How to Select the Right Solar Panels for Your Boat

Ensuring your batteries stay charged while the boat is away from the dock has become easier than ever, thanks to solar charging systems. Whether you’re trying to keep the refrigerator running, reduce generator runtime or maintain a full battery charge at the mooring, solar charging is typically the best choice.

Selecting the right solar charging system involves balancing power needs, budget and your boat’s design. Both rigid and semi-flexible panels offer distinct advantages and disadvantages. Your choice will typically come down to mounting preferences and budget considerations.

RIGID PANELS

Rigid solar panels have been around since the early days of solar technology. With real-world efficiency ranging from 16 to 24 percent, a long lifespan often exceeding 20 years and a cost of $0.50 to $2.00/watt, they typically offer the best value. Built with an aluminum frame and a protective glass cover over the solar cells, rigid panels are commonly mounted on solar arches, dinghy davits or lifeline rails, and are more durable and cost-effective than flexible panels.

However, rigid panels do have downsides. They are heavier, delivering about 7 watts/lb. They can’t be walked on and are vulnerable to damage from overhead hazards, like seagulls dropping shells. Larger rigid panels may also incur higher shipping costs.

When selecting rigid panels, there are generally three types to consider: standard, bifacial and half-cut. Bifacial panels are a relatively new option, offering about 18 percent higher efficiency than standard panels. They capture light from both sides, allowing them to take advantage of reflections from the water or deck, and perform better in low-light conditions. Even when installed in a way that partially blocks the underside, they can still yield up to 5 percent more efficiency than standard panels.

Bifacial panels may appear to be the superior choice, but standard panels remain the most popular, especially in the marine market. They are widely available, come in more sizes, and are often more affordable, making them a practical choice for many boat owners.

Half-cut solar panels are based on traditional crystalline solar cells but the cells are cut in half with a process called cleaving, allowing them to deliver the same voltage but at half the current. This reduces hot spots and increases efficiency by 2 to 4 percent. These panels are fantastic because of their ability to withstand partial shading—always a major concern on marine solar systems. Half-cut panel technology can also be applied to bifacial panels.

SEMI-FLEXIBLE PANELS

Semi-flexible solar panels are popular in the marine world due to their versatile mounting options and streamlined appearance. While they’re less efficient than rigid panels, with efficiencies between 13 to 17 percent, they do have a favorable power-to-weight ratio of 25 watts/lb. Other benefits include the ability to walk on them if mounted to a deck and their seamless integration into marine canvas.

Semi-flexible panels generally fall into two categories: budget and top-tier. The price difference is significant, driven by construction and material quality, as well as warranty terms. Budget panels from brands like Renogy, Lensun, EcoFlow and Topsolar typically range from $1.30 to $1.60 per watt. These are often a good choice when integrating with mid-life marine canvas, as their lifespan aligns with canvas materials like Sunbrella. Top-tier panels may offer superior construction, but all panels on canvas are subject to bending fatigue, which can limit the lifespan of top-tier panels to that of budget panels.

Top-tier panels from Solbian, Solara, Merlin, Sol-Glo and Xantrex are built with high-quality silicon cells and often incorporate advanced technologies like MTAT, MTW and blocking diodes, which improve lifespan, reliability and efficiency. These panels cost between $3.50 and $5.00 per watt and deliver added performance and longevity.

Semi-flexible panels do have some drawbacks. One of them is lifespan. Most semi-flexible panels last between 5 and 10 years, but if improperly mounted can fail in under 2 years. I often recommend budget panels for canvas, but recommend top-tier quality panels for deck-mounted installations, which can save you significant time and effort down the road if a manufacturing defect causes a panel to stop working.

KNOW THE PITFALLS

Several specific issues can further reduce the lifespan of semi-flexible solar panels, so understanding these pitfalls is essential if you’re considering them for your boat.

Excessive Bending: Most semi-flexible panels are rated for a maximum flex of 30 degrees. Bending past this limit can lead to cracked silicon cells and broken internal wiring. Panels are particularly vulnerable when bent inward, as the silicon cells are more prone to damage under compression.

