Mixing Solar Panels

[Kodydog]

I have an older Evergreen EC-110 solar pannel and I want to add to the array with another Evergreen ES-A-200 to 215 model Solar pannel. There is a difference in the specs with the ES-A pannels having higher voltage values. The EC Model has a Vp of 16.4 volts and the ES-A models have a Vp of 18.1 to 18.4 volts. Should I just buy two new ES-A pannels or can I combine?

[OneRVer]

Don't connect them in parallel if the voltages are different, and if you hook them up in series then that would give you 34.5 volts which you don't want either.

When solar cells have unbalanced output, some of the cells become reversed biased (current flowing backwards.) The lower voltage cell becomes a load. This can cause the cells to overheat, fail (even explode, according to one source.)

Reverse bias can happen with solar cells fairly easily. One set of cells in the shade, one in full sun, for instance. Good cells usually have "shunt diodes" to prevent the reverse current flow.

If your cells are equipped with shunt diodes, the lower voltage cell probably won't be damaged, but it won't contribute to the output current, either.

[Kodydog]

OK that answers that question quickly. This is what I though but just wanted to verify.

Time to sell one Evergreen solar pannel on Craigslist to help finance the new ones!

[SpursMVP]

Did you try call evergreen to validate this? I figure the manufacturer will know if you can mix and match panels if you give them the model/serial numbers.

My evergreens have diodes on this to help out when set up on parallel.

[Ed-Sommers]

There are thousands, if not ten's of thousands of us out here in the real world that have combined mixed panels in the same array, and have done so successfully.

While fully compatible panels are probably best overall, my mixed array totaling 1200 watts function just fine thank you, and am usually have topped off batteries by noon for most of the year, and around 2pm during winter months with the panels nearly flat.

I'd recommend you do the experiment yourself and if you perceive a problem you can then change them out!

Ed

[RocketDork]

You could also hook them up to a different charge controller.

[Spikester]

The only trouble with hooking cells that have different ratings together in parallel is you are not getting the benefit of the higher output cells/panels. The system (Panel) output voltage will only be somewhere near the lowest panel in the circuits rated output, the rest of the energy that is being produced by the higher rated panels is going to waste as losses mainly due to heat.
You'll get the most out of your system if the panels all have the same ratings, remember something as simple as the guage of wire used in your system has a noticeable effect on system efficiency/effectiveness/output.

Spike

[HandyBob]

It is possible to mix voltages in parallel, but it does cause some loss. It helps if you put the higher voltage panels further away from the combiner box or connection point so that the voltage drop in the wire brings the voltage level closer. I would not mix any as far a part as 16.4 & 18 without doing this. I have done this and it works just fine.

Warning: You can series panels to an MPPT controller and the voltage will add up, giving you higher voltage & lower voltage drop. Then the controller is set for the output needed by the batteries. However, the amps do not add up. You end up with the amps that the smallest panel puts out. Just another reason I have no faith in the RV Solar dealers. I have seen this done & measured the result. Lets not even talk about what happens when you park one end of the rig under a tree.

[Midniteoyl]

If your worried about one panel hurting the other, you could always use Blocking Diodes..

[HandyBob]

It is not a question of hurting the panels and all the good, larger ones have blocking diodes factory installed. Diodes don't help. The issue is whether or not you will get your money's worth out of all of your panels. By not thinking things through, it is possible to have a system that does not produce the watts that it should because of the interactions between unbalanced components.

Asking a solar panel manufacturer's phone answering flunky about this can get the right answer or not. You never know who answers the phone. Think about this; solar panel manufacturers are factories that build boxes to hold silicon wafers. Many don't make the wafers, but none of them make chargers. If you want the right answer, you must ask the right person. Back in the lighting business, I found that the majority of the time the light fixture manufacturer was rarely the right place to look for good advice about lighting design. Most of those guys just make boxes to hold light bulbs. Surprising, but true.

You can only parallel identical controllers and even then most will not work together because they are not in perfect voltage sync. Besides, if you parallel controllers with unbalanced input voltages you have just transfered the problem to a new location. The instructions supplied with many advise against this, so adding a cheap controller won't work. Yet I have seen many systems installed like this by "proffesionals". Again, you have to figure out who the right person is.

A guy who is trying to sell you his own special widget is the wrong one.

[Midniteoyl]

Quote:

Originally Posted by OneRVer Don't connect them in parallel if the voltages are different, and if you hook them up in series then that would give you 34.5 volts which you don't want either. When solar cells have unbalanced output, some of the cells become reversed biased (current flowing backwards.) The lower voltage cell becomes a load. This can cause the cells to overheat, fail (even explode, according to one source.) Reverse bias can happen with solar cells fairly easily. One set of cells in the shade, one in full sun, for instance. Good cells usually have "shunt diodes" to prevent the reverse current flow. If your cells are equipped with shunt diodes, the lower voltage cell probably won't be damaged, but it won't contribute to the output current, either.

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