How many times have we looked at clever innovation and wondered why on earth no one thought of doing it before? Often the simplest of ideas seem to lead to the most elegant of engineering solutions. The truth is, of course, that invention is only half of the story. Sometimes the right meeting of minds must happen before a bright idea can become a reality.
To the best of our knowledge, the direct supply of solar power to rail traction systems has never been done, anywhere in the world. Now, thanks to a collaboration between Network Rail and a social enterprise scheme called Riding Sunbeams, the very first solar farm to directly supply power to trains has been switched on. That’s right, not in a distant country with a hot climate and wall to wall blue skies, but right here in our cloudy UK, near Aldershot station to be precise. The new system went live on 23 August.
Riding Sunbeams is a joint venture between 10:10 Climate Action and Community Energy South. 10:10 is a registered charity on a mission to speed up action on climate change by inspiring more people to become involved, while Community Energy South was set up in 2013 as an umbrella organisation, enabling community organisations and local energy groups to grow as sustainable low carbon businesses.
Behind the Riding Sunbeams project is a pretty simple idea. It is that solar farms could be installed next to the train tracks – on embankments, train sheds, nearby fields and industrial buildings – and that these could power the railway directly to provide traction power for the trains.
In 2017, the 10:10 charity brought together experts from the Energy Futures Lab at Imperial College London, Community Energy South and electrical engineering specialists Turbo Power Systems, to find out whether the idea was feasible, and the answer was yes. It was estimated that solar traction power could realistically provide around 10 per cent of the energy needed to power trains on the UK’s 750V DC electrified routes.
Community energy, where local people own the renewable energy and benefit from it, is at the heart of this work. Riding Sunbeams has a mission to see community and commuter-owned solar farms powering the railways for the mutual benefit of the railway routes, the communities that host them and, of course, the planet. In other words, to have third-party funding contributing to the national rail network. This is no madcap scheme; the idea has huge potential for metros, trams and heavy rail in the UK and around the world.
Network Rail purchases an awful lot of electricity. The potential to obtain even 10 per cent of the DC third rail electrified network’s energy requirements from renewable sources, and at a cheaper rate, was worthy of consideration.
Stuart Kistruck is Network Rail’s director asset management for the Wessex route. In 2017, he had attended a presentation by Riding Sunbeams. “Making use of solar energy, produced on our own land, seemed like such an obvious thing to do,” he said.
“We started conversations and it became clear that the third-rail electrified Wessex route could provide favourable locations to trial the technology. We have many southerly facing cuttings that could be used for solar farms, which would not only provide some of our energy needs, but also relieve some of our commitments to vegetation management.”
Stuart also saw that community energy, where local people own the renewable energy and benefit from it, could be at the heart of such a scheme. “There is clearly an opportunity for community-energy funding to benefit the railway – connecting solar farms, not necessarily on railway land, to the rail network.”
The Riding Sunbeams’ ‘First Light’ demonstrator project has attracted funding from Innovate UK and the Department for Transport. Six potential sites for the trial were identified across the Wessex route, with a location near to Aldershot station being the one chosen for the pilot scheme. It offered a suitable area of waste land for the solar farm that was conveniently close to an existing traction power supply point (substation).
In terms of power transmission efficiency, the relatively low traction voltage of 750V does not lend itself to distribution over long distances. For that reason, it is necessary to provide third-rail traction supply points every three to five kilometres along the railway.
It was realised that it would be possible to connect solar farms into the existing 33kV AC feeder systems that carry power from the grid supply points (GSPs) to the substations. Although this approach will lead to some DC-AC-DC conversion losses, it has some practical advantages over DC-DC supply to the substations:
Equipment for connecting solar farms to high-voltage AC networks is very well established and widely available. Being able to make use of existing technology (usually used for something else) for deployment on the railways has reduced the development time from an estimated five years to about one year.
Connecting to the feeders helps to overcome the major technical challenge for solar traction power: intermittency. This is because each GSP supplies around ten to fifteen substations. The load is shared across all of these, creating a more stable demand than if only one substation were to be fed. It may also be possible to export small amounts of surplus power from the feeders back onto the grid via the GSP.
This approach should largely negate the possibility of DC voltage-range exceedances and other power quality issues on the tracks, which would have increased operational risk.
Despite the compatibility of the technology, which makes it straightforward to bolt the new equipment onto existing traction substations, Leo Murray, director of innovation for 10:10 Climate Action, explained that there are still technological challenges: “By its nature, the supply is intermittent and we have a very peaky load. And of course, the periods of peak demand and peak generation don’t coincide.”
Depending on the nature of the rail traffic, there can be long periods with no demand interspersed with periods of high demand. Leo continued: “A train under acceleration may draw up to 2,000 Amps. Lineside storage (batteries) could provide a solution, but the required technology for rail systems is not developed. We would be faced with perhaps a five-year development programme, which couldn’t pay for itself.
