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Ingenuous Modular Solar Power System

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Today we have a guest post from my good friend Doug describing his solar power system.  It’s unusual for two reasons 1) He used temporary solar mounts that are easily tilted 2) It’s modular, with multiple small, complete systems instead of one large system. Check out his blog at: 
Bob has asked me to go through my peculiar solar power system, and peculiar it is. Think of my system as “modular”. One solar panel, one solar charge controller, and one battery pack – nothing unusual about that. Each component is closely matched to the other to maximize performance and minimize cost. The difference is that, if you need more power you don’t then start upsizing the individual components. Instead, you simply add more of these modular solar assemblies to your project, placing them where you need them. I’ll be the first to admit that upsizing usually costs less per watt because a bigger solar panel usually costs less than two smaller ones and a higher capacity charge controller normally costs less than two smaller ones. Same for batteries.


In this picture you can see how the four, 195 watt solar panels are mounted. He adjusts them with painters extension poles available from Home Depot or any hardware store.

But, I’d stumbled upon a sweet-spot for my purposes: A 195W solar panel, a 180W solar controller that actually maxed out at 200 watts, and 208Ah of batteries. At least at the prices I was seeing online at the time, two of these systems cost less than swapping in a larger controller to deal with two panels and four batteries. Another consideration was that the devices that need power are spread throughout the trailer, and I had no desire or ability to bury long strings of wire within its existing structure. Because I was under a time limit, I ordered four panels (780 watts total), four controllers, and some batteries. I know, that’s a lot of watts, but my office is closer to a photography, video and audio editing workstation than it is a perch to check email on a laptop, so I needed that much power.
Doug's front office. He is a a heavy power user!

Doug’s front office. He is a a heavy power user!

I then found a local 1994 Gulf Stream Innsbruck Travel Trailer with the floor-plan I needed, and towed it home. Everything in it still worked, and it had a leak-free, one-piece aluminum roof. My hope of roof-mounting my panels evaporated however, when I found that the roof was so badly dented and unsupported that roof-mounting the solar panels was impossible even if I somehow found space for the panels – which I could not. That was lesson one, take a ladder when you buy an RV and check out the roof! Time to come up with Plan B.
Doug's son helping him with installing the solar mounts. If he had taken a ladder with him when he bought the RV, he would have known he couldn't mount the panels on the roof! Lesson learned!

Doug’s son helping him with installing the solar mounts. If he had taken a ladder with him when he bought the RV, he would have known he couldn’t mount the panels on the roof! Lesson learned!

Plan B was to mount the panels removably on the sides of the trailer. Since the trailer’s awning took up most of the passenger side, the only option was to rig up mounts all along the driver’s side. Since four 45-pound panels are quite a load and old trailers aren’t noted for having solid body structure, my son and I looked at the awning mount and decided that the similar header on the other side was our best bet if the wood wasn’t too deteriorated to allow wood screws to bite in. We’d rig up a mount that allowed hanging the panels and swinging them up into position with telescoping painter’s poles. They’d have to be dismounted and stowed inside the trailer for travel, and carrying and lifting them would be a significant nuisance for an older guy like me. But there just wasn’t any other choice; the roof couldn’t carry their weight.
My son cobbled up a system from the local hardware store parts bin, and started installation. It was difficult to blindly align steel hooks into loops, but it worked, and it held securely enough. Whew! It also had the huge advantage of easily allowing me to tilt the panels to get maximum solar output. Standard MC4 solar wires were then terminated in SAE plugs, which allowed power through specific points in the trailer walls, where the various battery packs and controllers would be. I put four 104Ah 12V deep-cycle AGM batteries in a closet in the office at the front of the trailer
A close-up of the mounts to give you an idea of how you can duplicate his system.

A close-up of the mounts to give you an idea of how you can duplicate his system.

The Modular Approach dictated that the four batteries be split into two independent systems to power all the office equipment, and this was accomplished with two small controllers mounted inside the closet. One panel, one controller, two batteries – times two. The closet wall next to the desk surface was populated with multiple cigar lighter-type sockets. A 300W inverter would allow everything needed to run. Done.
Here we see the four panels mounted inside the trailer for transport. He put cleats in the floor to hold them in place so they wouldn't slide around.

Here we see the four panels mounted inside the trailer for transport. He put cleats in the floor to hold them in place so they wouldn’t slide around.

