possible voltage of the panel in open circuit this means that if you have a panel rated for 20 volts you should set the multi meter.
As long as the amp meter is rated higher than the solar panel you will be able to measure the output effectively.
Attach the meter to the positive and negative terminals on the solar panel and make sure the panel is properly exposed to sunlight.
After doing your solar panel testing you should find that the solar panel output for the pv panel you built on the make solar panels page is about 18 volts and 3 5 amps.
To get an accurate measurement you will need to ensure that your panel is in full sunlight when you test.
Measure solar panel amperage.
To test a 18v solar panel voltage output directly put your solar panel in direct sunlight set your multi meter to the dc volts setting.
To determine the power that the solar panel is dissipating you need to measure the wattage and voltage.
To begin measure solar panel amperage.
Attach the meter to the positive and negative so that you measure the amp output of your solar panels.