Solar Panel Wiring

[tbeargladd]

Attachment 243230
Can I apply this function above. No good or do I have to do both pairs of panels in parallel or series but not like the picture?

[Pete7]

I have moved your thread,

Regards

Pete

[Dsanduril]

The answer all depends on the exact specifications of your proposed panels. There is nothing inherently wrong with the proposal (from a strictly “can it work?” perspective).

The import specification for parallel connections is “Vmp” (Voltage at maximum power). If the Vmp for 2x12V panels is very close (within a few tenths of a Volt) of one 24V panel then you’ll likely be able to harvest pretty close to maximum power for the entire array (with all the usual caveats about exposure, shading, etc.). If the Vmp differs by more than that then likely you will be losing some energy harvest, the exact amount could be calculated/estimated if Vmp, Voc, Isc, and Imp are known.

[sailingabe41ds]

i am at a loss...shouldnt you have a solar panel charge controler in there somewhere? i would do series 24v to get 48v ..do a long run to a charge controler then a short run to the batteries.
abe

[tbeargladd]

Thank you Dsanduril for your reply, I will try and answer your question.

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The import specification for parallel connections is “Vmp” (Voltage at maximum power). If the Vmp for 2x12V panels is very close (within a few tenths of a Volt) of one 24V panel then you’ll likely be able to harvest pretty close to maximum power for the entire array (with all the usual caveats about exposure, shading, etc.). If the Vmp differs by more than that then likely you will be losing some energy harvest, the exact amount could be calculated/estimated if Vmp, Voc, Isc, and Imp are known.
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For the 12 volt panels they are:
Vmp is 20.4volts
Voc is 24.3volts
Isc is 10.2amp
Imp is 9.80amp

For the 24 volt panels they are:
Vmp is 37.6volts
Voc is 45.4volts
Isc is 5.83amps
Imp is 5-36amps

Do I multiply the 12 volt panels times 2 because they're in series or is that not correct.

[goboatingnow]

Originally Posted by tbeargladd

Thank you Dsanduril for your reply, I will try and answer your question.

--------------------------------------------------------------------------------------
The import specification for parallel connections is “Vmp” (Voltage at maximum power). If the Vmp for 2x12V panels is very close (within a few tenths of a Volt) of one 24V panel then you’ll likely be able to harvest pretty close to maximum power for the entire array (with all the usual caveats about exposure, shading, etc.). If the Vmp differs by more than that then likely you will be losing some energy harvest, the exact amount could be calculated/estimated if Vmp, Voc, Isc, and Imp are known.
-----------------------------------------------------------------------------------------
For the 12 volt panels they are:
Vmp is 20.4volts
Voc is 24.3volts
Isc is 10.2amp
Imp is 9.80amp

For the 24 volt panels they are:
Vmp is 37.6volts
Voc is 45.4volts
Isc is 5.83amps
Imp is 5-36amps

Do I multiply the 12 volt panels times 2 because they're in series or is that not correct.

bear in mind Vmp falls quite significantly with temperature of the panel, often rendering MPPT controllers not as effective as you might think

[tbeargladd]

Thank you for your reply Sailingabe

Yes their is a solar controller MPPT - LCD L80 but question is can this be functional without damaging/blowing the 40amp breaker switch and or the MPPT controller. I am trying to get answer before I connect all the panels as shown above in the picture.
The previous person who installed the junction box had house panels x4 connected that were
Max power 224.0watts
Voc 36.6volts
ISc 8.33amps
Voltage Max 29.28volts
Rated Current 7.66amps
Maximum Sys 15amps

These panels x 4 are now off the boat because they were far to big 39" wide x 62" long which were around the mast which made the sailboat unfunctional to sail, so they had to go bye, bye! If the sailboat was never going to sail then that would have been fine (not really) if the boat was to be just a condo on the water but the new owner wants to sail. I am just the handy man to make things functional. So the 12 volts panel were represented as 24 volt panels that were sold as 24 volt panels, that came in the shipping box label 24 volt panels. Once I had a conversation with a friend and we got into the specifications of the panels, it was brought to my understanding that these were not 24 volt panels but 12 volt panels that can be modify to series for 24 volts but I didn't want 12 volt panels to plug in as series. I wanted 4 panels @ 24 volts and plug them all parallel. All this is for a 24 bank system on a 1988 48ft Pilot House Jonmeri, Finland boat.

[tbeargladd]

Thank you for your reply "goboatingrightnow"

So are you stating that the panels in that configuration will not preform the VMP once the temp rises? This boat is moored in San Diego, Ca so not too hot on the bay. Just concern how the functionality of the panels will suffice during our winter season when the sun isn't as strong and lots of marine over cast.

[tbeargladd]

Pete, thank you so very much for guiding me where I needed to be, very much appreciate your help!

[tbeargladd]

One other important question, Dsanduril
If the 12 volt panels that will be connected in series when the become shadow, I understand that both of the panels will be shut down but will the other two 24 volt panels not shadow be affected (by the pair in series) will they keep (functioning) sending power?

[Dsanduril]

Based on the specs the Vmp of the pair of series panels is 2x20.4=40.8V. Because of how the “knee” works the controller will likely run the entire array at the Vmp of the “24V” panels, ~37.6V. That means that in theory the maximum power you will get out of the “12V” panels is ~37.6x9.8=368W. If those panels ran at their rated values you’d get 40.8x9.8=400W. (There are some minor corrections to Imp that I have ignored).

So, on paper you are leaving about 30W on the table (when you are getting full output at the panels, proportionally less at lower outputs).

Goboatingnow is correct, the panels will rarely run at Vmp, that is measured at “standard test conditions” (STC) which have little to do with real world operation (in real world normal operating cell temperature [NOCT] conditions I would expect Vmp of your array at ~33-34V). But the math is still all the same, you lose about 30/400 (x100) = 7.5% of potential power from the “12V” panels (while retaining 100% from the others).

Whether or not that is acceptable is up to you, but that’s what will happen electrically.

[Dsanduril]

Shading is an interesting phenomenon, and there are hundreds of dissertations on the subject. But, in short, all other things being equal in a parallel array the unshaded panels can continue to produce.

[tbeargladd]

Thank you Dsanduril,
MMMM, that will be acceptable to me for as the person on the boat runs very little. The main draw would and will be the Heart interface Charger/Inverter, the two danfoss compressor's for freezer/refrigeration and her laptop, that would pretty much be all that needs to be powered. LED Lights for about an hour at night. The batteries to keep topped off will be " x 4 lead Acid Batteries" group 31 in series/parallel. She will also have the option to charge with diesel engine, diesel Kubuta genset, Honda generator, solar.