Four Solar Panels - Parallel , Series or Series-Parallel

[sailorboy1]

I keep reading this thread and others like it so I will know what the answer is when it comes time for me to do it. But i tseems that it always comes down to a "it depends" answer every thread.

Would the choice between series or parallel greatly come down to the installation and location of mounting the panels? If always out in the open so low shading = series; and if on bimini or something that is going to experience a lot of shade = parallel?

[s/v Jedi]

Originally Posted by noelex 77

if one panel is shaded. MPPT does not fix the high resistance in a completely shaded panel.

If one can't find a good location for a solar panel, installing it in parallel to others so it doesn't hurt the output of the other panels is a way of looking at the matter that will be welcomed by the manufacturers. However, for the user it might be wiser to not invest any $$$ in panel(s) that don't produce due to shading.

In other words: if you only have 1 good spot for a solar panel.... install 1 panel. Do not waste money on panels that can only be installed in problematic locations where they will not produce or only produce a fraction of their potential.

Is simplistic, naïve, or just wrong.

Then you should re-read the posts about currents and voltages and loss in controllers. Those are wrong and me saying so can be called blunt or worse, but not any of the 3 terms you chose.

ciao!
Nick.

[noelex 77]

Originally Posted by Don Lucas

I keep reading this thread and others like it so I will know what the answer is when it comes time for me to do it. But i tseems that it always comes down to a "it depends" answer every thread.

Would the choice between series or parallel greatly come down to the installation and location of mounting the panels? If always out in the open so low shading = series; and if on bimini or something that is going to experience a lot of shade = parallel?

Well Don It depends



Yes I think that’s a good summary, buts it’s very complex to model.



With many boat installations a mixture of 2 banks in series then the 2 banks connected in parallel works best, but the 2 in series should ideally see similar amounts of shade Even better if you can afford 2 MPPT controllers that will track the MPP of the 2 banks separately.

Some experimentation under different conditions, before the wiring is finalized will provide the best answer.

[noelex 77]

Originally Posted by s/v Jedi

If one can't find a good location for a solar panel, installing it in parallel to others so it doesn't hurt the output of the other panels is a way of looking at the matter that will be welcomed by the manufacturers. However, for the user it might be wiser to not invest any $$$ in panel(s) that don't produce due to shading.

In other words: if you only have 1 good spot for a solar panel.... install 1 panel. Do not waste money on panels that can only be installed in problematic locations where they will not produce or only produce a fraction of their potential.

Ideally only panels that are in full sun all the time would be used, but this is just not feasible on most boats. Unless you have 64 feet to play with

Most installations, of multiple panels, have some that have shade and some that are in full sun. The panels that are in shade are not wasted because as the sun, or boat, moves the panels that were in shade and performing poorly will become the panels in sun that are performing best and vice versa.

The problem with the above situation is connecting the poorly performing panels in series with the panels that are performing well. This can in some situations drastically effect the output from the good panels.

[senormechanico]

Originally Posted by Don Lucas

Would the choice between series or parallel greatly come down to the installation and location of mounting the panels? If always out in the open so low shading = series; and if on bimini or something that is going to experience a lot of shade = parallel?

That was why I suggested what I did.

[JiffyLube]

Originally Posted by noelex 77

Ideally only panels that are in full sun all the time would be used, but this is just not feasible on most boats. Unless you have 64 feet to play with

Most installations, of multiple panels, have some that have shade and some that are in full sun. The panels that are in shade are not wasted because as the sun, or boat, moves the panels that were in shade and performing poorly will become the panels in sun that are performing best and vice versa.

The problem with the above situation is connecting the poorly performing panels in series with the panels that are performing well. This can in some situations drastically effect the output from the good panels.

I know almost nothing about this topic but I'm trying to learn and understand, so if my questions seem dumb please bear this in mind.

I'm just going to throw a couple of questions out there, and see what you guys can teach me.

If some panels will be in the shade and some not (depending on how they are wired together parallel or series) will one shaded cell in one panel pull all the panels down? Or only that one panel with a shaded cell?

Would it be good or bad to not wire the panels together but let them function on their own independent of the other panels?

