Local Energy Scotland
Local Energy Challenge Fund
The Conversion of Curtailed Energy on Eday to Hydrogen
Final Report
Title Final Report Dissemination level Confidential Written By Dr Kris Hyde (ITM Power) 13/2/14 Approved by Dr Rachel Smith (ITM Power) 15/2/14 Stuart Baird (EMEC) 15/2/14 Ian Garman (CES) 15/2/14
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Executive Summary The European Marine Energy Centre has secured funding to purchase an electrolyser to convert electricity they are unable to export to the grid into hydrogen. This project has investigated the connection of the local community owned wind turbine to this electrolyser and has considered a range of hydrogen applications to establish which would be the most suitable for the LECF Phase 2 project.
The best application was using the hydrogen in a fuel cell which provided power to Kirkwall harbour and the three ferries which berth there overnight. This fuel cell will be configured as a training platform for those operating and maintaining similar equipment on ships. This will overcome one of the main regulatory hurdles preventing the implementation of fuel cells in marine vessels.
This system has been modelled in detail based on half hourly wind and tidal output, with the optimised parameters being:
Eday static store size: 450kg Fuel cell rated output: 80kW Harbour Stationary Store: 100kg Minimum threshold for returning to Eday 45kg
The result of this being:
ROC and FIT income to the turbine operators of £165k pa The difference between the electricity saved by the harbour and the hydrogen transportation costs being £16.2k pa
A net saving of 202 t CO2 pa
These results suggest that the project should be taken forward for Phase 2 funding.
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Contents Executive Summary ...... 2 1. Background ...... 6 2. The Project ...... 7 3. Hydrogen Applications ...... 8 3.1. Hydrogen Refuelling Station and Hydrogen Vehicles on Eday ...... 8 3.1.1. Proposal: ...... 8 3.1.2. Benefit to the Community: ...... 8 3.1.3. Technical Risk ...... 8 3.1.4. Scale of Hydrogen Consumption: ...... 8 3.1.5. Cost ...... 8 3.1.6. Timescale ...... 9 3.1.7. Consequence of Failures ...... 9 3.1.8. Simplified Carbon Reduction ...... 9 3.1.9. Conclusion ...... 9 3.2. Hydrogen Buses in Kirkwall ...... 9 3.2.1. Proposal: ...... 9 3.2.2. Benefit to the Community: ...... 9 3.2.3. Technical Risk ...... 9 3.2.4. Scale of Hydrogen Consumption: ...... 9 3.2.5. Cost ...... 9 3.2.6. Timescale ...... 9 3.2.1. Consequence of Failures ...... 9 3.2.2. Simplified Carbon Reduction ...... 10 3.2.3. Conclusion ...... 10 3.3. Supplying Hydrogen to Flotta Oil Terminal ...... 10 3.3.1. Proposal: ...... 10 3.3.2. Benefit to the Community: ...... 10 3.3.3. Technical Risk ...... 10 3.3.4. Scale of Hydrogen Consumption ...... 10 3.3.5. Cost ...... 10 3.3.6. Timescale ...... 10 3.3.7. Consequence of Failures ...... 10 3.3.8. Simplified Carbon Reduction ...... 11
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3.3.9. Conclusion ...... 11 3.4. The Production of Low Carbon Fertiliser ...... 11 3.4.1. Proposal: ...... 11 3.4.2. Benefit to the Community: ...... 11 3.4.3. Technical Risk ...... 11 3.4.4. Scale of Hydrogen Consumption ...... 12 3.4.5. Cost ...... 12 3.4.6. Timescale ...... 12 3.4.7. Consequence of Failures ...... 12 3.4.8. Simplified Carbon Reduction ...... 12 3.4.9. Conclusion ...... 12 3.5. Powering Kirkwall Harbour and Providing Fuel Cell Marine Training Services ...... 13 3.5.1. Proposal: ...... 13 3.5.2. Benefit to the Community: ...... 13 3.5.3. Technical Risk ...... 13 3.5.4. Scale of Hydrogen Consumption ...... 13 3.5.5. Cost ...... 13 3.5.6. Timescale ...... 13 3.5.7. Consequence of Failures ...... 13 3.5.1. Simplified Carbon Reduction ...... 13 3.5.2. Conclusion ...... 14 4. Details of the Proposed Project ...... 15 4.1. Overview ...... 15 4.2. EMEC’s Funded Project ...... 15 4.3. Connection of the ERE Wind Turbine ...... 15 4.4. The Size of the EMEC Stationary Storage ...... 16 4.5. Transferring Hydrogen between Stationary and Mobile Vessels ...... 16 4.6. Transportation of Hydrogen across Eday ...... 17 4.7. Transportation of Hydrogen between Eday and Kirkwall ...... 18 4.8. Static Hydrogen Storage on the Harbour ...... 19 4.9. Fuel Cell ...... 19 5. Model Starting Parameters ...... 21 6. Energy Available to Electrolyser ...... 22 6.1. Energy Available from the Tidal Turbines ...... 22
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6.1.1. Description ...... 22 6.1.2. Tidal Velocity ...... 22 7. Energy Available from the Wind Turbine ...... 26 8. Combined Energy Available ...... 27 9. Electrolyser Efficiency ...... 28
10. Modelling of H2 Production and Cascade Filling / Dispensing of Hydrogen ...... 29 10.1. Model Logic ...... 29 10.2. Model Results...... 29 11. Powering Kirkwall Harbour ...... 34 11.1. Background ...... 34 11.2. Electricity Demand ...... 34 11.3. Fuel Cell Efficiency ...... 35
11.4. Fuel Cell H2 Consumption ...... 35 12. Key Results ...... 38 13. The Effect of Changing Parameters ...... 39 13.1. Changing the Eday Stationary Store Size ...... 39 13.2. Changing the Fuel Cell Rated Output ...... 40 13.3. Changing the Harbour Static Store Size ...... 40
13.4. Changing the Minimum H2 Threshold before Allowing Mobile Store to Return ...... 41 13.5. Optimised Values ...... 42 14. Conclusion ...... 43
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1. Background The European Marine Energy Centre (EMEC) operate the UKs only tidal turbine test bed, based on the island of Eday in the Orkney archipelago. However, the test site can only export 4 MW to the local electricity grid. With the present plans for expansion, this limit will be reached and EMEC’s customers will be unable to export their electricity and thus lose both the sale price and the ROCs. This is undesirable for both EMEC and their customers. As such, EMEC have secured funding from another project to purchase an electrolyser to absorb some of the curtailed energy. However, to allow their customers to receive ROCs, the hydrogen must be put to good use, and not simply vented.
