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Old 03-20-2016, 07:58 PM
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Question How big a solar panel would I need...?

I'll be camping for a week with the Scouts, and I'm wondering if I could get a solar panel that could provide enough charge (during daylight hours) that I could run my ARB Fridge Freezer 24/7 without starting my engine for a week. Specs from ARB say: average DC power consumption: 0.7 to 2.3 amp hr.

I don't have the transit bag but I could buy or make one if this would help.

Looking at the Goal Zero website, they offer a Nomad 100 portable solar panel with "Solar Capacity: 100W." (It's spendy). Would this be enough to keep up with the amount of draw the ARB fridge uses?
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Old 03-20-2016, 08:32 PM
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A lot of variables there but 100w should do it. I'd think a 60w could do it under ideal conditions pending your trucks battery size and other draws you put on it.

I'm going to put a 120w on the roof of my pop-up. I'm not sure where the cut off is for a charge controller but at 100w you definitely want one. I'll have one in the camper system.
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Old 03-20-2016, 08:49 PM
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Goal Zero stuff is super expensive generally for what it is.

http://www.outdoorsolarstore.com/sol...FQiqaQod8eUGXg

3 different RV kits all including a basic controller and wiring to get the job done. Just a quick Google search. Can't speak for these systems.
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Old 03-20-2016, 10:46 PM
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I have a 100w panel on the 60 and it barely keeps up with the fridge in the utah summer heat. I'd double it to feel like I didn't even need to start the truck. As it sits it's good as long as I pay attention and start the truck every few days or so when it's cloudy out. When it's cold and sunny (like right now in colorado) it never needs starting.

Also, how much stuff there is in the fridge makes a big difference... the more the better

here's the panel I got, they are cheap:

http://www.ebay.com/itm/Renogy-100W-...8AAOSwWnFWBByI.

I mounted it under my Gamiviti rack and it is out of the way and solid. I throw crap on top of it an the rack all the time and it has never broken.

My opinion is that 200w would give you what you are after, but if you can stand to start the cruiser every few days or so just in case 100w is fine. you might get lucky with sun, fridge fill, and ambient temperatures that 100w keeps it going for a week though. Liek I said, right now that's bee working for me, but it's been cool out.
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Old 03-20-2016, 10:47 PM
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also i use a super cheap PWM charger and it's been great. I have it wired in with my dual batts.

http://www.ebay.com/itm/30A-PWM-Sola...sAAOSwXshWr4TJ
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Old 03-20-2016, 11:32 PM
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There is a huge difference between summer Utah heat and Colorado Mountains. I can go 4 days off my group 31 and transit bag in the mountains without issue. But go down to the desert and 100 degree temps with the truck closed up I'm lucky to get 48 hours.

Ambient temp, size of battery, Sun exposure, and how much warm beer you put in the fridge will dictate how much panel you'll need.

I agree with Marco under those conditions.
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Old 03-21-2016, 07:51 AM
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My rules is to double size the unit for what you need. Your setup would require 27.6 watts at maximum load, so 100 watts is more than enough on most days.
(just make sure you have enough battery to cover overcast days or days up north in the winter)
I am going with this setup. Much cheaper than the GoalZero.
http://www.amazon.com/gp/product/B01...ilpage_o08_s00
For a more portable setup you might try this one:
http://www.amazon.com/dp/B00HR8YNK6/...T8MBU510&psc=1
Both units can be used with a standard AGM deep cycle battery. My current choice is a Deka 31M intimidator.
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Old 03-21-2016, 08:27 AM
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I have two group 31's and that 100W panel, It works well enough that I've never added a panel but for it to be a never worry about it kinda deal I'd need to bump up the wattage. I unplug the fridge when not in use since it can discharge the batteries when the truck is sitting there. How much would i bump it up? Another 100w panel is cheap and easy since it fits under my rack and dosen't interfere with anything.. so that. would 150w get it? probably. Am I positive that with 200w I'd be set for good? yeah.

Also I have and edgestar 43 fridge FYI. with no transit bag.
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Old 03-21-2016, 08:32 AM
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My observation is that about 2 amps is what my Engel MT45 draws at battery voltage, so if it ran continuously that would be 2 A-hr or 24W-hr. If your panel produces 100W then you have enough capacity that the battery won't be drawn down.

However, a solar panel only really produces it's rated capacity at exactly the test incident angle, proper temperature and otherwise ideal conditions, no overcast, no aging, etc. So the reality is that you'll get somewhere between a little and lot less out of it. So you have to compensate.

They become less efficient as they heat up, so when you'll need the most power (summer) they will convert less energy. Their test temperature is usually 25C or about 75F, so at 100F they will be making less output. It's usually about negative 0.5% per degree C. Thus if a panel is rated 100W at 25C, at 35C it will be down about 5W. And this assumes it's sitting at ambient, since you have to place it in full sun and they are dark they absorb energy and will actually be quite a bit warmer than ambient. So say they are running at 40C you're down to 92ish watts.

The angle is also important, a PV cell wants to be orthogonal to the light. As the angle comes off 90 degrees the efficiency can drop fairly quickly. Here in the summer the sun is about 40 degrees over the horizon but it's always moving. If you just prop the panel against a tree at 45 degrees or leave it on your roof rack flat the actual power out will be lower. In particular left flat the incident angle is way off 90 degrees and the output will be quite a bit lower.

Point here is that you only really get 100W from a 100W panel at noon on a 70 degree day when the thing is brand spanking new and not starting to haze from UV and dirt. A 4x margin is probably not bad.

But also remember that a fridge is using 24W every hour it's running, thus 576 watts per day. That's not really true, but for the sake of argument. You can safely assume the duty cycle will go down considerably at night. Unless you open it a lot for beers.

You only get sun part of the day. So if your panel is making 100W and you take the time to follow the sun you might get that for 2 hours. The rest of the day it's somewhere lower. Say you average 50W and that's between like 10AM and 4PM. You have only made 300W of power and have a deficit on the battery that over time will discharge it.

The actual numbers are different, but you get the point. So making 250W peak and averaging 100W during your charging period of 6 hours in the example gets you 600W and ahead enough that the fridge only draws down the battery during a rainy day where you get no sun at all. If you build in enough capacity to run a day on battery alone then you're fine, although you'd never really catch up. So you should ideally build in enough capacity that you can increase a discharged battery from an extended non-charging period. So you need to average more like 200W in the example 6 hour charging period to cover the 576W fridge and put back 576W from previous day. Your peak power will be more like 400W I suspect in this example.

It's actually fairly difficult to bring enough portable solar panel to run forever and still be somewhat mobile. You need a combination of enough battery, solar panel and periodic engine running to really do it. At best you can hope to extend a camp stay from a day or two to 3 or 4 without flatting the battery. Running your engine and alternator for tens of minutes puts back as much energy as solar will in a day, so it's hard not building that into the equation.
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Last edited by DaveInDenver; 03-21-2016 at 08:52 AM.
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Old 03-21-2016, 08:49 AM
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Also, mine is mounted flat under the rack, so I have the losses that Dave is describing.... plus one 1" tube passing over the middle. not ideal, but not in the way either. My 200w is a thumb in the air guess. My 100W results are from several years of running the fridge in various places/conditions.
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