Solar, Wind, And SOFC? Oh, My!

May 1, 2023

An update on the ever-evolving world of renewable energy for RVers.

By Chris Dougherty, F263059
May 2023

I suspect many of my fellow FMCA members remember the days when all the off-grid power sources for RVs came in Onan green. Time, as they say, marches on. In today’s technological world, we have many more choices, and they’ve given us the ability to stay off the grid as long as we want, with most, if not all, of the comforts of home . . . and office.

Renewable energy systems can help RVers to enjoy camping in remote locations, such as Sandy Neck Beach in Massachusetts.

Even before the COVID-19 pandemic, more and more people were taking to the road in RVs, not just to recreate or retire but to work, live, and raise a family. Of course, this trend shifted into high gear during the pandemic and continues to this day. Such a lifestyle for younger working folks was unusual not long ago. From 1998 to 2008, this author, in his 20s and 30s, lived and worked full-time in RVs in upstate New York. I modified two Monaco motorhomes for better winter use between trips to Florida. Back then, solar power for RVs was in its infancy, and flooded lead-acid batteries were even more predominant. If you needed to work with a computer or have any amount of power for long-term use, an auxiliary generator was the only reliable off-grid option.

Fast forward to 2023, and the playing field has changed dramatically. Even the smallest RVs come well equipped to support RVers’ power needs. In addition, these technologies have become more affordable and efficient, and new technology coming online promises to make our lives on wheels even better.

RV Electrical System Foundation

When adding or upgrading a renewable energy system for an RV, it’s always best to start with the foundation. The battery bank is your storage medium — your tank. It must be able to handle your needs over time and with a reserve.

Many newer RVs come from the factory with a solar power system or at least a prep kit. Some also have built-in inverters, inverter/chargers, and lithium batteries.

Lithium iron phosphate — or LiFePO₄ — batteries have been a game changer for off-grid power. LiFePO₄ battery systems are lighter, require less maintenance, have more available energy, and have a much longer lifespan than legacy batteries. In larger configurations, LiFePO₄ battery systems can even power RV air conditioners for a short time. While the initial investment is quite a bit more than other types of batteries, over a LiFePO₄ pack’s lifetime, the cost will be lower compared to replacing several sets of flooded lead-acid, gel, or AGM batteries during a similar period. The biggest downside to the LiFePO₄ technology for some RVers is cold-weather charging restrictions.

Solar and inverter systems now can be controlled via panels inside the RV and apps on smartphones and other mobile devices.

Besides your batteries, wiring is the other piece of the puzzle that can be a challenge. There are many grades and sizes of cable, and people sometimes opt to go cheap here. Copper is expensive, as is the labor to install it. I always recommend upsizing the wiring, when possible, to allow for future expansion, especially where longer runs of direct-current (DC) power cable are concerned. If you increase the size of the solar system in the future, having appropriate wiring already in place can save money in the long run.

The other part of the system that requires consideration is the inverter or inverter/charger and how it will be wired into the RV’s electrical system. Many models and sizes are available, with various programming and system access options. Permanently installed models often utilize a transfer switch to select alternating-current (AC) power sources automatically. Some feature charge control of multiple DC power sources, such as solar and wind power.

Photovoltaic (PV) Charging

Solar, or photovoltaic, is unquestionably the most popular renewable charging method used in RVs today, and for good reasons. Solar product offerings are numerous, with varying sizes of solar panels, in traditional aluminum frames and glass, as well as glue-down flat panels. Charging systems for solar have grown in size and complexity, with the ability to monitor and control output from central touch panels or smart devices. And, as with the inverter and lithium systems, charge controllers can be connected to the internet, when available, for monitoring and access.

In simple terms, PV cells are devices made out of the second most abundant resource on earth, silicon, an element of sand. Crystalline silicon is a semiconductor that can take energy from the sun and give up electrons to create a charge. Applied to a glass or plastic substrate, metal contacts in the cell transfer the voltage to the cables and the solar charge controller.

