Hi everyone I am new to the forum and I am doing a 25 foot skoolie build. Trying to make it COMPLETELY OFF GRID. Anyways I have 910 watts of solar panels(12 volt system) and a 60 amp epever tracer mppt charge controller. So I did the math and whatnot and I am afraid my panel array may be too many amps for my charge controller. So I came up with 75-80 amp charge controller will be needed for 910 watts of solar in series. But with the panels having a maximum efficiency of maybe 25 percent my panels shouldn't ever really exceed 20-25 amps I think ?. I am new to solar so I am figuring things out. What I am asking if I would be able to use 910 watt solar in series(inline?) with with the 60 amp charge controller or if I am going to have to upgrade to a minimum 75-80 amp charge controller. If anyone can help I would appreciate it. Thanks
Have questions about charge controller sizing. Wondering if my solar panel array is going to be too much for my charge controller
- Thread starter devinbus
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LakeHouse
Solar Enthusiast
There will likely be times when your 910 Watt panels deliver full power, but that should be ok. I'm guessing what you've calculated is 910W / 12V = 75.8A, right? And that exceeds you SCC's rating of 60A. But that won't cause damage to the SCC, it'll just mean you lose some power that would otherwise go into the battery. The SCC is limited to 60A output, and any excess power available gets 'clipped', or essentially wasted. For the most part, that's ok as long as your SCC supports it, and it looks like all the Tracer 60A controllers have a max PV power rating of 1125W for 12V systems, so you should be fine there. Having more PV power available than the SCC can fully use is called overpaneling, and there's a good resource on the forum here: https://diysolarforum.com/resources/overview-of-over-paneling-an-mppt-controller.229/
What you do need to check is the open circuit voltage of your panel arrangement because while you can exceed the SCC's rated power, you CANNOT exceed it's maximum voltage without damaging it.
What you do need to check is the open circuit voltage of your panel arrangement because while you can exceed the SCC's rated power, you CANNOT exceed it's maximum voltage without damaging it.
If your scc ever outputs as low as 12V, your batteries are substantially low… most often it will be pumping 14+ your batteries would be below 10V if the scc was pumping 12.
Not to worry though. While the panels will be far better than 25A, it likely will top out around 45A with panels mounted flat, unless you get very lucky with solar aim…
Overpaneling is not a problem with most controllers. It helps output best charging in less than ideal conditions.
Your controller likely could handle 1200W of panels, on a flat array. Most you will get is 60A, but you should be closer to that capacity more of the day with overpaneling.
Not to worry though. While the panels will be far better than 25A, it likely will top out around 45A with panels mounted flat, unless you get very lucky with solar aim…
Overpaneling is not a problem with most controllers. It helps output best charging in less than ideal conditions.
Your controller likely could handle 1200W of panels, on a flat array. Most you will get is 60A, but you should be closer to that capacity more of the day with overpaneling.
MichaelK
Solar Wizard
There are the pen and paper calculations, and then there is what will happen in the real world. Most likely, laying flat, your panels will never output more than 60-70% of rated output. Charging will also likely to start at 12.5V, not 12. So the real world math is (910W/12.5V) X 0.65 =43.7A. You need to be paying more attention to the Voc then the total watts. More likely then not, you will need to add more panels, but wire them instead as 2P.
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I appreciate everyone's quick replies. That was a big help. That makes sense. So I have 2 455 watt mono panels with a voc of 49v per panel. The charge controller has voc of 150v. So with the 2 panels I should be at approx 100v voc I assume and I can't exceed 150 for the charge controller correct? So for every panel I would have to add the VOC and make sure the SCC can handle the VOC output of the panels correct?
Texas-Mark
Solar Addict
- Joined
- Aug 4, 2021
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While it may not cause any damage, some controllers will go into over-current condition and may need to be manually reset.
But as others said, he probably won't ever see the full panel rating anyway, especially if flat roof mounted.
Rednecktek
Solar Wizard
Correct for panels in series. It's a good idea to leave yourself some buffer on the VoC because panels produce MORE voltage when they get cold. Running panels of 2s at 98v is fine, but if you did 3 that would be 147v which could easily damage the SCC when the sun comes up on that cold winter morning.
If you wanted to expand the system you'd be best off getting another controller as adding panels to a system that already has the potwntial to clip is just going to waste any extra panels.
Q-Dog
¯\_(ツ)_/¯
During summer in South Louisiana the sun is directly overhead around noon, so I would not count on flat mounting to limit panel output. And since we get a lot of afternoon thunderstorms you can't count on panel heating to limit output either. I have seen 2 different kinds of panels put out 10% more than their rated output when the sun comes out from behind the clouds after a big cooling rain.
One more question for you guys. Do you think I would be better off wiring the two 455 watt panels in series or parallel to my 60 amp charge controller? I would think series but I have been looking through the forums and I'm not really sure at this point. The panels will be right next to each other and in the direct sunlight. Just want a second opinion. I am by no means a electrician but I'm catching on.
Series if shading isn’t a problem. Parallel if it is.
To calculate your MPPT charge controler, visit: https://www.victronenergy.com/mppt-calculator
Pretty solid way to go about testing different configurations...and not guessing.
Pretty solid way to go about testing different configurations...and not guessing.
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