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Johny London

Solar panel - mix and match?

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With spring just around the corner I'm thinking it is time to add some more solar panels to my roof.

I currently have 2x150w polycrystaline, in series.

I want to add two more panels in series (with each other) and either have each pair on a separate controller or better yet each pair in parallel on the same controller.

Now, I understand that panels should be similar spec when used together - in order to maximise power (?).

I have the option of two more identical panels, or two Monocrystaline, and I favour trying the latter.

The specifications between the mono/poly are indeed a little different...

 

Any thoughts before I order?

 

Monocrystaline solar panel spec.png

Polycrystaline solar panel spec.png

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They are very similar probably wouldn't make any noticable difference, whats more important is what controller are you using? Will it take panels in parrallel, double the amps.

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Hi I have a controller that can take all 4 panels, as far as current and voltage is concerned, and another that can take two, so there are my options. Ideally all panels on the higher rated controller would prolly be the neatest solution.

I just think the Monocrystaline ones might be that bit better especially in lower sun conditions.

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I have a mix of makes on my roof and they seem to work fine, I just have two more to wire in for 3.6KW on the roof. I have had the best year ever for solar dont know about others?

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not an expert, but possibly the max power point voltage for a mono panel is different for a poly, in which case putting them on the same controller is not going to optimise one set. I would be tempted to use separate controllers for the different types.  I am assuming you are going to wire them as two sets of series pairs, if putting all in series then the poorest panel will limit your power and also you will get more problems with shading.

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Other advantage of the mono over the poly, apart from the mono being of better quality, is that mono tend to have a smaller footprint over poly panels for the same output. 

 

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Right, I'm going to go for the monos then, prolly on the same controller, so any advantage gained in performance (over the poly) will most likely be nulled out by things not being at optimum for all panels.

Yes, two series pairs, in parallel, to avoid total black out during shading! They are also at opposite ends of the boat. I'm going to get some normal brackets and bolts (not specifically for solar panels as per z brackets etc) and do them so that they can "hinge" from either side by removing two bolts. So they will be just as low profile as my other two (currently on z brackets) and thus look rather neat, but I'll have the option, if I can be bothered, to angle up to the sun. I expect this will be worthwhile on marginal days and spring/autumn.

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Just another thought. One set of 4mm cables is going to be 13m long, the other set is half that. Thinking about voltage drop along the cable, and seeing that the monos have 16.6v and the polys 18v (operating voltage)...

Would I put the lower operating voltage ones on the longer cables where presumably the will be more volt drop, so likely they will be sitting at a bit less than the polys, or would I put the polys on the longer cables to "null out" their higher voltage with the drop in the cable? I can't figure which round to think it.

Sods law it will need to be the higher voltage panels on the longer cabling because I don't currently have it that way round.

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all are 150w each. I guess as they are the supply, and the controller is the load, the voltage drop will be to the controller, so the panels would sit at a slightly higher voltage than that which the controller would see. On the other hand, the controller would up its desired voltage input until it feels the panels are at optimum output, so the voltage could read higher at the controller than at the panels? I'm confused!

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If they’re the same power but one has a higher voltage then that one will be carrying

less current than the other and will therefore have a lower voltage drop. So the higher voltage one should have the thinner cable. 

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Cables are equally thick but one pair is longer which I guess equates to the same thing. So, the furthest away panels should be the higher voltage ones. I bet it would be just spot on like that as the voltage difference is only 1.4v and prolly part of that will drop on the longer cable so the panels will end up pretty reasonably matched. Only problem is of course they are currently set to be the other way around, so means moving my existing ones first. I wonder if it's really worth it.

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