Solar panel over sizing for rigid roof mount

[rk06382]

I have six 100 watt Renogy panels with a Epever TRIRON 40a MPPT solar charge controller rated for 550 watts. The highest wattage I have seen is 365 watts. That is about 60% of the 600 watts.

I am replacing the 40a MPPT with a Victron 50a SmartSolar MPPT 100/50 Solar Charge Controller with Bluetooth. The Victron 50a MPPT is rated for 700 watts. I plan to add 200 watts more for a total of 800 watts. The theory is the sun will never be 90 degrees to ridge panels mounted on the roof. I can either climb up on the roof to tilt the panels or add panels to get more power. I am too old to climb up on my roof everyday. It is easier to install the extra panels. I will also installed circuit breakers to limit the amperage to and from the solar charge controller.

This the question:
Does anyone else over size their solar panels? If so, please give details.



Thanks,

[babock]

Originally Posted by rk06382

I have six 100 watt Renogy panels with a Epever TRIRON 40a MPPT solar charge controller rated for 550 watts. The highest wattage I have seen is 365 watts. That is about 60% of the 600 watts.

With a PWM controller, that's about right. You get around 5.5A peak with a 100W panel. 6 x 5.5 x 14 = 462W.

People put more panels than the rating all the time. The Victron will limit output to 50A.

[richp]

Hi,

I went to 600 watts of Renogy panels, from 300, for the same reason -- I am too old (and lazy) to get on the roof to tilt panels.

With them, I went two months in Quartzsite this winter in my Silverback, and never had to fire up the backup genny. Lots of DVD and TV when I wanted at night, microwave, coffee machine, all the comforts of home...

FWIW.

Rich Phillips

[Paulie1138]

I didn’t overkill with lot of panels. I went a different approach. I did not use 12v panels. My thinking, in partial shade, they may not produce enough voltage to get the charger up and producing much voltage/current. I mounted mine flat on the roof, with about 2-3 inches vent space between the roof and panels. Made my mounts such that, they can be tilted with minor mods, but...who wants to go up there and fiddle? (I know....there is a play where somebody does....LOL)

I went with 2 full sized commercial 48v panels at 9.9amps each. Running into a Morningstar MPPT controller. That converts 48v to 12v. Side benefit, current goes up by about 4....in theory...and nothing is 100% efficient....but I have purposely ran my batteries to 50%, switched off the charger until I had mostly good sun (was still partially shaded....but not much) turned on the charger, it was blasting out almost 50 amps until it tapered off. Normal operation, by 9-10am, 100% charge. In theory, I can get somewhere around 75 amps on a good day, but I doubt I will ever see that. Also, the controller tops out at 60 amps anyway. Another benefit, I have room for up to 4 more panels. That would allow for a greater output on those dark and gloomy days. Time will tell.

Monitoring of the system and batteries is done with a Trimetric battery monitor.

Bought most everything off Crookslist. Much of the electrical Conduit, boxes, wire, was gifted by contractor friends, so not into the experiment for too much. Because of that, everything is done with #6 ga wiring. Overkill, but free.

Just back from just over 2 months out, only a few of those nights in a campground with electrical. I was able to run everything except the air conditioning. Hence the want to stay in a CG with electric. Never touched the generator, and regretted bringing it. It is only 1000 watts, but took up space, and not big enough for the air. Maybe next outing, bigger genny? More panels? MUCH bigger batteries? Naaaww....LOL!

[babock]

You will want to put your panels in a series/parallel config. The Victron MPPT requires 5v over battery voltage to even operate. I run my 4 175W panels in series/parallel to get 40V panel voltage coming in. I have lithium batteries so the voltage is even higher than FLA.

I installed one of these Victron controllers for my brother and it wouldn't even charge with his 2 125W flex panels hooked up in parallel.

With my panels, I run 8 gauge from the panels to a junction box where I make all the series/parallel connections and the 4 gauge down to my controller which is around a 12 foot run. I make sure everything is at most a 3% drop. In most cases, its far below that.

[babock]

Here is what my setup looks like...no shading! I have one of my panels above one of the vents so I didn't have to mount it next to the AC.

[Paulie1138]

Here is the rooftop of mine. I ran the wires down thru the roof, inside a wall, to the basement, to the batteries and controller. Hope the pix load.

[Paulie1138]

Babock, your pix did not load. Despite the appparent proximity to the air conditioner, shading has not been a problem as there is a bit more space than appears. Even if i get shading, since these are the high voltage panels, they are wired in parallel. I did add blocking diodes to the install to further minimize shading issues. Each panel has its own 2 conductors of #6. Line loss at 48v is negligible. Fully loaded at 9.9 amps, voltage drops to 44 volts, but that is per panel specification, not due to line loss.

From the controller to batteries, #4, about 2.5 feet with a fuse block in the run.

[babock]

Originally Posted by Paulie1138

Babock, your pix did not load.

