Series VS Parallel Solar Panel Wiring Tested for RV and Off Grid Applications

In this video we do a real time A/B test to see which is better, series or parallel wiring of Offgrid and RV solar panels.

[owenwalters]

*I use this solar **Generater.Systems** at work. The building is 80 years old so there’s not a lot of electrical outlets. I use it for lights, fans, charge phones etc. works great !*

[HutchinsonJC]

We can think through the test with electrical concepts, too.

Let's say we have panels rated for 20v and 5amps.

In series, two panels would be 40v and 5 amps.
In parallel, two panels would be 20v and 10amps.

Voltage is what pushes the power and a higher voltage can push more power across a thinner wire with less losses.
More amps creates more heat and resistance on the wire, which causes voltage drops across the distance of the wire.

If you were to do 10 panels in parallel you would be pushing 50 amps and you'd need thicker wire to do this and you would see more losses as heat within the wire. 20v * 50 amps = 1, 000 watts (with some of those watts more likely to be lost as heat).
If you were to do 10 panels in series, it's be just the 5amps. And that 200v would push the power through quite easily even on fairly thin wire. 200v & 5amps = 1, 000 watts.



The main reasons you'd want to parallel:
1) In a 4 panel example where two panels are positioned above the other two panels and where a tree or structure casts a shadow over the bottom two panels that can't be helped, it'd be best for them to be parallel connected to each other as the top two and the bottom two. This allows the two top panels that aren't getting a shadow to perform optimally and not be dragged down because of the shadow on the bottom two panels. If the 4 panels were arranged with two on top and two on bottom but they were all 4 wired in series, then that shadow hitting only the bottom two panels would actually drag all 4 panel's performance down.

2) You would use parallel if your equipment (charge controller) was rated for a max voltage of say 100v and 10 amps (1, 000 watts) where each panel you bought was 20v and 5 amps. 5 panels would reach the 100v limit so you'd have 100v and 5amps with 5 panels = 500 watts. But you could do a 5series 2parallel with 10 panels (two rows of 5) and have 100v and 10amps = 1, 000 watts. So depending on your equipment and what panels you buy, it may be in your best interest to parallel your panels to maximize power going into the system while staying under the max voltage allowed in the system.

[junkerzn]

Yup, series is always better. Power losses in cables and in regulators (including MPPTs) are generally only a function of the current. P = I*I*R. The current squared, in fact. A parallel configuration doubles the current and halves the voltage (P = I * V so the power output is the same), but cable and circuit losses will be 4x that of a series configuration. Higher voltages and lower currents are always better, as long as the equipment can handle it.

There are a few other gotchas as well. Lets say you had two series strings with 4 panels in each (8 panels total). If you gang the two strings together in a solar combiner box, then any partial shading of one string will reduce the MPPT efficiency for BOTH strings. Because the MPPT will not be at the ideal power point for either string. It is always better to put each string on its own MPPT. Then if panels in one string are partially shaded, each MPPT will be able to optimize for its respective string perfectly.

So, for example, if you take your four panels and put them in a 2s2p configuration with a combiner box (or just wired together for the test, since its only 2s2p), going into one MPPT, then a partially shaded panel will mess up both strings to some degree. But if you put them on separate MPPTs you will still get a full 3-panels worth of power production.

Partial shading of one panel is a series string does not effect the other panels in the series string (due to the magic of the bypass diode in each panel), so the MPPT will operate properly. This is also important for larger, older systems where one or more panels might have failed and is in bypass without the owner realizing it. In both cases, the bypass diodes take care of the problem. But if there is only one MPPT the owner might not realize that a panel in one of the strings has failed! Partial shading of one or more panels in a parallel configuration, on the other-hand, causes the MPPT to shift away from the optimal point for the other panels. This effect is only very slight, though, since a partially shaded panel is almost like a hole in the wall... it might as well be disconnected. So here one might think that parallel is better, but the currents involved wind up being so high that it winds up actually being worse (as well as a big pain in the butt due to wire sizing, etc).

Newer, modern high-voltage grid-tie inverters (the big ones, not the micro-inverters) have multiple MPPTs for this very reason, while older ones typically had only one MPPT.

Per-panel micro-inverters seem all the rage today, but the actual benefits are limited to a few special cases. They especially tout 'partial shading' performance. But actually, a micro-inverter is not going to improve performance verses a high voltage string by more than maybe 1% at best due to strong shadow partial shading. Because, as you saw, even shading just 2-3 cells in a panel effectively removes that panel from the system regardless of the configuration.

