The fuel cell system for an unmanned underwater vehicle
According to Wendy Laursen, fuel availability will be a key factor in the success of fuel cells for ocean-going vessels.
The fuel cell is no longer on board Wallenius Wilhelmsen Lines’ car carrier Undine. The test installation fulfilled its purpose which was to develop the fuel cell itself and to test out the regulatory requirements for using methanol as its fuel. However, at 20kW, the solid oxide fuel cell installed was satisfying only a small proportion of the vessel’s auxiliary power.
The group’s vessels require between 2-3MW of installed power. “If you look at it from a practical point of view it would be better to have one system for both propulsion and auxiliary requirements,” says Per Tunell, head of environmental management at Wallenius Marine. “You could possibly accept one type of fuel for auxiliaries and one for propulsion. That’s what we operate today – auxiliaries on MGO and propulsion on HFO.”
Mr Tunell is determined to find solutions that reduce emissions and he is positive about the future potential for fuel cells, but not yet. “It is definitely an interesting technology with a lot of advantages, but it is not yet mature enough to go on board as a real alternative to the systems we are operating today,” he says. “A battery hybrid could be interesting but the energy content of batteries is low compared to fossil fuels so they are quite a bulky option the way they look today.” Batteries enable a fuel cell to be run continuously, and that gives a better running condition.
Fuel cells convert chemical energy to electric power using anodes and cathodes in a way similar to batteries except that they are fuelled continually to produce power continually. They require either pure hydrogen or fuels that can be reformed into hydrogen without the presence of sulphur. This makes pure hydrogen, methanol or LNG obvious fuel choices. Proton exchange membrane (PEM) fuel cells use hydrogen and can be either low or high temperature. High temperature technologies such as molten carbonate and solid oxide fuel cells, each differing in the type of type of electrolyte used, are more flexible and can use methanol, ethanol, natural gas or biogas as well as hydrogen.
Depending on fuel choice, fuel cells can emit carbon monoxide and methane but in quantities significantly lower than combustion engines running on LNG. Hydrogen fuel cells do not emit any carbon compound emissions.
The size of fuel cell installations cannot yet compete with combustion engines. While they can achieve electrical efficiencies of nearly 50%, the power density of a molten carbonate fuel cell is around 15W/kg and the power density of a high temperature PEM is around 60W/kg. In contrast four-stroke marine diesel and marine gas engines have a power density of around 90W/kg.
Fuel cells have gained the confidence of the boating and yacht community as reliable auxiliary power providers, and companies such as installation engineers Ynovex and manufacturer Fuel Cell Systems report a rapidly expanding market. Products up to around 5kW are typically used which can run on a variety of fuels including diesel, methanol and hydrogen, and in the very small quantities required for this application, these fuels can be conveniently obtained and stored on board.
But for commercial applications, fuel is still an issue and many passenger vessel installations have involved the use of PEM fuel cells and shore-side hydrogen fuelling stations. Examples of successfully running vessels include Alsterwasser in Hamburg with 2 x 50kW units from Proton Motor Fuel Cell, Hydrogenesis in Bristol with 12kW installed, Hornblower Hybrid in New York with 16 modules delivering 33kW and Nemo H2 in Amsterdam with a 60-70kW installation.
Nemo H2, built by Scheepswerf De Kaap, has a hybrid propulsion system consisting of a direct power supply from a fuel cell from Nedstack and an indirect power supply delivered by 55 large batteries. The electric drive determines the switching between fuel cell and batteries. The batteries are used when maximum power is needed or for emergency backup and are therefore keep at least 20% charged. Six reinforced bottles are used to store the hydrogen at a pressure of 350 bar. A total of 30kg can be stored – enough for nine hours of operation.
Scandlines and FutureShip, a subsidiary of Germanischer Lloyd (GL), are taking the next step in fuel cell capacity with the design of an 8.3MW fuel cell system that draws hydrogen from 140m³ tanks, sufficient for a passage of 48 hours at 17 knots. The zero-emission propulsion system will use excess electricity from wind turbines in northern Germany and Denmark to produce hydrogen for the fuel cells to power electrical pod drives. Excess electricity will be stored in batteries for peak demand, while total energy needs are reduced by optimised hull lines, propeller shapes and procedures in port.
