Rail solar projects pave the way for renewables
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Electric trains could provide a huge guaranteed market for renewables, but it will need some railway-specific power equipment.
A British solar power company is working on technology that could enable railways all over the world to be powered by renewable energy.
Riding Sunbeams is the company behind a project of the same name that is already delivering power to trains on Network Rail’s Wessex route, which uses third-rail electrification, and in June 2020 it secured funding to develop equipment for the far more common overhead power lines.
Both projects are supported by the Department for Transport’s ‘First Of A Kind’ (FOAK) scheme to boost innovation in rail, and the firm also hopes to have a role in electrifying the South Wales Metro.
Alex Byford, chief technology officer at Riding Sunbeams, explains that the initial Wessex route installation at Aldershot is quite small, at 37kW, but it “enables us to prove to Network Rail’s product assurance and safety teams that renewables could be integrated without causing any issues with the rail network”. A data logger at the site is gathering information about power quality, to ensure that the equipment will neither cause problems nor itself be damaged as a result of being connected to “quite a dirty supply” that suffers from harmonics, reactive power and voltage fluctuations.
The Wessex line operates at 750V DC, so it’s surprising to learn that the solar installation uses inverters to convert its DC output to AC. Byford says this is because Network Rail supplies the line from its own private distribution network at 33kV AC. Plugging directly into that enables the use of the same off-the-shelf inverters that are used by other solar sites to feed into the grid. It’s those inverters that are now going through the railway approval process.
Most of Britain’s electrified railway network uses overhead power lines at 25kV AC. The new Daybreak project will develop a power conversion device to meet this requirement. It’s needed because the railway’s electricity supply is single-phase, unlike the three-phase national power networks. Byford explains why this matters: “Single-phase electricity is normally used in domestic installations at 240V, whereas this is at 25kV, so the issue is that no equipment has really been designed to change the output of the renewables to that single-phase electricity.” As well as the lack of power conversion equipment at the right size and price, there’s also the challenge of operating in a railway environment.
The Daybreak demonstrator will repurpose technology from other railway applications to create a new device that will provide the required power conversion. Byford says the plan is to use existing technology as far as possible in order to reduce development time and costs, and because power electronics equipment that is already certified for railway use can cope with the heavy duty cycles required.
Riding Sunbeams has formed a consortium with Network Rail, Angel Trains, Turbo Power Systems, the Birmingham Centre for Railway Research and Education and Ricardo Energy & Environment to deliver the project, with the help of a £400,000 grant from the FOAK 2020 programme. This will enable the team to procure the required equipment and modify it over a period of nine months. Riding Sunbeams will then install a solar array coupled with lineside storage at Quinton Rail Technology Centre at Long Marston, Warwickshire, and power a locomotive directly with ‘green’ electricity for the first time.
Byford explained: “Our new device will use a mixture of DC/DC converters to maximise the power output of solar panels and for the lithium-ion batteries, and an AC/DC bi-directional power electronic device to convert the DC output to single-phase AC.
“Working in conjunction with Angel Trains, we have sourced an AC/DC bi-directional power electronic device, which forms part of a traction converter as is standard on an electric train powered by 25kV 50Hz overhead wires. We plan to re-use this device and a 25kV/LV transformer from a train and also re-purpose some DC-DC converters, which are common in the renewables industry – with some new software algorithms that we will develop.”
At the Quinton test facility, the solar array and containerised battery energy storage units will be connected to the new power electronics conversion device, which will in turn be connected through a gantry to the overhead wires. “The power demand for a single locomotive (without carriages) should be entirely powered by our solar and storage systems,” Byford said.
The demonstration will provide a case for connecting to existing railway lines and also electrification of existing diesel lines with direct wire storage and renewables, he continued. “The main aim, however, is to prove that we can directly power both new and existing AC railways with direct-wire renewables with technology that is already at a high technology readiness level, so that we can progress with development of these sites in both the UK and abroad.
“Once we have completed our demonstrator project our next step will be to finalise the design and begin the product approval and safety methodology requirements for use on the operational railway.”
The company is hoping that its technology will be used in the project by the Welsh government and Transport for Wales to electrify 172km of the core Valley Lines as South Wales Metro. The avowed aim is to do this with 100 per cent renewable energy, of which 50 per cent will be Welsh-generated.
Riding Sunbeams comes in because it received funding from the Rail Safety and Standards Board (RSSB) to review the feasibility of integrating renewable generation into the newly electrified lines. One outcome of that was to make direct recommendations to Transport for Wales on how much generation could be put in and where it should be. This early involvement should reduce the cost of installing renewables, because the requirements can be factored in to the original design.
Byford acknowledges that directly connected renewables can’t provide all the lines’ power requirements, but suggests that 70MW is achievable through a mixture of solar, wind and energy storage.
The 2020 competition for FOAK funding was launched by then transport minister George Freeman at the Aldershot site, and he also met the company directors to discuss progress. Such government interest reflects the fact that a commercially viable railway-certified power converter would be “eminently exportable”.
Electric railways in many parts of the world use a 25kV single-phase supply: Byford cites China, much of Europe, India and Malaysia as examples. “Other countries are going to have the same issue in terms of equipment,” he notes. “It’s not technically difficult – there just hasn’t been the market to design it, so no one has.”
Trackside difficulties
One of the key lessons the Riding Sunbeams team have learned is that putting solar panels on spare bits of railway land isn’t as easy as it might seem. “I’m not saying it’s impossible, or isn’t the way to go,” says Alex Byford, “but it’s very difficult to find suitable land that will be economical to build on.”
For the Aldershot installation, it took nine months to find a site, gain permission to build on it, clear it, install and commission the panels and collect the data needed to do some modelling.
Byford explains that many trackside locations were rejected either because they weren’t suitable for solar panels or because it would have been necessary to halt train services while work took place.
“It’s very expensive to shut down a line,” he says. Moreover, “there’s a lot of contamination in the ground which makes it more expensive, and a lot of bits of land are in the wrong place, so you’d have to put a cable underneath the railway, which costs a lot of money. You’ve then also got shading issues, where there can be buildings and things in the way, and the panels have to be at the right angle, to ensure the maximum amount of solar generation.”
Taking all these factors into account, he continues, it starts to make a lot of sense to put in a very big site remote to the railway, connected through a private wire. “That’s largely one of the reasons we’ve gone down that route [in our recommendations for the South Wales Metro],” he says.
This approach also makes it possible to integrate onshore wind as well as solar, and it opens up more opportunities for sites.
It’s worth noting that policy in Wales has generally been more sympathetic to new onshore wind developments than in England, where they have effectively been banned in recent years, though an announcement in March 2020 has signalled renewed government support.
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