• Marine

    Future electric transportation with a highly efficient drive train will vary a lot in their reachable range because of the different energy demand requirements in different conditions, this is also called dynamic or variable duty-cycle. The main issue to improve the range of any means of transportation is the minimization of energy consumption!

    On the other hand it is important to recuperate or harvest energy whenever possible. For example, if a combustion process is used, why waste a lot of thermal energy from the exhaust? If the sun is shining on a ship, why not use it? Whatever the available energy, it has to go hand in hand with minimizing the energy consumption.

    Electric propulsion is very effective in ships (diesel-electric is only first step) that are operated in partial load conditions for a significant portion of their time, e.g. inland ships that require up-, down-stream, harbour and canal operation. The main advantages of the diesel-electric propulsion are: flexibility (better space utilization and redundancy), more economical operation, less maintenance and reduced environmental pollution. In these hybrid ships, the popularity of diesel-electric propulsion systems (0.5–3.0 MW range) is ever increasing, since potentially 10-25% diesel fuel can be saved on specific journeys. Of course, also in shipping applications operating costs should be minimized, hence it is no surprise that fleet owners are considering high-efficient direct-drive machines. Of course, there are different topologies requiring sizing criteria of components and related control strategies, finalized to maximize different objective functions: weight and space reduction on-board, fuel economy, pollution reduction or optimized efficiencies.

    Electric and Hybrid-Ship Propulsion Solutions

    Most inland ships today are still equipped with a traditional propulsion systems based on an internal combustion engine (ICE). However, new ways are continuously introduced to conceive propulsion and power systems for inland shipping. Within these propulsion solutions, medium-speed diesel or gas engines (variable speed ICE’s) are connected to the propeller through a reduction gear. Considering transmission losses, it means that for the same propeller power, medium speed diesel engines must develop about 2-5 percent more power in the geared design at full load. However, at partial load considerably more losses are present. A hybrid-propulsion could be considered as a first step to fully electric, where a propulsion with a geared ICE (medium-speed engine is connected to the propeller by a transmission and shaft) is combined with a high torque electric machine, i.e. a parallel hybrid solution.

    This parallel hybrid ship propulsion allows for three modes:

    • Electric cruise mode; at low speed, hence low power (<250kW) the boat is driven by the electric machine. Diesel-electric generator sets and/or battery pack are used to provide the energy for this electric cruising.
    • Generator mode; the propulsion is provided by the diesel engine(s) and the hotel load is supplied and/or an on-board battery pack is charged. This allows one or two engine-generator groups (or generator sets) to be switched off, since enough power can be generated in generator mode.
    • Boost mode; the high speed and high power (<350kW) range uses the Boost mode to support the combustion engine with the constant torque of the electric motor. Also an improved response of the propulsion occurs through the boost mode.

    The resulting fuel efficiency depends on many variables, e.g. ship type (length, width, hull profile, etc.), trajectory (river, canals, depth, etc.) and load-cycle (frequency and magnitude of accelerations, duration of the stops, distances to be covered, etc.). Although that on average a hybrid propulsion always improves fuel efficiency due to the smaller main diesel that can be installed. Considering the inland application, for some specific journeys, fuel savings can even be 25%.

    Waste Heat Thermoelectric Conversion From Steam

    How to convert waste heat into electricity? The co-called Green Turbine produces electric energy with co-generation of heat. This alternative renewable energy sources is surely not new. Within this system super-heated steam is converted into electricity by two counter-rotating turbine wheels that are directly connected to two high speed (>25,000 rpm) electrical generators. As such, various waste energy sources can be utilized by employing this system. For example, one of the applications of the Green Turbine is to generate 15kW of electric power from waste heat from a diesel engine (within the tailpipe about 150-200kW of thermal power). As such, energy is extracted from the process of pressure reduction in steam and is convert to electrical energy fed back into the grid and/or used for island mode on ships or remote locations.