Factory Solar Question

[Supercharged111]

My factory 80W solar has never kept the battery charged when the camper sits for a couple of weeks. Not an issue now as I store it inside a hangar plugged in, but when I first got it and stored it in an outdoor RV lot I observed this. I've come to a point where I want more solar power anyway for camping in places without power which tend to be much quieter. Is put a multimeter on the regulator and it was showing 13.4 coming off of the panels, with the DC system (plugged into AC) at 13.9. The dealer tech told me when I got the camper that the CO2 alarm would outrun the solar, either he was right or I have a draw. I'm just wondering what other people have observed with factory solar systems.

[pianotuna]

It depends. All MPPT controllers revert to being PWM once the batteries are no longer hungry. The way around that is to have a much higher input voltage to the MPPT so it stays in MPPT mode longer.

For example a 17 volt panel paralleled with a 17 into an MPPT controller and a battery at 13.2 volts may yield far less "power" than if the panels are wired in series (i.e. 34 volts).

Thanks for the link.

[work2much]

pianotuna wrote:
The problem with the calculation is the 80 watts is at the rated voltage of the panel. Unless it is an MPPT controller you won't "see" all of that. A rough approximation would be that around 60 watts may go into the battery bank.

That works out to about 300 watt-hours per day, or approximately 25 amp-hours.

But that is based on perfect conditions and tracking. So a real life number may be only 16 or 17 amp-hours per day for a fixed flat install.

I was always told of big differences in MPPT and PWM. Things like MPPT converts volts to amps" etc.

Here is an interesting video testing a bunch of solar chargers back to back with MPPT vs PWM. In some cases like good sun the PWM actually did marginally better.

Will is a little goofy but his test here looks pretty well controlled.

https://www.youtube.com/watch?v=kF_cVEYxj3E&t=1093s

[pianotuna]

The problem with the calculation is the 80 watts is at the rated voltage of the panel. Unless it is an MPPT controller you won't "see" all of that. A rough approximation would be that around 60 watts may go into the battery bank.

That works out to about 300 watt-hours per day, or approximately 25 amp-hours.

But that is based on perfect conditions and tracking. So a real life number may be only 16 or 17 amp-hours per day for a fixed flat install.

[work2much]

Ed_Gee wrote:
Please, O please, someone point me to an 80 Watt solar panel that has a specification of 6 Amp output, as posted above. The best mono crystalline 80 Watt panel I can find can only output 4 Amps..... My Zamp 100W monocrystaline panels are only rated at 5.5 Amps.

Panels are built with higher voltage than 12v. Otherwise they wouldn't charge the battery.
Usually 18-19v. for 12v nominal panels. If the panel is 80 watts at 18v it should be around 4 amps. Thats coming from the panel, not what's going to the battery.

The charge controller must lower the voltage to the 13 or so volts which raises current (amps)

It what comes out of the solar charger that's important.

[work2much]

Supercharged111 wrote:
In the summer, we have good sun angles and little cloud cover. That said, how can a guy record what a panel is putting out? We get beat hard with UV rays here, I have to wonder if the top of the skin isn't beat up and shielding some of those precious UV rays from creating useful electrons?

Get a battery monitor like a Victron. It gives you all kinds of instant data and aggregated data.

https://www.victronenergy.com/battery-monitors/bmv-712-smart

[Ed_Gee]

Please, O please, someone point me to an 80 Watt solar panel that has a specification of 6 Amp output, as posted above. The best mono crystalline 80 Watt panel I can find can only output 4 Amps..... My Zamp 100W monocrystaline panels are only rated at 5.5 Amps.

[Supercharged111]

In the summer, we have good sun angles and little cloud cover. That said, how can a guy record what a panel is putting out? We get beat hard with UV rays here, I have to wonder if the top of the skin isn't beat up and shielding some of those precious UV rays from creating useful electrons?

[work2much]

Ed_Gee wrote:

work2much wrote:
. An 80 watt panel getting 6 hours of sun should make 30 amps or so of power a day. The vampire draw is probably in the 24 amp/day range or less..

No way an 80 Watt panel will provide 30Ah in a six hour sun day.....even under ideal conditions. Between clouds, sun angle, etc. he will be lucky to get 10 or 12 Ah......which a measly 1 Ah vampire draw will exceed over night.....and I would bet his vampire draw exceeds that. Yes, 160 Watts would probably be minimum he needs.

Ideal conditions do not include clouds or obscure angles. This would be the prime 6 hours a day with sun fully on the panel, no shading, no clouds, in the south when the sun is high on cool day. In those conditions an 80 watt panel 80w/13v = 6.15 amp. 6.15x6 = 37 amps. My figure was 15% less than what should be an absolute max. I have never seen absolute max but I have seen over 1000 watts on our 1080 watt system under good conditions or over 90% of rated panel rating.

If your 80 watt panel is only producing 10-12 amps in 6 hours on a sunny day with good exposure you have an issue with something in your system. That is terrible production.

Also I noticed you left this part out of my quote which qualified the section you clipped. My message was that while an 80 watt panel could keep top under the right conditions, those conditions don't always exist nor should be relied on.

"80 watt may not be enough to keep your battery charged against vampire draws like the detector. The vampire draw is probably in the 24 amp/day range or less. Not always good sun though. I wouldn't want to rely on that in case of a couple cloudy days"

[Ed_Gee]

work2much wrote:
. An 80 watt panel getting 6 hours of sun should make 30 amps or so of power a day. The vampire draw is probably in the 24 amp/day range or less..

No way an 80 Watt panel will provide 30Ah in a six hour sun day.....even under ideal conditions. Between clouds, sun angle, etc. he will be lucky to get 10 or 12 Ah......which a measly 1 Ah vampire draw will exceed over night.....and I would bet his vampire draw exceeds that. Yes, 160 Watts would probably be minimum he needs.

[pianotuna]

This series of articles may help:

https://freecampsites.net/adding-solar/

[GeoBoy]

You will need a minimum of 160 watt panel.

[Lwiddis]

Two hundred solar watts is about the lowest I see on the road. Three hundred works for me. General rule is one solar watt per battery amp hour.

[Supercharged111]

I'm less worried about it draining the batteries when it sits (because it stays plugged in now) and more concerned with it dying while camping. Granted I can always just fire up the generator, but that kinda ruins the serenity. I'm glad to hear that what I'm experiencing isn't abnormal, I just need to beef up the panel and wiring aspect of it all. Chances are technology has moved forward and the space that my 80W panel from 2007 takes up likely can provide a bit more with today's panels.

[Lwiddis]

“My factory 80W solar has never kept the battery charged when the camper sits for a couple of weeks.”

My 30 watt solar system keeps the two T125s full indefinitely while in storage but the TT is completely cutoff. If all your loads are cut there’s something wrong with your solar system. Times two on fpoole’s “double” the size of the wire.