solar cell panel calculation question

[Peter Kuczynski]

Hi Dacian and everyone,

I am getting closer to selecting solar panels.

Please check out these 60 cell panels. I am looking at 4 in total.

https://store.santansolar.com/product/seraphim-305w/

As I understand it, 2 each panels are to be wired in parallel, to each dssr20.

Based on the numbers of these panels, I see the total output per pair will be around 610w on a perfect day.

32.3vmp x [9.45A x2] = 610w Amps double while volts stay the same ion parallel

Times two sets of panels, = 1200watts.

Thanks for reviewing these in advance,

Peter

[Peter Kuczynski]

I wanted to add that I am using 8 200 Ah batteries, in 24volt configuration.

[Dacian Todea]

Yes those panels will be a perfect match for that battery.

Battery will see about 10 to 11A from each panel so around 44A from all 4 panels depending on amount of sunlight and panel temperature so around 1150 if panels are cold enough in the afternoon.

[Peter Kuczynski]

Hi Dacian, now that I have had the panels working for a while , I wanted to ask if the  numbers I am seeing fit with whats expected. With 4 panels, 2 pairs wired in parallel.

Are my calculations correct?

32.3vmp x [9.45A x2] = 610w Amps double while volts stay the same ion parallel

Times two sets of panels, = 1200watts.

I usually see somewhere between 4-500 watts on a perfect day, at 4 pm, with some shading.

Also , I am not sure why I am only seeing numbers for the PV1 array and not PV2. PV2 shows 0. Why ?

I have 2 dssr20's, each controlling 2 panels.

Everything otherwise has been working perfectly, we have plenty of power.

Thanks !

Peter

[Gordon Bland]

Hi Peter, for your calculations replace the vmp voltage with battery voltage as the panels get pulled down to battery voltage. If you want the difference you'd possibly need to use a mppt controller?

Not 32.3vmp. So battery voltage 24v x [9.45A x2] = 453w Amps double while volts stay the same in parallel. (Battery voltage would normally be above 24v so calculation is on the low side).

Times two sets of panels = 906watts. Shading can also decrease panel output significantly. Having your panels flat mounted may not be as effective as angling them for the winter sun.

Refer to manual about PV2 as possibly not relevant? I  have 3 dssr20 and no PV2 reading on my small setup. 

Cheers, Gordon 

[Peter Kuczynski]

Hey Goddonb,

THANK YOU! I really  appreciate that and the support from this community. I really love my Electrodacus system.

Last bit I wanted to touch on. I believe somewhere Dacian recommended paralleling 2 panels each as opposed to placing them in series. I located the quote below, which may have come from a earlier manual.

PANELS
https://electrodacus.com/SBMS0/SBMS0v03d.pdf
For DSSR20 ideal and most cost effective is 6mm2 (AWG #10) PV cable for groups of two parallel panels.

So Q. Is my 10g wire [probably [10-15 feet max length from the roof to the dssr's] enough from the panels to the dssr20's. The wire isnt heating up, that I can tell, so not issues w Free electrons. So is paralleling 2 panels still the recommend wisdom when using 10g wire for a bus with 4 panels, which may see a mixture of open sky and shade when in state parks etc?

I haven't gotten out on the road yet, my build still have a year to go. Interior furniture etc.

Cheers and thanks!

Peter

#wildthingthebus

[Gordon Bland]

Hi Peter, 10g wire (6mm2) is ideal for connecting your panels in parallel to the dssr20's. On this website it appears 10awg (6mm2) can carry 44-54A so your 20A or less will be fine.

https://www.sab-cable.com/cables-wires-harnessing-temperature-measurement/technical-data/cables-and-wires/instructions-for-the-safe-application-of-cables/boundary-conditions/calculate-wire-cross-section-current-carrying-capacity-table.html

Also I tried a couple of different online voltage drop calculators and 10g carrying 24V and 20A over 15 feet is about 2.6-3% loss so acceptable as 3% loss or less is recommended. 

Cheers,  Gordon 

[Peter Kuczynski]

Thanks Gordon, appreciate it!

Im good to go for now then.

Cheers!

Peter