A community owned wind turbine on Eday, exports power to the same transformer as the EMEC tidal test station. However, the local grid is heavily constrained and up to 50% of the energy generated is curtailed and prevented from entering the grid. Thus, the community are losing considerable income, limiting the economic viability of the turbine. It would thus be of great benefit to the community if this wasted energy could be utilised in the EMEC electrolyser to provide an income.
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2. The Project The European Marine Energy Centre (EMEC) have received funding to purchase a 0.5 MW electrolyser to allow the generation capacity of tidal turbines under test to exceed their 4 MW export capacity. This project involves EMEC working with Community Energy Scotland (CES) and ITM Power to conduct a feasibility analysis of:
Connecting the community owned wind turbine to the EMEC owed electrolyser Determining the most suitable end-use for the hydrogen
A similar LECF project has been conducted by EMEC, CES and Orkney Islands Council (Surf ‘n Turf). This project is looking at replacing the diesel APU on the Eday ferry with a fuel cell and hydrogen store, which is filled from the EMEC electrolyser. They are also looking at connecting the community owned wind turbine to the electrolyser; however, the small power consumption of the end use will limit the hydrogen that can be generated.
Although this project and Surf ‘n Turf were originally intending on submitting a single Phase 1 application, bureaucratic reasons prevented this occurring. Thus, all partners have pooled work and expertise towards a single Phase 2 application. While this report is focussing on the modelling aspect of those activities, their report is more focussed on the marine aspects.
At the start of the project, considerable time and research was conducted into the best application for the hydrogen (particularly by the partners based on Orkney) looking for one that met the following criteria:
Provided maximum benefit for the community The application should maximise carbon savings The application must be practicable The hydrogen requirement must be of similar scale to the hydrogen production Could be achieved within the project budget Could be achieved within the project timescale Would be resilient to failures (for example a failed turbine or electrolyser would not leave the community short of an essential service)
As will be described in following sections, only 1 application met these criteria. Thus, rather than create a model for each scenario, as envisaged in the application, a pragmatic approach was taken by the partners to concentrate on the chosen application, and create a more detailed model encompassing as many factors as possible. Thus, the Phase 2 application could be based on the most detailed background knowledge possible.
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3. Hydrogen Applications All the hydrogen applications considered below result in increased ROC / FIT payments for the turbine operators, but have not been included to aid the differentiation between possible projects. While the exact benefit would vary on the detail of how the hydrogen transferred to the mobile vessel and how often this occurs, an income to turbine operators of ~£150k could be expected.
As the electrolyser is powered by otherwise curtailed renewable electricity, the hydrogen produced is zero carbon. However, the transportation of the hydrogen to the application will be carbon intensive and therefore consideration should be given to the net carbon footprint. However, a thorough assessment of carbon impact is complicated. For example, while the carbon saved by avoiding combusting a litre of diesel is simple (2.62 kg CO2), the transportation of that fuel to Orkney will itself have a high (and difficult to specify) carbon intensity. Thus, only a simple carbon analysis has been conducted. 3.1. Hydrogen Refuelling Station and Hydrogen Vehicles on Eday 3.1.1. Proposal: A compressor would be added to the EMEC stationary storage on Eday to increase some storage pressure to 400 bar. When combined with ~100kg of 400 bar storage and a dispensing nozzle, it would convert EMEC’s site into a 350bar Hydrogen refuelling station. The project would then convert a number of vehicles on Eday to combust hydrogen (similar to an LPG conversion). 3.1.2. Benefit to the Community: This would provide free transport fuel for owners of the converted vehicles. However, the island is only 15 miles long and therefore the requirement for travel is limited. If it is assumed that:
Each vehicle will travel 5000 miles per year The diesel car does 35 MPG and the petrol car does 30 MPG Diesel costs £1.15/L and petrol of £1.05 per litre
Then, this will save diesel car owners £748/yr and petrol car owners £796yr 3.1.3. Technical Risk The refuelling station is a standard product for ITM Power. The vehicle conversion is a standard product for Revolve; however, conversion is difficult to achieve for diesel fuelled vehicles as they lack spark plugs. 3.1.4. Scale of Hydrogen Consumption: There are 21 tractors, 45 petrol cars and 45 diesel cars on Eday, which are each expected to have a fuel consumption of 20, 6.8 and 6.5 MWh/yr, respectively. Based on a LHV of hydrogen of 33.3 kWh/kg, this implies 30 t H2 pa. This is similar to the expected production of 27 t H2 pa. Having slightly more demand than supply, could be considered an issue; however, as the vehicles would retain their original fuel source, running out of H2 wouldn’t be a problem. 3.1.5. Cost Cost of large capital items include: The compressor, high pressure storage, ground works and dispensing is estimated to cost £0.45m. The 120 vehicles are estimated to cost £30k each to convert (with the largest cost being the tank and time required to re-map the ECU), giving a cost of £3.6m, and a total cost of ~£4m. This is over the project budget.
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3.1.6. Timescale Only one company in the UK (Revolve) has the ability to do the conversion. Past experience suggests that they could convert 1 vehicle per month, requiring 110 months, which is outside the duration of the project. 3.1.7. Consequence of Failures As the vehicles original fuel source would be retained, there would be little consequence to the local population of a failure of a key component of the system. 3.1.8. Simplified Carbon Reduction
With no carbon associated with the transport of CO2 to a new location, this hydrogen application is estimated to save 158 t CO2/yr. 3.1.9. Conclusion This will not be taken forward as it is outside the cost and duration of the project. 3.2. Hydrogen Buses in Kirkwall 3.2.1. Proposal: An additional compressor and 1000 bar storage (to allow dispensing at 700 bar) would be installed at EMEC’s site on Eday. A high pressure mobile storage system would periodically transfer the hydrogen by road and sea to Kirkwall. There it would enter a stationary store and would power 2 fuel cell buses from a hydrogen dispenser. 3.2.2. Benefit to the Community: The benefits of this are less tangible. The operators of the buses would be able to pass on the fuel savings to passengers to provide low cost fares. However, between 10 passengers on 5mile journeys, the saving may only be ~25p per passenger, which is likely to be offset by higher maintenance costs. 3.2.3. Technical Risk The technology for hydrogen refuelling stations and buses is becoming increasingly mature and presents minimal risk. 3.2.4. Scale of Hydrogen Consumption: Each bus would consume ~35kg per day, giving a total hydrogen consumption of 25.5 t H2 pa, which is in close alignment with the estimated 27 t H2 pa production rate. 3.2.5. Cost Cost of large capital items include: The compressor, high pressure storage on Eday, 2x mobile stores, stationary store at Kirkwall and dispenser at Kirkwall would cost ~£950k. Each bus would cost £900k, giving a total project cost of £2.75m. 3.2.6. Timescale The buses would be the longest lead time item, although it should be possible to procure them for the project. 3.2.1. Consequence of Failures The buses would be hydrogen only. While the storage on Eday and at Kirkwall would provide some backup in the event of either a component failure or poor weather preventing ferry crossings, the buses would be inoperable within 1-3 days.
