Valleys Be? Tales from the Four Foot Eight and

How Green Will Our Valleys Be? *

A great deal is being written about the enormous investment being made by the Welsh Government into modernising and revitalising the railways in the South Wales Valleys. One aspect which does not appear to have been covered to any great extent, is the electrification of these Core Valley Lines, to bring them within the Welsh Government’s target of achieving net zero emissions by 2050.

This article is based upon a report produced by the Rail Standards & Safety Board (RSSB) and their help and permission is gratefully acknowledged.

Electrification of the Valley Lines

Electrification will increase energy consumption and TfW has committed to using 100% renewable energy, 50% of which will be sourced in Wales. With this in mind, TfW has been working with a consortium of partners led by Riding Sunbeams (see the article on pp – Ed) on a feasibility study investigating the potential to use lineside renewables to power the overhead electrification in the Valleys.

Following extensive research funded by the Rail Safety and Standards Board, and working in collaboration with TfW, Network Rail and the Energy Saving Trust Wales, Riding Sunbeams has found that solar traction power could supply at least one tenth of the energy needed to power trains on the UK’s DC electrified routes every year. It could also present a financial benefit for solar farms and rail operators right now as no public subsidy support is needed. Community energy, social impact, and the importance of working with lineside communities and rail users has been embedded in the heart of the project. The potential for this technology has huge implications for the UK and the world as we transition to a low carbon future.

The Green Valley Lines

The Green Valley Lines (GVL) is the name given to this project and refers to the feasibility assessment of direct-wire renewables and line-side storage to power the soon-to-be electrified Core Valley Lines (CVL) in Wales. The Core Valley Lines refers to an area of 85 route miles north of Cardiff Bay station. It includes all rail routes from: Cardiff Bay to Rhymney, Cwmbargoed and Coryton, and Cardiff Queen Street North Junction to Merthyr Tydfil, Hirwaun and Treherbert. TfW and KeolisAmey Wales are designing the electri-

*With apologies to Richard Llewellyn, author of “How Green Was My Valley”.

fication of the Core Valley Lines, which they took over from Network Rail via an asset transfer on 28 March 2020.

This report was drawn up by Alex Byford MEng MIET, (Chief Technology Officer, Riding Sunbeams), Dr Nathaniel Bottrell MEng, (Ricardo Energy & Environment), Ben Ferguson, (Energy Saving Trust Wales), Leo Murray, (Director of Innovation, Riding Sunbeams), Ernie Shelton BEng MSc CEng MIET, (Horizon Power & Energy), and Ben Whittle, (Energy Saving Trust Wales) with added input by Dr Dave Hewings (Network Rail), Graeme Brindle (KeolisAmey), and Natalie Rees (Transport for Wales).

The Aim of the Project

The Green Valley Lines (GVL) project has reviewed the use of renewable ‘green’ generation as part of the final design solution in the electrification of the Core Valley Lines (CVL) in Wales. The project has undertaken rigorous and iterative analysis across a range of workstreams to assess the engineering solutions, prospect for potential renewable energy sites, and identify the market conditions needed to finance viable, decarbonised power generation to the railway’s traction needs at a competitive and predictable cost.

Why the Core Valley Lines?

The Core Valley Lines were selected as a focus for this project due to the perceived design synergies that might arise where new rail electrification works and new sites for power generation were under parallel development.

The Valleys are particularly rich in renewable energy resources. The project has found that injecting power on to the rail network does not add a significant design or cost burden to the electri-

Network Map of the Core Valley Lines, terminating at Treherbert, Aberdare, Merthyr Tydfil, Coryton, Rhymney and Ebbw Vale

Electrification as part of the Decarbonisation of the Railways

In October 2018, the Rail Safety and Standards Board (RSSB) launched a competition to facilitate research and innovation in support of the industry’s decarbonisation challenge, in particular by developing intelligent, zero-carbon technologies to enable the UK industry to be a world leader in delivering low-carbon transport solutions. The call was aligned with the Rail Industry Decarbonisation Taskforce and the Ministerial commitment to phase out diesel-only trains in the UK by 2040. The RSSB competition focused on three key challenges:

A. High speed train power,

B. Freight traction power,

C. Infrastructure to support operations.

The Green Valley Lines project was funded under challenge C: Infrastructure to support new lower carbon traction operations.

