One of the most asked questions, by far, is how Frieda powers herself.  The non-vanlifers are usually pretty amazed just to find out its solar power.  However, the veterans of our craft obviously already know that and are simply inquiring about the more important specs.  I already covered the basics in The Basic Build-out of Frieda and will use this opportunity to get a little more in depth, as well as give info on how to install your own solar power system in a van.  If you still need more info, feel free to contact me.

guy dog and van build
In the middle of my build. Happier than a pig in shit. Also note that my co-pilot Achilles is eating the scraps.

How to calculate the size of your battery bank

To determine this you need to calculate your average watt-hours per day, this is the hardest part. You need to add the wattages of everything you plan on using. Your main wattages should be the fan and refrigerator. Those two should be running far more than anything else. Then, divide your watt hours by 12 to determine your amp hours. For the sake of this article, let’s just say that its an average of 50AH a day or 600W. You can also use this awesome PDF for your calculations!

For your battery bank, you want to calculate for (at least) three days with no sun. So 50AH x 3days = 150AH. Now, you don’t want to run your battery down to zero. Hell, you never want to even run it below 50%. So take that 150AH and double it. With the 300AH battery bank, you should be able to run 3 days with no sun and not drop below 50% state of charge (SOC).

AVERAGE peak sun hours for the United States (all 50) is 4.19 hours. For calculation ease, we will go with 4 hours in this article. To check your state (if you plan to be localish) you can use this nice chart from renogy.

If you have 300W solar panels: that’s 25A per hour for 4 hours. This equates to 100A under optimal conditions for average peak sun. We’ll do 75% of this because I doubt we will ever get optimal conditions. So 75% of 100A is 75A.

An MPPT charge controller is 94-99% efficient. 75A at 94% efficiency is 70.5A.

What does all of this mean? Calculate your battery bank. Then, ON AVERAGE, if you match your panels to your bank size, you should have about a 20% surplus of energy per day. Which is a good cushion for other than optimal conditions.  

Here is everything written above in formula form.

Average AH/day = D  //  Battery bank = Bb

AGM Deep Cycle: (D x 3) x 2 = Bb

Lithium: D x 3 = Bb

Peak Sun = S [average peak Sun for the USA is 4.19 (use your state if staying in place)]

Panels = P

P(watts) / 12 = P(amps)

[(P(amps) x S) / .75] / .94 = Pd (power created per day)

Make sure Pd is at least 20% more than D. On average, if P = D, you’ll be fine.

My vans solar setup, and my suggestions. 

Sprinter van dirty panels.JPG

Let’s start from the top and work our way down.  Obviously, that’s referring to the panels (in case you didn’t read the heading.)  Frieda is sporting three Renogy Eclipse 100 watt 12-volt monocrystalline solar panels wired in series and double-sided taped to her roof.  Yes, I said tape. 3M makes a super strong VHB tape used to attach side panels to Mack trucks.  I’ve had my panels secured for 2 years with it and have had zero issues.  Highly recommended. Also, don’t be like me.  Clean your panels regularly, it makes a HUGE difference.

Of course, you can do more than 300w on your solar setup.  I’ve read forums where people are doing upward to 1000w.  Personally, I think that’s a tad excessive.  We are van people, we try to live within our means and use our space wisely.  You don’t need to be able to fill your battery bank in 1 hour of sunlight.  I would recommend a larger battery bank though.  That way you can last a while when it decides to rain for 5 days straight.

Wiring in series or parallel

To start, I would recommend wiring in parallel vice series.  When in series, the current through each of the cells is the same and the voltage is compiled from the sum.  Parallel is the opposite, voltage is constant and current is summed. Why does this matter? The main takeaway (without getting too nerdy) is that partial shade can be a lot more detrimental to the charging process when in series.  However, wiring in series is easier and can use a thinner gauge wire. The lazy side of me decided to go with series and I haven’t had any issues so far. I would personally recommend the former though.

MPPT or PWM charge controller

Frieda is stocked with the Renogy Commander 40A MPPT charge controller.  I would almost call it essential to go with an MPPT charge controller.  And if you are wired in series, that’s double as important.  A PWM charge controller will limit your voltage to 12v, and if you read the above paragraph (I hope you did) then you would know that when in series your voltage is much higher than 12v.  Now let’s say you took my advice and wired in parallel. If you desperately needed to save money you can go with a PWM controller, but you will still lose a bit of voltage. Even a 12v system will hit upwards to 18v with perfect conditions. So, with that being said, when mounting your MPPT controller ensure that it gets a bit of airflow and is easily accessible.  I can honestly say that I kind of botched my electrical work and it is not too organized.  