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3.2.2. Simplified Carbon Reduction
Two buses driving 70,000 miles per year achieving 5 MPG will emit 333 t CO2 pa from diesel combustion. This would be replaced by 26 t pa of Hydrogen. With a 240kg mobile store, this will require 109 round trips between Eday and Kirkwall. A diesel tractor unit collecting store would be required to travel 12 miles on Eday, which at 10 MPG would emit 14 kg CO2 per journey, or 1.5 t CO2 pa. The emissions during the ferry crossing is difficult to quantify. If the ferry consumes 1 MPG during the 33 mile round trip, but those emissions are shared with 10 other vehicles being transported, then 47 kg CO2 would be emitted each journey, or 5.1 t CO2 pa. Thus total emissions are
6.6 t CO2 pa and total savings are 333 t CO2 pa, leading to a net benefit of 326 t CO2 pa. 3.2.3. Conclusion This will not be taken forward as it brings little benefit to the community and would be too reliant on hydrogen deliveries.
3.3. Supplying Hydrogen to Flotta Oil Terminal 3.3.1. Proposal: The project would transfer the hydrogen from the stationary store at EMEC to the Flotta Oil Terminal. There, it could be co-fired within their CCGTs to produce electricity. 3.3.2. Benefit to the Community: The 5x 3MW CCGTs at the Flotta Oil Terminal require 35MW of gas flow, or 306,600 MWh/yr (assuming they run continuously at rated output). The electrolyser would produce ~441 MWh of Hydrogen per year, or 1.4% of the demand. This would bring little tangible benefit to the community. 3.3.3. Technical Risk This would be a relatively simple project with capital cost limited to 2x mobile storage units. Hydrogen has different combustion properties to most other gases and therefore the CCGT manufacturer would need to be consulted. However, most CCGTs can accept 3-5% H2 without modification – considerably above the 1.4% average content expected. As there is no direct ferry link between Eday and Flotta, the timings of ferries would need consideration. 3.3.4. Scale of Hydrogen Consumption The CCGTs would accept whatever H2 was produced. At 1.4% average H2 content, they should not need modification. 3.3.5. Cost Cost of large capital items include: 2x mobile H2 stores would cost ~£300k 3.3.6. Timescale The mobile H2 stores could be delivered within the duration of the project 3.3.7. Consequence of Failures A failure of a key component, or poor weather preventing ferry journeys will have no consequence on the application as the CCGTs would continue operating on their usual fuel.
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3.3.8. Simplified Carbon Reduction Supplying 441 MWh of hydrogen to the CCGTs would offset the same energy of natural gas, which at a carbon intensity of 0.2 kg/kWh would represent a saving of 88 t CO2 pa. The 27 t pa of hydrogen would require 113 round trips between Flotta and Eday. This would require:
A tractor unit to travel 12 miles on Eday, which at 10 MPG would emit 14 kg CO2 per
journey, or 1.6 t CO2 pa. The emissions during the ferry crossing to Kirkwall is difficult to quantify. If the ferry consumes 1 MPG during the 33 mile round trip, but those emissions are shared with
10 other vehicles being transported, then 47 kg CO2 would be emitted each journey,
or 5.3 t CO2 pa. The tractor unit must then travel a round trip of 21 miles between Kirkwall and the
Houton Ferry Terminal, which at 10 MPG would emit 25 kg CO2 per journey or 2.8 t
CO2 pa. A ferry is required between Houton and Flotta. If the ferry consumes 1 MPG during the 16 mile round trip, but those emissions are shared with 10 other vehicles being
transported, then 21 kg CO2 would be emitted each journey, or 3.6 t CO2 pa. Thus
total emissions are 3.5 t CO2.
Thus the total savings are 88 t CO2 pa and the total emissions are 13.7 t CO2 pa, giving a net saving of
74.3 t CO2 pa. 3.3.9. Conclusion This will not be taken forward as it brings no benefit to the community.
3.4. The Production of Low Carbon Fertiliser 3.4.1. Proposal: To either:
React the hydrogen with nitrogen captured from air to produce ammonia. Transfer the
ammonia into a mobile store and transport to Kirkwall. React with CO2 produced from the Highland Park Distillery to form urea. Freeze dry and provide to local farmers Transfer the hydrogen to a mobile store and transport to the Highland Park Distillery near Kirkwall. React the hydrogen with nitrogen captured from air to produce ammonia. React
with CO2 produced from the distillery to form urea. Freeze dry and provide to local farmers 3.4.2. Benefit to the Community: Modelling of the proposed system suggests that with hydrogen production of 27 t H2 pa, 258 t pa of Urea will be produced. As urea presently retails for ~£800 per tonne, this would be worth ~£200k pa. This would have secondary benefits of increasing the growth rate of whatever plants were being fertilised, increasing yield and return. 3.4.3. Technical Risk While ammonia and urea production is conducted worldwide on a large scale (indeed 5% of global energy is used for the production of ammonia based fertilisers), small systems suitable for this project are not commercially available. ITM Power is presently leading an Innovate UK funded
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project with the University of Sheffield to develop small reactors for ammonia and urea production with a view to making these commercial products. However, this will not be completed in time for the end of the LECF project. 3.4.4. Scale of Hydrogen Consumption The reactors would be scaled to the size of hydrogen production. 3.4.5. Cost Cost of large capital items include: 2x mobile H2 stores would cost ~£300k. The reactors are presently not commercially available. However, it is estimated that they would cost ~£330k for the ammonia reactor, £180k for the urea reactor. In addition, there would be, £15k for the N2 generator and air compressor and £20k for ground works. This implies a project cost of ~£850k. 3.4.6. Timescale The ammonia and urea reactors would not be available for the end of the project 3.4.7. Consequence of Failures At present, fertiliser is imported to the Orkney Islands. These could resume if the equipment failed. 3.4.8. Simplified Carbon Reduction 1 Within 258 t of urea is 120 t of N2. In Europe, the carbon footprint of urea is 3.5 kg CO2 / kg N2 , leading to 421 t CO2 saved.
The emissions arise from:
A tractor unit to travel 12 miles on Eday, which at 10 MPG would emit 14 kg CO2 per
journey, or 1.5 t CO2 pa. The emissions during the ferry crossing to Kirkwall is difficult to quantify. If the ferry consumes 1 MPG during the 33 mile round trip, but those emissions are shared with
10 other vehicles being transported, then 47 kg CO2 would be emitted each journey,
or 5.1 t CO2 pa. The tractor unit must then travel a round trip of 3 miles between Kirkwall harbour
and the Highland Park Distillery, which at 10 MPG would emit 3.6 kg CO2 per journey
or 0.4 t CO2 pa.