A small solar system such as this one from GoPower allows RVers energy flexibility during short outings.

Traditional PV panels consist of one of two main types: monocrystalline and polycrystalline, although new technologies are developing. These aluminum-framed panels are made up of individual cells, and the panels, added together, make a solar array. Silicon is the most common semiconductor material used in solar cells. It converts the sun’s rays to electrical energy.

Monocrystalline cells, which are made from a single silicon wafer, are the most efficient on the market currently. Each cell has rounded edges, is black, and is cut from an individual silicon wafer, which increases the cost. Most RV panels are monocrystalline.

Polycrystalline cells are blue and use fragments of silicon wafers instead of complete wafers. This reduces waste and cost, but it also reduces efficiency. Small, portable trickle-charge panels often are made of these cells. The panels can have long strips or square cells, depending on the design.

Flat, glue-down thin-film panels are growing in popularity for RV and marine markets and are most frequently made of cadmium telluride (CdTe). Thin-film panels have various pros and cons and may be an excellent choice for some RVers.

If space is available, a larger system with aluminum-framed solar panels can be added.

Selecting panels involves several considerations, including overall energy requirements, available space for installation, efficiency, weight, labor, and structural attachment.

Traditional monocrystalline panels are the most efficient, at about 20 percent, at converting sunlight into electricity. While this doesn’t sound like much, polycrystalline panels are only about 15 to 18 percent efficient, and the thin-film version is approximately 10 to 12 percent. So, from an efficiency standpoint, monocrystalline panels are the best choice and will help folks to maximize their solar capacity for off-grid living.

Mounting the panels — whether traditional frame or glue-down thin-film panels — on the roof makes a big difference in efficiency. Since RV roofs have multiple appurtenances, such as vents, antennas, and air conditioners, there isn’t a one-size-fits-all solar panel. If maximizing the array output is of paramount importance, using varying sizes of traditional panels may be the best approach, as they can be placed atop some roof vents, and it doesn’t matter what else is under them. Thin-film panels, on the other hand, use an adhesive backer to stick to the roof, so they need to be mounted on an open expanse of roof, and the comparative lack of available sizes can make placement more of a challenge.

A larger solar system shown with flat solar panels.

A significant benefit of thin-film panels over traditional ones is the ease of installation. Traditional panels have a lot of hardware that must be laid out and screwed down to the roof, which is time intensive. Thin-film panels require that the roof be adequately cleaned, and then it’s a peel-and-stick process in most cases. So, while the thin-film panels tend to be pricier, the ease of installation may make them appealing for the do-it-yourselfer. Keep in mind, however, that the thin-film panels are less efficient.

Another benefit of thin-film panels is roof maintenance. When a typical RV roof is covered with traditional panels, resealing and cleaning can be a problem. Every panel has four to six brackets, each with two screws going into the roof, and all must be maintained with roof sealer. Thin-film panels cover the roof they are on, and other than wiring clamps and a wiring entry clamshell, which the traditional panels also have, no holes are required.

There isn’t much weight difference between traditional panels with hardware and thin-film panels. The thin film still has glass and a heavy-duty flexible backer, which adds weight.

Solar charge controllers come in two types: pulse width modulation (PWM) and maximum power point tracking (MPPT). PWM controllers are the least expensive and the least functional in an RV environment. A PWM controller is basically a switch that connects a solar array to a battery and brings the voltage level of the panels down to the voltage level of the batteries. While this may be usable for some installations, in the RV world, especially with LiFePO₄ batteries, the higher charge capabilities of MPPT are desirable. MPPT utilizes the maximum output ofthe solar array and “smart charges” the batteries. In other words, the MPPT controller can use higher voltage from an array. So, if multiple panels are installed, they can be wired in series, increasing the voltage and allowing for more efficient charging. In addition, the higher voltage in the array will allow smaller cabling, resulting in weight and cost savings. Because the MPPT is more efficient at harvesting power from the array, more energy is available during cloudy days or when panels are partially shaded than if a PWM is used. PWM has a limit on the amount of voltage the controller can provide based on the voltage of the battery bank it is connected to.

