Solar panels: how do they work on board?

This article offers a detailed technical analysis of solar panels applied to boats. We explore their basic operation and the different technologies available, the factors influencing their energy production in the marine environment, the specific challenges encountered on sailing boats - particularly in terms of bonding and aesthetic integration - and the impact of the democratization of custom photovoltaic cells, often imported from China.

The integration of solar panels on boats, particularly sailing yachts, has become a major trend in recent years. Once limited to land-based applications or costly experimental projects, this technology has gradually made inroads into the marine field, thanks to significant advances such as improved PERC (Passivated Emitter and Rear Cell) cells for greater efficiency or more resistant designs, and a significant drop in their production costs - for example, a drop of around 80% since 2010 according to IRENA.

Key figures

- Cost reduction: -80% since 2010 (IRENA)

- Typical output: 100 to 400 Wp/h 

- Service life: 20-25 years with maintenance (10-15 years for low-end flexible panels)

For sailors, solar panels offer a seductive promise: increased energy autonomy, reduced dependence on noisy, polluting diesel generators, and a silent energy source perfectly suited to life at sea.

However, the marine environment is not neutral ground for this technology. Conditions at sea - constant humidity, exposure to salt, incessant boat movement, limited space and aesthetic expectations, such as the need to preserve the sleek lines of a luxury yacht - impose unique constraints that complicate the adoption of solar panels. While their use can transform the sailing experience by reducing fuel requirements and improving on-board comfort, it requires a thorough understanding of their limitations and technical challenges.

Let's dive into the details to understand how solar panels fit into boats and what they really mean for users.

Solar panels are based on a well-established physical principle: the photovoltaic effect. This phenomenon occurs when cells, mostly made from silicon, but also materials such as CIGS (copper, indium, gallium, selenium) for certain applications, absorb photons of sunlight, releasing electrons that generate a direct electric current. This current is then routed via a charge controller to batteries for storage.

The rated power of a solar panel is measured in peak watts (Wp), a unit that represents maximum production under ideal conditions: solar irradiance of 1,000 W/m², a temperature of 25°C and a standard light spectrum (AM 1.5).

In reality, these optimum conditions are rarely found at sea, where climatic variations, shadows and boat movements strongly influence performance. However, in areas such as the equator in summer, irradiance can approach 1,000 W/m², although seasons and latitudes modify this potential. Understanding this principle is essential for choosing and sizing a solar system adapted to a boat's needs.

Solar panels available on the market fall into several categories, each with specific characteristics that influence their suitability for marine use:

These panels offer high efficiency, generally between 15% and 22%, thanks to the use of high-purity monocrystalline silicon cells. Their performance remains good even in low-light conditions, an advantage at sea where weather conditions can be unpredictable. However, they are rigid, often more expensive (e.g. €400-600 for 100 Wp) and less suited to the irregular surfaces of a boat. Their weight, typically 10-15 kg/m², can also be a problem on light sailboats.

Less expensive than their monocrystalline counterparts (e.g. €300-450 for 100 Wp), they are slightly less efficient, at around 13% to 18%. Their manufacture, using polycrystalline silicon, is more economical, but they lose performance in conditions of low light or intense heat. Like monocrystalline, they are rigid, with a similar weight (10-15 kg/m²), which limits their installation flexibility.

Designed to adapt to the curves of decks or biminis, these panels are lightweight (2-5 kg/m²) and easy to integrate on a boat. Their efficiency varies between 10% and 15%, although some recent CIGS-based models reach 17-18%. Their durability can be compromised by prolonged exposure to salt and UV rays, which can reduce their lifespan by 20-30% without adequate protection. They are suitable for temporary installations or confined spaces.

These hybrid models combine flexibility with enhanced robustness. Their efficiency is between 12% and 18%, and they are often reinforced to withstand marine conditions. With an intermediate weight (5-10 kg/m²), they represent an interesting compromise for sailors seeking to combine performance and adaptability.

To meet the demands of the marine environment, manufacturers have developed innovations that improve the durability and efficiency of solar panels:

- Anti-salt coatings : These protective layers reduce the adhesion of salt deposits, making cleaning easier and limiting cell corrosion. They are particularly useful in coastal areas or on long crossings.

- Reinforced encapsulants: Panels are sealed with moisture- and UV-resistant materials such as EVA (ethylene vinyl acetate) or POE (polyolefin), to protect cells from water infiltration and degradation by the elements.

Emerging novelty :

Bifacial panels, capable of capturing light from both sides, are emerging as a solution for catamarans, where reflection off the water can increase output by 10-15%. Their cost (€700-900/100 Wp) and weight still reserve them for niche applications.

These technological adaptations show that solar panels for boats are not simply copies of their land-based counterparts. They require specific design to meet the challenges of the sea, while offering reliable energy production.

