Finally hooking up my system, have some questions

caleb · August 2017

I bought this kit from NAWS. Now I'm finally getting around to hooking everything up. Couple questions have come up.

First, My shed, where my generator, my Outback FlexPower, and batteries are at is about 85' away from where the panels are mounted. I don't have an option to get it closer, other options would put it further away. Would it be better to run my H4 extender cables all the way to a combiner box in my shed near the Outback FlexPower or should I mount the combiner box closer to the panels and then run the output from the combiner box a longer distance? The cost of the extender cables doesn't bother me if that's the deciding factor. The other factor is next summer, I'll be adding a small hydro turbine to this system, that will feed back in to that same shed. If I put the combiner box in the shed, can I use that same combiner box for that?

Second, If I decide to only use three of the six panels that came with the kit, what issues will I run in to? I imagine that the battery bank is probably oversized for only three panels? This is all at a cabin where no grid power is available and I use it 3 out of 4 weekends each month with the occasional longer stay. Also my power demand/needs are very low right now (around 700W/h a day). So the batteries shouldn't be drained too much and will have plenty of time for any needed recovery. What other issues could I run in to?

I'm sure I'll have many more questions the further I get with the install. Thanks

Horsefly · August 2017

With the caveat that I don't know much about hydro power except from what I read and my EE background: I don't think you can just push the power form the hydro into the same combiner box with your PV. First of all it is AC, and the voltage will vary wildly. You have to run it through a rectifier and then probably to its own charge controller, with a dump load for when your hydro is producing more power than your batteries / house can use.

Although you can probably run H4 extension cables all the way to your shed and combine there, the general approach would be to combine at the PV array and bring a single pair of cables to the FlexPower. The panels you have would work well in two parallel strings of 3 modules in series, and the combiner box is good for combining those two strings. You then just need to buy the 100' or so of larger PV wire to go to your shed.

Raj174 · August 2017

@caleb
What brand and model batteries did you get and how will they be configured? If the batteries have been received, it would not be a good idea to let them sit around very long without charging them. To know if three panels will support the battery bank temporarily, then we need the panel specifications and the battery information. I agree with @Horsefly, the combiner box should be mounted at the array. It's usually less costly and more efficient. If using 60 cell panels, the the voltage on the 85 foot run would be about 93 volts. #10 AWG will have a 1.5% voltage drop and #8 AWG will have a 1% drop. Both are acceptable. Of course it's up to you, but I'd go with the #8 AWG wiring.

Edit: Sorry, I didn't see the link for the kit. The PV line voltage to the shed is valid. Also, three panels in series will give you about a 6% charge rate for the 428AH 24 volt battery bank with good sun. I don't see a problem with this supporting a load of 700 watt hours per day.
Rick

Photowhit · August 2017

I believe "HorseFly" is correct, I think some hydro generators rectify the current, it will still be wildly different than the current coming off the solar panels and would be troublesome for a MPPT charge controller, even if you could just dump everything. It will be a source of constant energy which can't be turned off, so you will need a dump load.

Due to the distances involved, I would run the panels in 2 strings of 3 and forego installing a combiner box, you may want to add to the system later, I'd buy a set of branch connectors and run the single set of wires back to the shed. This is perfectly legal and should meet code.

I'm not familiar with the pre-wired system, but they don't list a breaker ahead of the charge controller. This would be normal but perhaps they left it out since this could be wired as strings of 2 or 3 (though they only provide 2 breakers for the combiner box). Normally you would have a set of breakers for the incoming PV as well as between the Charge controller (CC) and the battery bank. I don't see those listed either.

I took a quick look at the Quick Start Guide and it does appear to be setup with a PV circuit breaker which you will wire the PV + input into (and a bus bar for the negative) typically if you had 85 feet to run and needed a 85 foot cable with a + MC4 connector and an 85 foot cable with a - MC4 connector, I would suggest buying a 200 foot extension cable and cut it...

Quick Start guide;
https://www.solar-electric.com/lib/wind-sun/fp1_qsg_na.pdf

I hope you haven't had this sitting idle too long, batteries like to be cycled and not just sit.

caleb · August 2017

Thanks guys. It's only been about 3-4 weeks since I started receiving parts, one panel was damaged in shipping so I've been doing pieces up to this point but now I have everything.

Wasn't sure on the hydro (still trying to understand solar) so I haven't done a ton of research into it. Sounds like at minimum I'll need another charge controller for that system. I'll visit the hydro next year

I'll mount the combiner near the array and make a single run back to the shed. So now I'm trying to determine the size of wire I'll need. If the reading I've done is correct, based on the specs of the panel (I have the 265W not the 270W like listed on the kit page, specs here) with these wired in two strings of three, each string would be 795W and 93V at 8.5A. Does that sound correct? If so then the charge controller (Flexmax 80) would seem to be too small??? Is that right? On the distance, looking at the calculators online, I've seen anything from 4 all the way to 00. What's the correct calculation to determine this?

Horsefly · August 2017

You use the Vmp and Imp to see what wire you have. Three panels in series will give 3 * 27.9 = 83.7V per string. Two strings in parallel will give you 2 * 6.85A = 13.7A. To get an acceptable 3% loss on the wire, you need the voltage drop to be no more than 1.5% on each of the positive and negative wire. 1.5% of 83.7V = 1.2555V.

