twin arrays

nick611 · Feb 25, 2013

i have to split my array over two flat roofs due to space. can i still do this with my single outlet inverter ? could i run two loops and join them in series at the isolator. if so is there a max cable length i can run ?

SolarCity · Feb 25, 2013

You can, but it is a bit more complicated than that. Do the two roofs have different shading issues or orientations?

If you need to do this then you're almost certainly going to be better off using an inverter with two MPPTs.

WRDEnergy · Feb 25, 2013

There are rules with volt drop.... so as you go further in length you will need to upgrade the size of the cable.

What solar said about the dual tracking might be useful although you only tend to get that on a 4kw system what size where you going for ? you said its a flat roof so I assume if your using buckets or something that they are all going to be at the same angle facing the same direction so dual tracking wont be as needed. even if they are slightly off they will just perform as well as the worst panel (worst one might still be fine) or you could use solar edge then face them in any direction you want all on one string. so depends on how many panels your using really and like solar said the direction and angle !

nick611 · Feb 25, 2013

11 x 250w panels . its a point scoring install on commercial new build. mistake by elec disigner on roof size. using 6mm. run will be 120m in total. using pro roof mounts. same orientation

WRDEnergy · Feb 25, 2013

Yeah I would just use a single 2500 personally. 120meters at 6mm might need to be slightly more, 99% of our jobs we are only running like 10meters of cable we use 6mm anyway I think you can go up to like 30 meters on 4mm so I assume your gonna need more than 6mm for 120 but I might be wrong can't be bothered to do the calc but I would use a 2500 inverter and not worry about them being on seperate roofs (just do 1 string as well) we did a 40 panel job on like 5 or 6 different roofs (was a weird one) but we used solar edge because everything is all complicated was going to be powing the lift so just used 3 phase, but 11 panels all facing same direction I would just use a standard 2500 inverter ! have fun.

nick611 · Feb 25, 2013

what is the voltdrop calc ? and max volt drop ? I COULD DO THE CALC

WRDEnergy · Feb 25, 2013

Ahhh man now your asking (going to show me up now) I have it written down in the office (I am at home now) so I can post on here tomorrow a quick google search I came across this Midsummer Energy - Voltage Drop Calculator now whether thats accurate or not I have no idea. but just put in the panel test volt and amps how much length you want to run but having a quick look at it you might have to go up pretty high

is there no way to bring the AC closer ? share some of the load your only allowed like 1% volt drop not sure if that's a rule or a guideline, I am just trying to remember these things off the top of my head. but 6mm at 120meters looks like your at over 20% volt drop which as I am sure you will agree is not great ?

WRDEnergy · Feb 25, 2013

off to bed now but ill post the equation tomorrow for you. (if i remember no promise) but I am sure if you google it you will find the equation.

SolarCity · Feb 26, 2013

To be fair, shading should be the number one consideration here. If the roofs receive different degrees of shading at different times of the day, then you really do need to consider either two inverters, a dual MPPT inverter or even a Solar Edge/Micro Inverter installation.

Depending on the panels you are using and how exactly you configure the system, 6mm is almost certainly going to be too small. Either bring the inverters closer (I'd strongly advise this) or upgrade the cable.