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Adding Solar Panels Question

ForestTheBoy

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Oct 17, 2020
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I've been running my system off of 2 210w panels in parallel and want to upgrade to reach my Epever Tracer 40a MPPT's max charge rate.

After some reading I realized that 520w isn't the max wattage allowed thought the mppt for my 12v battery, rather it's the minimum wattage to achieve 40a charging. That opens up my upgrade paths quite a bit.

I only have enough room on my vans roof for one larger (210w) panel, or 2 smaller (maybe 100w) panels. Should I go with one larger panel to make a 3p setup, or should I add two smaller panels to make a 2s2p setup? I don't know much about mixing/matching panel wattages and voltages.

Thanks in advance for all your help!
 
Which model of EPEVER do you have? What is the maximum safe VOC voltage?

To be able to combine multiple panels, you need to look at the IMP and VMP specifications.

If the IMP numbers are close, you can run them in series. The VMP voltages will add together while the IMP will be that of the lower rated panel. The VOC will also add together, and you must ensure the total VOC is about 20% less than the charge controller maximum input voltage.

To run panels in parallel, the VMP numbers need to be very close. The VOC will be about the same as the higher panel, and that should again, be 20% less than the charge controller spec. The IMP will be the IMP of the panels added together.

If you have the rating from your original panels and the charge controller, and the ratings of the different panels you are thinking of adding, then we can run the numbers and see what options can work. Do you run the panels on an angle, or just all flat on the van roof? You can parallel similar panels at different angles, and get more power over the length of a day by having some work in the morning while others work in the early evening. Peak power never exceeds the charge controller, but you get power over a longer time. I saw a large RV with 4 panels on the roof, and 2 more on each side wall. One side would get morning sun and start charging right at sunrise. Then the top gave power most of the day, and the other side would catch evening sun until sunset. He had the side ones hinged, so he could lift the bottom out to about a 45 degree tilt. And in mid day, he could lift them to near flat with the roof and he used one side as an awning. All 8 panels were identical 300 watt units in series pairs. That is a lot of power on an RV. He runs a refrigerator, mini split AC, full home entertainment system, and cooks with a microwave.
 
Dang, that sounds like a crazy setup!

I have the Epever Tracer 4210AN and my panels are flat on the roof. I don't think I'll really experiment with angled, I like the small amount of stealth I have.

Max Voc for the mppt is 92V at temperature 25c.

I'll look for my current panel specs. I think I've got a sheet around here somewhere.
 
Here's the listed specs for the panels.

ELECTRICAL CHARACTERISTICS
Power at MPP2 PMPP [W] 210
Short Circuit Current* ISC [A]
9.85
Open Circuit Voltage* VOC [V] 24.9
Current at MPP* IMPP [A]
9.3
Voltage at MPP* VMPP [V] 22.4
Efficiency[%]
≥ 18.7
Maximum System Voltage VSYS [V] 1000
Maximum Reverse Current IR [A] 20


The seller offers a newer version of the same panel I may look into buying. I believe the specs would be very similar with minor changes in efficiency, VOC and ISC.
 
From those specs, you could add the third panel and run all 3 in series. Your VOC would be 24.9 x 3 = 74.7 volts and x 1.2 is still 89.64, so you have a solid 20% margin. Your input current would stay ISC 9.85 and IMP 9.3 amps. VMP 22.4 x 3 = 67.2 volts at 9.3 IMP amps would be a peak power of 625 watts going into the charge controller. This could mean a peak charge current of 52 amps, so you will likely get some clipping. What are you using for batteries? Can they accept that kind of charge current?
 
I'm not too concerned about clipping, I'll just get more power on less optimal days.

I have a 280ah lifepo4 12v battery, so I've got plenty of charge current available. My BMS supports 120a, and I think the batteries could go higher if not throttled.

What would the downsides be of running in series? I know shading issues can occur, but are there any other problems? What are the benefits of series vs. parallel?
 
I just looked at the EP Ever spec sheet on the 4210. The maximum charge power is 520 watts with a 12 volt battery system. It will just go into current limit and you may clip off some power near solar noon. The input power limit for a 12 volt system is 780 watts. SO your 630 watt 3 in series setup looks good to go. The reviews on amazon has a guy running 600 watts in without a problem, he gave it 5 stars.

The only issue with series is shading. If just one panel is shaded, you lose output as all three are limited to the weakest current. But the benefit of series is the higher voltage and lower current. This greatly reduces losses in the wiring and even in the charge controller as it will demand far less input current. By your panel specs, I am assuming they are 36 cell panels. In the manual I found, it shows using up to four 36 cell panels in series, but best charging on a 12 volt system is just 2 in series. 3 panels is splitting the difference. It is safe, but there may be a slight drop in efficiency.

If you are in a location where you will have shadows that move across the panels, you may want to stick with parallel panels, but then you are up against the input current limit on the charge controller. Looking through the manual, I can't find an explicit input current limit rating. But if you parallel all three 210 watt panels, you end up at ISC 9.85 amps x 3 = 29.55 amps. That is a lot of current. The max power current is a little less, but still 27.9 amps. This is at a very efficient point on the 12 volt charging curve. They show as low as 17 volts in making 520 watts. So that is 30 amps of input current. It will work, and it is slightly more efficient than at the 3 panels in series voltage. But your losses in the wire will likely be more than the greater charge controller conversion efficiency. For a 30 amp feed from the solar panels, you would need at least #10 AWG wire, and they recommend #6 wire to reduce the losses. With the panels in series, you have less loss on just a #12 awg wire. With 1/3 of the current and 3 times the voltage, any series resistance in the system has far less effect on the amount of power transferred.

As an experiment, try just putting your two panels in series, and see if you notice any production difference. Be careful though, you may want to do the panel wiring at night. Solar panels in the sun can shock you big time.
 
Wire sizing was something I had taken into consideration designing my system. From the panels to the mppt to the battery it's all 8AWG at a run of less than 15 feet. I think that should negate a lot of losses, but I should double check with the new projected amps before I decide.

If I were to run all three in parallel are there any concerns I should have? I read on another thread someone mentioned fuses on each panel?
 
If you run parallel, yes, each panel should be fused. In series, one fuse protects them all.
 
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