Thus, total savings are 421 t CO2 pa, while total emissions are 8.5 t CO2 pa, leading to a net saving of
412.5 t CO2 pa. 3.4.9. Conclusion This will not be taken forward due to the inability to secure the ammonia and urea reactors before the project is concluded. However, this project offers considerable community benefit and carbon reductions and should be considered again in the future.
1 http://www.blonkconsultants.nl/upload/pdf/PDV%20rapporten/fertilizer_production%20D03.pdf
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3.5. Powering Kirkwall Harbour and Providing Fuel Cell Marine Training Services 3.5.1. Proposal: Hydrogen generated at EMEC will be transferred to a mobile store. This will be transported by road and sea to Kirkwall harbour, where it will be used to power a fuel cell. This will provide power for the harbour and 3 large ferries which berth there each night.
In addition, the enclosure around the fuel cell will be designed to meet the requirements for installation of hydrogen equipment on a ship. This includes features such as a sloping roof, specific air flow, hydrogen detectors etc., which will allow the unit to function as a training facility. This has benefit as while there is a long-term desire to replace the fleet of Orkney Ferries with hydrogen powered units, they will never be certified unless it can be shown that the crew have received specific training in the operation and maintenance of hydrogen equipment. Thus, while the training itself will be of benefit, it will facilitate the introduction of fuel cell powered ships. This increased demand for hydrogen will allow other community owned turbines to power electrolysers with their curtailed energy, providing them with additional FIT income. 3.5.2. Benefit to the Community: Modelling of the proposed system suggests that it will bring electricity savings of £50k pa to the operator of the harbour, Orkney Marine Services, who are owned by Orkney Islands Council. Thus, any savings made will be reflected in the council budget, which will benefit the community. 3.5.3. Technical Risk The mobile transport and fuel cell are commercial products and present little risk. The housing for the fuel cell that will mimic a ship’s compartment is something that will need to be designed and assembled as part of the project. While this inherently presents a risk, it is not considered a difficult task and should be readily achievable. 3.5.4. Scale of Hydrogen Consumption Modelling suggests that the fuel cell will meet ~2/3 of the harbour’s energy demand, so is of a suitable scale. 3.5.5. Cost Cost of large capital items include: 3x mobile H2 stores would cost ~£480k, fuel cell ~£300k and static storage at the harbour £75k. Total cost: £855k 3.5.6. Timescale All components could be delivered within the timescales of the project 3.5.7. Consequence of Failures The harbour would retain its present electrical connection, so there would be little consequence of a failure preventing the operation of the fuel cell. 3.5.1. Simplified Carbon Reduction
The fuel cell will output 418 MWh pa. With a UK grid carbon intensity of 0.5 t CO2 / MWh, this would save 209 t CO2 pa.
A tractor unit to travel 12 miles on Eday, which at 10 MPG would emit 14 kg CO2 per
journey, or 1.5 t CO2 pa.
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The emissions during the ferry crossing to Kirkwall is difficult to quantify. If the ferry consumes 1 MPG during the 33 mile round trip, but those emissions are shared with 10
other vehicles being transported, then 47 kg CO2 would be emitted each journey, or 5.1 t
CO2 pa.
This gives total savings of 209 t CO2 pa and total emissions of 6.6 t CO2 pa, leading to a net saving of
202.4 t CO2 pa. 3.5.2. Conclusion This hydrogen application provides reasonable benefit to the community, a good carbon reduction, and is achievable in terms of technical risk, cost and timescale. As such, this has been taken forward for further analysis.
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4. Details of the Proposed Project 4.1. Overview The model has been based on the following top-level vision for the supply of hydrogen to a fuel cell in Kirkwall harbour:
Excess energy from the EMEC tidal turbines is combined with curtailed energy from the ERE wind turbine This powers an electrolyser A mobile transport is always connected to the electrolyser. On connection of the mobile store, the 4 tanks will cascade fill into the mobile store. The electrolyser will preferentially fill the mobile store. Once full, it will fill each static tank in turn. When a depleted mobile store is returned from the fuel cell, it is swapped for the recharged unit The full unit is taken by ferry to Kirkwall harbour where it is connected to the harbour static store, which is connected to the fuel cell. The mobile and static stores are allowed to equilibrate The fuel cell preferentially drains the mobile store and swaps to the static store if empty. If the total harbour storage is less than a threshold level, every weekday the depleted store is returned on the ferry to Eday. When on Eday, the depleted store is swapped for a recharged store.
Regarding training, the project would involve two aspects:
The fuel cell will be installed in a 20’ ISO container constructed to meet marine fuel cell requirements. This includes a sloped ceiling, ventilation and hydrogen detection. This would provide a physical unit to show the technology and practice emergency procedures. A class room would be hired which would allow both a theoretical discussion of the advantages and hazards of hydrogen and allow practical experience of high pressure fittings, replacing parts, calibration of equipment etc.
However, as the marine aspect of the Phase 2 is considered further in the Surf ‘n Turf Phase 1 Final Report, it won’t be discussed further here. 4.2. EMEC’s Funded Project EMEC have received funding to purchase a 0.5MW electrolyser, a compressor and 250-500kg of 200 bar hydrogen storage. This will be located within a fenced compound adjacent to their tidal testing facility on Eday. It will have access from West Side road, allowing a mobile hydrogen store to periodically collect the inventory
EMEC have agreed with OFGEM that the use of an electrolyser to absorb excess tidal energy can be classed as a ‘permitted use’. Thus, if the energy supplied to the electrolyser is metered, OFGEM will allow ROC payments to be made to the tidal generator operator. 4.3. Connection of the ERE Wind Turbine The 900kW ERE wind turbine connects to the grid via a transformer on EMECs tidal testing site. Therefore, it will be an easy process to connect the turbine to EMEC’s electrolyser and £80k has
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been budgeted in Phase 2 for this activity (including the control system and equipment required to select and merge the two inputs). 4.4. The Size of the EMEC Stationary Storage While the wind turbine will supply the electrolyser on windy days, the tidal turbines will only provide the electrolyser with power at spring and neap tides. As such, the hydrogen generation will vary considerably. However, the mobile unit will be required to be regularly filled if the end use equipment is to function and thus a hydrogen store is required.
Although the EMEC stationary storage will be funded separately, they will be relying on the recommendations of this study before committing to a size of store.
