Bryan Appleby, aka the Xtreme Boondocker, reveals hard-earned lessons on RV solar panel systems, debunks battery and solar myths, and offers some battery bank best practices.
There was that sound again; “Knock. Knock..” on my truck camper door. Getting up from my dinette, I see two men smiling up at me, one with a note pad and pen. This is something I have experienced often, since installing the solar panel systems on my rig.
Upon seeing my rig, people frequently approach me and ask lots of questions about solar systems and battery banks. What these folks don’t realize is that many RVers don’t need a solar panel system and would be better advised to upgrade their battery banks. I often start my conversations with this point, as I will cover here.
The question most folks ask is, “Is a solar panel system a cost effective option for truck camping?” In other words, are the gains from solar panel systems worth the cost, and required holes in your truck camper roof?
In my experience, the answer in most cases is no. All too often, truck camper owners have not realized the full potential of their existing battery banks. They overlook the simple upgrade of bigger and better batteries, and aren’t properly charging, monitoring, and maintaining the battery bank they currently have.
With this article my objective is to help you answer the question, “Is solar the best option for the way I use my truck camper? Or, should I just upgrade my battery bank?” Let’s begin by dispelling some common solar myths that I hear during my travels.
Myth #1: RV Solar Panels Provide Their Rated Power
Logic dictates that a 100-watt solar panel would provide 1,000 watts of power over the course of a 10 hour day of sunlight, right? Unfortunately, this is not the case. Most solar panels only deliver about 60%, or less, of their advertised wattage on a daily basis.
Here are the most common reasons why this happens:
1. Changing Seasons: The angle of the sun, and thus the solar charge potential, changes throughout the year. For example, the peak summer sun offers more solar power potential than the depth of winter sun.
2. Daylight Hours: The length of daylight also changes throughout the year. For example, there are more daylight hours in the summer than in the winter. In the summer you’ll not only enjoy stronger sunlight, but longer exposure to that sunlight.
3: Shade: Potential solar power is lost to cloud shade, tree shade, building shade, and physical obstruction shade from roof installed features (like air conditioners) that block sunlight from reaching the solar panels. It’s amazing how many solar panel systems are blocked by objects on the RV roof itself.
4. Cable Length and Quality: Potential solar power is lost to resistance from the length, size, and quality of cable used for the solar panel system and battery.
5. Solar System Quality and Type: The quality and type of solar panels and solar controller also affect the ability of the system to charge your camper batteries.
6. Battery Bank Quality and Type: Finally, solar power can be lost from the age, size, and overall condition of the camper battery bank. More on this later.
Myth #2: More Solar Panels Are Better
Above: The solar panel set-up and battery bank on Bryan’s truck camper rig – click to enlarge
Upon seeing my set-up, some folks want to jump to the conclusion that more solar panels means more solar power. While technically true, solar power is worthless without a corresponding battery bank that can take full advantage of the power that the panel system can generate.
The size and capacity of your battery bank should compliment the size and charge potential of your installed solar panel system. The rule of thumb for a battery bank is 100 to 150 watts of solar panels for every 100 Amp-Hours of battery reserve.
Most truck campers have limited space for safe battery storage. This limitation will likely determine the size of your solar panel system. Anything more than your battery bank can handle will likely be wasted and/or diverted.
For example, a camper with two Group 27 or Group 31 batteries will produce between 100 and 240 AmpH battery reserve. Of that reserve, approximately 50-55% is available to use before the batteries will need to be recharged to maintain their full battery health. To compliment this capacity, 200-watts of solar is needed to satisfy a typical 20-40 Amp-Hour daily need. Under ideal sunlight conditions (no sunlight obstructions) anything more than 200-watts of solar would be unnecessary, under the right conditions. More on that later.
Myth #3: The Factory Installed 95-Watt Panel is Enough
A single 95 watt solar panel (shown above), or less, serves mainly as a maintenance power supply since it will not generate enough solar power to replenish a battery bank for typical daily use.
Imagine your battery bank like a bathtub filled with water, with the drain partially opened. If you have more amps/water going out the drain than water coming in, you will not be able to keep your bathtub filled up above the 50 to 55% requirement. To replenish what you use, you conceivably need more solar.
Myth #4: All Anyone Needs is 200-Watts of Solar
The amount of solar that works for one truck camper owner may not be the amount of solar that will work for you. To determine how much solar power you will need, you need to survey the amount of power, measured in Amp Hours, you use while truck camping.