Microcracks: Seen most often with marine canvas installations, excessive vibration and movement can create a phenomenon called microcracks in the silicon cells. These microcracks reduce output and can significantly impact the panel’s maximum efficiency. Deck-mounted panels are far less susceptible to this type of failure. For canvas-mounted panels, keeping the canvas taut and securing the panel firmly can help reduce vibration-induced damage.

Delamination: Delamination is one of the most visible forms of failure and often appears as a translucent white bubble on the panel’s surface. This issue typically results from water intrusion and is exacerbated by heat, which creates vapor pressure within the panel. Improper manufacturing, damage at grommets or panel edges, and stitching through the panel (to affix Velcro or zippers, for instance) can cause delamination. For canvas installations, we have found adhesive products to attach velcro or zippers to be more reliable than sewing and as they reduce delamination.

UV Degradation: Unlike rigid panels made with glass, flexible panels use plastic materials that become hazy with prolonged UV exposure. This issue is especially common in budget panels. To maximize lifespan, avoid allowing salt buildup on the panels and opt for ETFE-coated panels over PET-coated ones, as EFTE is significantly more UV-resistant.

Temperature Issues: Flexible solar panels are notorious for their inability to shed heat, as their solar cells are installed between two insulated layers. Excess heat can cause hotspots and accelerate UV degradation, delamination and microcracking. As blocked cells can consume power from other cells, even bird poop can cause excess heat generation. Cell damage and microcracks can also cause hot spot issues, which in rare cases can lead to combustion. Ways to reduce this issue include the use of higher-quality panels, proper handling and installation, keeping the panels clean and periodically checking for cell damage.

ETFE VS. PET

Semi-flexible solar panels generally fall into two main construction types: ETFE (ethylene tetrafluoroethylene) and PET (polyethylene terephthalate). ETFE, a fluorine-based plastic, is quickly becoming the preferred choice because it has superior mechanical properties compared to PET. ETFE panels offer enhanced UV transmittance, chemical resistance, resistance to dirt accumulation and temperature tolerance, among other advantages. PET panels are also notorious for developing discoloration and cloudiness over time, further reducing efficiency over time. The only notable drawbacks of ETFE panels are the higher cost and the potential for heat buildup due to their all-black design. Regardless, we highly recommend ETFE panels for all marine installations.

CRYSTALLINE SILICON

Used in both semi-flexible and rigid panels, crystalline silicon (c-Si) technology dominates the solar industry. Crystalline silicon cells can be divided into monocrystalline and polycrystalline cells. In recent years, monocrystalline panels have become the clear go-to due to decreasing prices, higher efficiency, and availability on the market. I would advise avoiding polycrystalline panels.

HOW MANY WATTS?

To calculate your solar requirements, a conservative approach is to match your daily energy needs (determined by a power audit) with a solar setup that can produce full output for at least three hours per day. For example, a 100-watt panel, generating around 8.3 amp-hours per hour, would yield about 25 amp-hours daily. This approach may be overly conservative for boats in sun-rich locations like the Bahamas, but it’s a good starting point.

Since keeping a refrigerator running is one of the most common reasons for solar installation, a good rule of thumb is to aim for a minimum of 300 watts of solar. Of course, the specific power requirements for refrigeration vary with the efficiency of the equipment and insulation, so calculating your actual daily energy needs is recommended.

When determining the solar wattage needed for your boat, we generally follow the principle that “more solar is better.” Seasonal variations in sun angle and daylight hours can lead to substantial differences in daily output, and while your batteries may hold at 13.3 volts in July with the refrigerator running, by September you might find the system struggling to maintain 11.5 volts. Additional solar capacity also helps to restore battery levels after multiple cloudy days.

Selecting the right panels is the first step in the process, but having a solid understanding of the available technologies is essential to maximize both your solar system’s output and its lifespan.

Mike Garretson owns Sea & Land Yacht Works in Wakefield, Rhode Island. This story was published in the January 2025 issue of Soundings magazine.