ORKNEY'S ENERGY FUTURE
MARINE TRANSPORT
BACKGROUND
INTRODUCTION
The ferry fleet serving Orkney is a vital social and economic transport service for the island communities. There are 9 internal ferries operating between 13 islands, and 4 passenger ferries and 1 freight vessel travelling to mainland Scotland. The marine transport sector accounts for 24% of Orkney’s energy demand from fossil fuels. The sector presents a significant challenge to decarbonise, with zero or low-carbon fuels providing different options but with varying limiting factors.
The fuel used for ferries is marine gas oil (MGO) and the annual fuel usage for all 14 ferries is over 12.2 million litres [1] [2]. In 2018, the energy consumption through MGO of the marine sector was 142.0 GWh [3]. Mainland ferries account for 72% of the consumption (Figure 1). Decarbonising the marine transport sector will be important in reducing Orkney’s greenhouse gas emissions.
Figure 1: Breakdown of equivalent energy consumption of sections of Orkney’s marine transport sector [3].
INTER-ISLAND FERRIES
The inter-island ferry fleet is made up of 9 ferries of varying size and journey length (Figure 2). The smallest ferry carries 40 passengers between the islands Westray and Papa Westray. The largest ferries travel from Kirkwall to the Northern Isles with the carrying capacity of 190 passengers and 22 cars. The average age of the fleet is over 30 years old and local MSPs are calling for the fleet to be wholly replaced [4].
MAINLAND FERRIES
The 5 mainland ferries (Figure 2) are larger than the inter-island ferries due to the need to travel further and carry more passengers, cars and cargo. One route is from Aberdeen to Kirkwall to Lerwick in Shetland and this route accounts for over 27% of all of Orkney’s ferries' fuel usage [2] (when considering the contribution the Orkney leg of the journey makes to fuel use only). It is challenging to decarbonise the mainland ferries because low carbon technologies are required to provide the required propulsion power without compromising the weight and balance of the boat.
Figure 3 shows a breakdown of the fuel usage of 12.2 million litres between the 14 ferries [1] [2].
Figure 2: Map of Orkney's ferries [4].
Figure 3: Breakdown of fuel usage of Orkney’s inter-island and mainland ferries [1] [2].
DECARBONISATION TECHNOLOGY
The three low carbon technologies considered to decarbonise the sector were batteries, hydrogen and ammonia. Battery ferries are advanced worldwide, with the technology comparatively as mature as electric vehicles and battery storage. There are a number of hydrogen projects on Orkney making progress such as BIG HIT [6] and HySeas III [7], although there is yet to be a hydrogen powered passenger ferry realised globally. Ammonia has been proposed as a solution, especially for large scale cargo shipping. The three technologies were scored using a weighted decision matrix based on 5 criteria (Table 1):
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Energy density of the fuel used in the technology
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Efficiency of the technology
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Suitability for the application
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Development stage of the technology – both globally and in Orkney
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Safety
Table 1: Decision matrix indicating initial screening process undertaken for determining which technology to analyse to decarbonise the marine transport sector.
The key factors considered in the decision making were:
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Energy density – a greater energy density extends range and capacity with lower mass of fuel; batteries (0.3 kWh/litre [8]) are lowest, then hydrogen (0.53 kWh/litre [9]) and ammonia (4.33 kWh/litre [10]) greatest, which therefore scores highest.
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Efficiency – battery powered systems can have grid-to-propeller efficiencies of 80-90% [11] compared to well-to-propeller efficiencies of systems using fuel cells with ammonia – 11-19% [12] – and hydrogen – 25-35% [13] – which are lower due to the energy required to synthesise the fuels.
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Suitability – hydrogen has been identified by research groups on Orkney as suitable to decarbonise the sector [7], batteries have been perceived as more suited to short distance maritime applications whereas ammonia is more likely to be suitable for shipping [14].
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Development stage – the HySeas III project aims to have a hydrogen passenger ferry running in Orkney by the end of 2021 [7] whilst there are battery ferries in operation globally [11]. Ammonia ferries lag behind the other technologies with limited development currently.
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Safety – hydrogen is highly flammable and ammonia is toxic, whereas batteries have no safety concerns with the operation of the technology.
Based on this, batteries and hydrogen were identified as the preferred technologies and were used to model the decarbonised marine sector.
REFERENCES
[1] Aquatera, "Orkney-Wide Energy Audit 2014: Energy Sources and Uses," Orkney Renewable Energy Forum, 2015.
[2] Aquatera, "Orkney-Wide Energy Audit 2014: Energy Sources and Uses - Addendum," Orkney Renewable Energy Forum, 2015.
[3] Orkney International Science Festival, "Orkney's Energy Revolution: Hydrogen & Energy Systems," YouTube, 3 September 2020. [Video File]. Available: https://www.youtube.com/watch?v=TCfYGdsSXSc&t=2389s&ab_channel=OISFestival. [Accessed 15 April 2021].
[4] F. Grahame, "Welcome Budget News For Ferries in Orkney," The Orkney News, 29 January 2021. [Online]. Available: https://theorkneynews.scot/2021/01/29/welcome-budget-news-for-ferries-in-orkney/. [Accessed 9 April 2021].
[5] "Location Location," Tim and Jenny's Orkney Website, [Online]. Available: http://www.barthorpe.me.uk/our-house-in-orkney/location-location.html. [Accessed 9 April 2021].
[6] BIG HIT, "About the Project," 2021. [Online]. Available: https://www.bighit.eu/about. [Accessed 9 April 2021].
[7] HySeas III, "The Project," 2021. [Online]. Available: https://www.hyseas3.eu/the-project/. [Accessed 9 April 2021].
[8] Clean Energy Institute, "What is a lithium-ion battery and how does it work?," University of Washington, 2021. [Online]. Available: https://www.cei.washington.edu/education/science-of-solar/battery-technology/. [Accessed 2 February 2021].
[9] M. Fung, "Energy Density of Hydrogen," The Physics Factbook, 2005. [Online]. Available: https://hypertextbook.com/facts/2005/MichelleFung.shtml. [Accessed 2 February 2021].
[10] T. Brown, "Ammonia for Power: a literature review," Ammonia Energy Association, 4 October 2018. [Online]. Available: https://www.ammoniaenergy.org/articles/ammonia-for-power-a-literature-review/. [Accessed 2 February 2021].
[11] e-Ferry Ellen, "The e-Ferry Ellen Information Package," 2017. [Online]. Available: http://www.conf.eferry.eu/InfoPackage/eFerry_Information_Package.pdf. [Accessed 12 February 2021].
[12] Trevor Brown, "Round-trip Efficiency of Ammonia as a Renewable Energy Transportation Media," Ammonia Energy Association, 20 October 2017. [Online]. Available: https://www.ammoniaenergy.org/articles/round-trip-efficiency-of-ammonia-as-a-renewable-energy-transportation-media/. [Accessed 1 February 2021].
[13] M. Kane, "Battery Electric Vs Hydrogen Fuel Cell: Efficiency Comparison," Inside EVs, 28 March 2020. [Online]. Available: https://insideevs.com/news/406676/battery-electric-hydrogen-fuel-cell-efficiency-comparison/. [Accessed 2 February 2021].
[14] N. Gray, S. McDonagh, R. O'Shea, B. Smyth and J. D. Murphy, "Decarbonising ships, planes and trucks: An analysis of suitable low-carbon fuels for the maritime, aviation and haulage sectors," Advances in Applied Energy, vol. 1, 2021.