At the moment GL is involved in several development projects under the umbrella of the light house project ‘e4Ships’ which are focusing on the use of high temperature fuel cells for the auxiliary energy supply of all kind of seagoing vessels. These fuel cells have a high energy efficiency compared to diesel generators and offer the possibility of using heat energy due to their high working temperature. For GL, the potential to use fuels like methanol or LNG is desirable as these fuels are expected to be available in sufficient amounts needed for the shipping industry in the short term and they can be a driver for the market entry of the fuel cell technology until a possible hydrogen infrastructure is developed.
The FellowShip project’s involvement with Viking Lady, an offshore supply vessel with a fuel cell running on LNG, has been a successful showcase for high temperature fuel cells, but it is not the only example. FuelCell Energy has a project with the US Navy Office of Naval Research to develop and test a hybrid solid oxide fuel cell-battery energy system for large displacement undersea vehicle propulsion. The project objective is to develop a refuelable power system, with high energy density, that is suitable for unmanned submersibles undertaking long duration underwater missions.
The system will be capable of generating power with no exhaust discharged outside of the vehicle. It will use JP-10 liquid fuel which is widely available at US Navy installations. JP-10 is a sulphur-free, synthetic fuel that displays very uniform properties and does not require a de-sulphurisation system. The fuel cell will be self-contained with no reliance on external air, and all fuel and oxygen reactants and all fuel cell products will be stored in the vehicle. The system is currently in laboratory development.
Additionally FuelCell Energy has pursued the marine market. With support from the US Navy Office of Naval Research and the Naval Sea Systems Command, the company participated in an advanced technology program to develop and demonstrate fuel cell electric power generators for surface ship applications. FuelCell Energy has demonstrated operation of its fuel cell technologies on natural gas, LNG, biogas, propane, coal-derived syngas, methanol, ethanol, biodiesel, and a variety of logistic fuels (JP-5, JP-8, JP-10, and NATO F76).
“A principal goal of this Navy Ship Service Fuel Cell Program was to demonstrate fuel cell operation on naval logistic fuels in a marine environment,” says Tony Leo, vice president for application engineering and advanced technology development at FuelCell Energy. “Special features were included in FuelCell Energy’s molten carbonate fuel cell design (trade name Direct FuelCell) to cope with shipboard operation including shock and vibration resistance, modified seals and insulation designs and provisions for the salt air environment.”
There are other projects underway to develop fuel cells suitable main propulsion. Bureau Veritas (BV) is providing classification services for a French project to develop a passenger shuttle which will include an 80kW solid oxide fuel cell stack. BV is also involved in the development of a fuel cell powered fishing boat design. This will involve education challenges as well as technological ones, says marine environment leader, Martial Claudepierre, as many fishing crews are not familiar with the combination of gas and electric propulsion. The 12m vessel will be designed for near-shore fishing.
Lisa Jerram, senior research analyst for Pike Research, a part of Navigant, is cautious about the commercial realities for fuel cells in commercial marine applications. “Over the next 10 years it will be a pretty small market unless we see some major shifts in terms of being able to use the fuel on the vessels,” she says. “I haven’t seen yet a company really break out and show that they can make the fuel cell commercially viable and grapple with the issues of getting the fuel on the vessel.” The impetus for fuel cell uptake might be more environmental than commercial, she says.
The growing adoption of hybrid electric powertrain systems and the projected growth in the number of vessels burning LNG as fuel, could lead to wider adoption of fuel cells, says Professor Zuomin Dong from the University of Victoria, Canada. Professor Dong has led multi-million dollar research programs on hybrid electric and fuel cell cars and, most recently, for a research ship.
The growing demand for dual-fuel and LNG engines for vessels means that the trading fleet will become increasingly familiar with the technology and more will be carrying LNG as fuel. Additionally, Professor Dong envisages more electric propulsion systems with a diesel generator because electric motor technology is continually improving. He sees the industry changing over the next 10-20 years to a position where fuel cells are used as auxiliaries. Beyond that, LNG fuelled engines could become the stepping stone for the wide adoption of LNG fuelled fuel cells as prime movers