Were the gas generation and consumption to be perfectly balanced, it would be possible to select a size of stationary store based purely on the minimum store level during the year that is sufficient to transfer the desired quantity of gas to the mobile unit on every desired day. If the generation was larger than this, then some energy will be wasted as the store will be full and the electrolyser prevented from operating. If the generation was less than this, then there would be insufficient gas to run the desired hydrogen application on some days of the year. In reality, the generation rate will be unpredictable and will not match the desired end use. Therefore a series of compromises must be made in deciding the size of the hydrogen store. 4.5. Transferring Hydrogen between Stationary and Mobile Vessels While the mobile unit has a maximum capacity of 240kg at 200 bar, this will not all be transferred from the ~500 kg 200 bar stationary storage on EMEC’s site. For example, if EMEC only had 240kg of 200bar static hydrogen storage vessels and attempted to fill the empty mobile vessel, the result would be that the vessels would equilibrate with 120kg of hydrogen at 100 bar in each.
An alternative filling method to this simple equilibration method is to ‘cascade fill’ the mobile vessel. Using this strategy, the stationary storage is split into several sections which have valved supplies to the mobile store which can be independently opened and close by the control system. The difference between the two methodologies is shown in Figure 1.
For both scenarios, the mobile vessel is sized to allow containment of 100kg of 200bar hydrogen and the stationary store contains 400kg of 200bar hydrogen. It can be seen that the cascade fill allows 17% more H2 to be transferred to the mobile vessel. Therefore, cascade filling was taken forward for modelling.
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Static Store Mobile Store Standard Filling Initial
200 bar 0 bar
Final:
160 bar 160 bar
Cascade filling: Initial:
200 bar 200 bar 200 bar 200 bar 0 bar
Step 1:
200 bar 200 bar 200 bar 100 bar 100 bar
Step 2:
200 bar 200 bar 150 bar 100 bar 150 bar
Step 3:
200 bar 175 bar 150 bar 100 bar 175 bar
Step 4:
188 bar 175 bar 150 bar 100 bar 188 bar
Figure 1. (a) Showing standard filling of a 100kg mobile (right) vessel from a 400kg static store (right) compared with (b) cascade filling. 4.6. Transportation of Hydrogen across Eday Once the hydrogen is produced, it is required to be taken from EMEC’s facility and exported from the island. Three options were considered to transport the hydrogen to the Eday pier:
Transportation by pipe. The proposal would be to take a ~3.5km pipe from EMEC’s site to the Eday pier on the east of the island. This would prevent the repeated use of lorrys along the islands weak West-Side road and allow the empty and full trailers to be swapped while the ferry was docked, preventing the need to wait for the next ferry.
The proposal is for:
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o A 3.5km, 21mm internal diameter pipe. Calculations suggest that at a flow rate 5 times higher than the average predicted, a pressure drop of only 20-30 bar is expected. o It is proposed that a wooden ‘ranch style’ fence is assembled, and the pipe is attached to the fence (above ground). o The pipe would be assembled to meet the requirements of the Pipeline Safety Regulations (1996), following the advice of Hydrogen Transport Pipelines by the European Industrial Gas Association. It would likely be an all-welded construction containing isolation valves, excess flow valves, check valves and pressure relief valves to ensure safety. o The pipe would require the permission of 3 landowners o The pipe would not cross areas protected by Scottish Natural Heritage o The estimated cost of the physical pipe is £60k, the fence is ~£20k; however, the cost to landowners is unknown. One or may choose to not allow access, or hold the project to ransom.
Transportation by sea from EMEC’s site. Unfortunately, no pier is available on the west side of Eday and boats are banned from landing on the local beach due to the presence of seals. Therefore, it is not possible to move the hydrogen by sea directly from EMEC’s facility.
Transportation by road. Eday has small roads which ‘float’ in places over boggy terrain. As such, limits are in place for vehicles’ weight and length over the entire island. These are: o 12t limit per axle o 24t total vehicle limit o 12m length limit
This significantly affects the amount of hydrogen that can be transported. Companies have been approached with varying approaches to this problem:
o Chesterfield Cylinders produce a hydrogen tube trailer. This would be a be-spoke unit requiring considerable design and testing. It would hold ~175 kg H2 at 200 bar and cost ~£300k (including design, build, ADR and IVA) o Luxfer cylinders produce hydrogen tubes in a 20’ ISO frame. This could hold 240kg H2 at 200 bar and costs £170k (plus a tractor unit)
The ISO frame was taken forward due to cost, the increased mass of hydrogen and the flexibility of only requiring one tractor unit for several ISO frames. Furthermore, by using standard equipment, it would allow the project to be expanded in the future. 4.7. Transportation of Hydrogen between Eday and Kirkwall Given that the owners of the wind and tidal turbines will receive FITs/ROCs for the energy that is absorbed by the electrolyser, it is assumed that the hydrogen will be essentially zero-cost. The main cost of the energy is derived from the transportation of the hydrogen between EMEC and Kirkwall.
The option with the lowest operating cost would be a direct pipeline between Kirkwall and EMEC, allowing considerable energy to be moved between the islands. While this would allow the output of many turbines to be exported without affecting the local electricity grid, initial estimates of the
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capital cost of this would be £6m, which is outside the scope of this project. However, this could be investigated further in future projects.
As such, transportation by boat is the only option available to this project. To minimise the number of journeys, it is therefore important to ensure that the storage vessels are full when leaving EMEC and are as near to empty as possible on their return.
Care is required to transport hydrogen by sea. If transported on the open deck ferry, it is considered ‘dangerous goods’ and consideration must be given to other dangerous loads which may be carried. For example, it would not be allowed to travel with a straw delivery. This will have the effect of limiting the number of journeys that are possible and risks angering islanders as their deliveries are prevented.
It is therefore important that for the return journey to Eday, the depleted store should not be considered as dangerous, requiring it to be completely empty and purged. Unfortunately, the fuel cell can only operate down to 5bar, leaving 6kg of hydrogen in the vessels. Ideally, a compressor would be used to transfer the gas to the harbour stationary store, before purging. However, discussions with compressor manufacturers suggest it would be more economic to vent the hydrogen. This would be a simple discharge from a high level vent designed to ensure that the H2 jets did not impinge on any ignition source. This would not present an environmental hazard or a significant noise issue.
A range of alternatives to transportation by ferry have been considered and companies with suitable sized ships have been contacted. However, they all similar several issues:
The cost was generally £600-800 for a round trip, compared to £200 for the ferry. This would have made the system uneconomic. Few boats could allow the mobile store to be driven on and off, meaning that lifting equipment would need to be installed to load the container.
