Combiner box

[Teddy]

Is a combiner box only needed when solar panels are connected in parallell?

If solar panels are connected in series thereby increasing the voltage but the current remains the same will it cause problems with the charge controller due to the higher voltage?
eg 3, 300W solar panels in series would be more than 12 V

 

[FilterGuy]

simple questions.... complex answers.

If solar panels are connected in series thereby increasing the voltage but the current remains the same will it cause problems with the charge controller due to the higher voltage?

It depends on the max input spec on the charge controller, the Voc (Open Circuit Voltage) of the solar panel, the number of panels in series, and the temperature conditions.

Lets walk through an example.

• Let's assume you have an MPPT charge controller with a max PV input voltage of 100V.
• Let's assume you have a bunch of pannels with Voc of 30V

Question: How many panels can you put in series?​

At first blush it would seem like you could put 3 panels in series for 90v and be OK for a 100V controller.... and that is true as long as it never gets even a little bit cold. With that combination, if it got very cold, the Voc would rise above 100V and possibly damage the controller. Consequently, you could probably only put 2 panels in series and still be safe. To learn more about adjusting Voc for low temp, please review this:

Adjusting Solar Panel Voc for temperature

When designing you solar panel system, it is important to adjust you solar panel Voc for temperature in order to ensure you do not over-voltage the PV inputs of your solar charge controller. This paper shows how to calculate the Temperature...

diysolarforum.com

Is a combiner box only needed when solar panels are connected in parallell?

From a pure functionality point of view, not having a combiner box will work fine for a single string of panels. In fact that is the way residential grid-tie solar was installed for many years. However, in code complaint solar panel array, the combiner box often houses several other safety related functions.

1. The circuitry for Rapid Disconnect Requirements are often implemented inside a combiner box. However, in the most recent version of the code, you pretty much have to have a disconnect circuit at each panel so maybe it would not be implemented in a combiner box any longer.
2. The circuitry for PV Ground Fault protection is often implemented inside a combiner box. However, this circuitry can be implemented in the charge controller so it does not necessarily mandate a box at/near the panels.