Solar experts....Matching solar panels help needed.

About a year ago I picked up 3 unused Kyocera KC50 50Watt panels for almost nothing and would like to put them on my 2009 Lance 845. While open roof space is somewhat limited on this roof, I think I would be able to find room for at least another 50 watt panel and I need help picking a panel that would work well with the 3 I have. I have looked at buying one or 2 larger panels instead of using the 3 I already have and most on these are too large to fit with the available roof space.

Here are the specs from the tag on my existing panels.

Pmax @25C 50W @45C 35.8W
Vpmax @25C 16.7V @45C 14.7V
Ipmax @25C 3A @45C 2.44A
Voc @25C 21.5V -----
Isc @25C 3.1A -----

Max Sys V 600
Series fuse 6A

Dimensions 25-1/8"X 25-5/8" Dimensions are not critical as I will be mounting the 3 panels I already have in one row and the 4th panel will be mounted alone.

Here are couple of panels I am looking at.

https://www.amazon.com/dp/B01CRA5WNU/?coliid=I3NDL237AHNBVG&colid=11UZ2A09YMR7C&psc=0&ref_=lv_ov_lig_dp_it

Maximum Power Pmax 50 W* (0%, +3%)
Cell type Poly silicon
Voltage at Maximum Power Point Vmpp 17.5 V
Current at Maximum Power Point Impp 2.86 A
Open Circuit Voltage Voc 22.0 V
Short Circuit Current Isc
3.17 A
Module Efficiency (%) 12.5%
Temperature Coefficient of Voc -0.37% /oC
Temperature Coefficient of Isc +0.035% /oC
Temperature Coefficient of Pmax -0.50% /oC

https://www.amazon.com/dp/B0159PHIXW/?coliid=I1VEFUGQTEKM21&colid=11UZ2A09YMR7C&psc=0&ref_=lv_ov_lig_dp_it

Maximum power (Pmax): 50W
Voltage at Pmax (Vmp):17.2V
Current at Pmax (Imp): 2.91A
Open-circuit voltage (Voc)?21.6V
Short-circuit current (Isc)? 3.23A

This last one looks pretty close to me, or am I missing something?

With 3 panels, I had planned to wire all 3 in series but if I add a 4th panel I may do 2 panels in series and then parallel the 2 series sets together.....provided my factory Lance 12ga wiring is heavy enough. I really would like to avoid pulling or routing new, larger wiring from the roof down to the solar charge controller. I installed a Trimetric 2030 and wired in a second battery that sits in the bed of the truck and pulling new wires/cables is not a lot of fun in a smaller truck camper like this 845. I can use larger wire/cable from the controller to the batteries, so that is not an issue. If the 12ga wiring is not heavy enough I would probably wire all 4 in series.

For a charge controller I am planning on a Victron SmartSolar MPPT bluetooth controller.

Also, what size fuse(s) would I need for either way of wiring?

Sorry about the length of this.

Thanks!

55 Replies

BFL13
Explorer II
Apr 30, 2018
If you can believe the specs! My 100w Coleman (Sunforce) has 17.1 Vmp while my other brand made in India 100w has 18.8 Vmp. I have two of those latter ones for three 100w panels.

I tried their Vocs and Iscs in real life and got identical 20.5v (panel heating reduces voltage) and 6.2 amps so I decided they were in fact the same ratings. I run all three in parallel with PWM and get 18.6 amps as expected.

I tried them with MPPT and got about the same 18ish amps to battery (panel heating affects MPPT, but PWM uses Isc value not voltage)

I tried the MPPT with them in parallel and in series same conditions, perfect testing day, got the same amps to battery.

So IMO, just use those 50s however, and it will all work out.
CA_Traveler
Explorer III
Apr 30, 2018
pirlbeck wrote:
I did a little testing of the panels today before I mounted them on the roof. The panel voltage checked with a Fluke Multimeter and no load,wired in series and in pretty much full sun was 40.3 for the matched pair (2 Kyocera KC50 50 Watt) and for the unmatched pair(1 Kyocera KC50 50 W & 1 Newpowa 50W) it was 41.7. Does testing the voltage this way tell anything and does this seem like these panels are a pretty decent match?

Thanks!
No load is Voc and no help there. What are the Imp and Vmp panel specs for the 2 panel types?

Imp of the series panels should be matched (or very close) and the Vmp of each series pair should be matched.
CA_Traveler
Explorer III
Apr 30, 2018
Likely minimual power loss because it's small. If it is large enough to activate the bypass diode which most RV panels have then you lose the voltage for those cells.

For example iIn a 6x10 panel with 3 bypass diodes then you lose 1/3 the voltage. Two panels in series then yields 1 2/3 the voltage or power. Same panels in parallel yields 1/2 the power.

With 2x2 series/parallel panels an activated bypass diode reduces the series voltage of that pair resulting with 1/2 power, while parallel would have 3/4 power.

Regardless of the voltage and amps an MPPT controller optimizes the charging power.

red31 wrote:
What would the IV curve look like if one series panel looked like this?

Would controller algorithm 'pick' the correct mppt?
red31
Explorer
Apr 30, 2018
What would the IV curve look like if one series panel looked like this?

Would controller algorithm 'pick' the correct mppt?
BFL13
Explorer II
Apr 30, 2018
IMO that is not too far apart. Vocs are all over the place while taking them, so it is hard to get good comparisons like that.

What counts is the voltage when all are connected as planned. The two sets will be in parallel (from a previous post)

"4 panels, pairing up 2 panels each in a series string and then paralleling the 2 series strings together"

An MPPT controller will pick a Vmp from what it "sees" to get the highest input wattage it can, so let the controller figure it out.
pianotuna
Nomad III
Apr 30, 2018
pirlbeck,

A good match is less than one volt difference. Sorry.
pirlbeck
Explorer
Apr 30, 2018
I did a little testing of the panels today before I mounted them on the roof. The panel voltage checked with a Fluke Multimeter and no load,wired in series and in pretty much full sun was 40.3 for the matched pair (2 Kyocera KC50 50 Watt) and for the unmatched pair(1 Kyocera KC50 50 W & 1 Newpowa 50W) it was 41.7. Does testing the voltage this way tell anything and does this seem like these panels are a pretty decent match?

Thanks!
CA_Traveler
Explorer III
Apr 22, 2018
IMHO The Littlefuse switch or the Blue Seas will be OK for your application. You could also get a DPST Littlefuse and parallel the contacts.
pirlbeck
Explorer
Apr 22, 2018
Almot wrote:
In theory, a quality product can be manufactured anywhere. In reality... take your chance.

IMO, 36V is pushing the limits.

Do you have a better suggestion? The Midnight Solar box you linked is going to be difficult to find a location for due to it's size.

Thanks!
Almot
Explorer III
Apr 21, 2018
In theory, a quality product can be manufactured anywhere. In reality... take your chance.

IMO, 36V is pushing the limits.