Eirill Bachmann Mehammer, Henrik Strand, Niklas Magnusson, Kristian Solheim Thinn, Espen Eberg
IMAGE LICENSED BY INGRAM PUBLISHING
Fishing fleets are targeted for electrification in many parts of the world. These vessels represent a large potential for emission reductions by transitioning from fossil to hybrid and electric propulsion. However, a massive electrification of such vessels requires a disruptive green shift, introducing safe and reliable battery charging infrastructure along the coastline. Up to now, electric energy has been supplied only, if supplied at all, for auxiliary loads, such as lighting, heating, and ventilation, when fishing boats are in a harbor. The standard connection method has been through industrial connectors. In other sectors, such as automotive, other connector types are used. When batteries are installed on fishing vessels, high charging powers and currents are deployed, calling for robust connector solutions.
The purpose of this work is to give insight into relevant connector solutions for electrical charging and their advantages and limitations. This forms the basis for comparing them with respect to desired characteristics, such as cost, safety, usability, capacity, and flexibility. The focus of this article is on small fishing boats, but the evaluations and findings are also relevant for other vessel segments that consider different types of connectors.
There is a need to develop standardized requirements for the interface between vessels and power stations in terms of power capacity, communication protocols, and endurance to the marine environment. There exist standard solutions for shore power connections for larger vessels as well as for aircraft connectors and electric vehicles, but the fishing fleet has different needs than those segments in terms of power demand, robustness, and ease of use. There also exist solutions with different automatic connection mechanisms as well as wireless inductive charging and battery swapping, but these are mainly designed for larger vessels, such as ferries. There is a lack of long-term experience with maritime plug-based solutions, and little is known about long-term aging and degradation under dynamic electrical loading in wet and salty environments, which may limit the lifetime of the connectors.
The risk of running out of power at sea is a major concern with the use of batteries on board fishing vessels. The low energy density of batteries compared to fossil fuels challenges the range and flexibility of the vessels. The operational pattern of the fishing fleet is highly irregular due to variations in fish location and weather conditions. To satisfy variable energy demands and ensure flexible zero-emission vessels, a proposed solution is to develop concepts for mobile offshore energy supply. In such solutions, which are expected to be costly, vessels can recharge from mobile power stations at sea, anchored near fishing sites. At the component level, knowledge is to some extent transferable between onshore and offshore systems. However, the absence of an electricity grid requires stand-alone systems and the optimization of energy efficiency for recharging. Both onshore and offshore charging concepts also require high-level data communication to monitor the load balance and control the power flow between vessels and charging stations. Another way to ensure that fishing vessels have enough energy is to use hybrid propulsion with backup fuel, where the batteries are dimensioned for regular operation.
The facilitation of power supply in ports for battery charging and auxiliary loads is turning into a requirement. In July 2021, the European Commission released the Fit for 55 package, with legislation to reach carbon dioxide reduction targets of 55% below 1990 levels by 2030. This is an operationalization of the European Green Deal targets and a major step toward a decarbonized European Union (EU) by 2050. The package includes the Alternative Fuels Infrastructure Regulation, which requires that all ports in the Trans-European Transport Network offer onshore power supply to vessels from 2030.
In Norway, the electrification of transport is mainly influenced by public procurement processes and regulations related to emissions (i.e., technology-neutral regulations). There are governmental support programs for the installation of equipment for shore power connection, onboard vessels and in ports, providing up to a 50% subsidy. Most of the existing battery–electric vessels are ferries operated in the national network, and the installation of the charging facilities for these vessels has largely been included in public procurement processes.
Norway’s first full-electric passenger ferry was launched in 2015. In July 2022, 58 electric ferries were in operation, with 14 more to come before the end of the year. The maritime electrification follows the Norwegian shift to electric vehicles, where 65% of all new passenger cars sold in 2021 were fully electric. Norway’s coastal fishing fleet, consisting of around 6,000 vessels, which predominantly use marine diesel for propulsion, may be the next target for an electrification revolution.
There is a wide range in size as well as energy and power needs of the vessels in the fishery and aquaculture sector. The Norwegian Shore Power Forum suggests vessel categories based on demand for shore power; see Table 1.
