Expected Losses in Wiring

InCogKneeToe

Ok, I am Still in Beginners Corner because I have so much to learn.

Week 4 of Over Tasking my System with a Bar Fridge and Wife's VACA.

I run 4, 100 watt 12v Panels on the Roof 4/12 pitch, facing West and Raised on the North Side 5" for angle Southerly. 2, 12AWG runs of wires, 1 30' the other 25' to the Controller Fused at 20A each.

Max Watts at the Controller that I have seen is 260w. If I remove a Fuse 1 side it drops to 140w, either fuse so it's not a Dead Panel.. 

What am I missing? Should I expect that kind of lost with 12awg in 30'?

The Fuse Holders do get Hot, like they are the Blockage. What Fuse Holder should I use?

mike95490

Automotive fuse holders often melt in solar usage.  If you only have an auto parts store, look for the MAXI fuses, they are bigger size wise, and have better contact area.
 But stay within the same amp rating of your wire
https://www.amazon.com/slp/maxi-fuse-holder/h7s4g8rb2pwa5n2

Photowhit

InCogKneeToe said:

Max Watts at the Controller that I have seen is 260w. If I remove a Fuse 1 side it drops to 140w, either fuse so it's not a Dead Panel.. 

What am I missing? Should I expect that kind of lost with 12awg in 30'?

NOT a wire loss issue! Solar panels rated vs actual output.

Solar panels have a name plate rating. these ratings are based on Standard Test Conditions (STC). In the real world they will produce less. Some now come with Normal Operating Cell Temperature values (NOCT) They are generally about 75% of the name plate.

These means you can expect about 75 watts out of a 100 watt panel. This is what you can expect when the panels are warm/hot. You may approach Standard Test Conditions(STC), in very cold fall days with good direct sun, but it will be rare.

Here are some example of panels ratings, Note the differences between NOCT and STC;

BB.

30' of 400 Watt panels on a 12 volt system with 12 AWG wire--Losses would be:

• 400 watts / 17.5 volts Vmp (est) = 22.86 amps

https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=5.211&voltage=14.5&phase=ac&noofconductor=1&distance=30&distanceunit=feet&amperes=22.86&x=0&y=0

Voltage drop: 2.18
Voltage drop percentage: 15.02%
Voltage at the end: 12.32

If you assume ~75% actual output from your solar array (typical very nice/cool/clear day, battery bank needing charging), add the 15% loss due to long wire run:

• 77% - 15% = 62% solar "efficiency"
• 400 Watts * 0.62 = 248 Watts, more or less, best harvest on a very good solar day

There is more math that you can play with--But 15% wiring drop is quite a bit... If you aimed for 3% drop, you would be closer to 6 AWG wiring:

Voltage drop: 0.54
Voltage drop percentage: 3.74%
Voltage at the end: 13.96

Is it worth it for you to change the wiring--Maybe. Large voltage drops in wiring can really cause less than idea battery charging conditions.

Vmp falls in hot weather (to as low as ~14.2 volts in a very hot desert), and with 2.18 volt drop, you are looking at 12.02 volts "optimum" solar charging voltage for your battery bank... That is way too low of charging voltage (you really need 14.75 to 15.0 volts minimum for most batteries).

Note the Vmp curve is not a mountain peak... And it can run a volt or so higher and still run some charging current--Just not as much as you would expect if you did not run heavier wire.

And this also brings up the advantage of MPPT controllers... Depending on what controller you get, you can run Vmp array from ~30 to 90+ volts at much less current (power = Voltage * current, 3x voltage, 1/3 current). For longer cable runs from array to charge controller, the MPPT controller with higher voltage arrays can really reduce the size of wiring needed.

-Bill

softdown

"4/12 pitch, facing West and Raised on the North Side 5" for angle Southerly"

We all do what we have to do. That may not be the finest angle for solar harvest. pvwatts.com can fine tune this with some effort. 

InCogKneeToe

BB. said:

30' of 400 Watt panels on a 12 volt system with 12 AWG wire--Losses would be:

• 400 watts / 17.5 volts Vmp (est) = 22.86 amps

https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=5.211&voltage=14.5&phase=ac&noofconductor=1&distance=30&distanceunit=feet&amperes=22.86&x=0&y=0
If you assume ~75% actual output from your solar array (typical very nice/cool/clear day, battery bank needing charging), add the 15% loss due to long wire run:

• 77% - 15% = 62% solar "efficiency"
• 400 Watts * 0.62 = 248 Watts, more or less, best harvest on a very good solar day

There is more math that you can play with--But 15% wiring drop is quite a bit... If you aimed for 3% drop, you would be closer to 6 AWG wiring:

Voltage drop: 0.54
Voltage drop percentage: 3.74%
Voltage at the end: 13.96

Is it worth it for you to change the wiring--Maybe. Large voltage drops in wiring can really cause less than idea battery charging conditions.
.

-Bill

2 runs of 12awg or 200w/12awg run.

I am seeing 14.2-14.4v and getting up to 18a @ the Controller.

So I will revamp my Fuse Holder to see what (the Heat) is robbing.

RCinFLA

What model is panels and controller.  Are you operating the four in parallel?

Mono cell '12v' panels manufacturers have been making 32 or 33 series cell panels.  These are not high enough voltage to run with an MPPT controller to 12v battery.  They should work with an PWM controller or do 2 in series / 2 strings parallel with MPPT controller.  If you don't have any partial shading then better off running all four in series to MPPT controller.

