Electrical energy is the lifeblood for any modern sailor, whether it's a day trip or a long-distance cruise. Between the navigation systems essential to safety, the daily comfort provided by domestic equipment and the autonomy sought away from ports, on-board energy management represents a major challenge. Today, batteries and solar panels offer efficient and sustainable solutions to meet these growing needs. This technological revolution allows boaters to rethink their relationship with offshore energy, by prioritizing autonomy and respect for the environment. Understanding the fundamental principles of these technologies, their respective advantages and their complementarity is essential to design an energy system adapted to your navigation program and optimize your investment over the long term.
Definitions
Why on-board energy is crucial for comfort and safety
The power supply of a boat goes far beyond simple comfort: it is a vital element for safety at sea. Navigation instruments, GPS, radar, VHF, and autopilot require a stable and continuous power supply. A power outage can quickly turn peaceful navigation into a critical situation, especially in bad weather conditions or at night.
In addition to safety, energy directly affects the quality of life on board. Food refrigeration, lighting, fresh water pump, charging of electronic devices: all this equipment contributes to the daily comfort of team members. Poor energy management considerably limits autonomy and can force navigation to be shortened or an itinerary modified.
Overview of available solutions: batteries and solar panels
Modern batteries, whether lead-acid or lithium, offer storage capacity adapted to naval needs. Combined with photovoltaic solar panels, they are a particularly effective duo for energy autonomy. This combination makes it possible to capture solar energy during the day and to release it as needed, creating a virtuous cycle of energy independence.
Other renewable energy sources complete this system: marine wind turbines, hydrogenerators or even engine alternators. The objective is to diversify sources in order to maximize production and secure the on-board electrical supply.
Understanding the energy needs of a boat
Evaluate your electricity consumption on board
Consumer devices: fridge, lighting, navigation electronics, etc.
The electrical consumption of a boat varies considerably depending on the equipment on board and the style of navigation. The refrigerator is generally the largest consumer, with 3 to 8 Ah per hour depending on its size and energy efficiency. A 130-liter fridge can consume between 70 and 150 Ah per day depending on the outside temperature and the frequency of opening.
Navigation electronics are the second consumer item. A GPS consumes about 0.5 to 2 Ah, an autopilot 2 to 8 Ah depending on sea conditions, while a radar can absorb 4 to 6 Ah in continuous operation. Modern LED lighting consumes little (0.1 to 0.5 Ah per light point), but can quickly add up with numerous lights on simultaneously.
The pumps (fresh water, sea water, drying) have a punctual but significant consumption, of 3 to 8 Ah depending on their power. Charging personal electronic devices (phones, tablets, computers) is approximately 1 to 3 Ah per device and per full charge.
Estimating daily Wh requirements
To correctly size your installation, it is necessary to accurately calculate its daily consumption. The method consists in listing each device with its hourly consumption and daily usage time. For example: refrigerator 4 Ah × 18 h = 72 Ah, LED lighting 0.3 Ah × 6 h = 1.8 Ah, GPS 1 Ah × 10 h = 72 Ah = 10 Ah.
A standard pleasure boat generally consumes between 50 and 150 Ah per day depending on the equipment and use. Equipped offshore sailing boats can reach 200 to 300 Ah daily with refrigerator, freezer, watermaker and complete electronics. This estimate makes it possible to size the battery park and the production of renewable energy.
A safety margin of 20 to 30% should also be provided to take into account seasonal variations, temporary breakdowns or exceptional needs. This methodical approach avoids unpleasant surprises and guarantees sufficient autonomy.
The challenges of energy autonomy at sea
Coastal cruise vs offshore crossing
Energy needs differ radically depending on the type of navigation used. During coastal cruising, regular access to ports allows batteries to be recharged from the mains and limits autonomy constraints. Solar panels are often enough to compensate for daily consumption, creating a satisfactory energy balance.
Offshore navigation imposes much more stringent constraints. The impossibility of external charging for weeks requires complete autonomy and system redundancy. Weather conditions can reduce the efficiency of solar panels for several days in a row, requiring energy storage to be significantly sized.