Table 1. The vessel categories based on demand for shore power.
The most relevant vessel categories with regards to electrification of the fishing fleet are categories 3 and 4, illustrated in Figure 1. These have the highest number of vessels and represent a large potential for emission reduction with a transition to electric propulsion. The difference between categories 3 and 4 is the option of dc shore power connection in the latter category, permitting fast charging.
Figure 1. Typical Norwegian fishing boats belonging in category 3 or 4, described previously.
The charging of electric and hybrid vessels can be divided into two main segments: fast charging and normal charging. Fast charging (typically using dc) is needed when a vessel is visiting a quay, for instance, during delivery at a fish processing plant, with limited time for charging. This can also be referred to as opportunity charging. Normal charging (typically using ac) can be used when vessels are in their home port and have more time for charging, often overnight.
In contrast to ferries, fishing vessels usually have a less predictable operational profile with frequent and rapid variations in power output as well as variable range requirements, demanding charging and bunkering flexibility. The operational patterns of fishing vessels are difficult to predict since they depend on the varying location of fish. Hence, the power needs and load profiles in ports will vary significantly. In some cases, charging solutions with high capacity (high power) will be needed.
The charging solutions for vessels in the fishery and aquaculture sector should be cost-effective and safe to make it attractive to transition from fossil to electric and hybrid propulsion. They should be prepared for future development while considering which technologies are commonly used today. Furthermore, the solutions should be easy to use—like the charging solutions developed for electric vehicles—but robust enough to withstand the maritime environment.
To ensure safe and easy-to-use charging solutions, data communication is key. Electric vehicle charging typically supports both low-level and high-level communication. Low-level communication is used for safety-related functions, such as providing the maximum permissible current and indicating whether the vehicle/vessel is connected and ready to charge. A pulsewidth modulation voltage signal alternates between two defined levels, transmitting information over the control pilot contact. Charging solutions for fishing vessels should, at a minimum, support low-level communication.
High-level communication is used for more complex data transfer, such as load balancing and battery control, dc charging, “plug and charge,†and authorization and payment services. The high-frequency signal is transferred using dedicated physical connections over Internet Protocol-based methods. Charging solutions for fishing vessels should support such communication in cases where there is a need for monitoring and balancing a charging station’s total load and power flow, which could be the case when a large fleet charges simultaneously.
A variety of connector types exist on the market today. Table 2 gives an overview of technologies considered in this article and in which markets they are used.
Table 2. The technologies used in different markets.
Vessel categories 1 and 2 in Table 1 use the following International Electrotechnical Commission (IEC) standards today, respectively:
These standards are, so far, mainly used for auxiliary loads and not for battery charging. Both refer to separate standards that describe the connectors, with design requirements and so on. Connectors for HV shore connections are described in IEC 62613-1 and 2, while connectors for LV shore connections are described in IEC 60309-5. IEC 80005-3 is a publicly available specification that is still under development and may eventually include vessel categories 3 and 4, thereby becoming more future-proof. It specifies a 350-A connector, which provides high capacity but is costly and cannot easily be handled manually. In terms of flexibility, the connector can be used at different voltage levels (e.g., 400, 440, and 690 V) but only in three-phase systems. It has a control pilot circuit but no other form for communication.
Industrial connectors are by far the most common connection type and found in the vicinity of industry buildings, marinas, camping sites, and parking garages. A main difference from many other connectors evaluated in this article is the lack of communication lines. In most cases, safe use requires administrative measures due to the lack of a control pilot circuit. On the other hand, industrial connectors are easy to use, and the cost is low. Furthermore, different types have been developed for several voltage and current levels as well as both one-phase and three-phase systems. The most relevant standard for industrial connectors is IEC 60309, but there also exist many vendor-specific types that do not, or only partly, fulfil the requirements of the standard. Figure 2 depicts the sockets of industrial connectors at a marina. Industrial connectors are commonly used by fishing vessels, especially small and/or old vessels (category 3, described previously). However, they are not considered future-proof since their suitability for the battery charging of vessels is questionable.
Figure 2. Industrial sockets (ac) installed at a marina.
