New Solar System Install

[CA Traveler]

Originally Posted by elkhornsun

For a long run from the panels to the converter having the panels in series will minimize the current loss. Drawback is reduced output with any shading of any of the panels in the series.

What do you base the reduced output in series on? I'm not convienced of this for panels with bypass diodes which most panels include.

In fact just the opposite might be the case. A 6x10 panel with 3 bypass diodes could lose 1/3 or 2/3 of the panel for partial shading. That leaves 2/3 or 1/3 of the panel voltage usable in series but none in parallel. Of course this only works for MPPT controllers.

[elkhornsun]

Originally Posted by CA Traveler

What do you base the reduced output in series on? I'm not convienced of this for panels with bypass diodes which most panels include.

In fact just the opposite might be the case. A 6x10 panel with 3 bypass diodes could lose 1/3 or 2/3 of the panel for partial shading. That leaves 2/3 or 1/3 of the panel voltage usable in series but none in parallel. Of course this only works for MPPT controllers.

It is the reverse. With parallel wiring the two panels operate independently. In series if the one in shade is the one connected to the C-box or controller then the ones downstream are going to be impacted. The type of controller used has no bearing on this.

[CA Traveler]

Originally Posted by elkhornsun

It is the reverse. With parallel wiring the two panels operate independently. In series if the one in shade is the one connected to the C-box or controller then the ones downstream are going to be impacted. The type of controller used has no bearing on this.

Let's try an example, 2 150W 30V 5A 6x10 panels with 3 bypass diodes.

In parallel with full shade you'll get full power from one panel. In serial with full shade you'll get full power from one panel minus the bypass diode drop. Let's assume the diode drop is 0.5V so you'll have 5A*(30-1.5)=142.5W. So I agree that parallel is better in this case.

But RV's are often subject to partial shade from a variety of sources. Let's consider partial shading on say 1/3 on the panel covered by a bypass diode. In this case parallel will give you full power from one panel. Serial will give you 150W+5A*(20-0.5)=247.5W.

Serial panels with bypass diodes and partial shading have advantages.

Controller type is also a factor. Serial panels mean the use of the higher cost and efficiency of an MPPT controller. Parallel can use MPPT or the lower cost and lower efficiency controller PWM controller.

The use of a PWM controller also means that for practical purposes the panels are limited to 12V panels. In todays market the trend is towards higher voltage and lower cost/W panels. Again controllers are a factor.