If you missed yesterday’s installment, part one, read it here before continuing.
By Dave Solberg
Deciding how many solar panels you need and how big you need them to be depends on a lot of variables. We covered some of those variables in yesterday’s segment, but here are a few more:
One other variable is your battery condition and an issue called sulfation, which is more prevalent in lead-acid and some in AGM batteries. As you drain power from your battery, sulfur collects on the plates. If you do not have a multistage charger or some type of battery conditioning system, your batteries will not be able to store a charge as designed. You can have the best solar panel system for your rig, but if your batteries are compromised, you will not be happy. Check to see if your house charging system has a multistage charger or battery conditioning mode such as the Charge Wizard from Progressive Dynamics, or if your solar panel has a multi-stage controller. Otherwise, it is a good idea to get some type of conditioner such as BatteryMINDer or the Charge Wizard.
One of the most popular questions I get in my boondocking seminars is, “How many batteries do I need?” This is a difficult question to answer as it depends on the amp draw calculation we discussed earlier according to usage. Batteries are rated in “group” sizes such as 24, 27, 31, etc. These are rated as to the amp hours available and the lowest group 24 has 80-100 amp hours and they go up from there. As we stated earlier, the lead-acid and AGM batteries can only be drawn down to 50 percent. We will cover batteries in a future article.
Rooftop vs. portable solar panels
For years, solar panels have been very large and very heavy so it made sense to mount them permanently on the roof rather than trying to find a place to store them and haul them in and out every day. Modern technology has provided lightweight versions of both, and portables have become a popular option. They are lightweight and fold into a convenient carrying case that can be stored easily. The advantage of the portable unit is you can park your rig under the shade and cool the interior down by more than 30%. This makes sense since you are probably dry camping and don’t want to run the generator to run the roof AC!
However, if you are under the shade of the tree, you don’t have much line of sight to the sun and therefore not getting much use out of your panels. With a portable system, you can park in the shade and put the panels out in the sun and get the best of both worlds.
You can aim the portable solar panel at the sun
Another advantage of the portable is the ability to place it at a direct angle to the sun. For example, in the morning, the sun rises in the east and rooftop panels may not get charging ability until the sun rises to a certain angle to the panel. Same with the evening when the panels are facing west. This could mean you only get a few hours for optimum exposure. However, with a portable panel you can place the unit facing east and move it west to get more charge time.
Some roof mount enthusiasts state they like to charge the batteries while driving down the road, but most RVs have a battery isolation manager solenoid (BIM) that provides a charge from the engine alternator to the house batteries while driving. Trailers with a 7-pin connection also provide a charge from the tow vehicle alternator.
One of the disadvantages of a portable unit is if you need a large charging solar system like 570 watts, you need several portable panels strung across the yard, and need to find a space to store them, and the task of setting them up and taking them down.
For the past several years, most RV manufacturers have been prewiring their coaches for solar applications. Roof-mounted panels typically have the correct gauge wire embedded in the ceiling and a sticker on the roof as a locator. Some are even mounting a plug that you can attach three panels to. This makes it easy to roof mount as you just need to attach the legs to the panel, apply a little butyl tape under the legs, and screw the feet to the roof. Make sure you verify what power cords and cables might be close to the area you are placing the panel. If your unit is not prewired, you will need to find a way to route the correct gauge wire through the roof and to the house batteries with a charge controller in-line.
We installed a panel on a 2003 Winnebago Brave and ran the wire under the refrigerator vent cover and back behind the refrigerator. Notice we took the “batwing” antenna off as they had previously installed a King Controls permanent mount model. We then applied a generous amount of self-leveling sealant, NuFlex 311RV, recommended by Winnebago for fiberglass material. Check with your manufacturer for the recommended sealant for other materials such as EPDM, TPO, and Alpha roof material.
The converter was located in the cabinet next to the refrigerator so we were able to mount the charge controller underneath and connect it to the battery cables on the converter. That way we did not have to find a path to the house batteries, which were located in a compartment behind the steps. On a travel trailer or 5th wheel, the house batteries are typically up front on the tongue or inside the front compartment, so finding a path from the roof to these is a challenge. That’s why it’s easier in most cases to use a portable and install the port up front.
Do I even need solar panels?
I get this question quite often at shows and rallies. The basic question you need to ask yourself is how often and how long will you be camping without being able to plug in? If it’s just overnight for a few times a year, the house batteries will be able to provide enough power to withstand that… if they are conditioned as we discussed earlier. In this situation, the investment in a solar system is a waste of money.
The need for a solar system is directly related to the amount of time you will be away from charging power either from a campground or shoreline source or generator power.
One other variable to consider is that more campgrounds are charging for electrical usage with a meter, so more RVers are using propane and inverters to power the TV and even the refrigerator. That means draining power from your house battery, which can be charged by free solar power. However, nothing is “free” as there is an initial investment in the solar system.