RV Solar Electric Power
Read This First: Disclaimer: I’ve written what I personally did, and my opinions. Don’t assume what I did was safe, and don’t assume it will work for you. Do more research, and make your own choices. I am not responsible for your outcomes!
A solar electric charging system is really not as complex as it may seem. There are only 2 primary components; the solar panels, and the charge controller. Other items needed to finish an installation include wire and cable, a fuse holder, and mounting hardware for the panels.
This can all be purchased in a kit, or assembled from individual components. Buying in kit form is convenient, and if you shop carefully it may be economical too. Be aware that prices vary greatly. The typical RV parts catalog may list systems for as much as double the price of solar specialty stores. Camping World is also over priced. I’ll give you a couple of recommended sites at the end.
Solar panels have largely become a commodity — that is to say, it really doesn’t matter if you buy Shell, BP, Kyocera, Sharp, etc. As long as you buy a reputable name brand, and get new panels (manufactured in the last 12 months) then you can compare them based on “$ per Watt”. Generally speaking, larger panels are more economical. So if you need 500 Watts of power it’s more economical to buy four 125 Watt panels than to buy five 100 Watt panels.
One note, be aware that some panels have a higher output voltage than others. A “12v” panel is probably putting out around 17 volts, but some brands/models may put out 17.6 (for example), so don’t mix them if possible. Also the higher voltage is better, all else being equal, because it will make greater use of the capabilities of your MPPT charge controller. What’s that? Read on.
Solar Charge Controllers All controllers are NOT created equal! For a serious system, you’re going to want a modern charge controller with features that optimize the system performance. There are several good brands on the market. On our first RV we had a BlueSky Solar Boost 2000e. For our new solar system we selected a Blue Sky Solar Boost 3024 which has a larger capacity. Both are electronic MPPT (Maximum Power Point Tracking) controllers. Another good brand to consider is Outback.
To avoid getting too technical, MPPT controllers are “smart”. They read battery voltage, read solar panel output, and adjust voltage and current flow to the optimum at this moment. Every few seconds it takes another measurement and makes adjustment so that you get the maximum benefit from your panels. They also have a battery temperature probe, and will adjust voltage output based on the battery temperature charging curve.
For your first solar install, it’s a good idea to get a controller with extra capacity. That way if you decide you need to add another panel or two later on you don’t have to also replace the controller.
Be sure the panels are solidly mounted on the roof. If you have a rubber roof over thin plywood (as we did on our old Southwind) you may want to use molly fasteners to get a better grip. Our National Islander has a more substantial plywood and fiberglass roof and I just used #10 x 3/4 stainless pan head screws.
How about tilt brackets? Some people mount all the panels permanently flat. This works fine in summer when the sun passes directly overhead; however, in winter you’ll gain some power if you’re able to tilt your panels to face the sun while you’re parked. Tilt mounts should be installed so panels can all be tilted the same direction. In the winter, you’ll position your coach where all the panels can be tilted South.
I’ve also seem RVers with one or more loose panels that they move around and point at the sun during the day. This is one solution to the problem of having to park in the sun, they’ll run 50′ of heavy wire, park in the shade, and put the panels in the sun. But watch out for thieves!
Two Tips you’ll thank me for
1. Wire size is often overlooked. Many factory “solar prep” jobs use inadequate wire as do some “professional” installations. It makes no sense to put $2,000 worth of panels on your roof and then lose 10% of their capacity because you used wire that was too small. Here’s a link to a wire size guide, and if you scroll to the bottom they have a voltage drop calculator. The target is under 3%, and I recommend using the largest size wire that can easily be run. In our first system with 440 Watts of solar panels we used #6 AWG. That was adequate, but on our new system I ran #4 welding cable.
2. Solar charge controller setup. You need to ensure that your batteries actually receive high enough voltage to charge them fully. The charge controller may be putting out 14.6 volts, but after voltage loss in the wires the batteries may only be seeing 14.3 volts. So you need to measure the voltage at the batteries with a good digital volt meter. I recommend measuring and adjusting shortly after the bulk charge phase is complete. At this point voltage is held constant while the batteries finish charging. Many charge controllers also have a temperature probe that monitors battery temperature and adjusts voltage accordingly. These are good to have and usually an inexpensive option. Controllers like my Blue Sky SB3024 have a separate control/monitor panel so the actual controller can be placed close to the batteries and monitored remotely. The closer the controller is to the batteries the more accurately it can monitor the charging voltage.
Here are some links to learn more about Solar Power:
Our Solar System – Blog entries from our solar panel installation
Solar Power, Inverters, Chargers, etc. – Scroll down for Solar, Mark Nemeth gives some great information
Phred’s Poop Sheet on Solar – All of Phred’s “Poop Sheets” are a Must Read for serious RVers
Optimum Panel Tilt Angle – All the technical details on panel tilting
http://www.jackdanmayer.com/rv_electrical_and_solar.htm Jack Mayer, a fellow SKP, has some excellent information on his web site. He also installs solar electric systems. So if you’d rather not do-it-yourself you might want to contact Jack and see if your paths will cross anytime soon.
Sources for solar equipment
www.rvsolarelectric.com RV Solar Electric. I purchased my first kit from them and several other items.
http://www.solar-electric.com/ Northern Arizona Wind & Sun. I’ve purchased solar panels, fluorescent lighting, and other components from them.
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