Can I mix Solar Panels?

If you have a pre-existing solar panel that you feel just isn't large enough for your energy needs it can seem very easy to just buy an extra panel and add it to the older panel, but there is a reason why this isn't recommended. 

Different electrical characteristics of panels can reduce the performance of a solar array and this can be caused by different sized panels or even same sized panels being made by different manufacturers. The output of a solar panel array will be governed by the panel with the weakest performance, which means your larger panels (or more efficient panels) will be less effective.

To help us in this article we will use our solar panels attached in series as an example (see our guide here on why this is recommended). Let's start with our Photonic Universe 100W Monocrystalline Rigid Framed Solar Panel which in this article will be our old panel, already attached to our electrical set-up. The key figures for this panel are as follows:

• Nominal power: 100W
• Max-power voltage: 20.2V DC
• Max-power current: 4.95A

If we attached this with one of our Victron Energy BlueSolar Monocrystalline Solar Panel Series 4a - 115W 12V with the following figures...

• Nominal power: 115W
• Max-power voltage: 19.0V DC
• Max-power current: 6.04A

We would see the following results 

As you can see, although we have increased our power output and were expecting to get 215W we are losing 10% of our overall panel performance. This is because our array is using the lower number of Amps produced by our 1st panel as this is the lowest value. This power loss would also increase if we added larger panels, e.g. a 175W Solar Panel instead of the 115W with a 34% loss (20.2V+19.4V = 39.6V x 4.95A = 196.02W). 

Even panels of the same size but manufactured by a different manufacturer can suffer from this power loss. For example, if we use the exact same size panel from a leading competitor with the following figures:

• Nominal power: 100W
• Max-power voltage: 18.4V DC
• Max-power current: 5.71A

We still see this power loss issue due to the differences in the voltage and amperage produced by the panel, even though both produce an overall total wattage of 100W. 

In order to get the best performance from your array it's important that you need to match older panels to new panels both in terms of brand and size. If you are unable to, however, you can buy a separate controller for the new panel and have both panels and both controllers feed the battery.

We hope you have found this article helpful.