The duration of the crossings also influences technological choices. A 3-week transatlantic crossing imposes different constraints than coastal hopping with weekly stops. Autonomy must cover the most unfavorable period possible.
Safety and reliability
The redundancy of energy systems is a fundamental principle of security. Having several sources of production (solar, wind, alternator) and storage (separate batteries for easements and engine starting) limits the risks of total failure. This approach is inspired by aeronautical practices where system failure should never compromise safety.
Component reliability takes precedence over pure performance. It is better to choose proven and robust equipment rather than the latest innovations that have not been tested in marine conditions. The marine environment (salinity, humidity, vibrations, extreme temperatures) subjects electronic equipment to exceptional constraints.
Preventive maintenance and continuous monitoring of energy parameters make it possible to anticipate failures. Solutions such as the Oria Marine IoT box offer real-time monitoring of batteries and charging systems, alerting to anomalies before they become critical.
The different types of boat batteries
Lead acid battery (or AGM, gel)
Advantages and disadvantages
Lead acid batteries remain widely used in boating due to their affordable cost and proven technology. The AGM (Absorbed Glass Mat) and gel versions offer better vibration resistance and can be installed in any position without the risk of electrolyte leaks. Their tolerance to overloads and their ease of recycling are significant advantages.
Their main disadvantages lie in their large weight (25 to 30 kg per 100 Ah), their sensitivity to deep discharges and their limited lifespan. A lead-acid battery hardly supports more than 500 cycles at 50% discharge, compared to 2000 to 3000 cycles for a lithium battery. Their high self-discharge rate (5 to 15% per month) penalizes wintering periods.
Charging time is also disadvantageous: it takes 6 to 8 hours for a full charge compared to 2 to 3 hours for lithium. This characteristic limits the efficiency of intermittent production sources such as wind turbines or engine alternators.
Lifespan and maintenance
The lifespan of lead batteries depends directly on their use. Regular 80% discharge drastically reduces their lifespan, while a maximum of 50% use can increase their lifespan to 8-10 years. This constraint imposes an oversizing of the battery park, increasing weight and size.
Regular maintenance is essential: checking the electrolyte level for open models, cleaning the terminals, periodic equalization of the elements. AGM and gel batteries require less maintenance but remain sensitive to extreme temperatures and unsuitable loads.
Voltage monitoring makes it possible to estimate the state of charge, but this method remains imprecise. A battery controller with shunt significantly improves the monitoring of residual capacity and optimizes energy management.
Lithium battery (LiFePO4)
Why are they revolutionizing onboard energy
Lithium iron-phosphate (LiFePO4) batteries are radically transforming nautical energy management. Their exceptional energy density (3 to 4 times greater than lead) drastically reduces weight and size. A 100 Ah lithium battery weighs around 12 kg compared to 30 kg for its lead equivalent, freeing up valuable space and improving the boat's attitude.
Their tolerance to deep discharges allows the use of 95% of their nominal capacity, compared to a maximum of 50% for lead. This characteristic doubles the energy actually available at the same nominal capacity. Their flat discharge curve maintains a stable voltage until completely exhausted, guaranteeing optimal operation of the equipment.
Fast charging is another major advantage: the acceptance of high charging currents (1C to 2C) allows a full recharge in 1 to 2 hours. This speed optimizes the use of intermittent production sources and reduces engine operating times.
Comparing cost/performance with traditional batteries
The initial investment of lithium batteries is 3 to 5 times that of lead batteries, but their total cost of ownership is often advantageous. Their lifespan of 10 to 15 years (3000 to 5000 cycles) largely amortizes the additional initial cost. A lithium battery can replace 3 to 4 generations of lead batteries over its lifetime.
Really usable energy amplifies this economic advantage. A 200 Ah lithium battery provides as much usable energy as 400 Ah lead batteries, significantly reducing the investment and space required. Weight savings also make it possible to optimize the boat's performance.