As such, the project has been based on using the ferry. 4.8. Static Hydrogen Storage on the Harbour Once the mobile hydrogen storage arrives at Kirkwall harbour, it will be connected to static hydrogen tanks. The requirements for these vessels have been discussed with two manufacturers, and it has been decided to base the storage on 11m long, 200 bar steel tubes, each holding ~40kg and costing £22k. The optimum quantity of storage required is discussed further in Section 13.3. 4.9. Fuel Cell Two PEM fuel cell manufacturers were approached during the project. The model selected is provided by Dantherm, who use stacks provided by Ballard. Their unit comprises of 5kW fuel cell modules within a container, allowing considerable flexibility in the maximum output. An inverter will be included to allow 3 phase output.
As discussed, the container in which they are installed will be fabricated to meet the requirements of installation of a fuel cell in a ship’s compartment and subsequently used for training. This will be discussed further in the Surf ‘n Turf Phase 1 report.
A site survey has been completed and an area identified on Kirkwall harbour that is presently used for storage. The British Compressed Gas Association’s recommendations for bulk hydrogen storage
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have been considered for the separation distances to sources of ignition including vehicles and unclassified equipment. Based on this, the static & mobile storage areas will be enclosed within a fire wall and a flood light will be either moved or replaced with an Ex model.
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5. Model Starting Parameters While the key parameters in this study were optimised in Section 13, the following values were used as a baseline:
Parameter Value Level of installed tidal generation 5 MW Mass of H2 in stationary storage at EMEC’s site 500 kg Mass of H2 in stationary store at Kirkwall harbour 150 kg Max mass of H2 in mobile store to allow it to be returned 35 kg Output of harbour fuel cell 75 kW Table 1. Key parameters used as a baseline for the modelling
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6. Energy Available to Electrolyser 6.1. Energy Available from the Tidal Turbines 6.1.1. Description The tidal testing facility operated by EMEC is located at the Fall or Warness off the Island of Eday in the Orkney archipelago. A narrow channel exists at this location which concentrates the tide as it flows between the Atlantic Ocean and the North Sea. Spring tide velocities of up to 4 m/s have been recorded at the site.
The power produced at each test bed will depend on:
The local velocity at the test site The power profile of the generation equipment being tested. The peak power of that equipment The equipment’s operational state at any given time.
The level of energy directed to the electrolyser will depend on the ability to export the generated power to the electricity grid. In turn, this will depend on how much higher the generation level is than the EMEC export capacity of 4 MW. 6.1.2. Tidal Velocity The tides are created by a superposition of the effects of the moon (on a monthly cycle) and the sun (on a daily cycle). The tidal velocity at three locations within EMEC’s test area has been predicted from a model provided by the DHI Group, based on the strength of the daily and monthly cycle and the local geography. Six months of data has been predicted based on 3 testing locations identified as North, Central and South. The complete data is presented in Figure 2.
Figure 2. The predicted tidal velocities for three locations of EMECs test area
At this scale it is not possible to distinguish the different velocities present. Figure 3 shows two days of data in detail, highlighting that the southern area is expected to have higher velocity.
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Figure 3. Two days of predicted tidal velocity data.
The power generated by the tidal velocity will depend on the power curves of the particular turbines used. Data was provided for two generic turbines, which were averaged. The turbine power curves are presented in Figure 4.
Figure 4. Power Curves for 2 turbines and an average. Power is normalised to the rated turbine power and the velocity is normalised to the rated turbine tidal velocity.
The average turbine power curve was taken forward for subsequent calculations.
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The total rated power of the installed turbines was set to 5 MW installed capacity with the spread being 2 MW in the southern location, 2 MW in the central location and 1 MW in the northern location. The rated velocity was set to 3m/s. The total installed capacity of 5 MW was taken forward for modelling on the advice of EMEC; however, it should be noted that this level of generation is presently not installed and may not be installed for the Phase 2 project.
The total generated tidal power is presented in Figure 5.
Figure 5. The total generated tidal power
Power will only be provided to the electrolyser when the generation exceeds 4MW; this is presented in Figure 6.
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Figure 6. The tidal power to the electrolyser demonstrating fortnightly cycles.
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7. Energy Available from the Wind Turbine Output data from the ERE wind turbine for a six month period was obtained. Anecdotal evidence suggests that the level of curtailment of the turbine has changed since the start of 2014; therefore recent data was used to ensure it was representative. To align with the tidal data, the first six months of the year was considered. It should be noted that wind speeds (and hence curtailment) are generally higher in the second half of the year, therefore these numbers are conservative.
From knowing the wind speed and the turbines power curve, it is possible to calculate the power expected from the turbine and compare this to the power exported to the grid. The difference between these figures is the curtailed energy which will be exported to the electrolyser. Analysis suggests that 45% of this turbine’s output is curtailed and this wasted power is presented in Figure 7.
Figure 7. The curtailed power of the ERE wind turbine
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8. Combined Energy Available The logic for combining the energy from the tidal and wind turbines is that:
The energy from the tidal turbines always has priority. EMEC own the electrolyser and hence must prioritise their customers having access to the equipment. The maximum power to the electrolyser is 0.5 MW. Note that it is possible for some designs of electrolyser to be ‘overloaded’ at the expense of the electrolyser’s durability. This reduction of life varies as a factor of: o The percentage of overload o The duration of overload o The frequency of overload.
At present, a dump load exists to absorb the excess power above 0.5 MW, and it is assumed that EMEC will not wish for the life of their plant to be compromised. Therefore overloading has not been considered.
The resulting combined input to the electrolyser is presented in Figure 8.
Figure 8. Power to the electrolyser comprising of the combined excess power of wind and wave turbines.
Despite combining two separate power sources, it is clear that there are considerable periods of little or no power to the electrolyser, implying that a reasonable level of storage will be required to maintain a continuous hydrogen output for the selected end-use.
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9. Electrolyser Efficiency The efficiency of an electrolyser depends on three key factors:
The technology of the electrolyser. Generally Proton Exchange Membrane (PEM) electrolysers offer higher efficiency at the same current density. The current entering the stacks. At higher currents, the efficiency, and lifetime will decrease. This will be offset by a decrease in the plant capital cost. The operating point will therefore be selected by the manufacturer to be a trade-off between these factors. The sacrificial power required for pumps, fans and the control system.
A typical graph of how a PEM electrolysers efficiency (measured in kWh of electricity per kg of H2 generated) varies with the incoming power is presented as the blue line in Figure 9.
Once the gas is produced, it is required to be compressed for storage. A model of compressor has been selected with an output of 1.33 Nm3/min at 200 bar. Its peak power consumption is 16kW, which when the plant generation and utilisation of 26% is accounted for, suggests that it will be operating for 33% of the time and consume 48 MWh/year. The amount of H2 generated is predicted to be 27.2 t H2 pa. This implies that the compressor will decrease the efficiency by 1.76 kWh/kg. This is shown as the red line in Figure 9. The maximum and minimum input powers are also shown in green.