Energy production from solar panels on a boat depends on multiple variables, some of which are amplified by marine conditions. Here's a detailed analysis of the main criteria to be taken into account:

Atmospheric humidity, ubiquitous at sea, indirectly influences energy production by modifying the scattering of sunlight. In tropical or near-coastal environments, where relative humidity exceeds 90%, cloud cover increases, reducing direct irradiance by 5-10%, according to tropical climate studies (e.g. University of Malaysia, 2017). For example, at 90% humidity in the equatorial zone, a 100 Wp panel could lose 5-10 W of output per hour.

The angle of inclination of the panels to the sun is a key factor in maximizing production. On land, an optimum angle (e.g. 30-40° near the equator) is easy to maintain, but on a boat, constant movement - rolling, pitching and course changes - complicates matters. A panel lying flat on the deck can lose up to 30% of its efficiency at high latitudes (e.g. 50°N), where the sun is low on the horizon. Rolling and pitching can vary output by 10-20% per hour. Solar tracker systems, which automatically adjust inclination, exist but are rarely used at sea due to their fragility and cost, although they are viable on large catamarans.

The boat's geographical position plays a decisive role in the amount of solar energy available. Near the equator, sunshine can reach 5 to 6 kWh/m² per day in summer, providing ideal conditions. On the other hand, in regions such as Northern Europe, sunshine levels drop to 2 or 3 kWh/m² per day in winter, or even 1 kWh/m² in arctic zones. For a 100 Wp panel, this translates into 500-600 Wh/day at the equator, compared with 100-300 Wh in the Baltic Sea in winter. Sailors therefore need to adapt their solar systems to their usual sailing zones.

Example of a practical calculation:

For a sailboat consuming 1 kWh/day (lighting, instruments, refrigerator) :

- Tropical zone: 2 x 100 Wp panels are sufficient (production ~1.2 kWh/day).

- Northern Europe (winter): 4 x 100 Wp panels required (production ~1 kWh/day)*.

While light is essential for generating electricity, excessive heat can paradoxically reduce panel efficiency. Each degree above 25°C causes a 0.3-0.5% loss in efficiency, depending on the technology used. At sea, a black panel under a tropical sun can reach 40-60°C, causing a loss of 6-15% (e.g.: -12 W for a 100 Wp panel at 45°C). Wind provides natural ventilation that limits this effect, but good ventilation under the panels remains crucial to maintaining their performance.

Partial shading, caused by masts, sails or other equipment, is a major problem on boats. A shadow on a single cell can reduce the output of a series string by 30-50%. Bypass diodes, built into modern panels, can bypass shaded areas to limit losses, but they don't eliminate them altogether. A well-thought-out installation that minimizes obstacles is therefore essential.

These factors illustrate the complexity of energy optimization at sea. Unlike a land-based installation, where conditions are more stable, sailors have to deal with a dynamic environment that demands constant adjustments.

Boats, with their limited surface area and functional requirements, present particular challenges for the installation of solar panels. Here are the main obstacles encountered:

Temperature rise in the passenger compartment

When solar panels are installed directly on the deck or roof, they absorb the sun's heat and transfer it to the interior of the boat. A 1 m² panel at 50°C can transfer 50-100 W of heat, making the interior uncomfortable in hot climates. To limit this effect, thermal insulation - such as a layer of polyurethane foam (€20-50/m²) - or a ventilated space under the panels can be incorporated. However, these solutions increase the cost and complexity of the installation.

Robustness and accessibility

On a yacht, solar panels are often placed in high-traffic areas, such as the deck or bimini. They must therefore be able to support the weight of a person, resist accidental shocks and vibrations caused by waves and wind. Micro-cracks, caused by vibration, can reduce efficiency over time. Rigid or semi-rigid panels are preferred, but their weight and bulk can be a problem on light boats.

Integration and aesthetics

The space available on a boat is limited, forcing sailors to make strategic choices: installing panels on the bimini, the deck, or even the sails. For example, a bimini can accommodate 200-400 Wp.Beyond functionality, aesthetics play an important role, especially on pleasure boats where appearance counts. Poorly integrated panels can clash with the clean lines of a sailboat, prompting manufacturers to offer more discreet, harmonious solutions.

Successful case study:

The GR 63 catamaran is an example of successful integration: 63 m² of semi-flexible panels (66 kWh/day) supply 100% of slow-sailing requirements. The panels are glued to the coachroof, preserving their aesthetic appeal.

Maintenance and durability

Constant exposure to salt corrodes electrical connections and panel fastenings. Weekly rinsing with fresh water and the use of anodized alloys or stainless materials can extend their lifespan, often 20-25 years for quality models. At sea, where resources are limited, this maintenance can become an additional challenge.

