Check the back of the solar panel and look for the voltage output. The label will either say 12V or 24V. This is the simplest and probably the quickest to find out. That said depending on the solar panel, the label may be small and you might need a magnifying glass to read it. A more practical way is to use the camera. If you know the wattage and current of your solar panel, you can use the simple equation to work out the voltage. Watts = Volts x Amps For example, if you have a solar panel that is rated at 175W and it produces a current of 7.42 amps, the voltage would be: Volts =. If you have a voltmeter, you can use it to test the voltage of your solar panel. This is the most accurate way to test the voltage of your solar panel. To test. If you still can't tell if your solar panel is 12V or 24V, the last resort is to check the manufacturer's specifications. Almost all solar panels will have their voltage specifications in the product manual. If you don't have the product manual, you can usually find it on the. Another way to tell if your solar panel is 12V or 24V is by checking the number of cells in it. If the solar panel has 36 cells, it is a 12V panel. If the solar panel has 72 cells, it is a 24V panel.