Mixing Solar Panels a Bad Idea?

[Wissel]

Now I know exactly what space I have on my roof, I need to order another couple of solar panels.

My MPPT can take 430w of panels and I currently have two 100w mono panels. This is my highly professional artists impression showing where the new panels can fit

I can either fit another two 100w panels or a 150w at the front and an 80w at the back. The second option I prefer as it fits nicer at the back and I max out capacity. With either option I'll stick with mono, but is it a bad idea mixing panel sizes?

I can't fit panels the other side at the back as new awning will get in the way. Also behind rear roof light isn't an option as this is changing to a MaxFan.

 

[two]

It will depend on how you intend to wire them up. Simplest to stick them in series, as long as the controller can cope with the combined voltage. If any will be in parallel, they will need to have identical voltages and, for that reason, I'd use identical panels.

 

[DBK]

Quick fire answer is go for four 100W panels. There is an argument which says if you mix panels the total will be limited by the smallest panel but when the sun is blazing who needs 400W? You need 400W of panels on a foggy day in November when such limitations are irrelevant.

 

[Wissel]

Cheers guys. I'll order two more 100w the same as existing (been reading up online the last hour as well).

@rogher - has to be in parallel unfortunately. My max VOC is 28v and my 100w panels 21v.
@DBK - yep agree.

 

[Urs4_2008]

If the panels have the same voltage you can parallel different panels. But not the best solution.

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[Urs4_2008]

Quick fire answer is go for four 100W panels. There is an argument which says if you mix panels the total will be limited by the smallest panel but when the sun is blazing who needs 400W? You need 400W of panels on a foggy day in November when such limitations are irrelevant.

Only if connected in series.

 

[andy63]

I usuall think of it like adding batteries. Ideally Same age /usage and similar capacity
... the ideal situiation with panels is to have your panels with similar voltage or current characteristics depending on whether connected in series or parallel.
http://solarpanelsvenue.com/mixing-solar-panels/
Andy.

 

[two]

That’s a useful article. I may have scanned it too quickly, but I did not see mention the use of blocking diodes (in the case of parallel connection). Schottky diodes are recommended these days and I think you can get ones which will plug in line to an MC4 connection. These will combat losses caused by performance differences due to shading (vents up) for example.

Once the (equal length) cables are brought together, you’ll have a lot of current flowing. I don’t know how far away your controller will be but I’d use thicker cables (10mmsq) for that bit.

I’ve only installed a single panel in the past (and get by without any at the moment) so all the above is based on the theory I have gathered out of interest in this subject.

 

[Wissel]

That’s a useful article. I may have scanned it too quickly, but I did not see mention the use of blocking diodes (in the case of parallel connection). Schottky diodes are recommended these days and I think you can get ones which will plug in line to an MC4 connection. These will combat losses caused by performance differences due to shading (vents up) for example.

That's interesting @rogher

I'll do a little research on this then order the diodes, but I assume they are placed inline before the panels are connected to a single wire?

Once the (equal length) cables are brought together, you’ll have a lot of current flowing. I don’t know how far away your controller will be but I’d use thicker cables (10mmsq) for that bit.

I used 10mm last time with just the two panels. I have a feeling the cables could be up to 5m long (from furthest panel) to MPPT, so may even fit 16mm from where they all join on the roof.

 

[two]

Can hardly ever have wires that are too thick, but routing around corners might become difficult.
Slip the diodes in just before the branch connectors, then everything will be in the same place.

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[pappajohn]

What is that dome thing and where will you put the aerial.

 

[Robert Clark]

I'm not convinced that having different size panels is a problem when connected in parallel, in the context of them being mounted on a MH roof.
If you're parked under or near a tree there is unlikely to be equal exposure to sunlight, which must affect the potential output of each panel, irrespective of the size

When I designed my system I wanted maximum potential output from the space available

 

[Wissel]

What is that dome thing and where will you put the aerial.

The dome is my old 3g antenna (it's going, 4g one ready to fit). The TV antenna did go in the little red hole at the front, but is going as well. We don't watch telly so no point in having one (haven't got an antenna on our house either).