Airports have standardized connectors for the power supply of parked aircraft, from aircraft ground power units. These are based on the International Organization for Standardization 461-1/2 standard. The power supply is 115 V, 400 Hz or 28 Vdc. The typical current rating of the ac system is 90 kVA, 450 A. Large airplanes may have multiple sockets.
The Norwegian Shore Power Forum is working to standardize a three-phase connector for the aquaculture sector that can be handled manually, has a sufficient power rating, supports communication, and is safe to use and mechanically robust for a maritime environment. The forum has decided to employ a connector with a current rating of 250 A and voltage level of 400 V at 50 Hz and 440 V at 60 Hz. Communication is said to be supported but not implemented in the current design of the connector. The four electrical contacts (three phases and a ground) and four pilot contacts are arranged similarly as the 350-A, 690-V design referred to in the IEC 80005-3 standard. Since the aquaculture connector standard is still under development, today’s use is limited. The aim is that battery charging should be supported in a better way than in the shore power standards. Furthermore, the cost is expected to be lower than for the IEC 80005-3 connector.
The IEC 62196 type 2 connector is widely used for charging electric cars, employing the grid voltage and frequency. The European Commission has announced the use of type 2 as the common standard for electric vehicles in the EU, resulting in mass production and low cost. The connector has a control pilot circuit as part of the low-level communication but no high-level communication. It has a rated charging power of 43 kW, which could be too low for some applications and the larger batteries of the future.
In North America and Japan, the type 1 connector is more common. The voltage and current characteristics are similar, and the communication protocol is the same for types 1 and 2; hence, only the socket (and not the entire charging station) must be replaced for different markets. Type 2 is more flexible than type 1 since it can handle both one-phase (70-A) and three-phase (63-A) ac, while type 1 supports only one-phase (32-A) ac.
Although there are already pilot installations, it is still unclear whether the type 2 connector can be applied to maritime vessels without modifications. For example, in Oslo, Norway, a maritime charging station for leisure boats has been installed with both ac charging type 2 connectors and dc charging with combined charging system (CCS) combo 2 connectors (Figure 3). Such low-risk installations will help to gain experience using automotive connectors in maritime applications. Several manufacturers are developing maritime charging solutions based on type 2, including Zaptec automatic power management and the Easee Equalizer.
Figure 3. A maritime charging station with a Zaptec charger and type 2 connector in Oslo. (Source: Plug; used with permission.)
CCS combo 2 consists of a type 2 connector with the addition of two pins for dc voltages up to 920 V. This enables faster charging but increases the cost compared to the type 2 connector since rectifiers are needed onshore. Both low-level and high-level communication are supported. The power rating is specified as 350 kW using dc. In North America and South Korea, CCS combo 1, which consists of a type 1 connector and two dc pins, is more common. CCS combo 2 is more flexible than CCS combo 1 since it can handle dc, one-phase ac, and three-phase ac.
CCS combo 2 is being considered for the charging of electric vehicles, electric vessels, and small electric airplanes. Tesla, the world’s largest electric car manufacturer, offers its new cars in Europe to be compatible with CCS combo 2. In Florø, Norway, the world’s first combination charger, which can be used by vehicles and vessels at the same time, has been installed. Another example is the Mine Smart Ferry, in Thailand, which uses 26 CCS combo 2 connectors for charging.
The Charging Interface Initiative (CharIN), the organization behind the CCS connector, is now developing a new charging standard for higher power: the megawatt charging standard (MCS), which was launched and demonstrated in June 2022. The final publication of the standard, with technical specifications and requirements, is expected in 2024. The MCS is intended for the charging of large electric vehicles, such as heavy-duty trucks and buses, but also expected to support applications in marine, aerospace, mining, and agriculture. According to CharIN, the MCS connector will be rated for dc voltages up to 1.25 kV and currents up to 3 kA, with a maximum power rating of 3 MW.
In the on-going EU project Transport: Advanced and Modular, where a battery-powered DNV class 1A high-speed light-craft-compliant vessel is developed, multiple CCS combo 2 connectors are used in parallel to supply 2.3 MW of charging power. It is planned to replace CCS combo 2 connectors with the MCS when it is commercially available. However, the MCS will be backward compatible with CCS (presumably through an adapter).
