From Waste Heat to Value: How we generate electricity from waste heat at sea

Step into the engine room and see how the surplus heat from ship engines transforms into steam – an energy source that both heats the ship and provides electricity for life on board.

When the two sister ships were launched in 2013-14, they became the world’s first large cruise ferries powered by liquefied natural gas (LNG). By producing useable energy from the surplus heat generated by the ship engines, Fjord Line took another major step forward in energy efficiency.

"We use the high temperatures from exhaust gases to create steam, which is then used both for heating and generating electricity through a steam turbine. The steam covers the heating needs, while the electricity powers lighting on board. You can compare it to a mini power plant," explains Jimmi Astor Soelberg, Senior Chief Engineer on MS Stavangerfjord.

From Engine Power to Light and Warmth

When a cruise ferry leaves the harbour and sets course for its destination, tremendous forces are at work. The four LNG-powered ship engines on each of Fjord Line's sister ships propel 15,000-tonne vessels at high speed, carrying up to 1,500 passengers.

These powerful engines emit exhaust gases at extreme temperatures of up to 480°C, which would normally dissipate into the air. On Fjord Line's two sister ships, however, this surplus heat is put to good use: heating the ship and generating on-board electricity. This reduces the need for electricity from the ship's diesel generators and for heating from diesel-fired boilers.

"By reusing this energy, we become up to 95% self-sufficient in on-board heating and achieve significant fuel savings on the on-board diesel generators and diesel heated boilers. Overall, we cover 40% of the ships’ total energy needs from waste heat," Soelberg states.

Into the Ship’s Heart

To understand how this process works, let's go behind the scenes and descend to Deck 2 – the technological heart of the ship, where heat transforms into steam and electricity. Deep within the ship, we find four LNG engines distributed across two engine rooms – one at the front and one at the rear. At the back of the ship is the control room – the ship's command centre.

"From the control room, we manage and monitor everything happening on board, including the engines and the steam turbine," Soelberg explains. "The ship engines drive the propellers using LNG, while the engines emit exhaust gases with temperatures reaching up to 480°C. It's this waste heat that we use to produce steam, which in turn generates electricity."

Senior Chief Engineer Soelberg has been part of Fjord Line for 17 years and played a key role in the construction of MS Stavangerfjord and MS Bergensfjord in 2013 and 2014. The LNG technology and the integrated mini power plant for energy recovery have been central to realising the ambition of increasing energy efficiency ever since.

No Heat Wasted in the Steam Turbine

Amid the steady hum of engines and machinery, the Senior Chief Engineer explains how the transformation process begins. First, heat from the LNG engines is directed into large steam boilers filled with water.

"The hot exhaust gases enter the steam boilers, heating large amounts of water circulating through a network of pipes. When the water reaches boiling point, it turns into steam. Some steam is used for heating, while the rest goes to the turbine room, where it drives a turbine that generates electricity via a generator," Soelberg explains.

Utilising waste heat for electricity generation reduces the need for energy from other sources and offers real operational benefits. The higher exhaust temperatures of LNG engines compared with traditional engines also make heat recovery significantly more efficient.

"This system allows us to reduce both emissions and fuel consumption by making greater use of the engines' waste heat," Soelberg says.

Fact sheet – Emissions