Recent developments open the way for cruise ships to enhance energy efficiency using batteries and waste heat energy
Cruise shipping is newly open-minded when it comes to the energy sources that can improve vessel efficiency and 2020’s global 0.5% cap on fuel sulphur content is not the only reason. Rapid advances in battery technology mean that the cruise sector could emulate the car industry in exploiting hybrid power, albeit differently packaged.
Projects seeking to optimise energy use begin at the design level for both newbuilds and conversions. Our starting point is to establish what the owner’s managers want to achieve and their thoughts on how to go about it. Then we analyse their wishes and make recommendations, advising them on the goals that are achievable and where we might have to look at alternative solutions.
Efficiency improvements could come from considering new energy storage techniques – either electrical or thermal – but they might also result from reclaiming efficiencies from existing systems. What is important is the complete energy flow of the vessel.
An overall understanding of the energy balance between production and consumption is needed, so that insight can be offered into where the energy should be used and where it is typically wasted. We need to establish what the energy sources of the vessel are/will be, and where efficiency gains might be available.
You could, for example, describe waste heat energy as an alternative energy source which can be reused by being fed through absorption chillers, organic Rankine cycle or steam turbines.
In the past, container shipping companies have used steam turbines to reclaim the plentiful waste heat generated by 60-70 MW two stroke engines. Until recently, cruise ship engines generating on average 9-16 MW have not been large enough to justify sizeable steam turbines, especially when considering the typical operational profile of a cruise ship. However, we are seeing a change because now it is becoming possible to fit small steam turbines on these ships, partly because of lower heat demand in traditional steam processes with LNG fuel and fresh water production and partly as a result of improved waste heat energy recovery systems.
Foreship is undertaking several feasibility studies evaluating next-generation waste heat recovery systems for cruise ship owners.
One goal is to minimise the use of oil fired boilers to save the fossil fuel that would otherwise be burned but while also serving the combined needs of the galley heating process, fuel heating and the reverse osmosis plant to produce fresh water and support laundry services.
New potential is also fast-emerging for cruise ships to exploit battery power, where the energy stored can be derived from a variety of sources.
Customer interest has always been there, but objections to battery technology in the cruise market has always been based on space and cost; now both are coming into place. Foreship has already been involved in a feasibility study to evaluate the use of battery power for a leading cruise operator.
Furthermore, shipboard battery options are developing fast. In late 2016, one battery maker was offering a 6.5 kWh battery with dimensions of approximate 36 cm by 30 cm by 30 cm. Six months later, the same supplier is offering a 9.7 kWh battery of the same size. Typically, a high charge and discharge rate has been one of the major criteria to minimise the size of these batteries due to their large size and weight. But, with increased density and lower price/kWh, we see a step away from this. With moderate charge and discharge rate, we expect a longer life time of the batteries as well.
It is not likely that we will see large numbers of ships operating solely on batteries but I believe 40-60% of all vessels could benefit from auxiliary battery load exploitation to support peak load shaving. A small number of ships – say, 5% of the fleet – will also use them for specific duties: in the cruise sector, for example, battery power could be useful during port entry, where the environmental gains would be strong.
About the writer
Foreship appointed Jan-Erik Räsänen as head of new technology in 2016. Mr Räsänen was formerly with ABB and is an acknowledged expert in shipboard energy optimisation. He has a breadth of experience in battery power and fuel cell development