Their higher charging efficiency (95% compared to 80% for lead) reduces energy losses and optimizes the production of solar panels. This efficiency translates into substantial savings in the size of the photovoltaic installation.
Choosing the right battery
Capacity (Ah), discharge depth, charger compatibility
The sizing of battery capacity depends on daily consumption and the desired autonomy. For lead batteries, double the daily consumption must be expected to comply with the 50% depth of discharge. Lithium batteries make it possible to size real consumption as accurately as possible.
The desired energy autonomy also influences the choice. Three days of autonomy without production represent the minimum recommended for coastal navigation, increased to one week for offshore vessels. This reserve covers periods of bad weather limiting solar and wind production.
Compatibility with existing chargers requires particular attention for lithium batteries. Their specific charging characteristics (end of charge voltage, maximum current) often require the adaptation or replacement of chargers. Integrated management systems (BMS) protect cells but can cause disconnections in case of inadequate parameters.
Solar panels for boats: clean and sustainable energy
How marine solar panels work
Monocrystalline vs polycrystalline cells
Marine solar panels mainly use two photovoltaic cell technologies. Monocrystalline cells, recognizable by their uniformly black color, offer the best energy efficiency (18 to 22%) and the best performance in low light. Their more complex manufacture results in greater cost, but their efficiency optimizes the space available on the deck.
Polycrystalline cells, which have a bluish marbled appearance, have a slightly lower efficiency (15 to 18%) but at a more affordable cost. Their tolerance to high temperatures is interesting in the tropics where the temperature of the panels can exceed 70°C. The choice between these technologies depends mainly on the budget and the space available.
New technologies such as PERC cells (Passivated Emitter and Rear Cell) improve efficiency by 2 to 3% by optimizing the capture of reflected light. These innovations are gradually reducing the performance gap between monocrystalline and polycrystalline.
Performance under real conditions (inclination, shade, salinity)
The theoretical efficiency of solar panels is obtained under standardized conditions (STC: 1000 W/m², 25°C, air mass 1.5) rarely encountered in navigation. Marine conditions generally reduce production by 20 to 40% compared to manufacturer specifications.
The inclination of the panels directly influences their production. The optimal angle varies according to the latitude and the season: 30° at our latitudes, 0° near the equator. On a boat, the inclination generally remains low (0 to 15°), reducing production by 5 to 15%. The permanent shelter of a sailboat can partially compensate for this loss of angle.
Partial shading affects production dramatically. A 10% shadow on a panel can reduce its production by 50 to 80% depending on the type of by-pass cells and diodes. The layout of bridge equipment (mast, boom, antennas) must incorporate this constraint from the design of the installation.
Marine salinity requires regular cleaning of the panels. Salt reduces light transmission and can cause micro electric arcs. A weekly rinse with fresh water maintains optimal performance.
Choosing the right type of solar panel
Rigid, soft, or semi-flexible panels
Rigid solar panels offer the best performance/price ratio and the greatest longevity. Their aluminum and tempered glass structure is resistant to marine conditions and facilitates maintenance. Their thickness (35 to 45 mm) requires installation on a dedicated structure but guarantees optimal ventilation and maximum performance.
The flexible panels impress with their ease of installation and their discreet integration. Glued directly to the deck or the upholstery, they eliminate snagging problems but suffer from overheating reducing their performance by 10 to 20%. Their limited lifespan (5 to 8 years) and their higher cost per watt penalize their profitability.
Semi-flexible panels are an interesting compromise. Their possible curvature (up to 30°) facilitates integration on non-flat surfaces while maintaining good performance. Their structure, which is more robust than flexible ones, improves their longevity, but their cost remains high.
Power adapted to its use
The size of the photovoltaic installation depends on daily consumption and sun conditions. In our latitudes, a 100 Wp panel produces an average of 300 to 500 Wh per day depending on the season, compared to 600 to 800 Wh in the tropics. These values include system losses and real navigation conditions.
To balance daily consumption, it is necessary to provide 1.5 to 2 times the power theoretically necessary. This margin compensates for days of low sunshine and system losses. A boat consuming 100 Ah/day (1200 Wh in 12V) requires an installation of 300 to 400 Wp in our latitudes.
