New solar install advice

[stevensuf]

ok i've got 4x 80w (20v-5a) panels and 30a mppt regulator, im having an arch fabricated, service batteries are under aft port cabin , i reckon a 20ft run from the panels to the controller then short foot or two from controller to batteries,

im thinking of linking all 4 panels in parallel at the arch (all have diodes -bypass and blocking) then fusing ,say 30 amp then running 8awg cables to the charge controller and same 8awg short run from controller to battery.

Any thoughts?

[Adamante]

Originally Posted by stevensuf

ok i've got 4x 80w (20v-5a) panels and 30a mppt regulator, im having an arch fabricated, service batteries are under aft port cabin , i reckon a 20ft run from the panels to the controller then short foot or two from controller to batteries,

im thinking of linking all 4 panels in parallel at the arch (all have diodes -bypass and blocking) then fusing ,say 30 amp then running 8awg cables to the charge controller and same 8awg short run from controller to battery.

Any thoughts?

That would depend on your MPPT controller. If it's capable of handling upwards of 80+ volts on the input, I'd be tempted to hook the panels up in series. With a 5 amp current, the wire size would be substantially smaller than with a 20 amp current. And if your controller is buck-only, you might be turning the MPPT on somewhat earlier in the day than in a parallel panel connection - and keeping it on longer at dusk (likely a marginal improvement, but still...).

The downside would be that you are now dealing with 80 volts DC, which can be potentially quite dangerous, so proper caution needs to be exercised when working on the system.

[stevensuf]

The mppt controller can accept up to 60v, i was more worried about shading issues if running in series, if all in series and one is shaded id loose lots of output far more than a few watts in the cable.

Anyone know of fuse issues? Im trying to figure out the best way of fusing the system.

[djmarchand]

Stevensuf:

Your initial thoughts seem to be right on to me. Check the panel specs but maximum current for 4-80 watt panels in series will be about 25 amps. #8 wire can carry much more than that, at least 50 amps. So put a 30 amp fuse near your batteries to protect the wire. Or you could run the output to your main DC panel through a 30 amp breaker.

David

[stevensuf]

Believe it or not there is a 0.4v drop at 20amp in 8 awg wire in a wire run of 20 ft, equating to about 8 watts lost in the cable run, im thinking of a bus bar nare the arch connecting all 4 panels in parralel going via 30 amp fuse then 8 awg down to the mppt then 8awg again to batteries.

[pillum]

Considering the cost of cable versus the panels, run a bigger cable to reduce the power loss and to minimize heating. Also you should consider a marine grade (flame-retardant) insulation type cable.

[stevensuf]

the mppt controller only accpets 8awg wire, though i could do the longer run in thicker cable then join to 8 awg just before the mppt controller to mimimise cable losses.. On teh fuse issue i am wondering if there is any point to it?

As the fuse will have to be greater than the output of solar panels ,so even if a short occurs further downlne, the fuse would never blow.

[stevensuf]

maybe just a fuse between the charge controller and the battery as close to the battery as possible in case of a short from the battery side?

[barnakiel]

I think wiring for higher voltage (regulator allowing) makes sense as you can use finer wires to the regulator then. Probably also - less issues with shading, etc.. The downside would be that breakdown within one panel will deprive you of solar power for a time.

We wired for 12 volt and used oversize wires to avoid voltage loss. The connection box has been placed under deck so that we can remove any single panel for inspection/repair/etc..

b.

[pillum]

Yes, a fuse close to the battery to protect against back-feeding a fault would be good electrical practice and should ensure safety. Since you have the power sources in parallel the fuse/cable should see no more than 16-20V at 20-16A so your choice of a 30A fuse should be OK.

[stevensuf]

I think i will settle on the 4 panels in parallel, junction box above deck in the arch somewhere , two 4 awg runs down to the mppt controller, changing to 8 awg at the controller, then 8 awg to the battery (both 8 awg runs will only be a foot or so, so minimal voltage drop, 30 amp fuse between charger output and battery positive.