Dirtbag beta wiring
See that tangle of wires? Only got worse.

The biggest piece of advice I can give on van electrics is to take your time and make it organized.

The charge controller I purchased came with its own MT-50 Remote Tracer Meter; an LCD screen monitor.  Whatever charge controller you choose should come with its own monitor.  I would personally ensure that the monitor isn’t too ugly, after all, it will be seen by everyone.

The battery bank

If the solar panels are the meat of the system, then the battery bank is definitely the potatoes.  And if you’re Arnold Shortman (Hey, Arnold) then maybe your battery bank is actually made of potatoes.  That joke really shows my age… Anyhow, I loaded Frieda up with two 12-volt 150 amp hour AGM batteries wired in parallel (12v 300ah) from a local supplier called Deep Cycle Battery San Diego.  I decided to go local for this because not only are batteries heavy (shipping cost) but this local supplier does some killer deals on blemished or lightly used batteries.  My total battery bank cost was just under $200 dollars. Pros and Cons? For the size of my battery bank, that’s extremely cheap. But since they were used, the life-span is not as long.  It’s been 2 years of hard use and I’m starting to see signs of it. I’m already looking for new batteries. However, I am looking for more discounted ones because I %100 think it’s worth it. If I had the money though, I would get Lithium.  Lighter, able to discharge lower and last the longest. Sadly, a decent sized bank (200+ah) will set you back about $2,300.

Changing from DC to AC

Dirtbagbeta sprinter batteries
My battery bank before the actual install

Without going super geek I am going to give some quick tips on inverting from direct current (battery power) to alternating current (the type of power in a home.)  This is relatively easy to do. You just need to buy an inverter.  Inverters come with a lot of options though.  First, I would recommend ensuring that you get a pure sine wave inverter.  A modified sine wave inverter may save you a few dollars but will probably end up costing you the money in the long run.  Not only will it not work a lot of modern sensitive electronics, but it will also make certain electronics run hot and can cause internal damage over time. Second, you don’t need to break the bank and get a million watts.  I have a 750w pure sine inverter that cost me about $150 and it has been working wonders for me.  I would personally recommend the PowerMax 1000 Watt Pure Sine Wave Inverter PMX-1000.  Its $160 dollars, pure sine, and can probably run a toaster and a TV simultaneously.  Lastly, get a remote for your inverter. Something so you can turn it on and off. If you leave an inverter on it will constantly draw a bit of power.  That little bit of power adds up over time on cloudy days!

Extra Beta

  • Directly wire a couple of USB ports to your DC circuit box.  This is so you can charge your phone and other electronics without inverting to AC just to convert back to DC and lose all that precious power.
  • Circuit breakers. Use them. Use a lot of them.  I would rather have too many circuit breakers than die in a fire.
  • On that note, buy a fire extinguisher.  You would be surprised by the peace of mind that comes from just having one.  Not to mention, again, I don’t want to die in a fire.
  • Make everything easy to work on.  It is going to break, and you are going to have to fix it.  Chances are that you’re going to have to do it in the middle of nowhere too.  
  • Keep spares of all your consumable parts! (splices, wire, breakers, clamps, ect…)
  • If you’re not full time in the van, keep a good amount of tools.  If you are full time, well, everything you own shown be in there.  I hope you own some tools.
  • Dirtbag beta dog in van
  • All my spare stuff…

I know that there are TONS more I can talk about.  Refrigeration, DC circuits, lighting, fan, AC wiring ect…  I can probably write thousands more words on everything. But I have to draw a line somewhere.  If you can’t take waiting for future posts or if you have more specific questions, as always, my email is open and gets answered quickly.  

8 thoughts on “Van Solar Power Setup. Tips and Calculations.

  1. > You don’t need to be able to fill your battery bank in 1 hour of sunlight.

    And you can’t, with lead acid chemistries anyhow. Absorption generally takes a few hours.


    I don’t bring up these typos to be pedantic — understanding what the acronyms stand for helps use understand how the controllers behave. If that’s not a good enough reason, fixing them will also increase SEO. 🙂

    1. Thanks for the corrections. I don’t know how that happened down there. The top was still right 😂.
      I don’t know what you’re talking about filling the bank in an hour. Where do I say that?

      1. I quoted it above. Here’s more context:

        > We are van people, we try to live within our means and use our space wisely. You don’t need to be able to fill your battery bank in 1 hour of sunlight.

        I was suggesting it wasn’t just unnecessary, it’s generally not possible unless one is running Li or some other exotic.

Leave a Reply