Why Riding Sunbeams?

In order to develop this project, it was necessary to find a partner who had experience in the use of alternative methods of supplying power to the railway. Riding Sunbeams Ltd is one such UK company that has proven experience in that it successfully delivered a real-world demonstrator of its technical solution for private wire supply of solar to DC traction networks, at a Network Rail site just outside Aldershot station.

This work proved that supply of solar power direct from the generator to the rail traction system could be done safely and efficiently and began to develop a commercial procurement framework to allow UK rail infrastructure operators to benefit from this novel approach. Before this, direct supply of solar, wind or hydro power to rail traction systems had never been done anywhere in the world. Riding Sunbeams’ corporate mission is to meet 10% of the UK’s rail traction load through direct supply from renewable generators, and to maximise the social benefits of doing so.

The Green Valley Lines Report (COF-IPS-05)

The Green Valley Lines (GVL) feasibility study addressed challenge C under the RSSB’s COFIPS competition: Infrastructure to support operations. This study sought to identify the optimal technology mix to allow the South Wales electrified railways to run fossil free in the future, providing direct power supply to the traction system from community owned renewable electricity generators, together with integrated energy storage, to reduce the overall costs of supplying traction power to these lines against a business-as-usual baseline. The key potential benefits include lower costs of service provision for network operators and large carbon reductions compared with grid supplied traction electricity, plus employment and clean growth benefits to lineside communities and local economies. Integrated lineside storage could also contribute to system resilience, and when combined with bi-mode and tri-mode trains with on-board storage and discontinuous electrification, could even offer a lower whole system, whole life cost alternative to conventional traction power delivery through full-route OHL electrification and associated distribution and transmission infrastructure reinforcements. Through exploring specific potential use cases on the South Wales Metro, the team looked to develop a more general understanding of the technical and commercial challenges around direct connection between renewable generators and AC rail traction systems, as well as the next steps required to realise this opportunity.

Objectives of the Study

1. To develop a technical proposal for a commercially viable power electronics interface and connection methodology for direct supply of electricity from lineside renewable generators to the 25kV AC rail traction system. The renewable generators will need to integrate with

IEC 61850 to provide a South Wales traction smart grid. 2. To identify the best value for money lineside storage technology facility to support rail traction operations and mediate power flow from intermittent renewable sources. 3. To identify the most promising locations and generation technologies for community-owned lineside renewable energy generation and storage facilities to support rail traction operations on selected South Wales electrified routes, and to develop outline business cases for a shortlist of these sites. 4. To determine the optimal technology mix of storage and renewable energy generation and supply to enable a fossil-free rail traction power system that can be delivered at a lower cost than conventional methods allow. 5. To make specific recommendations to Transport for Wales and Network Rail Wales on the design of the South Wales Metro traction system and other routes in South Wales to maximise the use of renewable energy and minimise costs. 6. To produce generic guidance for utilising lineside storage and renewable energy generation to lower the costs of AC rail electrification schemes. 7. To identify opportunities that Vehicle to Grid (V2G), if integrated with the traction system, might be able to provide in terms of increasing the amount of renewable generation that could be connected or being able to utilise regenerative braking as trains slow when stopping at stations.

