Electrical Efficiency Regarding PV Panels

ILFE · January 2014

Since I will be receiving a new MPPT controller soon (The Kid), I figured I would go and check out the Kid Sizing Tool to look at different figures.

Observation: While changing the parameters (number of panels in series versus strings, and system voltages), I began wondering which way would be best to wire the array.

Please keep in mind, this has nothing to do with my current loads. This will be a completely separate system from my existing array. (vtmaps was the one whom I got this idea from, in a post he made in one of my threads.) Also, this is completely hypothetical at this point.

Goal: What I am trying to learn here is, which, given the option, is the most efficient way to wire panels with this particular controller (The Kid), to my off-grid array.

Panels in Series: 2, Strings: 4, Batteries: 24 volts

Rated PV Array Power:
800
Watts

Anticipated Array Power @ 33C:
770
Watts

Rated PV Array Current:
22.16
Amps

Battery Charging Current @ 28.8 V:
27.8
Amps

VMP (Maximum Power Point Voltage) :
36.1
Volts

VOC (Open Circuit Voltage):
44.88
Volts

VMP @ 18 C°:
37.2
Volts

VOC @ 18 C°:
46
Volts

Panels in Series: 4, Strings: 2, Batteries: 24 volts

Rated PV Array Power:
800
Watts

Anticipated Array Power @ 33C:
770
Watts

Rated PV Array Current:
11.08
Amps

Battery Charging Current @ 28.8 V:
27.8
Amps

VMP (Maximum Power Point Voltage) :
72.2
Volts

VOC (Open Circuit Voltage):
89.76
Volts

VMP @ 18 C°:
74.4
Volts

VOC @ 18 C°:
92
Volts

Panels in Series: 1, Strings: 4, Batteries: 12 volts

Rated PV Array Power:
400
Watts

Anticipated Array Power @ 33C:
385
Watts

Rated PV Array Current:
22.16
Amps

Battery Charging Current @ 14.4 V:
27.8
Amps

VMP (Maximum Power Point Voltage) :
18.05
Volts

VOC (Open Circuit Voltage):
22.44
Volts

VMP @ 18 C°:
18.6
Volts

VOC @ 18 C°:
23
Volts

Panels in Series: 4, Strings: 1, Batteries: 12 volts

Rated PV Array Power:
400
Watts

Anticipated Array Power @ 33C:
385
Watts

Rated PV Array Current:
5.54
Amps

Battery Charging Current @ 14.4 V:
27.8
Amps

VMP (Maximum Power Point Voltage) :
72.2
Volts

VOC (Open Circuit Voltage):
89.76
Volts

VMP @ 18 C°:
74.4
Volts

VOC @ 18 C°:
92
Volts

Please keep in mind one constant. That is, the distance for the wires from any array to its respective controller, will not be farther than 6.0 meters, one-way. The respective battery banks will be within 1.5 meters, one-way, of the controllers.

So, would someone, please, give me your input on each of these results, and which (of each system) are wired most efficiently? Or, does it really matter, since the charging current is the same in both scenarios, and in both voltages?

I want to learn as much as I can. This forum, by far, has been the best way to do that since I began this journey.

Cariboocoot · January 2014

Re: Electrical Efficiency Regarding PV Panels

Same advice as always:

1). A 24 Volt system is more efficient than a 12 Volt system.
2). Array Vmp must be above charging Voltage in order for the system to charge properly.
3). They greater the difference between array Vmp and battery Voltage the less efficient the charge controller becomes (although the percentages are really quite small), so do go crazy on the high Voltage array unless you need it to overcome wiring losses (which you probably don't at 6 meters).

Were it me I would pick the 24 Volt system with two parallel strings of two (36 Vmp) panels in series.

In fact I did.

Electrical Efficiency Regarding PV Panels

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