Hydrogen, batteries and fuel cells contribute to making inland towage sustainable
Inland pusher tugs are being built in Europe with batteries, while others will use hydrogen with fuel cells. Environmental requirements for pushboats are tightening, mandating low emissions along inland waterways in continental Europe.
For zero-emissions operation, hydrogen is the cleanest option. But limited storage capacity and availability mean this fuel is only an option if there are sufficient supplies along regular routes. With a limited supply of other alternative fuels, batteries are used to operate alongside hydrogen-burning engines or fuel cells. Another benefit of battery power is the fast start-up and acceleration it offers.
“Batteries are used to accommodate the dynamic behaviour of the vessel which the other alternative fuels cannot supply the energy for,” says EST-Floattech founder and technical director Diederick Stam. The company has supplied energy storage systems to several all-electric pusher tugs, including 2022-built Elektra, which also receives power from hydrogen fuel cells for operations in Germany, and Kotug’s E-Pusher series.
“Fuel cells can be used for the full energy requirements of the propulsion systems, but they cannot be switched on at full power at once,” says Mr Stam. “That is where the batteries come in, as they can be immediately switched on at full power.”
EST-Floattech’s modular battery system Octopus is designed with one interface to handle different energy carriers and chemistries such as nickel, manganese and cobalt oxide (NMC) or lithium iron phosphate.
“Currently the most used chemistry is NMC,” says Mr Stam. “Battery modules with power converters are a relatively simple system. Batteries can supply the required amount of energy for sailing profiles, and they can charge more easily on shore where charging points can be fixed.”
Mr Stam says future pusher tugs will have a combination of hydrogen fuel cells and batteries. “Hydrogen still requires the battery system to perform during peaks or other dynamic energy requirements,” he says. “In combination and alongside each other, batteries and hydrogen fuel cells can make a major contribution to making shipping more sustainable.”
Technology to improve hydrogen storage would reduce these challenges and make it more viable for tugboats operating in ports.
Australian technology innovator Rux has developed metal organic framework tanks to store hydrogen in higher volumes and lower pressures than liquefied or compressed gases. This uses an iron salt-based powdered material that acts like a sponge for hydrogen, so around 900-1,000 kg of hydrogen could be stored at 30 bars.
Rux Energy has successfully tested a demonstration tank of this type as a prototype and plans to manufacture tanks to store up to 1,000 kg in future.
Rux worked with tug owner Serco and other companies in a UK government innovation study, to consider the technical and commercial viability of powering three tugboats supporting naval ship docking and manoeuvres in the Port of Portsmouth in southern England.
According to Rux Energy head of strategy Marius Bosch, this study demonstrated its technical viability and its potential commercial application over the 30-year lifespan of tugs.
“Our feasibility study shows this would work on a total-cost-of-ownership basis and would be more cost effective than diesel,” he says.
Renewable energy would come from a port-based solar farm to run an electrolyser to produce hydrogen stored in Rux tanks and be supplied to tugs running on dual-fuel or purely hydrogen engines, enabling ’charge and discharge’ and refuelling all year.
“We have shown it works for three tugs using technology we have developed,” says Mr Bosch. An electrolyser of around 4.0 MW would need to be installed, of which 3.4 MW would be required daily to ensure “there is enough for the entire year.” A solar facility of 100 m by 70 m could produce enough energy to run this electrolyser in a room of 50 m by 25 m.