These specific constraints show that installing solar panels on a boat is more than just a technical choice. It requires careful planning to balance performance, durability and practicality.

Panel bonding: a complex technical issue

On boats, bonding is a common method of attaching solar panels, as it avoids drilling holes in the deck and preserves the waterproofing. However, this technique has to meet stringent requirements in the marine environment.

Gluing methods

- Marine adhesives (e.g. Sikaflex): These polyurethane adhesives (e.g. Sikaflex 292i) are popular because they require no drilling. They offer good water resistance, but can degrade under prolonged UV exposure, losing 20-30% of their strength after 5 years (ISO 9227 tests). Application requires a degreased surface (e.g. with acetone) and 24-48 hours drying at 15-25°C.

Technical challenges

- Bending: Boat decks may bend under wave or weight pressure, which can break the bond or crack the panels, especially if they are rigid.

- Compatibility: The adhesive must be compatible with the deck material (fiberglass, aluminum, wood) and the panel material, which limits the options available.

- Durability: Thermal cycles (hot/cold) and consequent contraction/decontraction of materials and exposure to salt degrade adhesives over time, making periodic replacement necessary.
 

Aesthetic integration: harmonizing energy and design

In the marine industry, aesthetics are an important criterion, and design contributes to the overall experience.

- Visual contrast: Traditional signs, often black or blue, can clash with the light color of a boat.

- Congestion : Poorly positioned signs create traffic problems. 

- Unsuitable shapes: Standard rectangles don't always fit in with the natural curves of a sailboat.

Solutions

- Customized panels: Available in matte black, they blend in better with the boat's design.

- Semi-transparent panels: Used on biminis or skylights, they let light through while producing energy.

- Recessed: Panels recessed into the deck offer a smooth, unobtrusive finish, albeit at a high cost (€1,000-2,000/m²).

- Custom shapes: Some manufacturers offer panels cut to fit the contours of the boat. For example, the GR 63 catamaran incorporates custom-made panels developed by the shipyard to guarantee maximum, aesthetic coverage of production areas.

Solar glazing on the GR 63 

China has transformed the solar panel market, producing customized photovoltaic cells at affordable prices. This development has major implications for boats.

- Flexibility: These cells adapt to irregular shapes, such as the rounded corners of a deck or the curves of a bimini.

- Efficiency: Recent technologies, such as PERC (Passivated Emitter and Rear Cell) cells, achieve 20-22% efficiency, rivalling Western standards.

- Cost: A 100 Wp output costs between €150 and €300, well below the €400-600 price tag of traditional high-end panels.

Impact on boats

- Maximizing space: On a sailboat, where every centimeter counts, these cells can increase production by 20-30% by exploiting previously unusable surfaces. 

- Adaptability: they bypass obstacles such as masts or portholes, optimizing layout.

- Accessibility: DIY kits, selling for between €200 and €400, make this technology accessible to hobbyists.
 

Buying guide: How to choose a reliable Chinese supplier ?

1. Certifications: Require IEC 61215 (durability) and IP67 (tightness).

2. Customer reviews: Check feedback on nautical forums (e.g. CruisersForum).

3. Warranty: Minimum 10-year performance guarantee (degradation ≤20%).

4. Actual test: Request a sample to check salt resistance.
 

Precautions

The quality of Chinese cells varies from supplier to supplier. CE or IEC 61215 certification and salt and UV resistance tests (e.g. ISO 9227) are essential to guarantee reliability. Buyers should choose reputable resellers to avoid low-end products.

This democratization has opened up new horizons for navigators, but requires increased vigilance to take advantage of its benefits without compromising sustainability.

Solar panels on boats offer valuable energy autonomy, reducing dependence on diesel generators and improving on-board comfort thanks to a silent power source. However, their integration is far from straightforward. Technical challenges - reliable bonding, heat management, robustness against the elements - demand tailored solutions, while aesthetics and space optimization add a layer of complexity. The arrival of customized cells from China has democratized this technology, making it possible to produce energy more efficiently at lower cost. For example, a 10 m sailboat equipped with 300 Wp can cover 50-80% of its daily needs (lighting, navigation) in equatorial summers.

For modern sailors, solar panels represent a major asset, but their successful adoption requires careful planning. Correctly dimensioning the system, choosing resistant materials and anticipating marine constraints are essential steps. Future innovations, such as bifacial panels capturing light from both sides or more efficient lithium batteries, promise to further enhance their potential.

Future prospects :

By 2030, solar-wind hybrids (such as masts with integrated micro-wind turbines) and photovoltaic sails could revolutionize boat autonomy. The key is to strike a balance between innovation, reliability... and good seamanship.

With a thoughtful approach, this technology can transform navigation, offering a viable alternative to traditional methods while respecting the practical realities of life at sea.