“Even in the long term, the business case for using battery storage doesn’t look as good.”
This was another reason for choosing the Aldershot substation for the trial. The location should provide a reasonably constant load.
The Aldershot trial is a modest undertaking with a solar array that comprises just 135 panels, installed for Riding Sunbeams by local firm Basingstoke Energy Services Cooperative. Peak output is rated at 37 kW. Its purpose is purely to test the technology and the modelling that was used as part of the feasibility study.
Theoretical modelling of the systems was undertaken by Dr Nathaniel Bottrell, then with Imperial College. He has since joined Ricardo Energy & Environment as a consultant, and this company has itself become an important partner in the scheme.
Design work on the ‘First Light’ solar traction test unit was completed by Riding Sunbeam’s resident engineer Ernie Shelton, in dialogue with Network Rail’s Wessex Route’s lead traction engineer Nigel Wheeler – Network Rail effectively acted as the DC-traction engineering consultants.
As Leo put it: “The objective at Aldershot is to test the technology without spending millions of pounds.”
Data loggers would monitor the load, generation capacity and the quality of the supply.
Meanwhile, Network Rail is, of course, looking closely at the system performance and ensuring compliance with its own technical requirements for safe operation. These include protection settings and the fail-safe operation of circuit breakers in the event of a fault condition.
The quality of the supply is also under scrutiny, with the production of voltage spikes and harmonics being closely assessed. The potential for over-supply during periods of low demand and peak generation is another concern, but Stuart Kistruck is keen to stress that, overall, the position of Network Rail is one of collaboration and support.
There is also involvement from the electrical engineering department of Birmingham University. Using data gathered from the Aldershot installation, and from data loggers at the other five proposed sites, they will undertake sophisticated modelling. By pinning this to Network Rail’s traction model, it should be possible to predict accurately how a larger solar installation should perform. This work will be important in ensuring that a successful and commercially viable engineering solution is attained.
Assuming all goes well, by this time next year, the other five sites that have been allocated for trials on the Wessex route should be happily generating electricity for the third rail system. The trial itself is open-ended with no fixed timescale, but Riding Sunbeams has great ambition.
Leo Murray explained: “Once the technology is proven, we’ll go bigger, offering shares in solar farms to communities and commuters, so that local people will own and benefit from the clean energy powering their trains.”
There is no doubting the magnitude of the opportunities that lie ahead.
Leo continued: “We’ll be gathering electricity demand data from our six potential solar sites in the south of England. Putting this real-world data together, we’ll be able to work out how to plug in much larger solar arrays to power trains in future.”
It’s estimated that those arrays would each be capable of generating between one and four megawatts. All being well, the world’s first ever full-scale, community and commuter owned solar traction farm should be connected to the railway during 2020.
As we have seen, the generation of electricity using solar technology lends itself to supplying trains on the 750V DC third rail system. Looking ahead, though, Riding Sunbeams is working with Transport for Wales to build renewable energy into their plans to electrify the lines north of Cardiff using 25kV AC overhead line equipment (OLE).
The difficulty with retro-fitting existing 25kV AC lines with solar power generation is that the OLE feed points tend to be much further apart than on DC lines. They also tap directly into the national transmission grid, rather than distribution. This means that, even if a solar farm could be sited nearby, bespoke equipment would be needed in order to provide an interface.
An alternative would be to build new feed points near the solar farms, but this would create disruption to rail services.
Either way, the costs involved are higher, and the specialist equipment needed for feeding the OLE at 25kV would require development and approval.
That said, by taking account of solar-power generation at the design stage, the South Wales Green Valleys scheme should be able to accommodate new feeder substations close to the best sites for solar farms. Leo is enthusiastic about this, and about other possibilities too: “We’ll also be looking at the potential to use community wind turbines to power the trains.” There is currently a ban on new land-based wind farms in England, but not in Wales.
Back at Aldershot, if successful, the Riding Sunbeams: First Light project will prove that direct solar PV supply can be successfully integrated into UK railways without negatively impacting on rail operations or safety.
This is a world first and it should also establish the business case and contractual relationships needed to unlock opportunities for community energy groups and other renewable generators. It is as much about developing innovative ways of owning and financing renewable energy as it is about proving the technology.
The rail industry plays an important role in reducing carbon emissions and, as part of that, Network Rail is committed to making use of renewable energy. The necessary land is available, the technology exists and there is the will to take this exciting project forward. With the passing of net zero emissions legislation in the UK there has never been a better time for Riding Sunbeams to help the rail industry respond to this challenge.
To quote Riding Sunbeams, it’s time to get on board – here comes the sun!