Charge de Move (CHAdeMO) is a dc rapid charging system with a connector developed by Japanese automotive manufacturers and Tokyo Electric Power. The connector supports dc only, has a rated charging power of 400 kW, and supports high-level communication. The cost is similar to CCS combo 2. CHAdeMO was used on the Raicho 1 10-passenger vessel in Japan, in 2011. Since then, CHAdeMO has scarcely been used as a charging solution for vessels. However, it is still commonly used for the charging of electric vehicles produced by Japanese manufacturers.
The Guobiao (GB/T) charging standard is commonly used for the ac and dc charging of electric vehicles in China. The GB/T ac standard uses a connector with a pin layout similar to type 2, but the two connectors are not compatible. The ac connector is rated for a charging power of 28 kW and supports both one-phase and three-phase systems. The cost is slightly lower than for type 2. The GB/T dc fast-charging standard uses a different connector, shown in Table 3, which is rated for a charging power of 250 kW and supports high-level communication. The cost is slightly lower than for CCS combo 2 and CHAdeMO.
Table 3. An overview of common automotive connectors.
The China Electricity Council and CHAdeMO are developing a new unified ChaoJi system, also known as CHAdeMO 3.0, with charging power up to 900 kW. The new system will replace both GB/T dc and CHAdeMO and feature backward compatibility with these two connectors as well as with CCS, through adapters. Table 3 presents some of the most commonly used automotive connectors in the world today. Note that the MCS and ChaoJi are proposed solutions that have not yet been standardized.
In addition to conventional plug-based methods for power transfer over ac and dc, there exist alternative methods, such as automated connection, wireless charging, and battery swapping.
Many of the charging systems for electric ferries require power capability in the multi-MW power range. Furthermore, these systems usually have very short charging intervals and require fast and automated connection and disconnection, which complicates the use of conventional plug-based connectors. Several different concepts have been adopted depending on the requirements for individual vessels, including pantographs and open sliding contacts, gravity-assisted plugs, and wireless power transfer.
There are two types of wireless power transfer: capacitive and inductive. For high-power battery charging, most of the research and applications have been based on inductive power transfer, where the energy transfer is based on a magnetic field between a transmitter and receiver coil. The two coils act like a transformer, with a low mutual inductance. Converters are used for generating a high-frequency square wave voltage for the transmitter coil and rectifying the high-frequency output of the receiver coil. The two coils provide galvanic isolation so that there is no need for a dedicated onboard transformer. A 1.2-MW inductive charging system was successfully tested on the ferry MF Folgefonn in Norway, in 2017.
Using wireless power transfer technology for the charging of vessels has some advantages over wired solutions. First, because plugs, receptacles, and dynamic cables can be replaced by a set of coils, the maintenance requirements and safety issues associated with harsh environments and salt water are eliminated. Second, the technology enables the maximum utilization of docking time to charge batteries since there is no need for connecting and disconnecting plugs and receptacles. This is particularly advantageous in situations where vessels are frequently berthed for short periods. Enhanced available charging time decreases the required power level for charging, which may, in turn, reduce infrastructure costs.
Wireless charging systems also pose some challenges, for instance, related to cost and onboard weight. The efficiency of the power transfer is sensitive to the distance between the coils and requirements for maintaining the power transfer capability under misalignment of the coils. The efficiency can be improved by increasing the transmission frequency and/or coil dimensions. However, the transmission frequency is limited by challenges with losses and thermal management, while increasing the coil dimensions leads to increased weight and volume.
Battery swapping is a method where discharged onboard batteries are exchanged with fully charged batteries while a vessel is at berth. This rapid method can be suitable for vessels that have a critical docking time. Also, onshore battery packs do not have to be charged in a short time, thereby avoiding peak loads and allowing a flexible and smooth load profile. Hence, battery swapping can be less demanding for the local power grid compared to wired and wireless charging systems. Furthermore, the need for high-power onboard converters for fast charging is eliminated. However, battery swapping could require excessive capital expenditures since large robotic equipment to perform the exchange process and extra battery packs on shore may be necessary.
