Power System Redesign on a Fountaine Pajot 57

An experienced bluewater captain who has completed multiple Atlantic crossings contacted us to redesign the solar system on his Fountaine Pajot 57 catamaran. Spending extended periods aboard with his family, he needed a system that was not only powerful and reliable, but also visually refined.

This was not a basic upgrade. It was a full redesign of an already substantial energy system.

Existing Energy System

The vessel already had a serious house bank: eight PowerQueen 12.8V 300Ah LiFePO4 batteries configured in a 2S4P layout, creating a 25.6V 1200Ah battery bank. That equals more than 30 kWh of usable lithium storage — more energy than many small off-grid homes.

Solar production came from:

• Five rigid panels mounted on the hardtop bimini
• Multiple semi-flexible panels on the coach roof
• Three Victron MPPT charge controllers

On paper, the system looked strong. In practice, it had several limitations.

Identified Issues

After inspection, we identified four primary concerns:

• Aging flexible panels with declining output
• Poor installation practices using exposed metal fasteners that were already rusting
• A damaged rigid panel that had been stepped on
• Most importantly, aesthetics; the rigid panels extended to the edge of the bimini and were clearly visible from the deck on both sides

For a performance cruising catamaran of this caliber, visual integration matters. The owner wanted fewer rigid panels, better symmetry, and a cleaner profile without sacrificing output.

Design Goals

1. Maintain or increase total solar production
2. Improve aesthetics and deck sight lines
3. Optimize for real-world shading conditions
4. Reuse viable equipment where possible
5. Integrate full system monitoring

Flexible Array Redesign

For the coach roof and supplemental areas, we selected Solara Power M-Series panels. These marine-grade, walk-on modules are specifically engineered for:

• Harsh saltwater environments
• Curved mounting surfaces
• Mechanical durability under foot traffic
• Superior longevity compared to lower-cost flexible panels

The final flexible configuration included:

• Twelve 125W Solara Power M-Series panels
• Two 160W Solara Power M-Series panels

The 160W panels were positioned near the mast base where space allowed longer modules. The remaining panels were strategically placed across available surfaces to maximize production while preserving symmetry.

Rigid Panel Upgrade

We replaced the five rigid panels with three Meyer Burger 385W Black panels. These high-efficiency heterojunction modules provide:

• Excellent low-light performance, ideal for offshore cruising
• High energy yield per square foot
• A uniform all-black appearance that significantly improves visual integration

The three rigid panels were positioned centrally on the bimini and flanked on each side by flexible panels. This layout keeps the rigid modules away from the outer edges, so they are no longer visible from the side decks. The result is a cleaner visual profile while maintaining strong production from the primary rigid array.

Shading Strategy and MPPT Design

Shading is one of the biggest performance killers on catamarans. The boom, mast, and standing rigging create constantly shifting shadow patterns throughout the day. Instead of grouping panels purely by wattage, we divided them by physical location and expected shading exposure. Specifically:

• Port-side arrays were separated from starboard arrays
• Bimini panels were isolated from coach roof panels

This segmentation prevents a shaded section from dragging down the output of unshaded panels. The final system required five MPPT controllers, with two existing units reused and three new controllers added.

MPPT Allocation:

Qty	Panel Model	MPPT
5	125W	150/35
4	125W	150/35
3	125W	100/30
3	385W	150/70
2	160W	100/30

System Overview

The diagram above shows the final system layout and overall power flow. Solar arrays are separated by location and routed through dedicated MPPT controllers to reduce shading losses and improve reliability. All charging sources feed into the 25.6V 1200Ah lithium house bank through properly sized protection and busbars. A Victron Cerbo GX centralizes monitoring, allowing full system visibility at the nav station and remotely through the Victron app.

System Monitoring and Integration

To centralize monitoring, we installed a Victron Cerbo GX system.

The owner wanted monitoring capability at the navigation station in the main saloon. However, the power equipment was located near the transom.

We installed a 60-foot communication cable between the Cerbo GX and the GX Touch 70 display mounted at the nav station, allowing:

• Full system monitoring
• Solar production tracking
• Battery status visibility
• Remote access through the Victron app

The result is real-time energy awareness both onboard and remotely.

Additional Upgrade: Bow Thruster Charging

During the project, the owner requested an upgrade to the bow thruster battery charger. The thruster bank consisted of four 12V 80Ah AGM batteries configured in series to create a 48V 80Ah bank.

Unlike lithium systems, AGM banks do not require cell balancing and can be properly maintained with a dedicated charger.

We installed a Victron Skylla 48/50 TG 50-amp charger to ensure reliable charging performance and proper voltage regulation for the 48V AGM bank.

Commissioning and Programming

Upon completion, our team:

• Programmed all solar charge controllers for a 24V lithium profile
• Configured the Smart BMV-712 battery monitor
• Enabled Bluetooth connectivity across components
• Verified charge parameters, absorption settings, and system protections

Every charging source was synchronized to ensure proper lithium charging behavior.

Final Result

The finished system delivers:

• Over 3 kW of installed solar capacity
• 25.6V 1200Ah lithium storage (30+ kWh)
• Optimized shading resilience
• Cleaner deck aesthetics
• Integrated onboard and remote monitoring

The vessel can now operate for extended periods without running the generator, with full visibility into energy production and consumption.

This project is a strong example of what thoughtful system design can achieve: performance, durability, and visual integration working together.