Sunshine on my shoulders makes me happy! Okay, I’ll leave the song references to Mike Sokol, but sunshine can make your house batteries happy and happy batteries mean a happy camper. What I’m talking about is using the power of the sun to charge and condition your batteries using solar panels.
Price vs. quality
There are three types of cells available for manufacturers. Monocrystalline cells are the most durable and most efficient; however, they are the most expensive. Many discount tool stores and home improvement stores sell inexpensive solar panels that typically will not hold up to the abuse they encounter in the RV world. For the past five years, I have worked exclusively with Zamp Solar (now owned by Dometic) and Go Power! and have had great success. All the products we have installed are still working as designed. They are easy to install, use high-quality materials, and if a cell does get compromised, it doesn’t shut down the whole panel. There are some other good products out in the market, so enough of the commercial!
Here is how a solar panel works:
The solar panel catches the sun’s rays and converts them to DC charging power, similar to a filling station providing fuel. This fuel travels through a solar controller that monitors the amount of fuel in the battery and will shut off when the batteries are charged properly. A controller is important as a consistent charge to the batteries can overcharge or “boil” them and cause damage. This is a similar procedure the shoreline cord provides when plugged into a campground source as it travels through the converter and charges the batteries. If you want to get more technical into how the photons knock the electrons from the atoms and allow the flow of energy, click here.
The basics are this: Your house batteries simply store energy known as amp-hours, which run 12-volt DC components such as interior lights, roof vent fans, water pumps, and any LP devices such as refrigerators, stovetops, water heaters, and furnaces. As your battery is drained of amp hours, you will need to replenish them with either shoreline power or generator through the converter/charger or with a solar panel system. If you are boondocking or dry camping, you will need to either run a generator for long periods of time, or have a solar panel system.
What will my solar panels run?
Technically nothing! The solar panels only provide a charge to the batteries. The house batteries provide 12-volt deep cycle power for the components in your rig.
What size and how many panels do I need?
Solar panel technology has changed dramatically. The newer panels are lighter, smaller, more powerful, and more affordable. There are several sizes to choose from depending on your needs from small backpack-sized ones to larger 190-watt panels that can be combined to provide 570 watts of charging power!
To determine the size of panels and how many are needed for your rig you have to determine your amp draw needs. First, you need to identify the components that run on DC and how long you will use them in a day. Here is a chart with some common components and amp draws:
12-Volt amp draw:
- Incandescent Lights: 1.5 amps
- Halogen Lights: 1 amp
- LED Lights: 0.12 amp
- Smoke Alarm: 1 amp
- CO Detector: 1 amp
- LP Leak Detector: 1 amp
- Furnace: 10-12 amps
- Water Pump: 5 amps
- Refrigerator on LP Mode: 2-3 amps
- Stovetop: 1 amp
- Roof Vent: 3 amps
Note: If you have a residential refrigerator and run it through an inverter, this will deplete your batteries quickly!
What’s the calculation?
The next step is to multiply your total daily hours by the number of days you are going to be out and compare that to the amp hours your battery or batteries can provide.
The challenge most of us will have is trying to figure out how much and how long we are actually going to be using these items. It will change with the ambient temperature, how many people we take on a trip, and other factors. Go Power! has a very sophisticated calculator that you can download here.
Another good place to start is this simple chart provided by Zamp Solar:
How many panels and how big?
So, back to the question: How many panels do I need and how big/wattage? One group 24 deep cycle battery is rated at approximately 80-100 amp hours; however, you can only drain a lead-acid battery and AGM down to about 50 percent, so that means 40-50 amp-hours. A typical RVer could draw 1/3 usable amp-hours per day or more. A 100-watt solar panel can generate 5.5 amps per hour in full exposure, which means it could keep up in this situation if you get a full 6 hours of exposure. By the way, this comes from Dakota at Zamp Solar, who answers the phone every time I call and knows the product as good or better than the others I’ve talked to. I would highly recommend talking with him if you have questions!
But there are several other variables to consider, too, such as weather, temperature, and battery condition. Severe weather means RV owners are inside the rig more often and using components that draw more battery power. Plus, this generally means less exposure to the sun. Extreme high temperatures mean appliances such as the refrigerator run more often, and vent fans are running, which means more 12-volt power draw as well as the furnace in low temperatures. “Typical” usage in an RV is hard to calculate! Keep in mind, you can start with one or two panels and if that is not keeping up a charge, you can easily add more.