Battery swapping could be used for charging at locations with no grid connection, such as fishing grounds far from shore. Another solution for off-grid charging is using hydrogen fuel cells to power chargers. Both solutions require logistics in which batteries and hydrogen are transported to a mobile power station. Alternatively, the required electricity could be produced locally using offshore wind turbines, floating solar panels, or wave energy converters.
Even though alternative methods for power transfer, such as automated connection, wireless charging, battery swapping, and off-grid charging, have certain advantages, the conventional approach using physical connectors is still considered the most easily achieved and practically feasible solution to plug and charge the fishing fleet. The remainder of the article focuses on the reliability and quality of such contacts for maritime charging stations.
The (minimum) quality of a connector is closely linked to the standard it is designed for and tested under. The various connector solutions are related to one or multiple standards, each with a set of tests and acceptance criteria that the connectors must pass. The tests of three relevant standards are compared to assess their suitability for connectors used to charge fishing vessels. The following standards are considered (with their titles shortened to illustrate the most relevant market segments):
As indicated, LV port connectors are placed in the same category as industrial connectors since the tests of the LV port connection standard are very similar to the tests of the industrial connector standard.
Table 4 provides an overview of key electrical, environmental, thermal, and mechanical tests included in the three standards. In many of the tests, the acceptance criterion is no breakdown or damage. In other cases, and where appropriate, the acceptance criterion is given. Obviously, the test schemes cannot be fully described, and hence, the representation focuses on the main points.
Table 4. The key electrical, environmental, thermal, and mechanical tests from connector standards.
The testing schemes of the different standards are in many respects quite similar. This is the case for temperature rise, humid conditions, heat and fire resistance, and many of the mechanical tests. However, there are also some differences. The HV port standard sets, naturally, higher requirements for the electrical insulation and ability to withstand short circuits. For the tests on the insertion and withdrawal of the connectors, the HV port standard includes 350 operations, whereas the vehicle standard includes 5,000 and the industry standard up to 5,000 operations (depending on size), the latter while subjected to current and voltage. For a fishing vessel charger, the 5,000-operations range would be much more suitable than 350 operations, which correspond to only one mating operation per day for one year, far less than the expected lifetime of the connectors.
Thermal and current cycling is very important for the long-term quality of the contacts within the connectors but included only in the vehicle standard and there with only 250 cycles, in total. For fishing vessel applications, this likely represents less than a year in operation.
The corrosive conditions test is important for maritime applications. The industry standard recommends and the HV port standard includes salt spray tests. In the vehicle standard, the connectors are instead immersed (after the removal of protective grease) in an ammonium chloride solution. Notably though, the corrosion tests are not combined with current cycling, neglecting the long-term effects on contacts operating in corrosive environments.
The mechanical and initial performance of the connectors seem well covered by the standards compared in the preceding. However, the long-term performance of the electrical contacts within the connectors (cable to socket, socket to plug, and plug to cable) is either neglected or covered only limitedly.
The connector between the charging station and vessel carries a large charging current (up to several hundred amperes). The connector should have low contact resistance during its full lifetime to avoid overheating. The electrical contacts within the connectors are generally relatively inexpensive and seemingly simple. Neglecting the assurance of contact quality has proved to be a potentially hazardous approach. The contacts may be subjected to considerable electrical, thermal, chemical, and mechanical loads. These initiate contact aging and degradation, which potentially lead to increased contact resistance and temperature rise and, ultimately, fire hazards and downtime of a vessel and charging station.
The principles for qualifying the long-term contact performance of connectors for maritime charging stations are the same as for any other application. There should be a combination of cables, connectors, and tools (if any) that is proved for an application; i.e., the connection should be tested under a relevant testing scheme. A key question is, then, Under which conditions should the connections be tested?
For contact material (such as cable shoes) used by power utilities, the commonly used standard in Europe is IEC 61238. In this standard, the contacts are exposed to 1,000 current cycles, varying the temperature between 35 and approximately 100 °C, and six short circuits, raising the temperature to 250 °C within 1 s. This standard is considered reliable since very few (correctly assembled) connections tested according to it fail.