At the other end of the trailer, I needed a CPAP machine to sleep halfway decently. It had to run no matter how overcast the sky, or however I overused any other device, anywhere. Since it could run directly on 12VDC, I wanted at least five days runtime before having to pray for sun or plumb it into a different battery pack with an extension cord. It used a 5-amp fuse and included a heater for humidification, so it was no toaster, but was no LED light bulb, either. For the sake of weight, I opted for a single 104Ah AGM battery with the hope that a 195W panel would tend to charge it well even in heavy overcast. (This did work out just that way.)
In this picture you are looking forward toward the office from the back of the trailer. You can see the hallway where he stores the panels for transport just inside the door.

In this picture you are looking forward toward the office from the back of the trailer. You can see the hallway where he stores the panels for transport just inside the door.

Like most trailers there was a spot for a battery on the tongue and I mounted another 104Ah flooded house battery there. All that had to be done here was to mount the remaining controller near that battery (in a sheltered location under the trailer) and link it to its dedicated solar panel. A 150W inverter would be mounted inside near the center of the trailer.
Problems arise
I finally hit the road and at first all seemed to be working properly, But after a few weeks it was obvious something was wrong and the batteries weren’t getting charged. I called a Alt E Solar sales guy who immediately diagnosed the problem–I had simply purchased 18V panels without realizing it, and the behavior of the Brand X controller clearly showed it was a robust PWM unit that was rated at a nominal 12 volts only. He was upbeat, asked about the rest of the system, and confidently recommended two MPPT Morningstar controller models. What’s more, he conveyed not the slightest suspicion that he might be talking to the village idiot. That was the clincher. I ordered one as a test under a guarantee of functionality. It worked perfectly, and I ordered the remaining two, consolidating the office pack into four cells instead of two pairs. I was so grateful to have all systems up and running flawlessly that I almost gladly ate the extra $500 cost of the MPPT controllers. I was up to my eyeballs in 12V power in less than half a day. Lesson Two. Know exactly what you’re buying, and why.
That cost penalty now makes my system almost nonsensical. Sure, each subsystem is very compact and efficient, avoiding long internal runs of thick cable. But now that I’ve had time to review available space again, to have the truck and trailer weighed at each tire, and to let things in my brain soak, I think I’d only stick with the original plan if I’d intelligently ordered 12V solar panels. That still makes cost sense and keeps things simple. Nice as they are, multiple MPPT controllers make one’s wallet hurt, and point toward at least partial consolidation.
The panels hanging down on the side of the wall.

The panels hanging down on the side of the wall.

Lesson three came a little easier. I unpacked and installed my new 300W AIMS inverter in the office, and a 180W AIMS inverter in the living area for the TV. Booting up the computer was alarming – literally. The inverter beeped regularly, and the computer continually crashed and rebooted itself in a kind of dance of death. The inverter’s troubleshooting chart pointed toward the cigar lighter plug. I knew that the computer itself pulled a max of 115 watts, and that the Marinco marine plugs were rated to 180 watts, but I also hardwired the inverter directly to the battery anyway. No change.
The 180W AIMS inverter did the same thing to the TV, and alarmed constantly. As a test, I replaced it with the 300W inverter and it ran okay, so it wasn’t the trailer’s wiring harness. A call to the vendor to inquire produced an immediate offer of an RMA, with the explanation that, “yeah, they do that with some equipment.” Chhyeah! Well, thanks a pantload, Chet! I returned them and ordered two similarly-sized Samlex inverters from a different supplier.
The Samlex pure sine units were plug and play. I did end up hardwiring the bigger unit to the office pack, later. It worked fine through a cigar outlet, but the plug got warm to the touch when everything was turned on. No need to waste precious amperage to create heat instead of to power equipment.
How does this system perform now? In Arizona with its abundant sunshine, its overkill, but the upside is that none of the battery packs ever dips below a 75% state of charge even with heavy use. That’s extremely good for battery longevity, especially considering the cost to replace AGMs, and they should serve me for a very long time. In the Upper Midwest? The jury is still out. I’ll be returning there in the summer for three months. I expect to be humbled.
Another view of the panels mounted.

Another view of the panels mounted.

