How do hybrid vessels work?
Hybrid ships have exploded in popularity over the last decade as ship owners seek to decarbonize and reduce costs. Hybrid vessels use at least two methods of propulsion, usually diesel and batteries, to provide power for movement and station keeping. This combination of power methods provides vessels the benefits of long range diesel power with short-term bursts of electric power, smoother operation, and zero emissions station-keeping. Today we’re going to take a closer look at hybrid vessels, how they work, where they fit in between diesel and pure electric, and how OneStep Power fits into it all - read on!
Harvey Energy Tri-fuel vessel that runs on diesel, LNG, and battery power. Image from Harvey Gulf.
What is a hybrid vessel?
At their core, hybrid vessels use an engine combined with an electric battery system. These systems are recharged as the vessel travels and has excess energy, which is put into battery packs. The batteries can then provide extra power for peak shaving or fully run the vessel in lower power situations. For dynamically positioned vessels, hybrid power is especially useful as the DP systems give the ship the ability to hold station without dropping anchor, providing precise location keeping or moving along a precise route via computer controlled thrusters. These vessels may operate around rigs, offshore wind turbines, over research areas, and for offshore construction and repair. The ability to operate on 100% electric power reduces emissions and prevents issues with running generators at low load where they aren’t very efficient. The reduction in vibration from electric power is also more comfortable for the people on board who may be working, resting, or performing research.
Most hybrid ships have two methods of propulsion - most common is diesel and electric battery driven. Depending on the vessel, diesel direct drive can be used at high power and diesel electric or pure electric can be used at lower power. They can be small like an inland ferry or larger like an offshore support vessel. Although many new vessels are built with hybrid operation planned from the design stages, older vessels can be retrofitted for battery power. Companies like Wärtsilä offer hybrid retrofits for existing vessels like the Hagland Shipping AS Hagland Captain, a short-sea shipping vessel that was fitted with hybrid technology. Vard Electro offers turnkey hybridization solutions like the SeaQ Energy Storage System (ESS), commonly used in retrofits. Many of these new systems can be installed easily and some can even be containerized for an almost drop-in installation, as seen in the Rolls-Royce Marine battery containers below.
Rolls-Royce battery hybrid container solution. Image from DNV.
Why hybrid propulsion?
Battery hybrid power started in the 2010s as a way to increase fuel-efficiency on ferries and workboats. The solutions did and still do estimate fuel savings of 10-20%, but that’s only one of the benefits. Running a battery hybrid system, vessels should be tested to run in closed bus operation, which can save hundreds of thousands of dollars per year in costs. Peak load shaving helps reduce fuel consumption, where battery systems provide assistance during short-term spikes in demand to reduce the strain on the generators. Most ships can also run on battery power alone running in and out of port, and while performing dynamic positioning operations. All these factors reduce strain on generators and allow some generators to be safely shut down when not needed, lowering maintenance costs. Electric propulsion also creates less vibration, meaning more comfort for people on the vessel.
More recently, there has been a growing focus on decarbonizing shipping, and hybrid vessels can reduce emissions by 10-30% over regular diesel fuel ships. This is an important factor as shipping aims to reduce carbon intensity by at least half by 2050, with many companies like bp and Shell pledging carbon neutrality by 2050. Popularity of hybrid battery electric systems continues to grow as both monetary and environmental benefits become easier to achieve with more advanced and compact systems. Hybrid systems have also paved the way for electric systems and pure electric vessels, which are now becoming more common. Hybrid propulsion provides the extra benefit of energy dense fuel and generators with smooth running, no emissions electric power.
SeaQ hybrid power system with battery power in green and other power in red. Image from Vard.