The modularity of the installation makes it possible to adapt the power according to the evolution of needs. Starting with a basic installation and adding panels based on user experience is a pragmatic and economical approach.
Installing solar panels on board
Ideal location: bimini, portico, balcony
The choice of location determines the efficiency and sustainability of the installation. The bimini is the preferred location on sailing boats: optimal exposure, preserved cockpit protection, accessibility for maintenance. Its structure must be reinforced to support the weight and wind resistance of the panels.
The aft gantry offers an interesting alternative, especially on catamarans. The high installation avoids shading and facilitates the orientation of the panels. However, pay attention to the impact on the stability and the resistance of the structure to dynamic stresses.
The installation on the main deck maximizes the available area but exposes the panels to impacts and the shading of equipment. This solution is suitable for soft panels or for unmanned navigation (permanent bridge). Traffic and safety should never be compromised.
Fastening, cable routing, sealing
The fixing of the panels must withstand marine stresses: vibrations, shocks, tearing off by the wind. The anodized aluminum fixing rails offer flexibility and robustness, allowing optimal orientation and maintenance. Adhesive fixing systems are suitable for flexible panels but limit the possibilities of intervention.
Cable routing requires particular attention to watertightness. Marine cable glands guarantee long-lasting watertightness but require irreversible drilling. Existing passages (hollow mast, propeller passages) can be used with adaptations.
Accessibility for maintenance determines the sustainability of the installation. Provide access for cleaning, checking connections and possible replacement of components. An inaccessible installation degrades quickly and loses its effectiveness.
Management and optimization of the energy system
Charge controllers: PWM or MPPT?
Role and impact on system performance
The charge controller is the essential interface between solar panels and batteries. It adapts the voltage and current produced to the charging characteristics of the batteries, protects against overcharges and optimizes energy transfer. Without a regulator, solar panels would quickly destroy batteries by overcharging.
PWM (Pulse Width Modulation) controllers are the traditional technology. They work by quickly switching the panel-battery connection to maintain the appropriate charge voltage. Simple and economical, this technology is suitable for small installations where panels and batteries operate at the same nominal voltage.
MPPT (Maximum Power Point Tracking) regulators continuously optimize the operating point of the panels to maximize the power extracted. They convert excess voltage into current, increasing the energy recovered by 20 to 30% compared to PWMs. This technology is required for large installations or variable conditions.
Battery controller: monitor its consumption
Embedded screen, mobile application, alarms
Precise monitoring of the energy state on board is essential to optimize autonomy and preserve batteries. Modern battery controllers measure voltage, current, power in real time and calculate the residual capacity with an accuracy of 1 to 2%. This information makes it possible to anticipate needs and adapt consumption.
The embedded screens offer an immediate view of the energy parameters: charge status, charge/discharge current, remaining battery life. The advanced models include consumption histories and configurable alarms. The location of the screen should allow easy consultation from the navigation and living stations.
Mobile applications democratize energy monitoring by transferring the display to a smartphone or tablet. The Bluetooth or WiFi connection allows remote monitoring and archiving of data. Some solutions like Oria Marine IoT integrate the monitoring of multiple parameters (batteries, tanks, temperature) in a unified interface that can be accessed from anywhere in the world.
Other complementary sources of energy
Marine wind turbine
The offshore wind turbine effectively complements solar panels by producing energy day and night with sufficient wind. Its production generally starts around 7-8 knots of apparent wind and reaches its maximum around 25-30 knots. This complementarity with solar energy optimizes global energy production.
Modern offshore wind turbines incorporate automatic regulation and braking systems to withstand strong winds. Their noise level, which is critical for comfort on board, varies according to the models and wind conditions. The installation should focus on the distance from rest areas and provide for a walkout system for periods of calm.
The production of a 400W wind turbine varies enormously depending on the conditions: 50 to 100 Ah/day in moderate wind (15-20 knots), up to 200 Ah/day in strong winds. This variability requires careful and complementary management with other sources of production.