Cheap is relative
It’s valid to ask two questions here. The first is: Why AGMs, if you’re such an alleged cheapskate? Many knowledgable folks don’t bother with them, staying with standard flooded cells like what’s on my trailer tongue. However, I’d had quite a bit of experience with them in the past, and had seen what their constant bath of acid vapor does to plywood and painted metal over the course of several years. I didn’t want them inside a semi-sealed compartment with clothing or equipment, near me, or most particularly near anything involving flame or propane igniters. I have enough problems. I’m hoping to milk 10 more years from this 19-year-old trailer – full-timing, no less. I antied-up and spent the money.
The second question is: Why pure sine inverters? Two reasons. I got spooked by a little utility Xantrex unit I’d had for years. It is modified sine and warns in its manual to never plug anything into it that resembles a device battery charger, or it will damage the charger. That made me think. Was it going to be truly safe for me to operate all of my electronics and chargers on anything less than what they were designed for? I’ve invested thousands of dollars in my office equipment electronics, and some of it is now difficult to replace at any price. The replacement cost of any single component dwarfed the extra cost of the Pure Sine Wave inverters. Again, I antied-up.
The confession
One more thing. A major factor that I left out in aiming toward a multi-system is me. See, whenever I’m doing something I enjoy, time stops existing. I’m into it, in the zone. I forget the time, forget to eat, forget the coffee percolator, forget to turn off the hose filling the freshwater tank, you name it. Not a multitasker, no. Hard to imagine that I’m available, eh, ladies? Your birthday was when? Fortunately, you probably don’t have this issue, so it’s not a factor for normal humans. Because of this, I knew it’d be easy for me to mindlessly burn through one central pack and then have no lights, DVD, water pump or CPAP. All the alarms I’ve seen go off way too late. Separate packs and independent charging seemed like a good idea to protect me from myself, as would an ability to easily patch in power from another pack to run something normally unrelated to it. That’s just me.
If you have any questions or accusations, I’ll reply if I’m within emailing range.
DougB, Strolling Amok
Editors Note: I also am a believer in a modular system.  I have three distinct systems each its own panel, controller and batteries. I think it has three main advantages: 1) Redundancy– if one component fails, I still have power 2) Like Doug said, if I carelessly allow one to run down, I can simply connect my essential components to another system 3) Having too much power gets me through the low-sun months of winter and long periods of clouds.


  1. Openspaceman

    I love the idea of having all that power and I like dealing with Alt E…I got most of my stuff from them, reasonable and quick. My main concern is the wind. Gonna have to keep an eye on the weather. Other than that great idea and you got a nice big awning to boot.
    *Thanks for the post

    • DougB

      Good observation on wind, Openspaceman. I started out unashamedly paranoid about the wind flipping a panel over the roof. Since I wrote this piece, I’ve weathered various storms and rigged tie-downs. The results have actually been very different (and much better) than what I’d expected, so a follow-up piece will be showing up on my blog before too awful long.

  2. Douglas V

    Great idea. Definitely plenty of power most days in AZ. What is the web address for the Alt E?

    • DougB

      Douglas, it’s

  3. Al Christensen

    I always enjoy learning about unique solutions. Problem solving keeps life from getting boring.

    • DougB

      Yes, it does, Al. I enjoy solving problems. My matching trait that offsets it is laziness though, so the solutions can take a while to be implemented!

      • Al Christensen

        I call my laziness “considering alternatives.”

  4. Walt

    Interesting stuff. Solar is one of the things I definitely intend to have on my next rig, whatever it ends up being. So I am always on the lookout for interesting approaches.

  5. DougB

    I think solar is one of those things that can be just as simple or complex as you want to make it. It tends to scare a lot of folks away because the sophisticated approaches are so much more intimidating than connecting a few black and red wires to terminals. I’m glad I installed solar, and never bothered getting any generator type for emergency backup. It just hasn’t been needed.

  6. Russell Lawrence, Phd

    very interesting reading. I am new to RVing and am about to buy a Toyota Motorhome… they only have generally one deep cycle battery.
    I plan to add two solar panels to support the coach,,, lighting, entertainment and such…
    I agree with the AGM selection and giving each battery their own controller feeding the power grid…
    I also know that I need to expand my knowledge of the conversion of sun power to 12 volts and 110v…
    Thanks again for a great article.
    Russ Lawrence

    • DougB

      Thank you, Russell. This blog has plenty of posts on solar energy, deep cycle batteries as well as marine hybrids, and energy efficient gizmos, so you might want to peruse the archives for as much technical and practical info as you can dig up.

    • Bob

      Welcome to a whole new life, I bet you will love it. Those Toyotas are great little rigs, I know several people who have them and love them. If you have any questions about solar, feel free to write and ask me, I love to help.

  7. Bob Durkin

    This is a very, very useful posting, thank you gentlemen. I am bringing Van Home no. 2, a 2003 Ford E350 SuperCargo van, up to speed and on a hunch that multiple independent systems will work for me. My power needs are initially modest at this point: fans, lighting, lots of lighting in a van, 17″ laptop, occasional warm up with mild 12 volt heater. Looking later at more.
    So I bought two Harbor Freight 45 watt systems and have as yet to buy my batteries but this article answered some questions about that.
    So I will have a “front of the van” system and a “back of the van” system. For starters.
    PS, I also just bought two 145 wt panels for $305, that included shipping.
    Thanks again for verifying the independent, modular solar systems approach.

