ORKNEY'S ENERGY FUTURE
HYDROGEN PRODUCTION
WHEN AND WHY HYDROGEN PRODUCTION IS NEEDED
A use for the potential Wasted Electricity in Scenario 2a and 2b is to produce hydrogen as an energy storage solution. Two sectors identified as being potentially suitable for hydrogen use were public buses and the two mainland ferries which are not currently able to be replaced by battery ferries. As Orkney has already invested in hydrogen infrastructure and research in projects such as Surf ‘n’ Turf [1] this would be an appropriate continuation of that work. Hydrogen also makes up part of Scotland’s future energy strategy [2], so there may be opportunities for Orkney to become an exporter of hydrogen which could bring economic benefits.
MODELLING THE HYDROGEN PRODUCTION
To model the production of hydrogen, HOMER Pro was used. It calculated the potential hourly hydrogen production in Scenarios 2a and 2b. Scenarios 1, 3a and 3b were not considered because there was no wasted electricity because all the surplus electricity could be exported.
HOMER was setup so that:
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Hydrogen would be produced with any surplus electricity after the decarbonised electrical load was met and the energy storage batteries were 100% charged.
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No electricity would be exported to the grid to maximise the amount of hydrogen produced.
Figure 1: Schematic of the modelled created to calculate the hydrogen production.
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The electrolyser efficiency was set to 59%, consistent with the operational unit already on Orkney.
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This gives a power to hydrogen conversion of 66.7 kWh/kg based on a Higher Heating Value of 39.39 kWh/kg.
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The electrolyser was sized so that all the available surplus electricity was converted to hydrogen in every scenario.
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The hydrogen storage was infinite so all the available electricity could be used.
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No losses were factored into the model.
These parameters were chosen because finding the most cost-effective hydrogen production system was not part of the aims of the project. If hydrogen production was implemented on this scale, there would be a need for a more detailed simulation to find the most cost-effective use of technology and infrastructure and factor in losses.
As with the electricity generation, the hydrogen production was calculated for each year from 2014 to 2018. The production was calculated hourly and then averaged to give a representative year as well as a higher a lower bound. The production on a daily, weekly and yearly timescale was then calculated so it could be compared with the hydrogen demand from the 2 ferries and the buses.
RESULTS
Since hydrogen can be stored, the weekly demand and production provided significant detail to understand the requirements for the buses and 2 mainland ferries.
In Scenario 2a there would be enough hydrogen produced for the buses and either the passenger or freight ferry based on an average year. In the worst-case year (from 2018 wind data), only the freight ferry and buses could be decarbonised (Table 1). In Scenario 2b there is enough hydrogen produced for the buses and 2 ferries. There would also be a significant amount of annual hydrogen surplus of 4.88 kt which could be transported and sold or used to decarbonise other sectors in Orkney.
Table 1: Annual hydrogen demand and production in Scenario 2a and 2b.
There are no seasonal fluctuations in hydrogen production throughout the year, although there can be weekly fluctuations (Figure 2). This would allow the storage to be confidently sized, as there is reliable production of hydrogen.
Figure 2: Weekly hydrogen demand and production in Scenario 2a and 2b.
CONCLUSIONS
This study shows that there is the potential for further sectors to be decarbonised by using otherwise wasted electricity in the production of hydrogen in Orkney. This is most pertinent when used for the large mainland ferries which have been deemed infeasible as battery ferries. However, this investigation does not consider the feasibility of the hydrogen production system or the ships. This would require a more detailed study before being implemented in Orkney. The hydrogen demand for the mainland ferries is large and would require most of the planned wind turbines to be constructed and therefore requires a large investment.
The results show that public buses could be decarbonised by the hydrogen that could be produced in Scenarios 2a and 2b and with the continuation of the work already started in Orkney in the Surf ‘n’ Turf project could be a logical and achievable next step, especially given that there is an exemplar fleet of hydrogen buses already operational in Aberdeen.
REFERENCES
[1] Surf 'n' Turf, "Home," 2021. [Online]. Available: https://www.surfnturf.org.uk/. [Accessed 29 April 2021].
[2] Scottish Government, "Scottish Government Hydrogen Policy Statement," 21 December 2020. [Online]. Available: https://www.gov.scot/publications/scottish-government-hydrogen-policy-statement/. [Accessed 21 April 2021].