Installing serial solar panels

[Paul Elliott]

Originally Posted by ramblinrod

Not all solar panels have built in bypass diodes.

If not, one can install bypass diodes, but this may add components and complexity (waterproof junction boxes, connectors, diodes), that simply aren't needed when panels are connected in parallel.

Agreed. But the do-it-yourself bypass diodes will only bypass the entire panel. It appears that some panels have multiple subsection bypass diodes, which would be a big advantage in many partial-shading situations. There's no way to add the multiple bypass diodes yourself.

As I previously mentioned, I ended up with per-panel MPPT controllers. It's a bit of a science experiment, but it should be an improvement. If I had space and desire, an additional panel would have been a more cost-effective way to increase my solar power.

[noelex 77]

Originally Posted by ramblinrod

Not all solar panels have built in bypass diodes.

It is very rare to find any solar panels (that would be suitable for a 12v or higher voltage) without bypass diodes. Usually even the very cheap "no name" panels have at least 2 bypass diodes.

You can fit an additional single external bypass diode for each panel. I think this is probably worth doing if you want to wire your system in series. You can also fit an external blocking diode (for each panel or for the whole array) but this is rarely a good idea for either series or parallel connection.

It is not usually practical to add any other additional internal bypass diodes, as this involves access to the panel's internal wiring.

[john61ct]

Sounds like if you wanted to wire in series, a larger number of smaller panels say 50 or even 20W, with DIY bypass diodes would be good for shade tolerance, maybe worth the extra $/kW

[ramblinrod]

Originally Posted by john61ct

Sounds like if you wanted to wire in series, a larger number of smaller panels say 50 or even 20W, with DIY bypass diodes would be good for shade tolerance, maybe worth the extra $/kW

But why?

Just connect them up in parallel. Problem solved.

The only disadvantage of parallel connection I can think of, is that the current is higher. For a very large array, this can be an issue. For most boats, no biggy.

So 4 x 100W panels in parallel is a great solution for most boats 30 to 40 ft.

So the max current is likely in the neighbourhood of 20A. Big deal.

Ya know, just because an MPPT controller can accept a higher input voltage, there is no need to produce it, if it doesn't make sense.

[DotDun]

Originally Posted by ramblinrod

But why?

Just connect them up in parallel. Problem solved.

The only disadvantage of parallel connection I can think of, is that the current is higher. For a very large array, this can be an issue. For most boats, no biggy.

So 4 x 100W panels in parallel is a great solution for most boats 30 to 40 ft.

So the max current is likely in the neighbourhood of 20A. Big deal.

Ya know, just because an MPPT controller can accept a higher input voltage, there is no need to produce it, if it doesn't make sense.

Smaller wire, less voltage drop, easier to install.

If you are buying new panels that do not have bypass diodes, you should review that decision, IMO, you are buying the wrong panels. If you wire panels that have bypass diodes in parallel, you are gaining nothing, you will still lose the same number of cells when you have a shadow, hence nothing gained by wiring panels with bypass diodes in parallel.

[Mike OReilly]

I’ve been reading this thread out of interest b/c my panels are already installed, and I am very happy with the arrangement (400 watts, 4 panels, parallel, one MPPT). I get ample amps to maintain my house and starter banks while living on the hook for months at a time with little generator (alternator) support.

My panels certainly suffer from shading issues (based on experimentation), so parallel was a a no-brainer. When I sourced them they were/are high quality, marine grade, panels. So I am curious about these new panels with sufficient diodes that don’t suffer from significant shading issues.

I suggest people name the panels/brands/retailers so everyone can actually go and look at the specs. Those installing now can benefit from this information.

[ramblinrod]

Originally Posted by DotDun

Smaller wire, less voltage drop, easier to install.

If you wire panels that have bypass diodes in parallel, you are gaining nothing, you will still lose the same number of cells when you have a shadow, hence nothing gained by wiring panels with bypass diodes in parallel.

Wrong! You are gaining lower voltage. Less lethal. Lower cost components. Again, the bigger wire argument doesn't wash. The difference is peanuts.

[john61ct]

I know on land, when I want to park in the shade, and put a dozen foldout panels 50m away from the controller where there are zero shading issuez, 140+ volts is going to require quite a few pounds less copper than 20.