Your FlexMax 80 CC will be fine. Your taking 6 STC rated panels of 265W, so that is 1590W. Assuming you configure your 4 6V batteries into a 24V bank, the theoretical maximum you will be taking out of the charge controller is 1590W / 24V = 66.25A. That's well under the 80A the FlexMax can handle.

The loss on the wire is according to this equation: V = I * (D * Rd) where Rd is the resistance per foot of the wire, and D is the number of feet. So in your case 1.2555 = 13.7 * (85 * Rd). Use some algebra and solve for Rd, and you get a max resistance of 0.001078 ohms per foot. The resistance of wire is normally considered in ohms per thousand feet, which in your case would be 0.001078 * 1000 = 1.078 ohms per thousand ft. Then you look at the NEC table for wire (Ch 9 table 8), and you find that 10AWG stranded wire has a resistance of 1.24 ohms/kft, which is too high. 8AWG stranded wire has a resistance of 0.778 ohms/kft, which would work fine. So, I'd go with 8 gauge stranded wire.

Photowhit · August 2017

caleb said:

... each string would be 795W and 93V at 8.5A. Does that sound correct? If so then the charge controller (Flexmax 80) would seem to be too small???

The capacity of the charge controller is based on it's output in amps. So 2 strings of 795watts would be 1590 watts, 1595 in a 24 volt system would render 1590 ÷ 24v = 66.25 amps. Other things to consider is that panels in normal conditions only produce about 75% of their rating and the charge controller can limit output even if a larger array is connected.

caleb said:

On the distance, looking at the calculators online, I've seen anything from 4 all the way to 00. What's the correct calculation to determine this?

Just plug in the correct number into a voltage drop calculator. From the array you will have a maximum of;

93 volts (volts of strings in parallel don't add)
17 amps (amps in parallel strings do add)
90 feet (distance one direction, most calculators will do the round trip for you, give your self a little fudge factor as I find these distances tend to be a bit longer going around things)

10 gauge gives you about a 3% loss
http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=3.277&voltage=93&phase=dc&noofconductor=1&distance=90&distanceunit=feet&amperes=17&x=59&y=13

8 gauge gives about a 2% drop
http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=3.277&voltage=93&phase=dc&noofconductor=1&distance=90&distanceunit=feet&amperes=17&x=59&y=13

BB. · August 2017

Two calculations for the wire size from the array to the MPPT charge controller. One is based on the ampacity of the wire. Very roughly, your Isc (current short circuit) for the array (assuming you combine the two strings into one at the array, and use a pair of cables from array to Outback charger) would be 2x8.5a=~17 amps. I would multiple by 1/0.85 for ~20 amps minimum rated current for wiring.

Depending on which code your local building department uses (if you have one), the ambient temperatures, fill factor on conduit, etc. all affect the final "approved" wiring. As a start, here is one table:

https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

12 AWG is a good minimum, most likely, for your array (I am not a code guy).

Next is the voltage drop. In the end, usually you want heavier than minimum cable size for long cable runs (you don't want to waste your expensive solar energy heating the wires). Your array Vmp-array voltage is >72 volts which is good for, up to, a 48 volt battery bank. Normally we want around 3% to 1% voltage drop (3% maximum, 1% is usually the heaviest "cost effective" minimum drop). Using a simple voltage drop calculator for 85 feet and ~15 amps with 1% and 3% drop round trip wire run:

http://www.calculator.net/voltage-drop-calculator.html

http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=3.277&voltage=93&phase=dc&noofconductor=1&distance=85&distanceunit=feet&amperes=17&x=55&y=18

10 AWG:
Voltage drop: 2.89
Voltage drop percentage: 3.11%
Voltage at the end: 90.11

http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.8152&voltage=93&phase=dc&noofconductor=1&distance=85&distanceunit=feet&amperes=17&x=48&y=15

4 AWG:
Voltage drop: 0.72
Voltage drop percentage: 0.77%
Voltage at the end: 92.28

Anywhere between 10 AWG and 4 AWG will work fine. Other than losing a bit more power at 10 AWG, anything 10 AWG or heavier will work.

If you plan on adding to the system later, (larger battery bank, larger array, etc.), then you may want to use heavier cable--And/or bury a larger diameter PVC conduit so you can pull new/additional cable to support a larger array.

I even like to put several large conduits in the trench (if trenching). Allows you to add stuff later (120 VAC power to array area for doing work, pulling telecom cables for communications tower/antenna, water line to keep dust down/green area around array, etc.).

-Bill

PS: Sounds like you are using a 12 volt battery bank... If you are planning on a larger system later, should you be looking at a 24 or 48 VDC battery bank. With your array and presumed battery bank AH size, you are about at the maximum power/AH I would suggest for a 12 volt battery bank.

mike95490 · August 2017

You treat hydro power same as wind power. Always keep a load on the turbine, or it will over speed.
To regulate it, you need a stout Dump Load to burn up the surplus power.

Your standard charge controller with PV. needs to co-ordinate with the dump load, or else !!

caleb · August 2017

Wow, great info guys! Thank you.

My battery bank will be 24 volt (4x6 volt in series).

BB. · August 2017

Then, very roughly, you outback charge controller (80 amp?) can manage about 2x larger array.

And AH rating for batteries?

Bill

caleb · August 2017

I got the Surette S550 batteries so they're 428AH

Finally hooking up my system, have some questions

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