Solar and wind powered boat’s final voyage across the sea

The Energy Observer, a solar and wind-powered catamaran, is nearing the end of its extensive global journey, having sailed over 64,000 nautical miles while circumnavigating the globe. The vessel has demonstrated the viability of renewable energy-powered maritime travel, even across the most challenging oceanic conditions.

Last week, pv magazine USA met with Luc Bourserie, the systems engineer of the Energy Observer, in Boston Harbor. The 100-foot-long boat is powered by a sophisticated energy system that uses power from solar and wind, stores long-term energy in hydrogen and stores short-term energy in batteries.

The Energy Observer features 2174 square feet (202 square meters) of Solbian flex modules and newer bifacial modules. Rated at just over 33 kW, the real-world peak output of the panels is around 26 kW due to the panels’ fixed-angle placement all over the craft, optimizing for maximum cumulative output rather than peak efficiency.

At one point, solar panel upgrades were necessary. Initially, the vessel was equipped with hard-framed glass bifacial modules. Ocean water splashing forcefully broke some of the panels installed in front of the solar wings, so they were replaced with custom-made mono-face flexible panels. The bifacial panels that remained intact were kept at the rear, where reflection has a greater impact.

The design team selected flexible Solbian modules for their adaptability and durability and found that they were an ideal choice for curved surfaces, and their availability in various shapes and sizes ensured coverage for nearly any area. The modules are also robust enough to be walked on, a crucial feature for constrained spaces on the ship.

The ship uses 13 DC to DC converters, rated at 3 kW each, manufactured by BRUSA Electronik AG, an electronic mobility specialist based in Switzerland. These converters increase the voltage of solar output from 20 to 30 volts up to the 400 Vdc required by the main 100 kWh lithium nickel manganese cobalt oxide (LiNMC) batteries used for propulsion and the 24 Vdc 20 kWh battery used for control systems. The converters are equipped with Maximum Power Point Tracking (MPPT) controllers that optimize the conversion efficiency of solar modules under various lighting conditions. 

In strong winds, the Energy Observer can harness additional energy by engaging its propellers (in reverse), turning them into turbines that generate power. The ship’s innovative sails, known as Oceanwings, were first tested on this vessel and have since been adopted by the Canopée, a French container ship that transports rockets across the Atlantic. These sails cut fuel consumption by up to 30% compared to traditional diesel ships.

Bourserie said that the Oceanwings automatically adjust to maximize energy capture. These prototype sails have required ongoing development and some replacement components to withstand the rigors of maritime conditions.

The vessel is equipped with an innovative hydrogen storage and compression system that stores hydrogen at 350 bars in eight composite tanks, using a two-stage compression process developed with Nova Swiss to handle the transition from 30 bars (the electrolyzer’s output pressure) to 350 bars. The tanks offer a superior energy-to-weight ratio compared to batteries, storing ten times the energy at half the weight, and the multi-stage compressors are dramatically lighter weight than traditional models designed for fixed stations. This allows for efficient compression and storage of up to 62 kg of hydrogen.

The 62 kg of onboard hydrogen storage can power the ship’s fuel cells for approximately six days, providing 1 MWh of electricity and 1 MWh of thermal energy. Supplied by Toyota, the cells are a modified version of those used in the company’s Mirai vehicle.

While covering over 64,000 nautical miles, the Energy Observer generally navigated close to coastlines. However, it also undertook several significant open-ocean voyages across the Atlantic, Pacific, and Indian Oceans. These segments taught the crew to strategically manage their energy resources.

For instance, Bourserie told pv magazine USA, on days with good conditions – strong sun and wind that allows them to avoid using motors – “We don’t do electrolysis in navigation, [as it’s a] matter of protecting the compressors, and besides, the excess energy would not be so much. To continue harvesting power from the sun, we’ll cook in the afternoon for the evening or use the washing machine, producing fresh water from sea water at that time.”

On CNET, ship scientist Katia Nicolet underscored the daily importance of energy management on board. There were often instances where the crew would need to consult Bourserie on energy usage, asking questions like, “Can we run the dishwasher? Can we have a hot meal tonight, or are the batteries too low?”

The crew faced unique challenges from the COVID pandemic as well, including an extended period of greater than 45 days without docking, highlighting the resilience and self-sufficiency of both the crew and the vessel’s renewable energy systems.

As the Energy Observer prepares for its final Atlantic voyage from Saint-Pierre et Miquelon, it stands as a testament to the potential of renewable energy in powering our future on the seas.