400W Array Functioning at Only 64%.

[longbedbob]

I have been working on the system on my fifth wheel camper since we bought it a few months ago and finally completed the first array this weekend.

I have four x 100w Renogy panels arranged in parallel. They feed a Renogy 30A PWM charge controller through mostly AWG 10 wiring @25' but the newest and most distant panels use AWG 8 to create a total ~ 35' run. I am using new 4 x 100 amp hour lead acid batteries in parallel.

The panels are mounted flat and the battery was topped off. But I energized my inverter, dialed up the furnace and basically powered on all the DC load at my disposal.

At midday on Saturday all of the panels were seeing full sun, which was at ~ 62 degrees elevation. Using some trigonometry this yields 88% optimum PV so my theoretical maximum should be 352 watts.

However, the Renogy Bluetooth module was only stating that I was charging at 255 watts, or 72% of PV that was available.

I removed a panel and the power dropped to 190 watts. So, it seems that each panel is producing 65 watts or it's a bizarre coincidence that the panel production tracks the overall efficiency percentage (100 watt panels make the math easy, LOL).

I understand that there might be up to 5% voltage drop in the wiring by using AWG 10 for that run and the hot panels would diminish the output slightly. Also, PWM charge controllers are not that efficient but the DC to DC conversion shouldn't cause that much of a discrepancy.

Unless I have some defective equipment or wiring issues, the only thing that I can think of would be that the output from the charge controller is reflecting the state of the lead acid battery. Is the output of the charge controller "seeing" the battery charging inefficiency and the actual output would be higher for a resisitive load or LFP battery?

Thoughts?

 

[SolarQueen]

When I design an off-grid system, I calculate in 40% losses due to wrong angle, wrong direction, voltage drop, losses through the charge controller, losses through the battery, losses through the inverter, etc. So yah, flat panels on a 5th wheeler, that sounds about right.

 

[gnubie]

Depending on the exact model panel, Vmp is 17.9V. The 100W is achieved as 17.9V x 5.72A. If your battery is 12V the use of a PWM controller will see the panels pulled down to there. Power available now becomes a maximum of 12V x 5.72A, ~68W. The actual peak wattage will vary with battery voltage so it might be higher, might be lower. 68W x 4 = 272W. Your power production seems reasonable once you tack in the temperature derating etc.

 

[longbedbob]

When I design an off-grid system, I calculate in 40% losses due to wrong angle, wrong direction, voltage drop, losses through the charge controller, losses through the battery, losses through the inverter, etc. So yah, flat panels on a 5th wheeler, that sounds about right.

Thank you.

I'd like to add a second 400 watt array, but next time use an MPPT charge controller, 24v panels in parallel, AWG 8 wire and titlable mounts. Would I see any noticeable increase?

 

[gnubie]

An MPPT controller will usually make 90+% of the watts the panels are producing available to the load/battery so, yep 400 x 0.9 = 360W. Most MPPT controllers have higher efficiency than this at their peak.

A 30 amp MPPT controller will not be able to provide the peak wattage to the battery though because it will limit at 30A. 400 / 12 = 33A so you'd pick a 40A controller if you want to wring every last watt out.

You could reconfigure your existing panels to 2s2p, fit an MPPT controller and gain power that way too.

 

[chrisski]

I'm working on installing 600 watts on my RV, a 35' fifth wheel, and one useful thing I found about the MPPT controller, is I could put more panels in series and the higher voltages and less amps at those volts did wonders when calculating my DC loss and I was able to choose thinner gauge wire.

 

[longbedbob]

Thanks for the suggestions.

Our fifth wheel is semi permanently parked while we rebuild our cabin. There is too much shading to consider a series arrangement with either array.

There is only a brief window at midday when the entire roof is exposed to the sun. That's why I'm oversizing my PV.