Four Solar Panels - Parallel , Series or Series-Parallel

[noelex 77]

Wiring all 6 in series is not sensible IMHO. If you do this consider you are up to lethal voltages particularly around water. Wiring of these sort of voltages needs careful installation. For example running the wiring through ss tubing is not safe

[jaredko]

Originally Posted by noelex 77

If you are contemplating a series configuration of solar panels its important to understand that bypass diodes listed in the specifications and fitted by the manufacturer will only work within the panel . If you connect panels together in series and want to bypass a fully shaded panel this will require additional external diodes. They are not expensive if you want to include them.
I would encourage anyone to try different configurations before finalizing the wiring. The solar industry is dominated by domestic installations where multiple solar panels connected together experience the same conditions. The manufacturers recommendations reflect this and their wiring suggestions are often not optimum when installed on a boat.

I don't see how this is the case at all. Please explain why you would need additional diodes. A fully shaded panel will have all bypass diodes active and the current from the unshaded panel will pass through each of the diodes without issue.

[SV Demeter]

Originally Posted by noelex 77

Wiring all 6 in series is not sensible IMHO. If you do this consider you are up to lethal voltages particularly around water. Wiring of these sort of voltages needs careful installation. For example running the wiring through ss tubing is not safe

I considered that which is why im leaning towards a series-parallel configuration of (3) pairs of panels. Im thinking that bypass diodes between each panel in the pairs would be helpful with shading of one of the panels in the pair. If I understand correctly I would need 2 diodes for each pair? Question then becomes how to install bypass diodes on MC-4 connectors?

[jaredko]

Here is a good article that shows the benefits of series wiring and the layout of bypass diodes:
http://homepower.com/view/?file=HP107_pg86_Byington

[SV Demeter]

Originally Posted by jaredko

Here is a good article that shows the benefits of series wiring and the layout of bypass diodes:
http://homepower.com/view/?file=HP107_pg86_Byington

Ok so reading that leads me to believe that there is no need for me to install bypass diodes between panels wired in series. The panels already have the diodes built in so if there is any shading, partial or full, then the diodes in the panel will route the power around the shaded cells or whole panel. Am I picking this up correctly?

[jaredko]

Originally Posted by SV Demeter

Ok so reading that leads me to believe that there is no need for me to install bypass diodes between panels wired in series. The panels already have the diodes built in so if there is any shading, partial or full, then the diodes in the panel will route the power around the shaded cells or whole panel. Am I picking this up correctly?

Yes, you've got it. However, based on your description of how the panels will be mounted, the series-parallel arrangement makes sense. Putting all 6 in series would mean that if one of the sets was not angled the same as the others and was getting a little lower intensity light, it would reduce the output of the entire system. Best to put those sets in parallel so the fully lit panels will produce the full output.

[SV Demeter]

Originally Posted by jaredko

Yes, you've got it. However, based on your description of how the panels will be mounted, the series-parallel arrangement makes sense. Putting all 6 in series would mean that if one of the sets was not angled the same as the others and was getting a little lower intensity light, it would reduce the output of the entire system. Best to put those sets in parallel so the fully lit panels will produce the full output.

Whenyou say "Best to put those sets in parallel so the fully lit panels will produce the full output" are you meaning I should put all 6 panels in parallel or (3) sets of 2 in series-parallel? Im thinking each pair will be in series and then the 3 sets will be paralleled to busbars then to the outback flexmax 60 controller.

[noelex 77]

Originally Posted by jaredko

I don't see how this is the case at all. Please explain why you would need additional diodes. A fully shaded panel will have all bypass diodes active and the current from the unshaded panel will pass through each of the diodes without issue.

The problem with this approach is the large number of diodes the output from the good panels must pass through, if one, or more panels become shaded. Each diode producing some power loss. The Kyocera panels for example generally have 8 bypass diodes. in each panel.

[SV Demeter]

Originally Posted by noelex 77

The problem with this approach is the large number of diodes the output from the good panels must pass through, if one, or more panels become shaded. Each diode producing some power loss. The Kyocera panels for example generally have 8 bypass diodes. in each panel.

So with a bypas diode between the panels the output would skip the shaded panel altogether and only have to flow through 1 diode so less loss? What about in a case of partial shading? Are you advocating the use of bypass diodes between panels that are in series?

