Solar array voltage to take the biggest advantage of mppt SCC

[carolinabigfoot]

In my current setup I got 2 300W LG panels connected parallel: Voc=39.7V, Vmpp=32.5V, Impp=18.52A, Isc=19.4A for the array. My bank is 24V. After reading a few manuals for mppt controllers I got a feeling that I wouldn't really benefit a lot from getting one unless I wire the two panels in series since array voltage and battery bank voltage are not all that far apart from each other. When the manual of the Midnite Kid for example says that the controller needs the array voltage to be about 30% higher than the battery voltage to start charging, which voltage do they mean, Voc or Vmpp? (My guess is Voc, but I don't know for sure.) Would in my current setup a mppt controller then start charging at all on a cloudy day?

 

[DThames]

You would want to connect the panels in series for an MPPT. Some MPPTs state a min start voltage. You would have to know that to be sure. I think my EPever does PWM until the voltage gets to a certain level.

 

[carolinabigfoot]

If I have a very slight but permanent shading issue in my setup (shadows of 2 powerline wires 30ft above my panels), is connecting in series still o.k.?

 

[DThames]

Shading is a concern for sure. It is hard to guess about your actual results. You might try this test.....When that shade is on one panel, connect the shaded one only (to your current charger) and get an amp or watt reading. Then before conditions change much, connect the none shaded panel and get a reading. The current that flowed in the shaded test will be the current when you connect them in series under those same conditions. Or it will be close to that, I think.

 

[carolinabigfoot]

Thanks, that's a good idea.

 

[Mia]

Thanks, that's a good idea.

So…what did you find out? Just curious. Also, which version mppt SCC do you have?

 

[carolinabigfoot]

So…what did you find out? Just curious. Also, which version mppt SCC do you have?

Things are still in the making. Suffered a little set back/hold up today. But I will keep you posted, if you want.

 

[Mia]

Things are still in the making. Suffered a little set back/hold up today. But I will keep you posted, if you want.

Yes, definitely keep posting your progress, etc! ty!

 

[carolinabigfoot]

Yes, definitely keep posting your progress, etc! ty!

It's up and running again! The difference in amp output between the shaded and the not shaded panel was insignificantly small, even in full sun exposure. I got the Xantrex 30A MPPT charge controller. It's not bad. The charging performance, esp. when it's a little cloudy, is pretty good. I have seen the high voltage disconnect and reconnect of the cc working. I don't think that the temperature sensor is super accurate and I haven't figured out how to customize the low temperature disconnect. The manual claims that you can do that but doesn't tell you how. Right now I am contacting Xantrex' tech support about it. It's not a super big deal since the battery is inside my house and I don't expect it to drop below freezing in here when I am around. If I'm not here for a longer time in the winter I can simply disconnect the panels since the LFP battery doesn't require a maintenance charge and I don't have any appliances that need to run 24/7 no matter what. Still, I would like to add this safety feature. Other than that I'm glad that the lights and the fridge are back on.