Couple Questions, PNW Solar Use, Math Check

[cs0430]

First, I have read every solar/battery/fridge thread I could find on here and other online forums.

I'm looking to add a Dometic CFX-50 fridge soon and have two Rigid SRQ diffused lights to use for camp set-up. No winch, crazy stereo system, etc.

I'm thinking the best option for me is to change my stock battery out for a Group 31 and connect it to a 100W Renogy solar panel suitcase and an MPPT controller when the truck is parked for extended periods of time. I'd like to get the point where I could safely run my fridge 24/7 and lights infrequently for 3-4 days without the truck running.

1. Does the below math look correct? I made assumptions on power generation from the panel. Worst case scenario it looks like I can get 4 days until the battery reaches 50%.



2. My wife and I are looking to move to Portland soon. In general would the weather in the PNW render this solar system useless for maintaining a battery while a fridge is being used? If so, what is my best option? Buy a generator instead to keep the battery topped off?

3. Other than not risking depletion of the starting battery if something goes wrong or isn't monitored properly, I don't quite understand the reasoning for dual batteries over a larger single battery when running a fridge. Almost all auxiliary batteries I have seen installed are Group 34 - lessening the number of usable Ah before a battery reaches 50% (it's my understanding deep cycle batteries should only be discharged to 50% to preserve their life). Am I missing something?

 

[calicamper]

Winter months are tough add your farther north and its a bigger hit. My nor cal solar gen is about half output in Dec Feb than it is in end of June - mid August.

 

[Roger M.]

Winter season at or above the 44th or 45th parallel can make it almost impossible to depend on solar.

With only 8 hours of the day when the sun is even above the horizon, it can be nearly impossible to get more than a couple of hours where the typical PNW campsite has any sun at all on it.

 

[IdaSHO]

You just need to be a bit more creative during the winter.

During the winter our fridge is normally turned off, and the one compartment that is accessible from inside the cabin, and vented to the outside, is used for perishables.

Certainly cold enough around here during the winter :sombrero:

 

[rayra]

Look beyond the straightforward math and consider the overall system design and the reasons for it.

The Aux battery is sacrificial. It takes the abuse and heavy drains and if you guess wrong or there's a system malfunction of some sort that kills your battery, you just turn your key and start right up from your unmolested Starter battery and go your merry way back to civilization to buy another Aux battery and troubleshoot your mess.

 

[Endoftheroad]

You need a lot of solar to keep up with a fridge during a winter low pressure in the pnw . 180wts will not keep up with my Novacool fridge with heat on inside. Either pull out a generator or preferably do as IdaSHO suggests and get creative, lots of cold air when there's no sun. Anywhere that's below freezing, the challenge is happy medium between inside and out..

 

[rayra]

solar insolation / energy maps show a grim tale for solar in the wet zone of the PacNorthwest. You're gonna get about 1/3 the energy as the same system would in the Southwest.

 

[Endoftheroad]

That's an interesting chart, but when it's wet and dark for days, I'd love to be getting anywhere close to a 1/3 of what someone gets in the southwest. You are trickle charging. You will be slightly better than battery capacity alone when stationary in nasty weather.
You shut off fridge or fire up generator.. Or get a huge solar array..

 

[Hopeless Diamond]

We also have these big tall things called trees. Could be the sunniest day ever (ever hear the song "the bluest skies you'll ever see are in Seattle"). Little opportunity for solar if the sun can't get to the panels...

 

[cs0430]

Thanks for the replies everyone. Sounds like it doesn't make sense to invest in solar if the PNW is in the future. These 12v fridges seem to be more work than they're worth. Between a dual battery set-up, solar or a generator the investment would certainly buy a lot of ice for my Pelican cooler.

I see a lot of people here and on the other forums running these fridges without dual battery set-ups and solar so what do they do? Not spend more than a day in one place? Run the truck to power up the battery?

How well theoretically does the vehicle itself charge a deep cycle battery? Wondering how long I would need to run the 4Runner to top up the battery...

 

[dwh]

Another reason for dual batteries that wasn't mentioned is that you can quickly kill a cranking battery by deeply cycling it. So a cranking battery for the chassis, and a deep cycle for long term loads is the preferred method.

Automotive charging systems are designed to maintain a set voltage and supply what amps are needed to power the truck. They aren't designed to do a good job of charging since the only charging they normally do is to replace the 1/5 amp*hour you used to start the truck. That system can bulk charge a battery fairly well in a few hours, but it can take a lot of hours of engine run time to get the battery fully absorbed to 100% charged (maybe 6, maybe 36, depending on the specifics such as battery type and size, and voltage regulator setting).

 

[dwh]

And yes, your math looks right, though as others have noted, the daily harvest assumption seems somewhat optimistic.

 

[calicamper]

Solar is super cheap, its worth it. But winter months you just move to a reduced consumption method or charge up via other methods.

To scale up my $180 set up for a fridge and camper would add about $350 for a bigger battery set up and a lager panel, the rest of it would be perfectly fine.

But we dont have a fridge, and only use it in summer months and only burn about 6-8amps a day. The two little 10watt panels I set out and our tiny 18ah battery cover our use.

Winter time you probably need shore power or a generator if your consumption is as high or higher than summer months.

 

[dwh]

I know a bit about this stuff. My way is to buy a good cranking battery and not abuse it. Then I buy a cheap deep cycle and beat the crap out of it by completely ignoring the 50% rule.

Since I like to stretch a parachute over the whole area, including the truck (it holds up the center of the chute), I use the smallest generator I can find to power a decent charger and fire it up every few days to recharge the battery.

Of course, I have to replace the battery every two years (or less), but I don't care...I pay half as much when I do so it averages out the same.

 

[galvyork]

fridges are worth it 100%. i would spend the time getting it right now and then rock it out. I'm going to do an isolator on my main starting battery to my AUX and then let the truck charge both and also have a solar panel for when i'm stopped. The isolator will protect the start battery from getting to low.