Electrical Efficiency Regarding PV Panels
ILFE
Solar Expert Posts: 364 ✭✭
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 offgrid 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, oneway. The respective battery banks will be within 1.5 meters, oneway, 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.
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 offgrid 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, oneway. The respective battery banks will be within 1.5 meters, oneway, 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.
Paul
Comments

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.
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