[Bash]

Originally Posted by noelex 77

Most installations, of multiple panels, have some that have shade and some that are in full sun. The panels that are in shade are not wasted because as the sun, or boat, moves the panels that were in shade and performing poorly will become the panels in sun that are performing best and vice versa.

I couldn't agree more! My panels don't merely function as solar chargers. They also comprise my bimini, providing shade and weather protection in the cockpit. It cost me no more to build a solar bimini than it would have cost to build a fiberglass hard bimini. The later, however, would not have charged the batteries. Admittedly, I ended up going with more wattage in panels than I would have needed had I gone with something like a Solar Stik installation, but this was a concession I gladly made.

With my system, a parallel hookup makes all the sense in the world.

[hellosailor]

Of course, if you get the masthead mount for a Solar Stik and get those panels up where they'll never be in the shade...VBG...

[Aussie_Sequoia]

Hello CF,

I've worked in the domestic solar industry for 15 years. The explanations about MPPT above are accurate - and it is very confusing if you are used to the old on/off type of regulator.

One thing I'd like to add is that unless you have an amorphous / thin-film type PV panel (such as UniSolar) then you have what is essentially a grid of cells all wired in series anyway.

Each cell produces about .5 volts (regardless of surface area) and are soldered together in series grids of (usually) 36 cells. 36 cells x .5 volts give is a nominal 18 volt output (of course open circuit can be a bit higher and on a load it is a bit lower).

The point is if ANY one of these individual cells is shaded, it will stop output from the panel. Now some newer panels have 'sub-series' wiring with by-pass diodes that allow you to take energy from different sets of cells - but not all panels and certainly not older ones.

This is a concern because of the probability of partial shading on a boat installation... and I would definitely not wire all of my panels together in series because if one of your 144 individual solar cells is in shade - you will get (ostensibly) nothing from the rest.

Just my 2 cents.

[west coaster]

Hi

Thanks for the great responses to my post.

clearly the choice between these three different combinations of 4 panels is not that straightforward.

someone peviously pointed out that 4 panels in series probably a no-go given the MPPT max input-side Volatge of 57 volts and a V(open circuit) of each panel of 20 volts. even though it probably wouldnt see the OC voltage, i agree and had already pretty much decided no on this. i also assume this arrangement would be most sensitive to shading of an individual panel or significant portion of the panel.

so its parallel, or series-parallel. i assume from the prior discussion that complete shading of a single panel would knock-out ca. 50% of the available power in the series-parallel arrangement, but only 25% in the parallel arrangement. it is likely that at least one panel will be shaded much of the time, so I am leaning toward the parallel only option if this makes sense.

someone also pointed out blocking versus bypass diodes. quite correct. the kyoceras actually have bypass diodes - this should protect them in a series arrangement with partial shading, no? also i assume the blocking diodes are unnecessary with a charge controller. kyocera documentation (e.g. http://www.kyocerasolar.com/pdf/KC40T-KC130TM.pdf) seems to confirm these two points.

i may try a experiment to compare the two arrangements with similar irradiance of the panels and blocking one half of a panel then one panel in the parallel and then series-parallel arrangemet. and checking the charge current on my link 20 battery monitor (which is ultimately what i'm trying to optimize) with the battery in similar states of discharge. I'll have to quickly rewire them to the alternate arrangement to ensure similar irradiance and make sure there is no cloud cover. if i do , i'll post the results.

thanks again.

[noelex 77]

Originally Posted by west coaster

Hi



so its parallel, or series-parallel. i assume from the prior discussion that complete shading of a single panel would knock-out ca. 50% of the available power in the series-parallel arrangement, but only 25% in the parallel arrangement.

.

The solar panels in shade wont be in complete darkness so the % reduction is not as great as you have indicated above, but the essential principle is correct even if the numbers are wrong.

Originally Posted by west coaster

Hi

. the kyoceras actually have bypass diodes - this should protect them in a series arrangement with partial shading, no? also i assume the blocking diodes are unnecessary with a charge controller. kyocera documentation (e.g. http://www.kyocerasolar.com/pdf/KC40T-KC130TM.pdf) seems to confirm these two points.

.

You do not need any additional blocking diodes. The Kyocera panels do have a large number of bypass diodes which does improve there shade tolerance particularly when connected in series with a MPPT regulator. The effect will depend on how much shadow is present, how deep is the shadow, and how many sub panels are effected.