Key Workstreams

1. Workstream One: Interface design Assessing options and developing a proposed technical specification and connection method for a power electronics interface between renewable generators and the AC traction network. 2. Workstream Two: Load profiling and matching Analysing the South Wales Metro system’s electrical architecture and projected spatial traction load characteristics for all selected routes; and modelling the compatibility of solar and wind generation profiles with the traction system’s load profiles. 3. Workstream Three: Resource mapping -

Mapping the land use constraints and renewable energy resource opportunities along the selected routes, compiling a shortlist of site opportunities for potential wind and solar traction power generators, and developing outline business cases for the most promising sites. 4. Workstream Four: Lineside storage analysis

Appraisal of the energy storage technology options available and their suitability for deployment on the rail network, and exploration of the potential system services that lineside storage facilities could provide rail infrastructure operators. 5. Workstream Five: Synthesis Summarising and synthesising the findings from all workstreams to develop high level technical and commercial parameters for integrating renewable energy sources and storage to AC rail traction systems in general, alongside specific recommendations for the South Wales Metro traction system.

Putting it into Action

It is one thing to come up with a design, but it is how that is translated into plant on the ground that matters. The project obtained the major feeding diagrams of the proposed electrification works for the lines terminating at Treherbert, Aberdare, Merthyr Tydfil, Coryton, Rhymney and Ebbw Vale. The demand and voltage profile for the different sections was provided from Network Rail Wales for the Ebbw Vale line and KeolisAmey for all other lines.

A spreadsheet-based model was developed to match the generation profiles with the demand profiles in the different electrical sections. This model calculated the expected amount of generation which could be used by the traction load, the amount of generation that would need to be exported at the Grid Supply Point (GSP) or curtailed, and the percentage of rail demand which could be met by the generation sources.

Transport for Wales has a policy objective that all traction electricity demand from the trains on the South Wales Metro should be supplied from renewable generation sources and 50% of that generation should come from Welsh producers. This aim was stipulated in the terms of the Transport for Wales Rail tender won by KeolisAmey. This model was used to estimate how much renewable generation of different technologies would need to be directly connected to the traction network to reach or exceed the 50% target.

The Present-Day Electrical Situation

The electrical network of the Core Valley Lines is split into three electrical sections. Two are supplied from the Upper Boat GSP and the third is supplied from Network Rail’s Imperial Park GSP, which also supplies the Wales mainline between Cardiff and Newport. The demand on these lines is highly variable and has the potential to become negative if the trains are regenerating and there is insufficient on board and line-side battery capacity available to capture the generation.

The demand on the section to the north of Upper Boat may range from 8 MVA export to 16.9 MVA of demand within a 15-minute period, while the demand on the section to the south of Upper Boat may range from 7.27 MVA and 41.3 MVA of demand within a 15-minute period. There is likely to be a minimal base load for the renewable generation to provide on these route sections. Not all the electricity from traction-connected wind or solar PV generators will be able to be used by the rail network. This is particularly true for wind energy, due to its less predictable generation profile that is less well aligned with rail operating timetables than solar PV generation.

Any control system for PV or wind generation curtailment is unlikely to be sufficiently responsive to the changes in demand. Therefore, either battery storage is needed to prevent export at the GSP, or export at the GSP is required to balance the difference between the renewable generation output and traction demand on the section. If export volumes to grid are minimal this is likely to be considered as an acceptable ‘spill’. However, for larger volumes, a formal export arrangement with both grid operators and the electricity supplier would be needed, as well as written consent from the regulator. Currently Network Rail exports around 60GWh of electricity from their single-phase 25kV traction GSPs on to distribution networks nationally each year, exclusively from regenerative braking.

NR are remunerated for this electricity under their main traction power supply contract. This is classed as De Minimis activity under NR’s Network Licence with the Office of Road and Rail, but larger export volumes would likely require written consent from ORR to be classified as Relevant Other Business. Existing connection agreements at traction GSPs would also need to be revised via Modification Applications, and export meters added.

PV generation has a higher utilisation than wind generation. Utilisation is defined as the proportion of generation yield that can be consumed

by the rail demand and which doesn’t need to be exported or curtailed. This higher utilisation is explained by PV only exporting during the day, while wind generation also outputs at night when there is no traction demand. The trains operate between 6am and 11pm. While PV generation has a higher utilisation than wind, for the same installed capacity, wind generation can supply a higher percentage of the traction demand than PV. Therefore, less wind generation will be required to achieve the policy target of 50% of generation from Welsh generators. This is because wind generation has a higher load factor, of approximately 26% compared to 12.6% for PV. This is explained by solar generation output being far lower in the winter months and in evenings than wind generation, which generates during evenings and in winter. The low utilisation factor for wind but high load factor mean that wind would be a highly effective means to provide zero carbon generation to the railway, however the ability to receive income for export to the grid through the GSP is crucial to the business case.

