The study claims that boil-off gas could prevent many LNG-fuelled ships from fully switching to shore power while in port. File Image / Pixabay

A new study commissioned by German environmentalist NABU and carried out by research institute CE Delft found that many LNG-fuelled ships are technically unable to fully switch to draw electricity from an onshore power supply during port stays.

This technical drawback is due to LNG-fuelled ships producing boil-off gas during fuel storage, even when engines are switched off, NABU said in an email statement on Wednesday.

If this gas cannot be safely used or removed while connected to shore power, it can lead to methane emissions or safety risks from rising tank pressure.

Onshore power is seen as a keyway to cut GHG emissions and air pollutant emissions from ships at berth and will become mandatory for many vessel types in the EU ports from 2030.

"The study also makes it clear that technical ship design and regulatory requirements for emission-free port operations have not yet been sufficiently coordinated," NABU said

"One particular problem is that LNG ships still have to safely discharge excess gas even when connected to onshore power, without being able to use it effectively for energy generation."

NABU said this means LNG could undermine emission reduction efforts in ports. It also warned that methane released from LNG ships has a much stronger short-term climate impact than CO2.

The study concludes that LNG is not a suitable long-term transition fuel and calls for greater focus on other low-carbon marine fuels such as green ammonia or methanol, alongside better coordination between ship design, port infrastructure and regulation.

"The results clearly show that LNG is not a viable transition technology for shipping," Sonke Diesener, shipping expert at NABU, said.