Originally Posted by west coaster

Hi



i may try a experiment to compare the two arrangements with similar irradiance of the panels and blocking one half of a panel then one panel in the parallel and then series-parallel arrangemet. and checking the charge current on my link 20 battery monitor (which is ultimately what i'm trying to optimize) with the battery in similar states of discharge. I'll have to quickly rewire them to the alternate arrangement to ensure similar irradiance and make sure there is no cloud cover. if i do , i'll post the results.

.

That would be great. The information would be of interest to many people, it’s a common question.
If you have the opportunity I would also be interested in difference bypassing the regulator (in parallel only obviously) to show how much gain the MPPT is producing.

[noelex 77]

Originally Posted by JiffyLube

I know almost nothing about this topic but I'm trying to learn and understand, so if my questions seem dumb please bear this in mind.[IMG]file:///C:/DOCUME%7E1/Skipper/LOCALS%7E1/Temp/msohtml1/01/clip_image001.gif[/IMG]

I'm just going to throw a couple of questions out there, and see what you guys can teach me.

If some panels will be in the shade and some not (depending on how they are wired together parallel or series) will one shaded cell in one panel pull all the panels down? Or only that one panel with a shaded cell?

Would it be good or bad to not wire the panels together but let them function on their own independent of the other panels?

There are no dumb questions on this subject. Its complicated. A lot of the information and data is from the domestic solar industry. They have the luxury of mounting the panels in a shade free place . When they talk about shade they are referring to clouds which will shade all panels reasonably evenly. Shadows on boats are very different, the mast or boom can cast a deep shadow on only some of the panels.
When there is debate about fundamental questions such as series or parallel connection it indicates there is a lot to learn. As the boat solar market is small I think boat owners themselves are going to have to do some of the basic research.

To answer your question shade on one panel will reduce the power produced by that panel and the reduction will be a lot more than you would expect from the surface area of the panel.
Other panels connected in parallel will be unaffected by the shaded panel and will still deliver there full power.
Panels can only be connected in series with a MPPT regulator. Panels in full sun connected in series to a shaded or partially panel can be effected. Depending on the degree and amount of shade the power from the good panel can be drastically reduced, in some situations it is not effected much and in other situation the MPPT controller can extract slightly more power from the shaded panel when it is connected in series.
In other words panels in series with a MPPT can produce much less power or a bit more.
Once the voltage of the solar panels is well above the battery voltage there are no further possible gains from series connection and the risks of losses increases with every panel added in series. So there is no advantage in connecting more than 2 (nominally 12v) solar panels in series (There is a very slight possible gain from a reduction in wire losses, but this is small on the short runs found on a boat)

[Thank you dad]

I will be using the same panels but only 2 of them, I will be connecting in parallel to my battery bank, 4 lifeline agm group 31 and a similar agm though I cant remember off hand which, starting battery , and I was wondering what I should use for a charge controller?

Thanks

[Windseeker]

Originally Posted by Aussie_Sequoia

Hello CF,

The point is if ANY one of these individual cells is shaded, it will stop output from the panel. if one of your 144 individual solar cells is in shade - you will get (ostensibly) nothing from the rest.

This was my Ah-Ha monent. I was initially thinking the solar panel as a varistor. Now, I see it can be an open circuit! I plan to mount my panels above the bimini on a mount and below the boom. From, my initial reading, I was thinking 2 big panels in series since they will get the same sun less the boom shading. That should not be a problem? The boom could not take more then 10% away from one panel. Wrong!

I think the key will be to look for the maximum amount of subgroups or bypass diodes in a single panel. Or, go for 4 panels with the maximum subgroups.

Thanks! That was a great discussion. At least I think I know what direction to head.

[Aussie_Sequoia]

Glad to help. Now there may be people with more boat-specific experience than me who say it doesn't shut down completely (I've read 50% above?) but this is due to varying degrees of shade and sunlight. I stand by my statement and challenge anyone to place their hand over a single cell (touching the glass) and watch their voltmeter drop to nothing. This is of course unlikely to happen in reality... but I was just trying to explain how the cells work together in series.

I think your final plans sounds very good. Let us know how it turns out.