How about now?

[aeblank]

Originally Posted by babock

I installed one of these Victron controllers for my brother and it wouldn't even charge with his 2 125W flex panels hooked up in parallel.

I'm installing my panels tomorrow with a Victron controller. This is super concerning.

I wanted parallel for shading. Now I can't do that?

[babock]

Originally Posted by aeblank

I'm installing my panels tomorrow with a Victron controller. This is super concerning.

I wanted parallel for shading. Now I can't do that?

I would make sure that you have it so that you can go parallel/series if it doesn't work well.

What panels are you using? What are the specs?

[Paulie1138]

Babock, they are up! Looking nice, BTW

[aeblank]

Originally Posted by babock

I would make sure that you have it so that you can go parallel/series if it doesn't work well.

What panels are you using? What are the specs?

I have 4ea 150w panels. I forget the brand, eco-worthy maybe. Then the appropriate Victron with Bluetooth.

[rk06382]

Originally Posted by babock

You will want to put your panels in a series/parallel config. The Victron MPPT requires 5v over battery voltage to even operate. I run my 4 175W panels in series/parallel to get 40V panel voltage coming in. I have lithium batteries so the voltage is even higher than FLA.

I installed one of these Victron controllers for my brother and it wouldn't even charge with his 2 125W flex panels hooked up in parallel.

With my panels, I run 8 gauge from the panels to a junction box where I make all the series/parallel connections and the 4 gauge down to my controller which is around a 12 foot run. I make sure everything is at most a 3% drop. In most cases, its far below that.

Manual reads: "PV voltage must exceed Vbat + 5V for the controller to start.
Thereafter minimum PV voltage is Vbat + 1V." (see Page 6)

• Manual: Victron MPPT Manual-SmartSolar-charge-controller-MPPT-100-30-&--100-50-ENglish .pdf

Looks like 10 AWG or larger cable is a critical part of the system. I have two 10 AWG cables pairs running through my fridge vent. My Open Circuit Voltage (VOC) is 20v. In low light VOC is still 20v. The voltage drops when the amperage starts flowing. If voltage drops below Vbat + 1V controller shuts off.

I should be okay to run eight in parallel. I will let you know after install. I am waiting on Amazon delivery.

My roof with 600 watts.

[babock]

Originally Posted by rk06382

Manual reads: "PV voltage must exceed Vbat + 5V for the controller to start.
Thereafter minimum PV voltage is Vbat + 1V." (see Page 6)

Well that's good.

Are you worried about shading on your panels next to your AC? Looks like could be an issue for sure. In fact, I see a shadow on one in the picture.; I probably would have moved the 2 that are next to it closer to the other end of the vehicle.

To me, 10 gauge would have too much voltage drop at the over 30A current you might have with 600W of panels. I try to make sure to have 2% max voltage drop in my cables.

[rk06382]

Originally Posted by babock

Well that's good.

Are you worried about shading on your panels next to your AC? Looks like could be an issue for sure. In fact, I see a shadow on one in the picture.; I probably would have moved the 2 that are next to it closer to the other end of the vehicle.

To me, 10 gauge would have too much voltage drop at the over 30A current you might have with 600W of panels. I try to make sure to have 2% max voltage drop in my cables.

Sorry, I was not clear, I ran two pairs of 10 AWG solar cables to the roof. I edited the last post to add pair. My amperage is divided between two 10 AWG cable pairs.

[babock]

Originally Posted by rk06382

Sorry, I was not clear, I ran two pairs of 10 AWG solar cables to the roof. I edited the last post to add pair. My amperage is divided between two 10 AWG cable pairs.

OK..much better. What is the total length of each pair?

[aeblank]

Originally Posted by babock

I would make sure that you have it so that you can go parallel/series if it doesn't work well.

What panels are you using? What are the specs?

I just bit the bullet and ran two sets of panels in series, and of course those sets in parallel. So, 24v. Less line loss in the wires, I suppose. A bit more sensitive to shading.

Got panels mounted wired and mostly sealed (panels sealed, wires not yet). Removed fridge, ran wires, controller in, inverter in, all wired.

Front box with current shunt and breaker still pending. Also jumpers to batteries...

[PSU Turf]

I have 2 100 watt Renogys on the roof and 2 on the ground. If we have a full sun site the 2 on the roof are adequate to keep the batteries fully charged. If the site is part shade we add the 2 panels on the ground. We have a Bogart SC-2030 charge controller hooked to the panels. Have never had an issue with too much current from the panels.

[rk06382]

Originally Posted by babock

OK..much better. What is the total length of each pair?

About twelve feet from the MPPT and the first MC4 Y branch connectors.

You mentioned Victron MPPT controller. Do you have a Victron BMV?

I have a BMV-712 with bluetooth and plan to link it to my Victron SmartSolar MPPT 100/50a Solar Charge Controller with Bluetooth networking.