I used a combination of published Amp-Hour totals for common RV items – including the RV furnace and RV refrigerator – and through the use of a Kill-A-Watt Meter. A Kill-A-Watt meter is an electricity usage meter that can determine the power draw of any 110-volt appliance or product.
Above: A Kill-A-Watt meter allows you to determine the voltage and current draw of 110 Volt electronics and appliances. When a 110 Volt device is plugged into to Kill-A-Watt, its display will show the energy used in voltage and current. This information is bound to give you a few surprises!
The following power use chart (click to enlarge) shows the power use in my truck camper rig. I strongly recommend conducting your own power use survey prior to designing a solar power system for your truck camper.
I do not recommend estimating this data. Finding the actual power usage often comes as a surprise. You can also conduct a home power use survey and find out exactly how much power turning off every light saves.
Above: The completed power survey – click to enlarge
With a completed power survey, you have a great start in determining whether you need a solar panel system, or should just upgrade your battery bank and power use habits.
Myth #5: RV Solar Panels and Components Last Forever
Above: The Morningstar TriStar MPPT 45a charge controller
Like a floodgate, a charge controller will divert excess power from the solar panels to prevent over charging. This will help to maintain the health and longevity of your battery bank. A charge controller will also provide temperature compensation during different charging seasons.
Above: The Morningstar TriStar TS-RM digital remote meter. This three function controller displays information about your solar harvesting and the charging of your battery bank.
Solar panels, cable insulation, charge controllers, battery monitors, and batteries all have an expiration date. Just like anything that generates power, including hydroelectric dams and nuclear power reactors, solar panel systems and their components have a limited number of charge and discharge cycles. From the minute you start using solar panels and batteries, they begin to slowly degrade over time.
What determines the life of a solar panel system is how much you use them. For a heavy user, like myself, I should get five years out of my batteries, ten years out of my cables and charge controllers, and twenty-five years out of my solar panels.
Battery Bank Best Practices
Batteries allow truck campers to cut the 110-volt shore power cord, and explore territory well beyond campgrounds and driveways. The quality, quantity, and capacity of your battery bank will determine just how far and for how long your cordless adventures can go.
In many cases, improving your battery bank is a more efficient approach to extending your truck camping capabilities than adding a solar panel system. The trick is to know what your power needs are, and how to get the most from your battery bank. This last point is often not as intuitive or easy as you might think.
During my first two years of full-time truck camping, I went through two pairs of Group 27 wet cell batteries and one pair of Group 27 AGM batteries. This happened because I was fully discharging my batteries many times, and spending weeks in below freezing temperatures, while boondocking off-the-grid. Eventually, a mistreated battery will no longer hold a charge and needs to be replaced. As you might imagine, these were very expensive and frustrating battery lessons to learn.
After plenty of trial and error, and lots of feedback from expert sources, I learned how to properly charge the batteries, maintain the batteries, and monitor the state of charge for the batteries. Here’s my best advice on these topics:
Above: A battery acid hydrometer. This testing instrument is used to measure the relative density of the sulfuric acid solution in a flooded wet cell battery and provides the approximate state of charge by the density.
1. Start with a healthy set of batteries. Make sure your batteries are healthy by measuring their strength with a battery tester. Age, temperature, and use cycles wear down batteries leaving them with less and less capacity over time. Make it a habit to routinely test your batteries. Obviously, properly maintained and healthy batteries will yield significantly more Amp-Hours than abused unhealthy batteries.
2. Maximize Your Battery Size. Most truck campers come with Group 24 or Group 27 batteries. If you can fit larger batteries, such as Group 31 batteries, you will greatly improve the amount of Amp-Hours available. Even going from Group 24 to Group 27 batteries will make an important difference. Ideally, your camper would have 200+ Amp-Hours of deep cycle battery reserve, or better. If you have the space, go for Group 31 batteries.
Above: Two Lifeline Group 31 AGM (Absorbent Glass Matt) batteries
3. Consider Upgrading to AGM Batteries. Maintenance free and spill-proof AGM (Absorbent Glass Matt) batteries offer longer service life, more tolerance for heat, cold, and vibration, and overall better reliability. Of course they also cost considerably more. When making this decision, make sure to read up on the specific pros and cons of AGM versus traditional wet cell batteries. AGMs are not for everyone, but I have been impressed with their performance and recommend them highly.