Network Rail estimates that the annual demand on the Ebbw Vale line would be 2,768.42MWh, which is low. As the Ebbw Vale is supplied from Imperial Park GSP, any excess generation would be used on the mainline services and not exported to the grid at the GSP. A critical element for sizing the generation when looking over the whole of the Core Valley Lines is the thermal capacity of the overhead wires. The overhead wires will be the distribution system for the generation, and a single track OHL is rated to a maximum capacity of 10MW and a double track to 20MW. This technical constraint must be compared with the minimum economically viable site for wind and solar, to determine the ultimate mix of wind and solar. The Treherbert, Aberdare, Merthyr Tydfil and Coryton branch lines are all single-track sections. The Rhymney route after Bargoed is also likely to be single track, as is the Ebbw Vale lane. Other route sections of the Core Valley Lines are double track.

Key Findings

Direct supply from lineside wind and solar PV generators could meet 38% of the total traction demand across the Core Valley Lines and Ebbw Vale on commercially attractive terms. By electrical section, this would comprise 79.51% of demand on the newly electrified Treherbert, Aberdare and Merthyr Tydfil lines, 25.34% of demand on the Coryton and Rhymney lines, and 86.36% of traction demand on the Ebbw Vale line if it is electrified in the future. The resource mapping and shortlisting process identified 96.5MWp of generating capacity across seven potentially attractive solar and ten potentially attractive wind development sites.

Together these make up around a third more generating capacity than the rail traction system could accept private wire supply from (estimated at 21MWp of solar PV and 42MWp of wind in total). This is a positive finding as not every site can be expected to successfully secure land rights and planning consent to be built.

The cost of the converter for connecting private wires to the OHL is the most critical factor for the financial viability of any given generator site. Obtaining a suitable converter at a price point below £250,000/MW is therefore critical. There are no such products available in the market today that are also likely to be able to withstand the duty cycle needed on the railway. Deployment of traction-connected renewable generators at these scales depends on the ability to export surplus electricity to the distribution network from rail GSPs; if grid export is not possible, generator capacity and yield volumes may need to be sized too small to be commercially viable. Obtaining all necessary consents to export to grid from rail GSPs is therefore critical. Written consent from the Office of Road and Rail (ORR) may be required, and a Modification Application will need to be filed with National Grid to export from the Upper Boat GSP.

Debt service cover ratios strongly influence the financial models, therefore securing suitable financing arrangements is also critical to underpin deployment. As a rule of thumb, commercial and technical constraints require individual AC OHL traction-connected solar site capacity to be between 5-20MWp, and wind site capacity to be between 2-20MWp (10MWp maximum if connecting to single track route sections). 20-25-year power purchase agreements (PPAs) will be required to underwrite investment in these new generators.

Under present market conditions, developers will need to be able to secure PPAs of 8-10p/kWh from rail operators for sites to be financially viable. The high capital costs of integrating storage mean this does not improve the economics of any individual traction-connected renewable energy development, but lineside storage facilities could be economically advantageous to mediate power flows across an entire route section, ideally co-located with the GSP with an export connection agreement to allow sale of ancillary services to the grid. Lineside storage facilities could supply a lower cost solution to supporting traction requirements in scenarios where full route electrification is prohibitively expensive and grid capacity around islanded sections is weak. Local socio-economic benefits from supplying the South Wales Metro from lineside renewable generators can be maximised through established models for community involvement and ownership. Similar parameters to those summarised here are likely to obtain elsewhere on the UK’s AC OHL electrified rail networks so this learning is expected to be widely applicable beyond the South Wales Metro.