Solar Panels - Wire in Series, or Parrallel ?

[Talbot]

Giving some thought to the wiring of solar panels and with MPPT controllers able to cope with high voltages, it seems to me to make sense to wire solar panels in series rather than parrallel, and then allow the controller to sort out the result.

If you have a wind generator as well - should that also be in series?

What do you think?

[Viking Sailor]

You definitely don't connect your wind generator in series or parallel with the solar panels. The wind generator is connected via its own charge controller to the battery bank.

Skipper, in order to provide you with the best help possible, please provide the solar panel wattage and nominal voltage, and which MTTP controller you will be using. Also, any info on how and where on the boat you will be mounting the panels could be helpful in answering your questions.

[Talbot]

Originally Posted by Viking Sailor

in order to provide you with the best help possible, please provide the solar panel wattage and nominal voltage, and which MTTP controller you will be using. Also, any info on how and where on the boat you will be mounting the panels could be helpful in answering your questions.

3 - 5 60w panels, with an Outback Flexmax 60

[Eleven]

I'm told by my techy bro that for optimum currents each panel should have it's own controller delivering 12V dc. Shading, even partial, requires the working panels to drive through the resistance of the shaded panels. By letting each one do it's own thing you'll get optimum output. This particularly applies to coach roof installation on sailing boats. And keep them clear of the mast ( it's the ropes that lay all over them) and give yourself good footways to the mast. If you are laying them on the coach roof then be aware that they trap water behind them which gathers all the grit gunge and green stuff available. Either space them off with an air gap behind or seal around the edges. I'd prefer an airgap to help shade the boats interior and to keep the panels cooler, their output reduces when they get hot (like in sunshine!).

[cfarrar]

Shading is certainly an issue, though panels connected in parallel do not reduce each other's output when shaded - only when connected in series. That's partly what drove Viking Sailor's question, I believe. A crude example: envision four 60W panels, connected (in series) into two pairs, and the pairs (in parallel) to your controller. In this setup, a shaded panel would reduce your total output potential by 50%. If they're all connected in parallel you would lose 25%. So, the optimum wiring scenario depends on the number of panels, where you mount them, the likelihood of shading more than one panel at a time, the distances of your wiring runs, etc.

[rebel heart]

Maybe I'm dumb... doesn't hooking two 12 volt sources in series generate 24 volts? And since those panels are normally in the 14-15v spectrum, now it's ~30v? Is that the idea, that if you have one completely shaded panel and the other unshaded you'll still get 12v? I don't get it.

[SailFastTri]

Originally Posted by rebel heart

Maybe I'm dumb... doesn't hooking two 12 volt sources in series generate 24 volts? And since those panels are normally in the 14-15v spectrum, now it's ~30v? Is that the idea, that if you have one completely shaded panel and the other unshaded you'll still get 12v? I don't get it.

MPPT controllers will down-convert higher voltages to the correct charging voltage for the batteries. They function as a DC-DC converter.

[cfarrar]

It might be me who's dumb, RH. You're right about creating a 24 volt system, and that has it's advantages. However, when two panels are in series and you shut one down (due to shading), you effectively break the series connection... ie, zero volts. Solar panels themselves are comprised of cells wired in series, which is why only a few shaded cells can shut down the entire panel. But hey, I admit I have no real world experience using solar panels in series. My three solar panels are wired in parallel.

[SailFastTri]

Originally Posted by cfarrar

It might be me who's dumb, RH. You're right about creating a 24 volt system, and that has it's advantages. However, when two panels are in series and you shut one down (due to shading), you effectively break the series connection... ie, zero volts. Solar panels themselves are comprised of cells wired in series, which is why only a few shaded cells can shut down the entire panel. But hey, I admit I have no real world experience using solar panels in series. My three solar panels are wired in parallel.

Actually the shaded cells become power consumers, and can cause hot spots that degrade the panel. The heat becomes even more intense at higher voltages, which is why bypass diodes are used in some setups. Search the web for "bypass diode" and "solar" and you'll find some articles that describe this better.

[Talbot]

Having given this some thought, it would appear to me that a multi panel system wired in series with bypass diodes is likely to work significantly better in overcast conditions, but may work less well in high sunlight.

My panels will be on the platform above the davits across the stern (no backstays).

[Sandero]

parallel... with a regulator to convert the output down from what is typically 18+ v to the proper charging voltage which is around 14v bulk and 13v float.

[Viking Sailor]

Solar panels have nominal voltages of 12, 18, 24, 36, 48 volts. Since you have not yet purchased your panels and assuming that you want to charge a 12 volt battery bank, I recommend that you get panels with a nominal voltage of at least 18 volts. These panels will have a maximum voltage of around 25 volts which the MTTP controller will down convert to 13.5 to 15.5 volts needed for the various charging stages. Although I haven't checked, the selected MTTP controller may be able to handle even higher voltage panels. The panels should also come with built-in bypass and blocking diodes. And to finally answer your question - they should be wired in parallel using at least number 6 AWG wire.

[rebel heart]

If he's on the low end with three sixty watt panels the idea of running 6 gauge seems a little nuts. I have two 135w panels and 10 gauge over 20' results in <4% drop if I remember correctly from sizing the thing.

[zeehag]

mine donot shut down in shade--they produce less but shade still has uv in it-- i have each panel independent of the others-- 2 are on same controller, but enter individually. controller has places for more than one panel input, as long as not in excess of the number of amps controlled by that controller. i have 2 of the 3 amp rated panels on one 6 amp regulator and i have a 130 wt panel on my 10 amp regulator. both are wired onto my electrical panel to a breaker .
WHEN i get my wind genny , i will have it on a separate breaker and a separate controller and will be able to shut it off when the sun is shining-- and turn it on when the wind is blowing enough to make a difference--sometimes the wind source can make the sun source shut down--so i want different breakers for them.

[barnakiel]

One must be careful wiring both wind and solars into one regulator as some regulators may damage the windmill.

I think Rutland makes a regulator that will take both.

b.