100w Solar Not Enough Or Am I Doing Something Wrong?

Hi.

I'd like your opinion on what could be going wrong here. We have a 560 Ultra, no AC, with solar option, AGM battery. Here are the primary draws of electricity:

1. Dometic Cf35
2. Fantastic fan
3. Lights
4. Charge phones, etc

I also have a 100w foldable solar panel that I have plugged in. I just plugged it in and the solar controller states that it's charging and the voltage of the battery shot up to 13+ volts.

We went camping over the long weekend (late Friday night to Monday around noon) in a relatively shaded spot. I tried to keep the panel in the sun but was mostly unsuccessful. By Monday, the voltmeter was showing 12.2 volts and the fridge basically was not running very much (I have it set on Medium cutoff).

My hope was to be able to go a week with the fridge running fine with the 100W solar. Is that sized wrong? Is something else wrong? I thought the 12V by itself should last the 2-3 days that we got out of it, so it seems like the solar didn't really do anything this trip?

Tips?

 

First things that come to my mind is:

1] is your panel angled to point to the sun
2] Is your panel got any shade on it? 100% sun is required for panels to work.
3] Is your panel dusty? Might not seem like much --- but dirt/dust will hurt your cells performance
4] Check your connections are secure -- voltage can flow and give you the higher voltage, but willl restrict current flow --- amperage.

Think of it as water or air through a straw --- how hard you blow is voltage. Think PSI. The amount of air that comes out is amperage. If you are blowing (same PSI) through a McDonalds straw --- lots of air will come out. But blowing through a swizzle stick...very little air.

PSI versus Volume of air. This is volts, and amps respectively in electrical terms.

Do you have an ammeter? How many amps are you showing when charging? you should see around 7-8 amps on a 12 volt 100 watt panel. 100 (watts) /12 (volts) = 8.3 amps -- this does not count for loss of efficiency in the charger etc.

8.3 amps should be enough unless you are charging LOTS of batteries and running the fan continuously. The fan is probably your biggest power hog. I THINK it is fused at 4amp. So, its probably using 2.5-3 amp, which is 1/3 of you charging with....

Hope this helps.

Key thing is turning things off when not in use. The air conditioner won't be a facotr, its 120 volt and is not impacted by the battery. The furnace (if equipped) is a different story, the fan and control board on it is 12 volt...

 

I have a 100 W panel and have gone over a week with a fridge and the power kept up fine. I was, however, in full sun. When camping in the woods I have had the same problem as you and keeping things going takes a lot of attention, more than I am willing to give usually. My solution was to buy an extra battery to use solely with the refrigerator when things were stretched. Even that is limited of course, but it will get you through even a long weekend generally. With the fridge as you know, the weather outside has a lot to do with the time you get.

I first used a big, Chinese lead acid battery that was quite a pain to carry along. When it quit, I recently got a lithium battery to replace it and am delighted with it. I also installed a DC-DC charger in my old Honda Pilot so that I can charge it up from the car when necessary. This I realize is a lot more than most people would be willing to do and it is probably enough to convince most owners that they can get by with a cooler after all. I however, have reached Power Nirvana.

My charger installation. Yes, I know the car looks like hell but this is my camping/hang gliding vehicle and I don't care. The two switches are for power and a current limiter in the charger.

 

One more thing...
I suggest you set your fridge to shut off at the lowest available voltage setting. When the fridge powers on, it will drop the voltage from the battery so the voltage the fridge is seeing is not the resting voltage the battery will show when it cycles off. When I spoke to the tech guy for SnoMaster, the fridge I use, he told me that the fridge should ALWAYS be set there because of that effect, otherwise it will shut off before it really needs to.

 

I don't think you're doing anything wrong.

100 watts should be enough as long as you're getting enough sun every day. Unfortunately the group 24 battery just doesn't hold much power. Going multiple days with minimal sun will tax your battery to the limit.

You didn't mention the ambient temp or where you store the fridge. The galley can get hot even in the shade which will cycle the fridge more often. If possible, leave galley hatch open or make sure to let it breath often.

Depending on the speed and running time, the fan can also add to the strain on the battery. Try not to run it more than necessary. I've used my fan overnight a few times but always run it on low and have it draw out the inside air. With the fridge running and warmer night time temps it seemed to draw more than I might have expected.

You mentioned kids before. Make sure they aren't running lights or other power draws that get left on 24/7 without your knowledge.