[jaredko]

Originally Posted by noelex 77

The problem with this approach is the large number of diodes the output from the good panels must pass through, if one, or more panels become shaded. Each diode producing some power loss. The Kyocera panels for example generally have 8 bypass diodes. in each panel.

Interesting point. You're suggesting a Multilevel bypass arragement as shown in section 5.3 of this page:
Bypass diodes for solar panels

This may be worthwhile if certain panels are likely to be fully shaded for a significant part of the time, such as mounted on a dodger under the boom.

[jaredko]

Originally Posted by SV Demeter

Whenyou say "Best to put those sets in parallel so the fully lit panels will produce the full output" are you meaning I should put all 6 panels in parallel or (3) sets of 2 in series-parallel? Im thinking each pair will be in series and then the 3 sets will be paralleled to busbars then to the outback flexmax 60 controller.

- Series-Parallel pairs: Would allow use of smaller gauge wire (or lower line loss) as it will operate at 24v nominal instead of 12v. However, partial shading on one of the pairs (even 1 cell) will eliminate output from both panels in the pair.

- All parallel: Possibly better performance in shading as the other panel in the pair could continue to contribute if not shaded.

[SV Demeter]

Originally Posted by jaredko

- Series-Parallel pairs: Would allow use of smaller gauge wire (or lower line loss) as it will operate at 24v nominal instead of 12v. However, partial shading on one of the pairs (even 1 cell) will eliminate output from both panels in the pair.

- All parallel: Possibly better performance in shading as the other panel in the pair could continue to contribute if not shaded.

Unless I used a bypass doide between the two panels in each seriesed pair?

[s/v Jedi]

some remarks:

A fully lit panel produces full output regardless if it is connected in parallel or in series.

6 panels in series can give a voltage of up to 150V. I don't consider that more dangerous than 230V or 110V (somebody once said anything over 48V can kill a human). The cable you -should- use is rated for 400V anyway so you don't need special insulation and can put that cable inside stainless steel tubing without a problem. As for any voltage, you must make sure that the insulation can't be damaged where it enters/exits tubing (add protection).

The example of 6 panels that get mounted as 3 pairs.... your MPPT controller can take all 6 in series I think (check max voltage). What exactly is the problem when all 6 are in series and 2 panels get shaded? Can somebody calculate what the loss would be in that case for series and for a 3x2 series/parallel setup? For practical matters (not always all panels installed etc.) it might be handier to make it a 3x2 setup but not for efficiency I think...

ciao!
Nick.

[jaredko]

Demeter: Nope, sorry. All parallel sets will need to operate at the same voltage (unshaded panels are still running at max voltage). As shaded sections are bypassed, they no longer contribute, so the unshaded, unbypassed cells will be driven to a higher voltage, higher than the open circuit voltage, meaning that no current is produced, and that pair has no output.

Here's a thread with more detail and some great calculation. Running that same calculation for a string with only 2 panels in it shows that the cell voltage is pushed past the Voc.

Two Strings in Parallel with Unequal String Voltages - Solar Electric Power Discussion Forum by Northern Arizona Wind & Sun

[jaredko]

So to summarize the discussion on the best approach for panels on a boat, with shading consideration:

Series:
- Best shade handling if all panels get the same illumination (pointed the same way)
- Does not perform well when the panels have different illumination levels. If the panels are facing different directions, such as some are tracked to the sun while others are mounted flat. In this case, the amount of current produced will be limited to the lowest panel.
- Lower current (higher voltage) means lower line loss or use of smaller gauge wire
- Shading performance depends on number of bypass diodes built into the panel. Shading of 1 cell may result in a loss of only a portion of the panel's output
- If a panel is shaded frequently, there may be benefit in adding a diode to bypass the entire panel
- Need to be sure your charge controller can handle the higher voltage. Requires MPPT controller.

Parallel:
- Shade: 1 cell shaded will eliminate output of the panel
- Lower voltage will work with PWM controller, higher amperage requires larger gauge wire
- Handles different illumination levels well as each panel will put out as much current as possible given the amount of light

Series-Parallel:
- Series connected strings act as a large solar panel, that is connected in parallel with other large panels.
- Key benefit is ease of wiring and higher system voltage vs pure parallel.
- Will not handle shading as well as either pure series or pure parallel as 1 shaded cell will eliminate output from the string rather than 1 set of cells (series) or 1 panel (parallel)

Is this a fair summary? Anyone have thoughts?