Ingenuous Modular Solar Power System
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: http://strollingamok.wordpress.com/
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.
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.
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
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.
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.)
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.
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.
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.
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.
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.