Micro-inverters can have better performance in diffuse shading environments, though, where many panels are getting different amounts of light. That is their main use-case. But they are also expensive and more maintenance-heavy as systems age verses a modern high-voltage string inverter with multiple MPPTs that is easily accessible in the garage or side of the house and can handle 60+ panels.

-Matt

[Davesivak]

If your cable runs are longer, you will see the series connection outperform the parallel connection because of the higher voltage, less loss over the longer run.

[Sirfixalot]

I've decided to run Series because of this video, thank you.

[billcrane]

Exactly the info I've been searching for. I've been debating going all in series on 6 panels vs 2 strings of 3. It looks like it's more cost effective to go all in series. It will save on wiring, fuses and complexity. Shading will be an issue at times since it's on an RV. The effect of shading appears to be close to the same whether in series or parallel. Thanks.

[AskIveSolar]

I have nothing to add but watched the video and wanted to drop a comment

[fiveangle]

Assuming you size the cabling to be equivalent loss (e.g. higher gauge wires for parallel panels), the peak production will be very similar. However, the real benefit of series is that they will reach the minimum voltage level of the controller earlier in the morning and later in the evening, allowing you to capture slightly more overall energy per day. This is especially true when you are comparing larger systems with 48v battery. Most 150V max PV input controllers will have a typical "turn on" voltage of ~80V when used with a 48V battery system. If you have 6x 55V MPP panels, with a 2S3P panel configuration, no power will be collected until each panel exceeds 40V (loaded) production. However, with a typical 500V max PV input controller and a ~80V "turn on" voltage, in a 6S1P panel configuration, production will begin when each panel reaches just 13.3V (loaded).

It would make an awesome video if you did a test to show the overall daily production difference between series and parallel as I don't think I've seen such a test !

[leea]

Great video, I love learning stuff like this. Thankyou!

[mauricioweber]

Great real time and side by side test.. thanks

[TheReignharder]

Answering all the questions I had! Great vid - just did this on the weekend - my results are very similar. Thanks for the confirmation. As David said in the comments - I think that's the "multiplier".

[patkarp]

Thanks for the video. Great way to learn.

[JusttheofUs]

The advantage of series is that they start producing earlier and later in the day because of the higher voltage. All my installations are strings of series at the maximum voltage for the controller in parallel.

[ronic]

Nice nice. That was a great video not enough of those at all. Great presentation 👏. Very practical simple set up and well illustrated. Thumbs up brother 👍🏾

[louf]

Great demonstration and observations. Surprisingly, I guessed the scenarios correctly. And, the short run with MPPT showed little benefit, as it should - longer distance and day's worth of output should be a bit higher yet.
BTW, you said "blocking" diodes, but they should be bypass diodes (which think you know).
Nice capacity setup.

[shaneross]

I really loved this experiment. Thank you.

[brianwolf]

Thank you I appreciate your time and effort. You really help me out keep the going.

[RiDankulous]

This is a superb test but would also be nice is do what is sometimes done in medical or dietary research: crossover trial: so record your testing for this setup used and then switch the panels so the one that was serial run it in parallel and vice versa. By the way I'm no expert in solar: I don't own any.

Further, the batteries may impact power charge (maybe). They may have to be swapped. It would take a lot of time but testing like this may be worth it if you learn something significant about your batteries and setup.

I wondered by running a higher voltage and it's benefits. One guy I saw who is not a formally trained expert seems to think that running in serial allows your charge controller to use a wider range to run to the batteries, and that provides more energy efficiency. I don't know his justification for the statement though. I always like to know the source and review the research.

[enejohn]

this video has helped in explaining the benefits of series panel connections. thank you all who have added meaningful comments. I am grateful

[alishabab]

thats why for my camper trailer Ive ordered 3x 200w custom shingle panels and ill be getting 3x anti shading devices for them which boost the watts if one or part of a panel is shaded when in series.. they will be on my rooftop tent.. but I also have a 300w solar blanket thats 70.8v and I'll order another one thats 440w and 50v.. both on 20m of solar cable so even if its shaded on the rooftop tent or I want to park in a shaded spot I'll still be able to place the 2 blankets anywhere upto 20m away to get a total of 740w