Sizing my solar setup


#1

Hi guys, I’m looking for some advice on sizing my solar setup for my van. Im planning on having a total of 365 watts of rigid solar panels on the roof of my van with a MPPT charge controller, and 3 x 140amp hour AGM batteries. I will also be charging the batteries from the alternator of the van when it’s running. I’m hoping that this is enough to run all of my electronics, and ideally not have to plug in or run a generator at all. I’m trying to keep everything 12v to maximize power. I will be running a 12v cooler style fridge/freezer (door on the top), 2 x 12v maxxair roof vents, 12v LED puck lights, 12v shurflo water pump, and also charging a laptop, camera batteries, and cell phone. I will also have a 2000 watt inverter/charger but to be honest I doubt I’ll be using the inverter much, if at all.

Im basically maxed out for room on the roof and this was the best option I could come up with to fit my van.

I really appreciate any input on if this system will work for me, and if not any suggestions on how to change it to make it work for my daily power needs.

Thanks so much!!!


#2

Greetings!

3 x 140ah batteries = 420ah of battery capacity. 420 x 3 =1260 watts of solar for a semi reliable system. Solar is never reliable, because it counts on the weather, and the length of daylight hours. That’s why it’s only popular with newbies, and the promoters who get paid to promote it. Most of us with experience, after multiple attempts with solar have ditched it all together. Vans just don’t have enough roof real estate for enough panels for that much battery capacity.

I have also read where AGM batteries require extra stuff to be charged by alternator while driving, something you’ll want to research. I just use cheap deep cycle junkyard, or recycled batteries myself. I’m approaching year 7 on my under $20 junkyard deep cycle house battery, year 6 on my deep cycle junkyard starting battery. Even though deep cycle batteries aren’t ideal for starting purposes, I wanted to be able to use it as backup power. It starts my van just fine. Battery protectors / low voltage cut offs, can greatly extend the life of your batteries, and guarantee you always have enough power left to start your vehicle.

If you ditch the power hog fridge, you could downsize to a single battery, and then you’d have enough solar, and plenty of power for everything else, but very few people have had success with solar long term. 3-way RV style fridges/freezers, or plain old ice chests are both better choices than 12 volt fridges.

No system is complete without a generator, because solar is too unreliable. It doesn’t work well on short winter days or cloudy days. Most of us feel solar is optional, but a generator is a must have. Most people with solar, still need a generator to have a reliable power system. Even mainly charging while driving, which is much more reliable than solar, I wouldn’t be without a generator. I no longer have an inverter, if I need shore type power, my generator can supply it.

Heating, cooking, and refrigeration are best accomplished without using battery power.

Cheers!


"I can live like a king because I work like a dog." ~ An anonymous vandweller


#3

VD… is 3X a good rule of thumb for minimum solar requirements relative to battery capacity? Is this why you wrote the following to arrive at the 1260 watts of solar number:

“3 x 140ah batteries = 420ah of battery capacity. 420 x 3 =1260 watts of solar”


#4

Greetings!

Yes, 3x battery capacity. Double can work in the summer, but in the winter when the days are short and the sun is low, 3x seems to be the most recommended.

A good backup plan is also highly recommended because in some areas you can go for a week or even multiple weeks without seeing the sun, or very little of it.

Being prepared can save a lot of anxiety, aggravation, and stress down the line.

Cheers!


"I can live like a king because I work like a dog." ~ An anonymous vandweller



#5

It’s well thought out and should work as designed. Since you are actively seeking feedback, I’ll kick around some ideas while I drink morning coffee. I am not recommending changes to your proposed setup and I do not claim to be an expert. I do have a working setup and loads analagous to what you describe.

  • The battery bank is larger than average, maybe larger than it needs to be. As others have pointed out, it really would take 2:1 to 3:1 solar to keep the bank healthy with solar alone. But with the added alternator charging I think it will be fine. To put it in context, isolator charging provides the equivalent of 520-1000w of solar during Bulk charging (as in the morning). Not bad for something that costs <$100 to install!
  • You’d probably also be fine with only two of those batts, or the traditional “2x 6v golf cart batts in series for ~220Ah” setup. The latter would be about $225 instead of the $1000 I’d guess you are budgeting for the 3x agm. There are valid reasons for paying 2x for AGM (need to lay on side, built into an inaccessible place, medical conditions, need to run high-amp loads like microwaves or coffee makers) but can be a counterproductive default choice absent a compelling reason. I blame the AGM craze on youtube and instagram.
  • your approach to the inverter use is wise. Oftentimes people think that having a 2000w inverter on hand means there is an endless supply of power behind it. There’s not…
  • AGM can pull a ton of current during charging, depending on manufacture. Depleted to 50% depth of discharge the bank could pull C/3 or 140A from the alternator. Flooded lead-acid batts typical pull a max of C/5. That’d be 84A with a 420Ah bank, or 44Ah with the golf cart bank described above.
  • 12v compressor fridges are rather efficient. My 15L alpicool is an outlier in terms of size and consumption, but it averages 12Ah/day as measured with a Watts Up meter. Larger compressor fridges are closer to 20Ah/day. You’ll be able to find posts where folks have taken measurements on the one[s] you are looking at. Freezing requires much more power than refrigeration. You can mitigate thiis somewhat with additional insulation.
  • insolation maps will tell you how much solar power to expect based on location and time of year, based on historical measurements. Yay, science!

Unrelated: I also responded to your “large panels on van” thread with pics of my own sideways-mounted panels on a vantech H3 rack.