Hydrogenerator
The hydrogenerator produces electricity from the speed of the boat in the water. It therefore only works while sailing, with production in proportion to speed: 2-3 A at 5 knots, 8-10 A at 8 knots. This source of energy is particularly interesting for long passages where the boat is constantly sailing.
Modern models incorporate variable-pitch propellers or turbine systems that minimize drag. Some retract automatically in case of overspeed or entanglement. The installation requires a watertight shell passage and a robust attachment capable of resisting hydrodynamic forces.
The maintenance of the hydrogenerator requires regular underwater interventions to clean the propeller and check the tightness. This constraint limits its adoption on boats without the possibility of frequent fairing.
Common mistakes to avoid
Undersize batteries or panels
The most common mistake is underestimating your real energy needs. Theoretical calculations do not take into account seasonal variations, periods of bad weather, or the natural evolution of the equipment on board. Initial undersizing requires costly corrective investments and complicates the integration of new equipment.
The sizing of solar panels must include the least favorable conditions of the year and the navigation area. Forecasting only for Mediterranean summer conditions condemns to energy difficulties as early as autumn or in northern latitudes. A margin of 50% on theoretical calculations is a prudent minimum.
The natural evolution of on-board energy needs also justifies a generous initial sizing. The addition of equipment (more powerful plotter, larger refrigerator, additional lighting) is often necessary after a few seasons of sailing. Anticipating this evolution avoids complete installation overhauls.
Neglecting battery ventilation
Battery ventilation is an aspect that is often overlooked but crucial for battery life and safety. Lead-acid batteries release corrosive (hydrogen sulphide) and explosive (hydrogen) gases during charging, particularly at the end of charge or at high temperatures. Insufficient ventilation causes corrosion of surrounding equipment and presents risks of explosion.
The location of the batteries must allow natural or forced ventilation to evacuate the gases to the outside. Waterproof battery boxes require dedicated ventilation with fresh air intake in the lower part and evacuation in the upper part. An electric extractor improves forced ventilation, especially in the tropics.
Lithium batteries do not emit gas during normal operation but require thermal monitoring. Installing them in a dry and ventilated room prevents the risk of overheating and facilitates the intervention of the BMS in the event of an anomaly.
Forget about maintaining electrical connections
The marine environment particularly attacks electrical connections: galvanic corrosion, salt water infiltration, permanent vibrations. Contact oxidation increases electrical resistance, generating heating and power losses. A faulty connection can cancel out the benefits of an otherwise efficient installation.
The protection of the connections involves the use of suitable materials (tinned brass, stainless steel), the application of protective grease and careful sealing. Crimp connections surpass screwing or soldering in vibration resistance. Biannual inspection and preventive cleaning prevent major failures.
Oversizing conductors limits overheating and voltage drops. Using larger sections than theoretical calculations improves performance and reliability. This approach is particularly important for high-power circuits (alternator, charger, converter).
FAQ: the most frequently asked questions
1. What is the best battery for a cruising sailboat?
For a modern cruising yacht, lithium LiFePO4 batteries are the optimal choice despite their high initial cost. Their exceptional lifespan (10-15 years), their weight reduced by 70% and their tolerance to deep discharges more than make up for the investment. For a limited budget, marine grade AGM batteries offer an acceptable compromise with a lifespan of 5-7 years with moderate use.
2. Can we be 100% autonomous with solar panels?
100% autonomy with solar panels is still possible but requires generous sizing and rigorous consumption management. In our latitudes, it is necessary to provide 2 to 3 times the power theoretically necessary to compensate for days without sunlight. The association with a marine wind turbine or a hydrogenerator secures energy autonomy and reduces the size of the photovoltaic installation.
3. What is the lifespan of a marine solar panel?
A quality marine solar panel maintains 80% of its nominal power after 20-25 years of use. High-end models benefit from manufacturer warranties of 10 to 25 years on performance. In a marine environment, the practical lifespan is generally between 15 and 20 years, limited more by technological obsolescence than by physical degradation.