    • Bob

      Bob, wow, that’s a lot of panels! But you won’t regret having too much! In the winter your power output drastically drops and we have had 3 days of clouds and many of us are running short of power. But you’ll have 380 watts which get through you through cloudy days in winter. It may or may not be enough to use an electric heater. You need heat in the winter and in the winter the short days and sun low on the horizon greatly reduce your power. You will just have to try it and see how it works
      That’s a great price on those 145 watt panels!! Be sure you match the voltage of the panels to the voltage of the controller when you get it. Feel free to ask any questions you may have about installing the system.

    • DougB

      Thanks for sharing that, Bob D! An E-350 ought to do it!
      The one good thing about the way the panels are mounted on the Enterprise is that when they face south (or north), they can all be aimed into direct line with the sun’s arc, so winter charge differences are mainly due to shorter days, not panel misalignment. Many folks with rooftop panels rig up adjustable mounts to do the same thing. Mine can easily be made to go overcenter – if you have enough oomph to push them that high!
      Bob D, my personal bias is that that 290W pair of panels ideally shouldn’t power much more than 200Ah of battery, especially if you are likely to pound the pack with anywhere remotely near 50% discharge. The risk is an inability to fully recharge them by the end of each day, which would shorten their lives. Two of my three packs use a measly 100W/100Ah panel/battery relationship, but are typically only discharged to about 75% capacity. In full Arizona sun, the AGM office pack has no problem recharging way early, while the house marine hybrids just make it with 1-2 hours to spare. With a deeper discharge or on a partially cloudy day, the AGM pack slows by an hour or two, and the hybrids never complete. Fortunately, each pack has enough capacity to span several days without any sun, if I trim usage sensibly. Through experimentation, a 150W/100Ah relationship seems best for me all-around: the hybrid pack for obvious reasons, and the office pack because I use the equipment hard both early in the morning and while recharging during the day. Some upcoming changes based on usage will be on the blog.
      By the way, a 27″ iMac makes a great room heater at about 120-150W on AC power. You may find that even a small electric heater demands too much power, over the time period needed. I assume you’re thinking of a truck window defroster? You’ll need to insulate very well, or be prepared to switch to some type of fueled heater should things not work out well enough. Good luck – and enjoy the process!

  8. Brian

    I really appreciate your posts and Guest posts Bob. I have found a lot of other great blogs through yours. I’m currently converting my Dodge van now for living. I have been reading your blog for about six months. All the info here has been very helpful, encouraging, and inspiring. I will be taking a trip out to Quartzsite in mid January, hope to see ya!

    • Bob

      Brian, if you are here in january try to make it to the RTR (Rubber Tramp Rendezvous). You can meet MANY of us there! Let me know if there is anything I can do to help you in your build!

  9. openspaceman

    I didn’t think I could find a dude with more solar than you…but check out this guys rig. You guys would have fun comparing notes.

    • DougB

      Wow! That photo of the roof is stunning! Nothing but acres of panels! You know, my electrical needs would be much more ordinary if I didn’t insist on having a full, working office/studio. Still, some of the rigs around me here in a LTVA are in my ballpark.
      And by the way, you will find some early answers to your side panel wind concerns (and additional photos) in the longer version of this article on the Strolling Amok website. Bob had to abridge it for CheapRvLiving because, well, nobody wants to saw their way through the “War and Peace” of solar trivia on a real blog! I’m impressed by his ability (and patience) to trim off the unessentials.

      • Openspaceman

        Not to mention the interior…awesome. Next time I see an old moving van I’ll wonder if there’s a log cabin hidden inside it.
        *I’ll be sure an’ checkout your full report on your solar build…I’m not a technical guy…but I’m glad now that I built mine myself it’s the best way to understand it. Thanks.

  10. Dee White

    Wow! That is really ingenious! (I presume you mean ingenious and not ingenuous). Gives a whole new set of ideas getting a solar installation on our motorhome. Thanks for the information and helping me think outside the box!

    • Bob

      Dee, I’m surprised you are the only one who caught that dumb mistake!! My spell-checker doesn’t have ingenious and I din’t notice it had the wrong word. I very nearly did it again just now. Yes, it is honestly ingenious! Glad to pass along my readers creative answers to common problems.

    • Bob

      Bogdan, I’m interested in what you are saying but don’t have time to do homework. Can you summarize what you mean.

  11. Nishan

    I always enjoy learning about unique solutions. Interesting indeed.
    Also, I like the idea of wind as well

  12. ELTEC

    Does solar really save you money?

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