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Old 06-23-2020, 12:05 PM   #1
brp
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Pure Solar vs. Solar+Alternator

Hi guys. I am working on a new vehicle and trying to decide on my electrical system layout. I never had a house battery charged exclusively by solar, but I am considering it now.

The bus I'm working on will primarily be in the Salt Lake City area, a sunny area. I have a 12v fridge, a diesel/12v heater, and a probably a 105ah SLA battery.

When looking at the prices of a C-tek or Renogy DC/DC MPPT unit, or a Blue Sea ACR and MPPT, plus a bunch of heavy cable....well you are getting into a few hundred bucks, a few hundred bucks that could buy a few hundred watts of solar.

I have tons of roof space, I'm imagining something like 300 watts.

I am just looking for general experience/advice on this topic.

Thanks a lot everyone.
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Old 06-25-2020, 04:18 PM   #2
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I’m running 200 watts of solar charging two 6v cart batteries around 235ah. Not running too much, fan, fridge, lights, water pump, and occasionally an inverter. Since installing the solar I have not had to charge via the alternator.
I did run a separator as well as a blue sea system battery switch to not constantly have the alternator charging the house batts.
Come to find the solar is plenty for keeping them charged so the battery switch is always off.
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Old 06-25-2020, 04:27 PM   #3
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Depends on your driving vs parking time. New vans have 500 amps of Alternator output, so that’s 6,000 watts. About half that would be usable for battery bank charging. A short amount of driving can charge more than a day of solar, as long as your batteries and BMS can manage that much. But if you stay out for days at a time, solar starts to make sense.
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Old 06-25-2020, 09:28 PM   #4
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Thanks for the insights. I am going to go straight solar for now, probably 300w, plus a broom. Keeping snow off the panels when running the diesel heat is my main concern. I'll add a Blue Sea ACR if I find I need more power.
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Old 06-25-2020, 10:14 PM   #5
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I highly recommend doing some quick math to estimate your solar usage so you size your system appropriately. No sense in overdoing it, and of course you'll be kicking yourself if it falls short of your expectations. This site does a pretty good job explaining all the ins and outs, considerations, etc. when designing your electrical system:

https://faroutride.com/van-electrical-sizing/#solar
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Old 06-25-2020, 10:31 PM   #6
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320W running two 12s and a kodiak lithium (90ah). 300AH total. 100% charged all the time running snowmaster DZ, lights, espar heater, etc. Occasionally it dips below 95% when in low light conditions. Haven't had much winter experience with it yet. Using an isolator of some sort (mine is manual) will allow for either alternator or solar. You get the onboard jump start if needed. I'd advise some kind of electical isolator as the manuals clack throughout the night when the two battery systems try to 'speak' with one another every 10 mins or so (atleast with my system).
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Old 06-25-2020, 10:59 PM   #7
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No offense, but 100% charged all the time isn't possible if you have any kind of current draw at night (no solar)--which presumably you do with your DZ. Just sayin'.
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Old 06-26-2020, 07:57 AM   #8
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I'd always go for both and the cost of alternator charging isn't overly expensive. It's pretty much limited to some cabling and some sort of battery isolator (solenoid,"Battery Doctor", etc.)

"Heavy" cabling isn't necessary for your solar given that the distance between your panels and controller will be fairly short. There are numerous calculators online, but 10 awg is typical. The savings here can offset the cost of the heavier cabling necessary for alternator charging.

You might also want to consider two 105 Ah batteries. At the very least, make sure there's adequate room to add one later. Additionally, although they're a little more expensive, a true deep cycle battery is preferable to the typical Marine/RV dual purpose battery. Here's one option:

https://www.lowes.com/pd/Mighty-Max-...ies/1001401826
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Old 06-26-2020, 08:40 AM   #9
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Sounds stressful to me. You'll constantly be worrying about whether you're parked in an exposed enough location and wondering whether to sweep snow off the panels throughout the day when you should be inside relaxing or out recreating.

While it obviously depends on your parking and driving habits, I expect that whatever savings you get from not wiring up the alternator will be offset by the decreased battery life from being deeply discharged for longer periods of time.

I can't tell from your post, are you also omitting a plug-in AC charger? Then you'd really be at the mercy of good weather. You certainly wouldn't be able to camp in the Pacific Northwest except in high summer. I have 200W of solar in theory, but between the trees and the clouds, getting more than 2A is the exception, not the rule, and that's for only a couple hours a day in winter.
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Old 06-26-2020, 09:29 AM   #10
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Quote:
Originally Posted by AndrewInSeattle View Post
I can't tell from your post, are you also omitting a plug-in AC charger? Then you'd really be at the mercy of good weather. You certainly wouldn't be able to camp in the Pacific Northwest except in high summer. I have 200W of solar in theory, but between the trees and the clouds, getting more than 2A is the exception, not the rule, and that's for only a couple hours a day in winter.
Wowza, that low?! Great point though, latitude/location matters. I have 2x190W panels in parallel, and I've seen the full rated current (19A) on sunny CO days even in winter (with no trees). We typically end up camping in or near trees of course, but I still see 7-9A regularly. I deliberately did not include a plug-in AC charger in my setup, so I'm 100% dependent on my solar and alternator DC-DC charger (Kisae). This has proven to be more than sufficient with an 100Ah Li battery, but we typically don't stay in one place more than a couple of days either so the alternator contributes significant charge @30A each time we drive to a new site.

Note that a solar controller requires a minimum voltage in order to produce useful charge. If you're regularly faced with low light conditions, it would be better to wire the panels in series to increase the voltage--the tradeoff being that you lose the improved performance with partial shading that you get from a parallel setup.
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