Figure 9. The efficiency of a typical 0.5MW PEM electrolyser (blue), and the efficiency including the compressor (red), as a function of input power. Also including the equations for the lines of best fit and the minimum and maximum cut offs, outside of which the plant will not operate.
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10. Modelling of H2 Production and Cascade Filling / Dispensing of Hydrogen 10.1. Model Logic The cascade filling and dispensing of the tanks is based on the following logic:
Only run the electrolyser if the incoming power is above 12.5% of maximum. This is because differential pressure electrolysers always have a small level of hydrogen cross-over of the high pressure hydrogen to the atmospheric oxygen side. This is normally diluted to below dangerous levels by the generated oxygen (which is subsequently vented). However, at low powers, little oxygen is generated and it is possible to generate an explosive atmosphere. Therefore, the minimum power is limited. The electrolyser will not operate when the storage is full. The size of the stationary storage is initially set to 500kg, but is a key variable of the model. A consequence of this is that if the tanks are full, curtailed energy will not be processed and will be wasted and the turbine operators will not receive their FITs/ROCs. The amount of energy wasted in this manner will be a metric for determining the best parameters to recommend. A mobile store is always parked at EMEC’s site. When a full one is taken away, it is replaced by a depleted one. Limit the electrolyser incoming power to 500 kW (allowing an average of 5.8 kW to for the compressor, which will operate intermittently). Any power above this level will be sent to the dump load. Calculate the hydrogen generated per 30min period of data based on the incoming power and the efficiency curve presented in Figure 9 Split the stationary storage into 4 equal sized tanks Once the depleted mobile tank is connected, ‘cascade filling’ from the four stationary tanks commences as each is allowed to equilibrate in turn. Subsequently generated hydrogen is used to fill the mobile store preferentially, then each static tank in turn. The depleted stores are only returned on weekdays (it is assumes that the project will not have drivers working on weekends) and whether there is less than a threshold level at the harbour. 10.2. Model Results The mass of hydrogen generated each day is presented in Figure 10.
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Figure 10. The mass of hydrogen generated each day, including the mean and standard deviations.
There are several points to note from this data:
The mean generation rate is 71.4kg/day. If the end use hydrogen consumption is less than this value, the stationary stores will fill and energy will be wasted. If the end use hydrogen consumption is more than this value, the store will become depleted and there will be times when it will be unable to operate continuously. There is a large spread in the amount of hydrogen produced, and despite having two sources of energy, there are many days when no hydrogen is generated.
The total storage level in the stationary tanks is presented in Figure 11.
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Figure 11. The total hydrogen store level as a function of time.
As expected, there is considerable variation in the total storage level over the six months, with almost no gas entering it in May (as gas was being pumped directly into the mobile store, which never filled). The mass of hydrogen in each individual tanks over the six month period is presented in
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Figure 12. When the level reached 500kg, no further H2 is produced.
Figure 12. The mass of hydrogen stored in each of the four tanks over a 6 month period.
This is shown more clearly in Figure 13, where the first two months of data is presented.
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Figure 13. The mass of hydrogen stored in each of the four tanks over a 2 month period
This demonstrates the cascade logic: All tanks start empty and gas only enters the stationary store once the mobile tank is full, at which time Tank 1 is filled. Only when Tank 1 is full, does Tank 2 begin to pressurise. Gas is withdrawn from Tanks 1 and 2 by successive cascade fills. After 3 weeks, Tank 3 pressurises, followed by tank 4 after 5 weeks. Dispensing can be seen to occur from any tank with sufficient stored gas.
The mass of H2 taken from EMECs site each day is shown in Figure 14. Note that the data is very polarised with most days the tank either not being collected (a zero value for the mass taken away), or the tank is at capacity. This indicates that the model is minimising the number of trips to the harbour.
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Figure 14. The mass of H2 taken away in the mobile store each day.
By conducting a cascade fill from the stationary tanks into the mobile store and forcing the subsequent gas generation to feed preferentially into that store, it is maximising the hydrogen that can be transferred to the fuel cell. When a transfer occurs, the mean mass of Hydrogen taken is 190 kg.
It may be counter-intuitive that the average daily hydrogen generation (Figure 10) is considerably lower than the average amount transferred to the mobile store (Figure 14). In a closed system, this could indicate a calculation error. However, hydrogen generation occurs every day (therefore averaged over 365 days per year), but the transferring of hydrogen to the mobile store only occurs when the store is returned, leading to different input and output averages for the same throughput of hydrogen.
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11. Powering Kirkwall Harbour 11.1. Background In addition to several buildings, Kirkwall harbour provides power for 3 large ferries which dock in the harbour overnight. It is suggested to power the harbour from a fuel cell (FC), powered by hydrogen from the EMEC electrolyser. The model is based on taking the mobile store to the harbour and allowing it to equilibrate for 3 hours with a stationary store (any faster could risk overheating the stationary store). During this time, a valve is open between the two tanks, so any hydrogen consumed by the fuel cell will be depleted from both tanks. Once equilibrated, the valve between the two tanks is automatically closed and the mobile store is preferentially depleted. Once it reaches the minimum input pressure for the fuel cell (5 bar), drawdown is allowed from the stationary store. This method ensures that the mobile store is rapidly emptied (minimising the number of boat trips required for the mobile store), while leaving the stationary store to supply hydrogen to the fuel cell when the mobile store is away. To further minimise the number of boat trips, a limit was added so that the mobile store was only returned if it contained less than a threshold mass. This was initially set to 50kg. 11.2. Electricity Demand Data has been recorded at the harbour every half hour since 2006. Based on this information, the average energy demand has been calculated for every day of each month for the 6 months studied in Section 6. This is plotted in Figure 15.
Figure 15. The daily average energy demand for the harbour
The most obvious features are that each month has a distinct average profile and that there is a lower power demand in summer. There is thus a good synergy with the hydrogen generation (Figure
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10) which showed a similar summer reduction. The harbour power demand has a peak of 128 kW, a minimum of 17 kW and an average of 70kW. 11.3. Fuel Cell Efficiency Fuel cell manufacturers have been contacted to provide pricing and specification information for a 75 kW fuel cell. This is a scalable unit normally sold in a 10’ container that comprises of multiple 5 kW modules and has an inverter to provide a 400V 3 phase output.
On request, they have provided a graph for how the gas consumption of each 5kW unit varies with power draw. This has been scaled to the desired output and, on the supplier’s advice, an additional 10% has been added to cover the losses of the inverter and control electronics losses. This is plotted in Figure 16. It should be noted that the final graph equates to a HHV efficiency of conversion of H2 to electricity at full capacity of ~45%, which disagrees with manufacturer’s specified value of ~40%. However, in the absence of any other data, this graph has been taken forward.
