67 replies to this topic

[Boonie]

Hummm, I seem to be having trouble getting the question across, so let me fill in a few other details. I am in the process of building my rig. (see my build thread "'81 Grandby on a '91 Jeep YJ-New build") At the start of that thread I stated that all campers are a compromise. One of my compromises is weight. When my camper target weight is 650 pounds adding a second solar panel, 25 pounds, and a second battery, 55 pounds or 80 pounds is huge! So can I make what I have more efficient? How much more efficient can I make it? Based on that information, what is the maximum amperage load that I can safely install in my rig?

 

What I am trying to do is reverse engineering.

[Stalking Light]

My GoPower 100w flex panels weigh under 3# each if weight is an issue, fwiw.

[Boonie]

Thanks, Charlie. (That's plan B, but don't tell anyone. I'd like to stick to the question.)

[MarkBC]

Because I'm interested in the answer (even though there still isn't a simple answer), I did a search and found the website where you can find something like an answer:  

 

U.S. Solar Radiation Resource Maps:  Atlas of the Solar Radiation Data Manual for Flat-Plate and Concentrating Collectors

 

Using that site, I went ahead and generated some comparison maps of "insolation" -- solar power-per-area.

 

These two maps compare the average power received in March for a horizontal surface and a full-tracking surface:

 

As you can see from the maps, these are real averages, not just theoretical calculations based on latitude. They include the effect of days when there's cloud/rain-cover -- which is why the usually-sunny Southwest has the most insolation.

 

So, for example, if you were camped in Wyoming in March a horizontal panel would receive 4 - 5 kWh/m²/day while a full-tracking panel would receive 7 - 8 kWh/m²/day.  Moving your panel dawn to dusk to track the sun would give you, in that "March in Wyoming" scenario, about 67% more energy than a horizontal panel.

 

More maps, with comparisons for December and June:

 

In December in Wyoming you'd get (on average) 120% more energy by tracking the sun compared to horizontal, while in June you'd get about 40% more energy .

 

These maps show why it's kinda hard to answer: "Can I get by with my current system if I move the panel to track the sun all day?"  It depends a lot on what season you're camping and where you're camping.  A systems that's adequate -- with full tracking -- in June probably would fall short in December, and one that's adequate in Arizona probably wouldn't be adequate in Wisconsin.  And if you're not going to add more battery storage then you won't have more back-up for overnight or heavy clouds.

 

That said, I'm glad I found this insolation resource for my own use if nothing else.

[cwdtmmrs]

If you use your 3 way fridge, install led lights and watch your usage of a forced air furnace (or go with a Wave heater) I am not sure you need solar at all unless are staying in one spot for a long time. A 100ah battery with 100w panel should be more than enough even at 50%. At 3# per panel, not much weight added.

 

cwd

[Boonie]

MarkBC,

 

I think you hit the nail on the head. What you have verified is consistent with the article by Charles R Landua that Advmoto18 linked and a solar calculator that I found. Yes, there are seasonal differences especially in June, but overall a 100w portable/suitcase is able to recharge batteries equally as well as a 160w flat fixed panel.

 

CWD

 

I can tell you have been following my other threads. I believe your rig and your thinking are similar to mine, so you have taught me to keep track of who says what. As a local radio host says "You need to know where I sit before you know where I stand"

[MarkBC]

...but overall a 100w portable/suitcase is able to recharge batteries equally as well as a 160w flat fixed panel....

 

 

I think that's right but I'd add:  "...if you're moving the portable to track the sun all day".  

(I know that's what you meant, but just to avoid any misunderstanding by someone who reads that one bold line without reading your intention earlier in the thread.)

 

The biggest difference between horizontal and tracking is in December, when the sun is low in the sky so a low angle to a horizontal panel.

[cwdtmmrs]

MarkBC, I just don't think Boonie's per day amp usage is going to going to enough to worry about moving a portable unit more than once a day if at all. If he is in camp, no problem. If he is out of camp for a day or so, nothing will be running anyway.

 

Boonie, maybe use one of the charts on the forum to figure your total per day amp requirements and work from there. The good thing about the portable solar is that if your trip requires driving every day, you can leave it at home.

 

cwd

Edited by cwdtmmrs, 19 January 2017 - 11:29 PM.

[MarkBC]

MarkBC, I just don't think Boonie's per day amp usage is going to going to enough to worry about moving a portable unit more than once a day if at all. If he is in camp, no problem. If he is out of camp for a day or so, nothing will be running anyway.

... 

 

That's probably right, but I wanted to answer his original question anyway for others who may wonder.  

And I was glad to find that useful site about insolation, for my own future use. 

[craig333]

Besides having enough solar even when the conditions aren't optimal, I rarely use my portable anymore after finding it always in the shade. Seemed every time I'd wander by I'd have to move it back into the sun. That got old quick especially if you aren't around camp much.

 

If he's running a compressor fridge then it is using power even when he's not around.