One should note, though, that most utility contacts are exposed to limited load variations during their lifetime—for many contacts, between only 40% and 60% of the full load—leading to moderate temperature variations. In contrast, for contacts used in charging applications, the load often varies between zero and the full load, sometimes with several cycles per day. Hence, there is reason for some concern. For instance, in medium-voltage grids, field experience has revealed numerous failures in systems with high and intermittent loads.
For maritime charging applications, an additional aspect to consider is the presence of humidity and salt, which increase the risk of corrosion and can accelerate the aging rate of the contacts. The influence of corrosion on maritime charging connections needs to be determined.
In Table 5, different connector solutions that exist on the market today are compared with respect to the desired characteristics discussed in the scenario guideline. With an eye on the demands of the fishing fleet, requiring communication possibilities and high-capacity charging, the list can be narrowed. Neither shore connectors nor industrial connectors enable communication. The same is partly true, or at least unknown, for the aquaculture connector, which also lacks a track record. The type 2 connector allows charging powers up to only 43 kW, a clearly limiting factor. CCS combo 2, CHAdeMO, and GB/T connectors have many features in common. They all emerge from and are proved in the automotive industry, and they allow communication and fast charging. CCS combo 2 is the most widely used connector today, across land, sky, and sea. It is also the most flexible solution since it supports dc, one-phase ac, and three-phase ac.
Table 5. A high-level comparison of existing market solutions.
Hence, CCS combo 2 seems suitable for the battery charging of small fishing vessels. This is a mass-produced standard solution with standard communication protocols and battery management systems. If fast charging is not needed, the lower-cost type 2 connector is a viable alternative. AC shore power should then be connected to a vessel’s dc bus through standard onboard chargers prepared for 400 V (and for 230 V in Norway). Two type 2 connectors can be used in parallel if the ac power demand of the vessel is greater than 43 kW over time.
Although the CCS combo 2 connector has many favorable characteristics and, in most respects, is tested according to a well-suited standard, its suitability for long-term operation in maritime environments should be assessed. The vehicle standard includes only 250 temperature cycles, and these cycles are not combined with corrosive exposure.
To establish a testing regime suited for connections for the fishing fleet, a research study is indeed welcome. Such a study has the possibility to include many different parameters (overcurrent, overtemperature, corrosive exposure, and vibrations) and can perform many thermal cycles on multiple connectors. The goal would be to determine which parameters determine the long-term connector quality and set appropriate testing parameters and acceptance criteria.
On a final note, a connector should be tested under the applicable standard using the correct installation tooling and connected to the very cable type that will be used in the application. A recurrent problem is that contacts and connectors may be designed according to a standard, following the general geometrical and material requirements, but not be tested appropriately, and hence, particularly, their long-term performance is unknown. This lack of quality verification represents a substantial risk to the reliability of the connectors.
The charging of small fishing vessels with electric and hybrid propulsion has many similarities to the charging of electric cars. Among the connectors on the market today, we recommend going for a CCS combo 2 connector when high charging powers are needed. Where solely lower charging powers are needed, the type 2 connector can be more suitable and less costly.
However, the coastal climate in which fishing vessels operate urges studies on the influence of humid and corrosive environments on the connectors’ long-term performance. Tests reflecting such conditions should be part of any future standard for connectors for the fishing fleet.
This publication has been prepared as part of ZeroKyst KSP (grant 328721/E22), funded by the Research Council of Norway. The authors would like to thank Thor André Berg, Plug; Svein-Joar Husjord, Elmea; Thomas Høven, Norwegian Shore Power Forum; and the other industrial partners in the ZeroKyst project for valuable discussions. Read more at https://www.zerokyst.no.
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Eirill Bachmann Mehammer (eirill.mehammer@sintef.no) is with SINTEF Energy Research, 7034 Trondheim, Norway.
Henrik Strand (henrik.strand@sintef.no) is with SINTEF Energy Research, 7034 Trondheim, Norway.
Niklas Magnusson (niklas.magnusson@sintef.no) is with SINTEF Energy Research, 7034 Trondheim, Norway.
Kristian Solheim Thinn (kristian.solheim@sintef.no) is with SINTEF Energy Research, 7034 Trondheim, Norway.
Espen Eberg (espen.eberg@sintef.no) is with SINTEF Energy Research, 7034 Trondheim, Norway.
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