Figure 16. The gas consumption of the fuel cell against the output power, including the equation for the line of best fit
11.4. Fuel Cell H2 Consumption A 75kW output fuel cell has been taken forward for analysis; thus any harbour demand higher than this (or when the mobile and stationary harbour stores were depleted) would need to be provided by the grid. This had the effect of only producing 402 MWh of energy annually by the fuel cell, compared to a total demand of 612 MWh, leading to 66% of the demand needing to be met by the fuel cell. The efficiency in Figure 16 was applied to this data to produce the half-hourly H2 consumption. The daily average of this data is presented in Figure 17.
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Figure 17. The mass of H2 consumed / day at the pier based on a 75kW FC.
Before allowing the mobile tank to return for refilling, it must have reached a minimum threshold. A value of 35kg, was used. Each day, the amount of hydrogen that is left in the mobile store is assessed, and is shown in Figure 18. It can be seen that most days the tank is returned with 6 kg of H2 remaining (the equivalent of 5 bar – the minimum that the FC can use to operate). While this low level is good for minimising the number of boat journeys, it is insufficient to prevent the storage being classed as ‘dangerous goods’ on the return journey. This would require the tanks to be emptied and purged. Options for residual hydrogen in the mobile store to the static store have been investigated; however, for the little amount of hydrogen involved, it would be more economic to simply vent the hydrogen to atmosphere. At present, it is assumed that the residual hydrogen is returned to Eday. This value is taken into account when working out the amount of hydrogen that will cascade fill into the mobile tank.
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Figure 18. The mass of H2 left in the mobile store each day.
For this scenario (500kg of stationary storage, 75kW FC) the resulting effect on the harbour energy usage is summarised in Table 2 below:
Total demand: 612 MWh/yr Energy unable to be produced by FC due to its 92. MWh/yr (15% of total demand) capacity: Energy unable to be produced by FC due to 113 MWh/yr (18% of total demand) mobile store being empty: Energy produced by FC: 402MWh/yr (66% of total demand) Table 2. The summary of key energy flows at the harbour.
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12. Key Results The key objective of the project is to provide benefit to the community. This project has the potential to provide direct benefit on several levels:
By providing a useful load for the tidal turbines, it will allow testing above the export limit to take place and allow the turbine owner’s to claim ROCs for each MWh of electricity from the turbines that is consumed by the electrolyser By providing a useful load for the wind turbine, it will allow the operator to claim generation FITs for each MWh of energy from the turbine that is consumed by the electrolyser. The use of a fuel cell on the harbour powered by ‘green’ hydrogen will lower the carbon footprint of the harbour and their grid electricity bill. These savings in electricity will be offset
These key values (based on non-optimised parameters) are presented in Table 3.
Parameter Value
FIT income generated from wind turbine £66.9k pa
ROC income generated from tidal turbine £93.0k pa
Harbour electricity saved £48.2k pa
Cost of transporting H2 on ferry £28.8k pa
Table 3. Summary of key results from the project based on the non-optimised parameters.
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13. The Effect of Changing Parameters The effect of changing the various model parameters has been noted of the key metrics of:
Total FIT & ROC income (The harbour electricity saved) – (the cost of transporting on the ferry)
The parameters varied are:
The Eday static store size The harbour static store size The maximum left in the mobile tank before it is allowed to return to Eday The fuel cell size 13.1. Changing the Eday Stationary Store Size The effect of changing the Eday store size on the total ROC + FIT income and the difference between the harbour electricity savings and the transportation costs were investigated and presented in Figure 19.
Figure 19. The effect of changing the Eday static store size on the ROC + FIT and (electricity saved - Transportation costs).
The results suggest that t would be beneficial to decrease the static store size to 450 kg. However, given that the cost of storage is ~£50k / 100kg, reducing the storage to 300kg would save ~£75k in capital costs and only lose ~£8k pa in income.
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13.2. Changing the Fuel Cell Rated Output The effect of changing the fuel cell rated output on the total ROC + FIT income and the difference between the harbour electricity savings and the transportation costs were investigated and presented in Figure 20.
Figure 20. The effect of changing the fuel cell rated output on the ROC + FIT and (electricity saved – Transportation costs)
This suggests that the present fuel cell output of 75kW should be increased to 80kW. 13.3. Changing the Harbour Static Store Size The effect of changing the harbour static store size on the total ROC + FIT income and the difference between the harbour electricity savings and the transportation costs were investigated and presented in Figure 21.
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Figure 21. The effect of changing the harbour static store size on the ROC + FIT and (electricity saved – Transportation costs)
This suggests that the store size should remain unchanged at 100 kg.
13.4. Changing the Minimum H2 Threshold before Allowing Mobile Store to Return The effect of changing the minimum threshold at which the mobile store was allowed to return to Eday on the total ROC + FIT income and the difference between the harbour electricity savings and the transportation costs were investigated and presented in Figure 22.
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Figure 22. The effect of changing the minimum threshold for returning the mobile store to Eday on the ROC + FIT and (electricity saved – Transportation costs)
This suggests that the threshold should be increased from 35 to 45kg. 13.5. Optimised Values Based on the results of Sections 13.1 to 13.4, the values of the key parameters were changed to:
Eday static store size: 450kg Fuel cell rated output: 80kW Harbour Stationary Store: 100kg Minimum threshold for returning to Eday 45kg
The effect of these changes is shown in Table 4.
Parameter Before Optimisation After Optimisation ROC + FIT £159.9 k pa £165.2 k pa (electricity saved – transportation costs) £19.4 k pa £16.2 k pa Table 4. The effect of optimisation of parameters of the key metrics
While the optimisation has resulted in a net increase in money generated, the effect is small and the second metric has decreased, suggesting that this system is near optimisation and that by refining for individual parameters, the combined effect is to largely cancel out the benefits.
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14. Conclusion This project has worked with the Surf ‘n Turf Phase 1 project to investigate details for the Phase 2 application. This has included consideration of several hydrogen applications, with the most promising being taken forward for detailed modelling.
It was concluded that the Phase 2 project should be based around transferring the hydrogen produced by the EMEC electrolyser to Kirkwall where it could be used to power a fuel cell to supply electricity to the harbour and berthed ships.
Modelling suggests that once optimised, this should bring an income of ~£165k to the turbine operators and the difference between the harbour electricity saved and the hydrogen transportation costs would be ~£16k. In addition, the project will result in net carbon savings of 200 t CO2 pa.
In addition, the fuel cell (and a class room) will be used to provide training for people operating and maintaining fuel cell equipment on ships, which will allow future conversion of ships’ APUs or propulsion systems to fuel cell based units. This larger demand will allow renewable generators to convert their curtailed energy into hydrogen, providing further income for communities.
Based on these results, it is recommended that this project is taken forward for Phase 2 funding.
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