And yes I'll be careful 8-)

[s/v Jedi]

Let's say we have two panels and each has 3 strings with bypass diodes. We first connect them in parallel and shade 1 cell of 1 panel. This will knock out 1/2 (1 panel) of total capacity.

Now we do the same for series. This will knock out 1/6 (1 string of 1 panel) of capacity. Series connection is 3x as efficient as parallel.

The dangerous high voltage also means high efficiency. Not just for the wiring losses but also for the MPPT controller that loves higher voltages because it can charge better in low light periods (because the voltage is high enough for charging for a longer daily period).

It's just not a valid argument to say that there are panels without diodes because you just buy panels with diodes. I thought all panels manufactured for the past 25 years have the diodes but hey I'm sure some weird panels exist.

The 1 MPPT controller per panel will outperform every other option, mainly because each panel has perfect MPPT tracking instead of an average for the whole bunch. On a boat the panels all have very different situations as compared to a large array on a roof or in the desert. The more difference, the better the small Genasun controllers will outperform.

It has all been posted before, people have all tried it before, nothing new.

[DotDun]

Originally Posted by ramblinrod

Wrong! You are gaining lower voltage. Less lethal. Lower cost components. Again, the bigger wire argument doesn't wash. The difference is peanuts.

Specify the wrong in my post with facts!

Smaller wire = true!
Less voltage drop = true!
Easier to install ( due to smaller wire and easier connections) = true!
Shading has same effect on paralleled panels that have diodes! = true!

The open circuit voltage on my (3) 60 cell panels is 108v, far less than my 240v shorepower, and I ain't scared of either one!

[Stu Jackson]

Originally Posted by john61ct

I know on land, when I want to park in the shade, and put a dozen foldout panels 50m away from the controller where there are zero shading issuez, 140+ volts is going to require quite a few pounds less copper than 20.

And yes I'll be careful 8-)

Pretty big yacht!

[DotDun]

Originally Posted by Mike OReilly

I’ve been reading this thread out of interest b/c my panels are already installed, and I am very happy with the arrangement (400 watts, 4 panels, parallel, one MPPT). I get ample amps to maintain my house and starter banks while living on the hook for months at a time with little generator (alternator) support.



My panels certainly suffer from shading issues (based on experimentation), so parallel was a a no-brainer. When I sourced them they were/are high quality, marine grade, panels. So I am curious about these new panels with sufficient diodes that don’t suffer from significant shading issues.



I suggest people name the panels/brands/retailers so everyone can actually go and look at the specs. Those installing now can benefit from this information.

https://www.wholesalesolar.com/cms/s...4055806412.pdf

Available from Sun Elec. for $.58/watt

[noelex 77]

I think there is some confusion about bypass diodes, so here are some points to consider:

1. Virtually all solar panels come with internal bypass diodes as standard. So you do not have to be concerned you may be buying a panel that has no bypass diodes.
2. Bypass diodes are primarily fitted to avoid overheating the cells of the panel, but they do help with shade tolerance.
3. The consensus (which is widely believed, but still may be wrong) is that solar panels connected in parallel have better performance when shaded than solar panels (with bypass diodes) that are connected in series.

The wiring for panels connected in series is considerably cheaper and easier because of thinner wire, so the crux of the matter is how much overall performance you gain (if any) on a yacht, by wiring the panels in parallel.

[ramblinrod]

Originally Posted by s/v Jedi

Let's say we have two panels and each has 3 strings with bypass diodes. We first connect them in parallel and shade 1 cell of 1 panel. This will knock out 1/2 (1 panel) of total capacity.

Now we do the same for series. This will knock out 1/6 (1 string of 1 panel) of capacity. Series connection is 3x as efficient as parallel.

This is just completely incorrect.

Show me how you arrived at this conclusion.

[newhaul]

Originally Posted by s/v Jedi

Let's say we have two panels and each has 3 strings with bypass diodes. We first connect them in parallel and shade 1 cell of 1 panel. This will knock out 1/2 (1 panel) of total capacity.

Now we do the same for series. This will knock out 1/6 (1 string of 1 panel) of capacity. Series connection is 3x as efficient as parallel.
.

Dont you mean that shading a single.cell would reduce a single panel ( built as you describe) output by 1/3. Or 1/6 of the total of both panels that are wired in parallel and installed as a single array.
Which would be.the same loss as when wired in series.

However even if we went with your assumption of loosing 1/2 of one panel that would only be loosing 1/4 of the total array s output.