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skuner asked

Which panel solar configuration?

Which panel solar configuration?

Hello,

I need an advice for the best panel solar system to install on my 30 feet sailing boat cruising in the Caribbean.

The current situation is :

2 x115 Ah Trojan deep flooded services batteries (in parallel)

2 solar panel of 105 W in parallel (Impp=5.66A)

8 AGW cable from panels to controller (35 feet length)

1 PWM controller of 30 A


I’d like to add 2 other panels. So what is better to do:

1. Put all the 4 panels in parallel (105x4 W) / change cable / keep the PWM controller of 30 A or buy a new Blue solar charge controller MPPT 100/30 ?


2. Put in parallel only each 2 panels (105x2 W x2) / run 2 x 8AWG cables (30 feet length) from panels to junction box close to the controller / run 1 x 8 AWG cable from junction box to the controller / keep the PWM controller of 30 A or buy a new Blue solar charge controller MPPT 100/30 ?

Thanks for any advice.


solar
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jan-kees avatar image jan-kees commented ·

Shading. I see a few comments about shading, but what is the real effect of it besides less efficient. Tall panels have by-pass diodes, so it looks like the only thing influenced is the output.

If the panels are all in series, and one wil be shaded. a series configuration will put out 3/4 of the voltage. You still have the thinner cable than with parallel.

As you look to the way most MPPT's are configured, you see that there is a preference for higher voltage, versus Amps.

Please correct me if I am totally wrong.

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jan-kees avatar image
jan-kees answered ·

You do not mention the the VOC. Using Victrons numbers your 105 W panel wil be around 22V

your IMPP is 5.66 A. so if you place all 4 in SERIES the voltages become around 90 V, and the current only 5.66 A. No need to parallel any panel. with solar panel you always want to get the voltage as close as possible to the maximum your MPPT can handle.
This also means less loss than using them in parallel. with a current of 5.66 and a total of 2 * 30 FT cable you will only get a 2% voltage drop over the 8 awG cable.
The MPPT 100/30 can take the 100V and will maximize efficiency, and put out a max of 30 amps.
wich is as close as you can get. plus only one set of cables from all 4 panels to the MPPT.

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skuner avatar image skuner commented ·

Hello,

first of all thanks for the answers.

I admit my ignorance about MPPT controllers.

So, if I put all the 4 panels in series I get 91.6 V (Voc = 22.9) and 5.66 A (Impp).

Then from the panels I run only one 8 AGW set of cable (+ and -) to MPPT 100/30 controller.

The controller receives this voltage and current and it can handle to put into the batteries till 22.64 A (5.66A x 4) though it receives only 5.66 A. That’s right?


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JohnC avatar image JohnC ♦ skuner commented ·

Almost. Nominal figures - Panels 420W, batt 12V. 420/12 = 35A. The 100/30 in practice will be a perfect match. The output wires sized for 30A, not 5.66A. Tis just the V that does that, hey.

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skuner avatar image skuner JohnC ♦ commented ·

Thanks, so if I understood correctly, the output wires sized for 30A is from the controller (MPPT 100/30) to the battery and from the panels ( in series) to the controller the output wires sized for 5,66A, right?

I think I’ll get only one panel for a total of three panels to put in series.

I think the new configuration will be ok :

Three panels of 105W in series

Panels 315W - battery 12V - 315/12=26A

Voc = 22.9x3= 68.7V

Impp=5.66A

One set of cable of 8 AGW from panels to controller

One MPPT 100/30 controller

One set of cable of 6 AGW from controller to battery

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Gary Pacey answered ·

If a pair of panels had similar shading constraints, for example, both on a cabin top on the port side of the boom, one might run them in series. If they were on either side of the boom, they would be best in parallel.

If you had two pair of panels, one pair on port and the other pair on starboard, a series/parallel configuration would be best. Alternatively, use separate controllers for each pair.

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jan-kees avatar image
jan-kees answered ·

I still would get 4 panels , yes the max output you get from the 100/30 for a 12 V system is only 360 Watt. BUT when do you have 100% sunshine at the correct angle?
Thus by having 4 panels you wil get longer the full amount of energy put in the batteries.

At the same time 105 wat panels are not that expensive

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skuner avatar image skuner commented ·

Thanks for the answer.

Just a last thing.

The position of three panels will be the same, nearly horizontally on a rollbar. The fourth panel will be aside on the rollbar with a different angle.

So is it ok to put the fourth panel in series with the others three?

Thanks

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Nickus de Vos avatar image
Nickus de Vos answered ·

Depending on your panel placement on the boat, just keep shade on the panels in mind.


I'm busy planning to mount solar panels on my camping trailer, because of shading, I'm going to connect my 3 panels in parallel rather than series despite the higher amperage requiring thicker and more cables. I'm not sure what the situation is on a boat, I guess it depends on the type of boat, but on a camping trailer because of trees, shade on different parts of the roof at different times of the day is a reality.

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