Point the solar panel towards the sun... using a volt meter hold the meter probes on the red and black solar panel wires.(exposed wire)
If the your volt meter is reading 18+ volts your good to go
Solar panels create a very small amount of current that can only be measured by connecting the leads of a volt meter in series on the positive lead that connects between the panel and a battery. Voltage is measured across both leads of a given voltage source, such as a battery. By connecting the meter in series, you are measuring the small amount of current being created by the panel that is being sent to the battery, much like measuring the flow of water going through a hose to a bucket. By testing the panel in this fashion, you will clearly see how these panels put out a lot more current in direct sunlight than they do on a cloudy day.
You will need to change the positive lead on your meter to the DC Amps or A socket to read current. Connect the end of the positive or red lead from your meter to the positive lead of your solar panel. Connect the other or black lead from your meter to the positive terminal of your battery. In this fashion, current must flow from the panel and through the meter to reach the battery.
If you get confused and end up connecting to the negative lead of the panel, not to worry. Your meter will likely auto range and show a negative value of the same amount.