When wired in series, the 3 connected panels (often called a series "string") will have a voltage of 36 volts (12V + 12V + 12V) and a current of 8 amps.
In the diagram above, the output voltage of each panel is 6 volts. At the end of the series, the cumulative output is 18V (3 panels x 6V = 18V). What's crucial to note is that while the voltage output increases with each panel added to the series, the amperage remains the same.
When you connect solar panels in series, the total output current of the solar array is the same as the current passing through a single panel, while the total output voltage is a sum of the voltage drops on each solar panel. The latter is only valid provided that the panels connected are of the same type and power rating.
If you want to connect the above solar panels in series, you will have to connect the positive (+) terminal of Solar Panel 1 to the negative (-) terminal of Solar Panel 2, and then connect the positive (+) terminal of Solar Panel 2 to the negative (-) terminal of Solar Panel 3, as shown in the diagram below: The total voltage of the array would be:
What happens when you connect solar panels in series?
When you connect solar panels in series, you connect the positive (+) terminal of one solar panel to the negative (-) terminal of another solar panel. The total voltage of the array will be the sum of the voltages of each solar panel, while the current will be the same as that of the solar panel having the lowest current specifications.
When you wire in series, you add the voltage of each panel together. If you connect 2 x 12V panels, you get total output voltage of 24V. Make sure the combined voltage doesn't exceed the maximum input capacity of your solar inverter or charge controller. Do solar panels charge faster in series or parallel?
It's technically possible to mix 12V and 24V solar panels. But it's not ideal. It's best to opt for panels with as similar specs as possible. If you must use equipment with mixed power ratings, wire two 12V panels together in series before wiring them in parallel to their 24V counterpart.