Solar panel wiring (series and parallel)

[Johny London]

I couldn't find this online - plenty of how to series and how to parallel but nothing on an array consisting of both together. As discussed in other threads I have 2x150w panels series into 20a tracer mppt. It would be very neat and cost effective to add two more exactly identical panels in series, in parallel with the first two... if I make myself clear. My understanding is that the mppt adjusts for max panel efficiency so dissimilar panels are nearly always not such a good idea. I can get two more panels identical to the first two (save they will be one year newer!). So the excess current will be dumped - best I ever get is 12a, so that would be 24a so only really loosing a bit on the brightest days - the rest of the time I'd still be getting everything they can give, if my theory isn't flawed?

Otherwise it looks like I can put all four panels in series, but I'd rather not...

Technical - Tracer A Series 2210A

• Nominal System Voltage 12/24V Auto
• Battery Input Voltage Range 8V ~ 32V
• Max Charge/ Discharge Current 20A
• Max. PV Open Circuit Voltage 100V (At minimum operating environment temperature)
• Max. PV Open Circuit Voltage 92V (At 25 DegC  operating environment temperature)
• MPPT Voltage Range +2V ~ 72V
• Max Rated Charging Power (20A), 260W (12V), 520W (24V)
• Max. PV Array Input Power 780W (12V), 1560W (24V)
• Wiring Connections, Solar +/-, Battery +/-, Power Output +/-, Temp Sensor, COM RJ45
• Working Environment Temperature Range - 25  to +45 DegC
• Humidity Range <95%
• Enclosure IP30
• Dimensions 220mm x 154mm x 52mm
• Power Terminals 6AWH (12mm sq)
• Weight 1.1Kg

 

Has anyone else got series and parallel panels?

[WotEver]

Yes, there’s absolutely nothing wrong with having another series pair in parallel with the existing pair. As you described, they ideally need to have closely similar characteristics to get the best out of the four. 

[Johny London]

Excellent - case closed I think. 

....although, maybe I'll chance a pair of electrically similar monos then

Will report back in due course.

Edited June 5, 2018 by Johny London

[Chewbacka]

If the panels are 'industrial' they will probably be something like 37v open circuit so 4 panels in series would be getting on for 150v.  This is way too much for your controller, so your series/parallel proposal at about 75V is much better.  Also working on a DC system at a peak of 150V is getting a bit dangerous.

[Johny London]

I don't think they are industrial...

Technical Specifications

150 Watt (with 1m Cable & MC4 Connector Plugs)

• Maximum Power (Pmax): 150W
• Maximum Power Voltage (VMP): 18V
• Maximum Power Current (IMP): 8.33A
• Open Circuit Voltage (VOC): 21.60V
• Short Circuit Current (ISC): 9.17A
• Weight: 9.85KG
• Size: 1480*680*35mm
• Power Tolerance: +/-3%
• Maximum System Voltage: DC1000V

Looks like 4x o/c voltage would be ok. Options I suppose.

[Detling]

4x of voltage is over 60v and regarded as hazardous by those fun preventers in elth and safety.  Having 2 series pairs in parallel will work well and if one panel or pair gets shaded the other pair will continue to work, all in series one shaded the current will drop to that panels output. All in parallel is best for partial shading performance.

[MtB]

How long before we get the first death from DC electrocution caused by people stringing together four solar panels and having no respect for the combined output?

 

Sooner or later I bet solar installations fall prey to BSS inspection.

[Johny London]

As the aboves... (shading and high voltages) hence my intention of going series/parallel!

[Boredrider]

We have 6 X 100W semi flexible panels, wired in two series strings of three panels paralled into the controller.  On the advice of the panel supplier, and the controller supplier I have used a schottky diode in each string to prevent current flowing back into a shaded panel. The diodes sit on heat sinks in the junction box. 

 

This setup has performed well over the last three years, but (not being an electronics guru myself!) I often wonder whether the diodes are strictly necessary.  On a sunny day, particularly after a bit of random shading as the boat moves along, the heat sinks are hot to the touch - so some energy is being lost. 

 

 

What do the experts on this forum think, and should the OP be considering the use of diodes in his setup?

[eggpie]

I'd second (third? Fifth? Seventeenth?) the series / parallel wiring. My only concern is putting 4 x 150w panels into a controller that is rated "Max Rated Charging Power (20A), 260W"..

[WotEver]

51 minutes ago, Boredrider said:

We have 6 X 100W semi flexible panels, wired in two series strings of three panels paralled into the controller.  On the advice of the panel supplier, and the controller supplier I have used a schottky diode in each string to prevent current flowing back into a shaded panel. The diodes sit on heat sinks in the junction box. 

 

This setup has performed well over the last three years, but (not being an electronics guru myself!) I often wonder whether the diodes are strictly necessary.  On a sunny day, particularly after a bit of random shading as the boat moves along, the heat sinks are hot to the touch - so some energy is being lost. 

 

 

What do the experts on this forum think, and should the OP be considering the use of diodes in his setup?

It is very rare these days for a panel to not contain bypass diodes. So I’d say check first. If the panel already has bypass diodes then there’s no point adding extra ones. 

[Richard10002]

3 hours ago, WotEver said:

It is very rare these days for a panel to not contain bypass diodes. So I’d say check first. If the panel already has bypass diodes then there’s no point adding extra ones. 

What does a bypass diode look like. In the black box on the back of my panels, (where the wires connect), there seems to be some kind of small cylindrical electronic gizmo soldered across the terminals IIRC

 

[MtB]

I'm not convinced a bypass diode is the same thing as the "schottky diode in each string to prevent current flowing back into a shaded panel" mentioned by Boredrider in post 9.

 

Just off now to look up "schottky diode"

[MtB]

Ok the shot key diode seems to require a lower forward voltage than a normal diode across it before current flows. 150-450mV instead of 600-700mV.

 

[Chewbacka]

8 hours ago, Mike the Boilerman said:

Ok the shot key diode seems to require a lower forward voltage than a normal diode across it before current flows. 150-450mV instead of 600-700mV.

 

So less power loss than a ‘normal’ diode, and therefore doesn't get as hot - both good things.

Edited June 7, 2018 by Chewbacka

[cuthound]

2 hours ago, Chewbacka said:

So less power loss than a ‘normal’ diode, and therefore doesn't get as hot - both good things.

 

Shottky diodes have a lower turn on voltage and faster switching action than normal diodes. These chsracteristics make for better voltage stabilisers.

Edited June 7, 2018 by cuthound
Spillung

[Richard10002]

nothing to do with diodes, but this is the best video I've seen which shows how to connect 2 panels in parallel: