Solar Panels: series vs parallel

[Optimistic Paranoid]

. . . I'm really fighting the urge to go 24V for less Vdrop and better inverter choices and safer, lower current wiring. I have done some rudimentary testing with 24-12V DC-DC converters which I can use for the lighting, furnace and HVAC controls, and replace the water pump with a 24V. I may do this when I go to a DC compressor fridge... I'd get a 24VDC charge controller at the same time.

Sucks being an engineer sometimes. :dodgy:

Seemed to me this was worth discussing in a separate thread. 

I was understanding that wiring panels in series makes you more susceptible to power loss from shading, that is, if shade falls on part of one panel, it ends up affecting ALL the panels in a series string.  Sort of like the old Christmas lights where if one bulb burned out, NONE of them lit.

Based on that, the theory is that series could work very well, perhaps even be necessary, on residential installs with lots of panels and no shading issues, but was a bad idea on mobile set ups that are being parked under trees and such.

Or am I misunderstanding some of this?

Regards
John

 

[Optimistic Paranoid]

This was lifted from A. M. Solar in Oregon:

Case in point ... We have two customers who both have the same solar panels and controllers. They ended up parking side by side in the desert by chance. One of them had four 100 watt solar panels in series and the other had four 100 watt
panels in parallel. They decided to see how the two systems compared since they were both in the same climatic conditions. They looked at the charging amperage when both systems were in full sunlight with no shade on the panels and found
the guy with the paralleled panels had a slightly higher charging amperage. Then they had their wives monitor the charging amperage while they went up on the roof of their RVs. They stood so that their shadows fell on one out of the four
panels on each of the arrays. The guy with the four panels in series had a drop in charging amperage that was very dramatic, almost to the point of having none! The guy with the four panels in parallel found that his charging amperage only
fell by one quarter. The three unshaded panels kept on cranking out their power. The message here is that in the world of RVs (where shade can happen depending on where you park and where you place the panels), it is better to have your
solar panels wired in parallel.

Regards
John

 

[SternWake]

That 'case in point' sounds a little 'too perfect' an example.

The exact effect of partial shading will be determined by the bypass diodes in the panels in use, from what I've read, and I am no expert in this matter.
Broad brushes can be highly inaccurate. The broad brush in the example above makes it sound like the series panels are a waste of time and effort in anything but a residential application where no partial shading could ever occur.

Voltage drop is the enemy of DC systems. Whether higher voltage of series rather than parallel setups is worthy in a particular system, is arguable.

Anyway, it should be an interesting thread.

 

[LeeRevell]

Partial shading very definitely does happen on residential homes.  I have looked at my home's roof to see where the best place for solar panels is.  One corner is best throughout the day.  Every where else is sunny or shaded depending on the time of day.  A van/RV has the advantage in being mobile.  If you get shade in the evening, move. If you are in a CG spot that will be shaded at a certain time, you live with it or use portable panels.

 

[GotSmart]

On grid systems have microinverters, which cut out the problem of losing a series when one panel is shaded or gets a newspaper on it.

 

[sushidog]

There are a couple of other things to consider when evaluating parallel vs series panel wiring. In early morning and evening hours and in winter, when the sun is low on the horizon and your panels are mounted flat on your roof, the series wired panels will produce many more watt/hrs. of power. Series wired panels have even been known to produce measurable amperage parked under artificial lights, such as those found in Walmart or other shopping center parking lots. Unless you plan on using high voltage panels, like those found in residential systems then they will not produce enough voltage to accomplish this. Also remember that the more amperage you have coming from your panels the larger the wire you will need. This means that 4 panels wired in parallel will require 4 times the weight of wire (at over twice the wire expense) as 4 panels wired in series. This is not to recommend one over the other, as both methods have advantages and disadvantages, it's just so you can understand the differences to make an informed decision.

Chip