Hybrid vs battery power
Hybrid has long been the favorite when compared to pure battery power for its versatility and familiarity. It’s versatile in that it provides a way for ships to reduce costs and lower emissions while keeping the traditional diesel power plant with which mariners are familiar. But hybrid power has opened the door to fully electric ships, with many people asking: “why don’t we just make ships fully electric?” To explain why electric hasn’t taken off as fast as it has with other industries, let’s take a look at automobiles: since Tesla popularized the electric vehicle, many automakers have followed suit. Car companies all over the world are electrifying their lineups, and many luxury automakers like Bentley, Cadillac, and Mercedes plan to go fully EV by 2030, with others following suit after. Only recently has motor and battery technology matched up to make these vehicles possible with the right combination of power, efficiency, and range. So why not make ships electric? Large container ships and ocean crossing vessels need too much energy to be powered by current electric technology. Fossil fuels have a higher energy density than batteries, which means they can travel farther with the same amount of energy storage space dedicated to a fuel tank rather than a battery or fuel cell. However, electric ships are already here and quickly gaining popularity for shorter voyages.
As battery technology continues to improve, we are seeing fully electric vessels like ferries and short trip transport ships. Ferries are ideal for battery power as they generally have short voyages, are smaller than large cargo vessels, and need good stop and go power. The elimination of emissions, noise, and vibration are welcome benefits to passengers and coast line residents. Ferry routes are regular and fixed, so charging infrastructure can be installed and maintained easily. Scandinavian ferry operators led the way in popularizing electric and hybrid ferries, but other countries like the United States are quickly following suit. The largest plug-in electric vessel currently is the Color Line Color Hybrid, a 160m long ferry with capacity for 2,000 passengers and 500 cars. It has a 65 ton, 5 megawatt battery pack that can be recharged on shore in an hour. It operates silently in Norway, without any emissions, on environmentally friendly power.
“Color Hybrid (Copyright: UAvpic)”. Image from Marine Log.
As the entire maritime sector seeks to decarbonize, some areas fit especially well with hybrid technologies. Offshore wind farms seek to provide green, renewable energy, but need offshore support vessels, or OSVs and construction vessels to build and maintain the wind farms. Hybrid vessels have plenty of fuel for long transits to the worksite, while allowing for battery-only operations once on location. CWind has developed a new crew transfer vessel, or CTV that is a hovercraft with catamaran hulls that runs on hybrid power. The dual system means it can reach wind farms that are being developed further offshore while reducing emissions. It can also travel at speeds of over 43 knots with 24 passengers on board, and is more than 20% more efficient than a traditional CTV travelling at only 24 knots. It is expected to be zero emissions while on site at the turbines providing a total emissions reduction of 30-50%, according to CWind.
Equinor sought to decarbonize early on and Eidesvik Offshore responded by converting the Viking Energy into a plug-in hybrid vessel. The 5000 ton supply ship received “a massive 30% reduction in consumption and emissions when operating in dynamic positioning (DP) mode”, according to Equinor. The vessel was built in 2003 as the world’s first dual-fuel platform supply vessel (PSV), using diesel and LNG, or liquified natural gas. In 2015, they were the first to install a 653 kWh/1600 kW battery on a supply vessel for propulsion. Fuel consumption has been reduced by about 16-17% on average, with as much as a 28% reduction at times. The crew credits the battery system for a quieter, smoother, and more maneuverable vessel, all which makes the ship safer and more stable.
“Knut Idar Haugland in Equinor, captain Svein Kallevåg and Jan Lodden of Eidesvik on deck with the battery pack in the background. The fact that a battery pack of this kind can be installed at any time makes this technology a little more flexible than many other “green” solutions.” Image from Equinor.
Hybrid vessels paved the way for more technology and all-electric vessels, but they have a place in their own right. Hybrid systems can make ships safer, more fuel efficient, reduce maintenance costs, lower emissions, and provide a smoother ride for the crew. Until batteries can provide an energy density equivalent to fossil fuels, hybrid vessels give the double benefit of travelling long distances with the savings and smoothness of batteries and electric drive. It’s getting easier to convert older vessels to hybrids - we look forward to the future electrification of ships, and getting those ships into closed bus operation!
OneStep Power tests vessels so they are prepared to run in closed bus operation. Case studies are finding running in closed bus can save over $750,000 per year on a dynamically positioned rig. Our technology makes closed bus testing fast and easy, and completely safe for all ship systems. Give us a call if you’d like to learn more about running your vessel more efficiently, saving money, and reducing emissions!
Happy Fun Fact Friday!