Solar panel output

[Viajante]

Trying to interpret the efficiency of the solar panel. I have a 96w panel mounted flat on the roof.

I’m thinking that the maximum panel output is 5.33 amps (96/18v) going to the controller. But how many amps is the maximum that the charger sending to the battery at 13.7v? (96/13.7=7 amps? In other words, what is the theoretical maximum I could see on the controller screen?

Thanks.

[Sean Murry]

I am no expert by a long shot, but wouldn't it be 96/12 not 18 for a maximum output of 8 amps

[Vermilye]

It depends on the type of controller you are using. A PWM (the least expensive type controller) uses the turning on & off the current going to the battery to prevent over charging. With a PWM controller you wil never get more amperage than the panel can produce at its current rating.

A MPPT controller had a built in DC to DC converter that can better match the panel output to the needs of the battery, and can, when lowering voltage, increase amperage.

In all cases, the wattage rating is pretty much an ideal. Unless it is cold out & the sun is perpendicular to the panel, and no clouds, haze, etc, you will not get any where near the panel rating.

[Eggscape]

Having looked at the output of a solar panel when it is flat and directly pointed at the sun, there is a huge difference. Unless the sun is directly over your roof top panel you will never get its maximum output.

[Ron in BC]

Originally Posted by Eggscape

Having looked at the output of a solar panel when it is flat and directly pointed at the sun, there is a huge difference. Unless the sun is directly over your roof top panel you will never get its maximum output.

Absolutely and when the panel tracks the sun it's even better. Maybe that's why I find one 100W panel meets my needs. My portable panel is used for my trolling motor battery.

Ron

[Viajante]

Vermilye, I think you’ve answered my question. I have the GoPower PWM controller so as I understand it the theoretical max amperage will 5.3 (96/18v). The PWM controller will knock the voltage down to 13.7 but not increase the amperage.

Eggscape and others, thanks for your comments. I am aware that the actual amperage reading will vary with angle, clouds, battery state of charge, etc. That’s why I was looking for the theoretical maximum to have something to compare with the actual reading.

[alanmalk]

Another way to interpret Vermilye's excellent summary is to look at Watts coming in from solar vs Watts going into the battery. With more modern MPPT controllers you can expect 95+% efficiency. More Amps out than in, but essentially the same wattage minus a bit. With Escape's original PWM, a good deal of the wattage can be wasted and Amps out can never exceed Amps in.

[John in Santa Cruz]

My MPPT controlled 360W rooftop panel can make around 2400 watt hours a day, given wide open sunny skies ( and batteries flat enough to actually suck that much down)