Wind Power

Wind generation isn’t new to RV territory, but its benefits as a stand-alone energy source for RVers are questionable. Instead, it may be most useful for supplementing charging sources such as solar, employing it only when conditions are appropriate. A windmill generator can be an excellent addition for those who RV in predominantly windy areas, including beach camping.

Wind generation systems are available online, but check reviews carefully. You may have to pay a little more for reliability.

Windmills for RVs are simple affairs. They consist of a blade system connected to a DC generator mounted in a case with a 1.5- to 2-inch (outside diameter) pipe fitting, depending on the manufacturer. The current is fed through a charge controller (internal or external), which charges the battery if there is enough voltage and amperage.

Of course, output from the unit is based on the wind speed, how sustained the wind speed is, and the unit’s design. Some do better at lower speeds than others.

In addition to the charge controller, a wind generator requires a brake unit to lock the unit down or a load dump to accept excess power from the windmill to prevent free-wheeling damage. Unlike solar, a wind generator requires continuous amp draw resistance to slow the unit, or it must be turned off by using the generator as an electromagnet to stop the rotation. Without these, if the amp draw drops because the batteries are fully charged, the windmill will spin without resistance and can damage the bearings or even spin itself to death. Primus Wind Power models, for example, have self-braking and regulation inside the turbine for a hands-off solution. Others, like those from Missouri Wind and Power, require a load dump to prevent over-speed.

Any properly sized pipe can suffice as a tower, but the windier it gets, the more stress is applied to the pole and mountings. Many users have found that a heavy-duty RV flagpole works well, with either a tire mount or other brackets attached to the RV’s structure.

Several brands and models of windmill generators for RVs and boats are available online, but some are poorly designed and have bad reviews. Few can support the higher voltage charging requirements of lithium batteries. That said, there are higher-end models from companies such as Missouri Wind and Solar and Primus Wind Power that, while more expensive, promise to provide a much better experience.

A significant benefit to wind generation is that the wind often blows at night, which can supplement a solar system after dark. One downside is carrying the unit to set up when you camp. This technology also has a bit of a learning curve, but it works when it’s appropriately sized and the wind is strong enough.

Solid Oxide Fuel Cells

If you haven’t heard about solid oxide fuel cells, or SOFCs, you’re not alone. They’re not even on the market as of this writing. But when they do hit the market, SOFCs promise to make other forms of RV power generation take a back seat.

What is an SOFC? According to WATT Fuel Cell — or Working All The Time — in Mount Pleasant, Pennsylvania, “A fuel cell is an elec-trochemical device that converts chemical energy stored in fuels directly into usable electrical energy.” While a gasoline- or propane-powered generator uses an engine to create mechanical energy that turns an alternator, SOFCs use stored chemical energy in propane to produce electrical energy silently and with basically no emissions, according to WATT Fuel Cell. It will use propane as a fuel for a chemical reaction to create power with only a tiny amount of CO₂ (not CO, as with a fuel-burning unit) and water. It sips fuel at ⅓ pound of propane an hour at full power, so a 20-pound cylinder lasts about 60 hours. Using less power preserves the propane.

The WATT system is a hybrid system; the solar charge controller in the RV is eliminated and instead is fed into this system, which intelligently controls the charge rate into the RV batteries. In other words, the WATT system now controls all charge sources into the batteries.

The system was displayed at the RV Open House for RV dealers in Elkhart, Indiana, in 2019, and according to RV electrical expert Mike Sokol, the company promises to have a production model available in 2023.

There have never been more choices for RV owners who want to have the flexibility of alternative power for their RV adventures. While solar remains the best option for most RVers, adding wind can help round out a renewable energy platform. While SOFC has much promise, time will tell whether the technology will be practical and affordable for RVers.