4. Improve Your Battery Compartment Insulation. Batteries do not last as long or perform as well when they’re cold. If there’s an opportunity to improve the insulation of the battery compartment and battery compartment door on your truck camper, it’s worth considering. This could be as simple as putting closed cell foam insulation on the compartment door and sides of the battery compartment. Please insure proper venting is maintained, while using wet cell batteries.
Above: A TriMetric battery monitor can be mounted in a location away from your solar battery bank. A TriMetric battery monitor will tell you how charged your battery bank is by percentage, full and discharged, as well as information in Amps, Watts, Volts. It will also provide audible alarms for low battery levels. This is a must item for those learning how to keep tabs on their battery and state of charge.
Above: Many will want to just have a digital reader in a simple form like this digital battery tester. This, too, will provide you the health of your battery bank status.
Above: A digital clamp meter tester, like the Milwaukee Clamp Meter 2237-20 shown above, works well, but can be pricey. A digital clamp meter provides the ability to clamp around a cable and read the current traveling through that cable in Voltage and type (AC/DC) and frequency. It’s all done without direct contact of the core of the cable. The result is viewed on the display.
Above: One of the easiest devices to acquire and use to quickly check the state of charge of your battery bank is a battery load tester (shown above). While not the most accurate, a battery load tester will show the health and status of your battery bank.
5. Use a Battery Monitor. A battery monitor like the TriMetric 2025RV or a simple multi-meter is a good way to keep track of your battery bank state of charge. For example, when your battery bank is reading 12.2 volts (at resting rate) or lower on your meter, it’s time to charge your battery backup as soon as possible. A simple check in the morning and before going to bed provides reassurance that your batteries are operating well.
6. Completely Charge Your Batteries. One common cause of battery issues is leaving a battery bank at a low state of charge (less than 12.2 volts at resting rate) for any period of time. It’s just as important to fully charge a battery bank when recharging. This means recharging to 90-100%. For many truck camper owners, this may be as simple as leaving home with a charged battery bank, and plugging back in when they return.
Recharging can also be accomplished by connecting to shore power, running a built-in or portable generator, or driving your truck. A few hours of driving is often all that’s needed to completely recharge a battery bank from the previous day’s power usage.
Many of us have attempted to charge our batteries for hours on end after a discharge. For example, after a cold night or running the furnace, perhaps you’ve run your generator for hours to top off your depleted batteries.
It’s actually more efficient and more effective to charge a battery for 1.5 hours, allow the battery to rest for 1.5 hours, and then charge them again for 1.5 hours. This approach reduces the surface charge of a battery during the rest time, and is a significantly more efficient use of your battery charger.
Surface charge occurs when the surface of the lead plates inside the battery become fully charged, slowing the rate of charge deeper into the battery plates. By allowing the batteries to rest for 1.5 hours, the surface charge is slightly discharged allowing for deeper plate charging.
If you’re using a built-in or portable generator to recharge your batteries, this charge-rest-charge approach will also improve efficiency, and reduce generator fuel waste, and wear. Plus, your nearby friends and campground neighbors will appreciate the breaks from generator noise.
The Big Decision: RV Solar Panel System, or Battery Bank Upgrade?
So what happened to the folks that came to talk to me in Death Valley? Like many of the truck camper owners I encounter, they were not using their campers often enough to warrant an expensive solar panel system. What they needed, at least initially, was an upgraded battery bank with better and larger batteries and more Amp-Hours.
A solar panel system might be in their future, but the campgrounds they frequent feature thick tree cover, and frequent overcast weather. For now, the improved battery bank, and better battery bank care and maintenance practices would give them what they really needed; more Amp-Hours.
Take Away Points
Often the best improvement to be made is to upgrade and maximize the size and quality of battery your truck camper battery compartment can accommodate.
For example, if you can go to a set of Group 31 AGM batteries, that will make a significant improvement to your available Amp-Hours and may be all that you need. Even with an AGM battery you can change the orientation of the battery in the supplied battery compartment. No solar panel system necessary.
Additionally, it’s absolutely critical to accurately monitor your battery bank. Never let your batteries get below 12.2 volts, and charge them completely when you recharge them. There’s no sense in improving your batteries if you’re not going to care for them properly. Besides, as I found out the hard way, they can be very expensive.