If you know you will be traveling places where you will have questionable sun, you might consider looking into one or more solar generators. I have a few. They aren't cheap, but they are handy and can be charged at any nearby 110V plug. (Think Starbucks, McDonald's, or any nearby quick stop location. )

One last suggestion (sorry about trying to spend all your money)...You might consider having the trailer retrofitted with solar. The rooftop option is more efficient than the portable panels and comes with 126 watts. I've had good luck charging on very cloudy and overcast days since it's always on and you don't need to adjust anything. It's not impervious to multiple days of bad weather, but I've been quite impressed with the results. And the best part about it is that you don't have to do anything. It starts at first light and runs until dark. Of course you do want to park it where it will get the best exposure to a clear sky. But I've found even with overhanging trees I've gotten pretty good results from even a partial day of sun.

 

This past weekend in Michigan it was a perfect 75 degrees with clear skies. I had the fridge stored outside of the camper for the most part and it was down to 50/60 during the day. Our campsite was shaded and while I did chase the sun around a couple of times, I obviously wasn't going to spend all day doing that!

I'm just disappointed that even with shade I wasn't able to make the fridge run on 12v battery into Monday (again on medium voltage cutoff). This intuitively does not seem right to me. Like in the middle of the day even if shaded my panel shouldve been putting out ~30w?

 

What exact panel do you have? Is it a rigid panel or a "portable"/cloth type panel? Neither of those panels will put out anything if shaded due to a lack of bypass diodes. Between the two a rigid panel will produce better in sun because it dissipates heat better and as such remains cooler than the so called portable panels. I have one of each of those kinds and have done numerous tests at home to prove that out. But if you shade even one cell your output drops to nothing.

FWIW, the panels CI uses are CIGS and do actually produce to some degree even when shaded. I've experienced it when camping.

 

I have ROCKPALS RP082 100w Foldable... https://www.amazon.com/dp/B08CDNFH7M?ref=ppx_pop_mob_ap_share. According to at least one review, one person was able to get 33w in the shade. I confirmed this by plugging it into my 560 today while the panel was inside my garage and my voltage went up to 13v+.

 

IMO, solar panel reviews contain tons of bad information due mainly to people not understanding how they work or the effects of the conditions under which tests are carried out. Panels will pick up varying amounts of wattage under cloudy conditions as the intensity of the sun varies. If that's what they mean by shaded, I can understand that. But if you stick your hand over a small portion of the panel on an otherwise sunny day your wattage is going to drop to near zero.

I can't tell you why your voltage went up, but if your panel is truly in the garage it's not producing wattage because it's not receiving any from the sun. (Unless it is coming in through a window.) It would probably be beneficial if you had some type of software that would read your input and output. That would show you the exact wattage being captured during the time it is in use. I don't believe that data is available with the CI built in solar option.

The first photo is an example of the data I download from my Victron controller after a completed trip. This is of course measuring my rooftop data. I can also capture a "moment in time" data as in the second photo.

 

Thanks for the complment --- I hope it helps someone. I've seen diagrams of cartoon guys crawling through tubes to explain it -- but I think concrete examples of air or water through a hose --- things you can actaully see and have likely experimented with are better.

On your comments: Bad! Bad camperdude! You should be ashamed (or proud) of yourself.

 

No question is a dumb one. Answers however....

I got my camper with the ctek, and the ameter is already there. Its in the right hand storage bay showing voltage and charger amperage, not 'use" -- it doesn't tell how much "draw" there is only output from the charger.

If you want to install one permanently it probably left to some one who knows the rules. Its a two part installation --- the gauge itself, and a "shunt" which measures current flow....really clever how they work. But hooked up incorrectly, you should have some sparks....

I think the BEST electrical presentation I've ever seen is by a Terry Cooper who runs an RV academy. RVTechCourse.com. I think he's sold it, he is not the spokesman for the business any more. They do have a youtube channel as well. But he is a phenomenal instructor.

I bought this course when I bought a "big rig" and had my doubts that I'd get much out of it...but it did not disappoint. It really is overkill for our little trailers. Our tiny campers aren't nearly as complicated as the "city on wheels" that a class A can be. In a class A you've got 3 complete electrical systems (110, "house" 12 volt, and "chassis" 12 volt) plus septic, fresh water, refrigeration (evaporative, which is completely different than compressor based), propane...there's just a lot there.

There are thousands of videos on the topic of Ohms Law & Watts law.

 

Under average conditions, you get about ⅓ of the rated output from solar. Just what I’ve come to believe.

 

If chasing sun is not what you want to do, position the panel to face south and position it in a place to get the best afternoon sun, even if that means it’s in the shade when you leave camp in the morning.

I suggest a couple of extra extension cords. My panel (Zamp 120 watt) has a 15 foot cord. I have 2 15 foot extension cords for it (I rarely need more than 1). This allows more flexibility in positioning the panel.