My solar array (3 x 410 watt 31.42v panels) will need to be 80 meters from the battery bank. I have done the voltage loss calculations using the victron tool app and it shows a 7.4% loss if I use 10 AWG (6mm2) wire. I am wondering if i can run two 6mm2 wires in parallel for each the positive and negative connections to reduce the loss by half…?
Hi,
For a 3% loss with all panels in series (operating voltage ~93V), you will need 16mm^2 conductors.
Best to put a junction box close to the array where the PV cable transitions from the Panel cables to the thicker wire. You should also include an isolating switch at this point.
for the 16mm^2 wire, a standard cable in conduit can be used.
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As the sun costs nothing I’d rather invest in a slight overpanelling then in copper.
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@ludo The sun might not cost, but panels and mounting systems do.
Also, in our local installation standard, the max dc loss is 3%, Ac feed-in loss 2%.
(if you are building to standard)
Either way, the cost of 80m of 2 x 16mm^2 is not that great as a standard stranded cable, rather than 4 x 80m of 6mm^2 PV1-F solar cable.
In this case I’d build a small system converting solar to 3x230v ac beneath the panels, then 60 meters is no problem.
Thank you Mike. 16mm2 wire is definitely best for reduced voltage loss. I have some extra 6mm2 around so thought I might get away with the double stranded approach although it really only achieves and equivalent of 10mm2 wire when combined. The result would be 4.7% loss which does not meet the 3% standard. If I decide to move ahead at a 4.7% loss I know I loose overall charging efficiency from the panels but aside from that do you think there would be any other negative ramifications to the sytem? I appreciate your insight and help.
Aside from the loss in energy, there won’t be any othe
r problems. Again, using the highest possible string voltage will keep the losses low.
@Ludo if you convert to ac, yes the voltage losses will be lower, but the equipment costs will be higher.
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You’ll need ac anyway, so it shouldn’t matter where you produce it, use ac high voltage pv inverters
@Ludo, thanks for the suggestion. I have a 45v to 3000watt inverter charger already but need to get power to battery bank first to use it. Not sure is there is another option to convert to A/C directly from the array to then covert back to D/C to charge the batteries. I live up in the Yukon, Northern Canada, and a battery bank is necessary especially in winter…
Could be ok, but avoid the cheap ones, they tend to burn on high currents.
You could use standard electrical components for the 16mm^2 - 4 or 6 AWG cables. Do use a weatherproof connection box for an isolating switch and fuses close to the array. MC4 connectors are useful, but expensive and not always necessary.
I’d go with the dual 6mm^2 solar cables (total 12mm^2). There should be a reason for choosing those, for DC distribution.
Yes, you could go AC coupled, with (micro) inverter at panels’ site, then connect (with normal “AC cable”) to ACout of (a) Victron Multiplus II, observing the 1:1 rule. This way, the battery will be also (solar) charged. But it gets a little complicated, so I prefer DC MPPT controller.
Even if you cannot increase PV DC (adding 4th, 5th… panel), your ~90Vdc from panels (Vmpp almost constant) is not so bad… Impp is 13A at max, with max irradiance of 1000W/m^2. I would argue that in Yukon, you can have half of those Amps (i.e. 700Wp), in some June days. By this, real life scenario, you have <3% DC losses (and those at months/days/middays that you have peak production, so you care less to spend some).
I am interested in knowing how the standard specifies the <3% dc loss (under what conditions?).
The <3% dc loss is at the 1000w/m^2 irradiance. This is a theoretical calculation, made with cable lengths , sizes, string and array currents at the expected temperature - if you want to go that far.
Isc and Imppt are both temperature dependent, and specified at 25C.
Where you are, you will have much lower temperatures - Increasing Voc, and decreasing Impp/Isc.
Where I am - 19S, I have recorded peak irradiance of 1360W/m^2.
Hello Dimitis,
Thank you for your comment. I believe there is a general standard to try to keep voltage line loss <=3% in North America. Why? not sure but assume it is for safety and efficiency…
I am leaning to go with the dual strand 6mm2. In the winter it will normally be colder and the voltage should increase, which will drop my amperages so my loss will be minimalized. As you suggest we have long summer days this far north, so the efficiency loss in summer should not be such a problem.