Building a Low-Cost RV Solar Power System

If you’re thinking about going solar, you need to stop thinking about it and do it. Solar is easy to install, is practically maintenance free, and doesn’t take up valuable storage space inside your RV. Perhaps more importantly, solar doesn’t require fuel like a generator, is clean and quiet, and utilizes a free and renewable source of energy that is good for the environment. Many RV’ers like the idea of going solar, but don’t know where to begin or where to go to buy what they need. That’s where this article comes in. I’ll explain to you not only what you need, but also how to buy it at a fraction of the cost of what the RV solar power companies charge for their ready-made solar power kits.

Fortunately, an RV solar power system isn’t that complex. A solar power system consists of one or more solar panels to generate a charging current, a charge controller to regulate that charging current, and one or more deep cycle batteries to store that current. It also consists of ancillary components such as a roof top combiner box for connecting multiple solar panels to the system, mounting brackets for attaching the solar panels to the roof, wiring to connect everything together, and fuses to protect your system from shorts and power spikes.

First, don’t buy ready made kits from the big RV solar power stores. Sure, they include everything you need, but they’re also ridiculously expensive (the lone exception being Renogy Solar’s Solar Power 100 watt Starter Kit available on Amazon.com. It includes everything you need to go solar for only $164.99). Buy your components piecemeal via the Internet or locally. Shop around and look for the best bargains. Buy your solar panels from established, well-known manufacturers like Kyocera, Solarworld, and Grape Solar, and avoid Chinese-made junk. It doesn’t matter if you buy Monocrystalline or Polycrystalline solar panels. A 120 watt polycrystalline solar panel generates the same output as a 120 watt monocrystalline panel. In order to have an effective system that will keep your RV’s batteries charged, I recommend a minimum of at least 100 watts of solar panel, though more is better. I like to follow the general rule of 100 watts of solar panel for each battery in your RV.

The type of charge controller you decide on will determine what voltage of solar panel to buy (if you’re still undecided, check out my Solar Power 101 article on the pros and cons of each). If you decide on the cheaper pulse width modulation (PWM) controller, then you’ll need to buy 12 volt panels for your system. However, if you elect to go with the more expensive maximum power point tracking (MPPT) controller, you’ll have much greater latitude on the voltage of panels to buy. This gives you the option of buying 12 volt panels, 24 volt panels, and 36 volt panels to run on your RV’s 12 volt system. The great thing about going this route is that higher voltage panels are generally cheaper than 12 volt panels. Just make sure you buy the same voltage panels for your system or it won’t work properly.

Having a healthy bank of 12 volt (or 6 volt) batteries is vital to the performance of your RV’s solar power system. Technically, they aren’t part of the solar power system, but without them, you can’t capture the electrical energy being created by your solar panels. Buy only deep cycle batteries for your RV (these are rated in amp hours). Avoid hybrid marine batteries that are rated in cold cranking amps (CCA) as these are not true deep cycle batteries and won’t hold up as well over time. As for the kind of batteries you buy for your RV, Wet Cells and absorbed glass mat (AGM) batteries work best. Wet cell batteries are cheaper in cost, but require watering to keep them operating in peak operating condition. For this reason, I recommend AGM batteries. They require no watering, can be mounted on their side, and charge faster than wet cell batteries.

Where should you go to buy RV batteries? Costco and Sam’s Club have the best prices for Wet cell batteries. Both chains buy in large volume and are able to pass those savings on to the consumer. The last time I looked both chains were selling their 6 volt batteries for around $70 a piece with a core return. As for AGMs, yes they’re more expensive, but as time goes on they’re becoming less so. You can now find an AGM Group 24 battery for as low as $130.00. Good makes for AGM batteries include Deka, Duracell, Trojan, Universal, MK, and Lifeline. Shop for the best deals. The Internet can be a great source, but don’t forget about local dealers. Going this route may also save you in shipping.

When buying wire for your solar power system, make sure you purchase 10/2 gauge and 8/2 gauge wire (the first number identifies the gauge of wire while the “2” identifies the number of conductors or wires within the sheath, one for positive and the other negative). Make sure the 10/2 gauge wire is UV resistant since this wire will be used on the roof. For inside your RV, go with 8/2 wire gauge, though for very short runs of 4 feet or less 10/2 gauge is perfectly acceptable, too. Again, it pays to shop around when buying wire. You can often score pretty good deals on Craigslist, Amazon.com, and from both local and online solar power stores. However, finding a cheap rooftop combiner box can be a little more difficult. You can save if you make your own or you can go the easy route and buy a ready-made combiner box like the one AM Solar offers. Yes, they can be a little spendy, but they’re well made and don’t require any modifications. Finding 30 amp breakers or in-line fuses is much easier and can be found at any local auto parts store.

As for the mounting brackets for the solar panels, there are two basic styles you can buy, fixed mount and tilt mount. At about $8 for a set of four, the fixed mount brackets are cheaper, but they also don’t allow any tilting for cleaning and maximizing the angle to the sun. On the other hand, the tiling mounts are much more expensive, but they also allow you to tilt the panels when needed. The choice is yours. If you’re planning on doing a lot of winter boondocking, then buying tilting mounts is probably the better way to go in order to capture the lower angle of the winter sun. As for where to buy them, it’s best to deal directly with RV solar power stores, since they cater directly to this market.

Lastly, you’ll need a strip of very high bond (VHB) tape to bond the mounting brackets to the roof of your RV and a tube of Dicor lap sealant to water proof the mounting brackets after they’re screwed into the roof. You can purchase the Dicor at any RV supply store, but the VHB tape can be a little more difficult to find. Again, I prefer to buy my tape at RV solar power stores as this is the stuff that will bond better and last longer than your typical, run of the mill tape.

So to recap, here’s what you’ll need:

1. One or more Solar Panel(s) (a minimum of 100 watts)
2. One Charge Controller (either MPPT or PWM)
3. Two Wet Cell or AGM Batteries (two 6 volt or two 12 volt)
4. Wiring, 10/2 and 8/2 (length depends on your application)
5. One Roof Top Combiner Box (needed for multiple solar panels)
6. Two 12 volt, 30 amp auto reset circuit breakers or two in-line fuses
7. Solar Panel Mounting Brackets (four per panel)
8. Installation Supplies (Dicor Lap Sealant, mounting screws with large threads, and Very High Bond (VHB) Tape)

Good luck! And if you have any questions, don’t hesitate to ask.