 

[Wissel]

You could be right @Robert Clark

It does seem a contentious subject from reading elsewhere. Thing is I have the choice, so may as well just stick with 4 x 100w the same. 30w isn't going to make a great deal of difference (especially as starting the van engine delivers a real 60a per hour).

 

[Tykatem]

I have 2 solar panels connected in parallel 1 x 120w & 1 x 80w (chosen for their actual size LxW) and they always keep my 2 x 95w batteries topped up over the winter, including the last 4 or 5 days at a damp and overcast Chester.

Pete

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[andy63]

Good point Robert @Robert Clark couldnt really dispute it .. thats the real world and the reality..
Butci would still try and match my panels to suit , depending on how i connected them.. that way under ideal conditions you get the best out of your set up..
Andy

 

[two]

One of the difficulties is that many alternative arrangements will work but I’m not sure how well. Someone’s unlikely to notice performance differences unless charging stops altogether and it’s difficult for an individual to get meaningful comparisons. I asked the Centre for Alternative Technology some specific questions about the performance of solar panels and they were unable to answer (but invited me to sponsor a research project if I was keen to find out).

My view is that panels are likely to work best together if everything is matched and I wouldn’t experiment with anything else if they can be.

 

[Minxy]

I've been reading this with interest as I'm trying to decide what to put on our new van, the options appear to be:

1. Remove the existing 60w semi-flex panel from my FamilyScout and put it on my new PVC along with the new 100w semi-flex panel giving 160w in total (using my existing LR1218 controller).
   
   
2. Leave the 60w panel where it is on my FamilyScout and instead get a second 100w semi-flex panel to match the new 100w semi-flex panel and put them on my new PVC giving 200w in total, and buy a new controller.
   
   
3. Leave the 60w panel where it is on my FamilyScout and sell my new 100w semi-flex panel then get a single 200w semi-flex panel (or a rigid as cheaper) and put it on my new PVC and buy a new controller.

Thoughts?

NB: I assume joining them in parallel format would be best if I have 2 panels?

 

[two]

I would go for option #2. Carrying over old kit should only be done when desperate. New kit has usually improved in the meantime and comes with a guarantee. Old kit has been used and may not transfer well. As for mixing, that’s not what I would ever wish to do.

Will you need a second panel? I’d get a controller that could accept the power from two and leave that option open.

I think that parallel connection has been the vogue on motorhomes and regulators match the voltage for that. I don’t think the method of connection would make much difference, although I’d favour a series connection because that’s the way I originally considered better and there’s been no significant persuasion (other than the availability of regulators) to think otherwise since.

 

[Minxy]

I would go for option #2. Carrying over old kit should only be done when desperate. New kit has usually improved in the meantime and comes with a guarantee. Old kit has been used and may not transfer well. As for mixing, that’s not what I would ever wish to do.

It'd mean I wouldn't have to fork our £70+ for a new controller for my Schaudt unit but might not prove an economical move in the longer term, plus of course there's the aggro of trying to remove a Sikaflexed semi-flex panel from the roof and clean it all up!!!

Will you need a second panel? I’d get a controller that could accept the power from two and leave that option open.

As our new camper has an 'all electric' fridge freezer I don't think 100w will be sufficient for our needs as we don't use sites or have EHU ... I've waited 3 years to have one big enough to be able to have food AND ice cream in so last thing I want is for it all to melt!

I think that parallel connection has been the vogue on motorhomes and regulators match the voltage for that. I don’t think the method of connection would make much difference, although I’d favour a series connection because that’s the way I originally considered better and there’s been no significant persuasion (other than the availability of regulators) to think otherwise since.

Thinking about it more, I can easily get back the cost of the new 100w panel I bought so won't lose out on it so I'm now leaning more to one large 200w panel as it will take up less roof space than 2 x 100w ones and if I find I need more in the future I can add to it, one large one will also mean not having to connect them together either so a simpler installation. Now should it be rigid or semi-flexible ... semi-flex are easier to fit as they just stick on (no brackets to mess about with) but are quite a bit dearer than a rigid kit ... our SF has performed perfectly for 3 years, despite it only being 60w, but I know a few people on here have reported issues with theirs.

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[two]

I'd be happy to stick a flexible panel to a steel roof. I think it'd be neater, too.