InCogKneeToe

12v Coleman branded Sun Force Poly Panels, Parallel (can't be series) Xantrex C40 PWM controller 12v setting.(of course).

The 5" of lift to the South was more for Cooling than Alignment, but if panels are only 75% effective in Real Life, it makes sense I am only looking for a 15% loss @ 260 watt harvest. 75% of 400 being 300w, 260w being 85% of that.

So, why then was my old 30A PWM Controller only rated for 450w array, if 450w will only produce 337w (under normal circumstances) ?

softdown

Panels can produce a lot more power when very cold. 

Bit unfortunate that manufacturers need to make all product directions compatible with both extreme heat and extreme cold. Extreme dryness and extreme humidity as well. 

InCogKneeToe

Trace sold a display for the C40 showing voltage and daily/accumulated amp hours. FWIW my C40 briefly registered 57.5 amps without shutting down. My unit ran from 1996 until just last week with 100% reliability.

https://forum.solar-electric.com/discussion/comment/410823#Comment_410823

So, knowing Panels don't produce Max Stated Out Put, does anyone Over Panel their Controller?

Example, my 400 watts of Poly Array is producing 18a at the CC. round that up to 20a with better fuses (hopefully).

20a is 1/2 of my C40's capacity, what happens with another 400w Array? Even 300 additional watts is below Actual Harvest.

706jim mentioned 57.5a to a C40 briefly without it shutting down.

BB.

Solar panel voltages (Voc and Vmp) are very much affected by panel temperature. Higher temperature, lower output voltages.

However, solar panel current (Isc and Imp) are much less affected (something like 1/5 or 1/10 the amount that voltage output is affected). And the current goes up with increasing temperature (a small amount)--So most of time, temperature effects on panel output current are ignored.

MPPT (maximum power point tracking) charge controller will safely and reliably limit their output current to the rated value. And since they are "power converters" they can take the range of variable input voltage (and current) and efficiently convert to voltage/current for the battery bank.

It is very common to "over panel" an MPPT controller by 1/0.77=1.3x to account for the fact that most solar arrays "run hot" under full sun and therefore waste very little energy by clipping the output to rated controller current.

However, PWM (pulse wave modulation) solar charge controllers only pass the current from the array... They cannot do anything with the panel voltage (i.e., if battery bank is charging at 14.8 volts, the solar array is near 14.8 volts too). The extra energy of a cold array (sub freezing temperatures) is "lost".

And PWM controller cannot limit their output current... Too much current and they will shut down (or over temperature shutdown). Check the manual and see what the maximum array limit is.

-Bill

InCogKneeToe

Thanks Bill.

You have taught me that PWM Controller like I am using does not draw as many mA at idle compared to MPPT. (My Winter issue) But at the same time, a PWM will not harvest as much in Freezing Temps? (if the panels are not covered).

So I am confused. My system will always be 12v at this point. I am not about to change Inverters for the little I use it. However I am going to add panels, possibly to the point of a second Controller. Should I run PWM of MPPT, or 1 of each?

BB.

The typical "increase" in harvest for subfreezing weather with MPPT over PWM is something like 10-15% typically... When you have only a few hours of weak sun, that is not that much of an improvement.

If you want to make up for PWM over MPPT harvest efficiencies, just add (1/0.85=) 1.18 or ~18% more panels vs getting a new controller and array.

Typically, where PWM controller start to "peter out", is when you have hot panels and low Vmp, and cool batteries needing higher charging voltage over >~15-16 volts when EQing the battery bank (you still get charging current, but less because Vmp-array-hot voltage is very close to Vbatt-cold/EQ voltage. Note that Vmp/Imp are relatively rounded curves... You will not see everything working at 14.8 volts and zero current at 15.0 volts (EQ) charging.

Generally, I suggest that you look at two things. One is any new/improved features you may want (remote access/configuration/logging/alarms), size of the array (when you are over a few hundred Watts and need more than 10 feet of wire run--Running array at Vmp~30-36-100 VDC lets you use much smaller copper cables/run longer cable distances from array to battery shed). Also one 300 Watt panel connection vs 3x 100 Watt panel mounts+connections is nice (with panels over ~170 Watts, usually need two people to safely handle the panels.

Usually the big difference is the cost of >200 Watt "GT Designed" solar panels (can be found near $0.50 per Watt or even less--Find leftovers at a GT Solar installer, etc.). Vs $1.00 to $2.00 per Watt for many ~140 Watt or smaller Vmp~18 volt solar panels. When you get over ~400-800 Watt arrays, "cheap" panels plus "not cheap" MPPT Controllers usually make a bid difference.

Other issues like winter float charging--PWM and low current draw can be nice for dark days/snow covered arrays vs MPPT running a few Watts just to keep the microprocessor and networking connections alive--Neither will produce any energy when covered with snow.

If you want to have a larger array "more power" when you are there (clearing snow, non-winter time)--MPPT just maybe more cost effective and give you more placement options for the array.

Keep the present PWM controller to float your array during the winter (turn off array+battery bus to second MPPT controller over winter), and the PWM will add its own charging power during the rest of the year (paralleling different charge controllers on one battery bank is not a big issue--My suggestion is to "home run" from each controller and its own wiring back to the battery bus+fuse+breaker).

If you daisy chain (one wire run, with multiple charge controllers), the "electrical noise" from each controller can confuse the other charge controller and lower its harvest efficiency.

The other issue is $$$ at site--Between Vandals and thieves, you may not want to leave too much there--And find that panels shattered and/or grew legs and walked away while you were gone.

No one right answer... Do a couple paper designs and see what works best for you.

-Bill