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The deployment of solar power has grown in the UK over the past few years, and is now one of the most popular renewable energy technologies among the British public. At the same time, the rail industry has set out on an ambitious path of emissions reductions – but the two sectors have seen little crossover – until now.

Researchers from the Imperial College of London, together with climate charity 10:10 have announced the Renewable Traction Power project, a world-first investigation into the use of track-side solar panels to power trains.

The project, funded through Innovate UK’s Energy Game Changers programme, will also bring together Turbo Power Systems and Community Energy South as partners.

This initiative comes at a crucial moment for both the renewable energy sector and the rail industry.

Across large parts of the country, particularly in the south of England, the electricity distribution networks are at their voltage maximum, which imposes constraints on the supply of power to rail companies. This means that trains can be underpowered, and no new rolling stock can be added on crowded networks.

However, Professor Timothy Green, director of the Energy Futures Laboratory at the Imperial College of London and Leo Murray, director of strategy at 10:10, think they’ve come across a perfect win-win scenario. By connecting parts of the electrified network directly to track-side solar farms, the pressure to the grid can be relieved, and more clean-powered trains could be potentially added to busy routes in a cost-effective manner for both the buyer and the supplier.

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“Using renewable energy to power public transport is a dream come true from our point of view,” says Murray. “Happily, this project also helps to solve a bunch of problems which already exist both in the energy sector and in the rail sector.”

 Hacking the win-win scenario

Despite encouraging growth in the solar market over the past three to four years, which saw UK photovoltaic (PV) capacity almost double from 2.8GW to nearly 5GW in 2014, a set of recent subsidy cuts from the government has hit the sector hard.

“The government has prematurely thrashed subsidies for small and medium-scale renewables,” Murray says. “That’s had a terribly damaging effect on the British native renewable energy sector and we’ve had 12,500 solar job losses since the Conservatives won the majority government in 2015 and went about removing all the subsidies.”

As a result, the business model for making a profit in this sector has completely changed. In order to commercially function in the absence of the subsidies, the UK’s renewable energy sector is now looking at ways to install and displace grid imports.

“Using renewable energy to power public transport is a dream come true.”

“In the absence of those subsidy payments, the only scenarios where it still makes sense commercially to deploy things like solar PV is where you could displace retail cost of power, as export to the grid is no longer sufficiently rewarded to recover capital investment,” Murray says.

Added to this, the UK has a particular problem with network capacity constraints, especially in many rural areas across the south of England.

“I know from conversations with franchise bidders that on the south-west route out of London, they would like to add trains and carriages but they have been told they can’t do it by the distribution network operators who supply electricity to the line,” Murray says.

“So in the long-term it’s possible that by installing a lot of solar power, you can actually support greater capacity on those routes.”

A world-first experiment

“I’ve had lots of research projects in my career and this has generated by far the most interest,” Professor Green says.

In its initial stage, the project will focus on using the Third Rail System, a type of electrified track which, instead of using overhead catenary wires, it relies on an additional conductor rail to provide traction to the locomotive. Third Rail Systems can be found in south England and Merseyside, powering most suburban rails as well as the London Underground.

The system relies on direct current, which provides a very close match to the voltage of a solar array and therefore is a fairly inexpensive starting point. From here, the plan is to connect solar panels directly to the lines which provide electricity to trains, and completely bypass the grid.

If successful, the innovation could contribute to the setup of multiple small and medium-scale solar farms, and provide a stable financial model for both the rail and energy sectors.

At the moment, the power purchase agreement (PPA) is gaining ground as an alternative, lucrative business model for both the supplier and buyer of renewable energy. To set these up, companies are seeking “high-energy users they know are going to remain in-situ for the life of the equipment,” Murray explains.

“The railways are staying put, and so what you have there is a very stable customer who you know is going to remain in-situ and keep needing electricity for decades to come. That’s exactly the kind of profile that you need to support a PPA-based solar development,” he says.

Appetite for cross-sector collaboration

Despite their optimism, researchers are aware of the upcoming challenges.

For a start, “there’s no set of equipment ready that connects solar panels of about 200VDC to the traction supplier at 750VDC,” Professor Green says. “So there’s some equipment design to do.”

These fluctuations in power demand that will come with a railway are another hurdle.

“If you take a track of railway, sometimes it will be busy, with trains heading in both directions, so there is a lot of consumption, and then ten minutes later it might be quiet and the consumption has dropped,” he says.

“So the local solar farm has to manage its export of power to match what the trains require and we need to study just how much the demand for electricity rises and falls and how much electricity storage we need in order to smooth that out.”

“The innovation could contribute to the setup of multiple small and medium-scale solar farms.”

“We [also] need to make sure we don’t interfere with the signalling communications systems that exist. There’s quite a lot of information gathering that we need to do in this project.”

“I think there’s an appetite in the rail industry to engage with this and there’s an appetite in the solar farm developer community to engage with this,” Professor Green adds.

On 1 February, a six month-long feasibility study will begin, looking at these and other issues. If the results are positive, the next step will be liaising with community energy groups and locate already existing solar farms adjacent to rail tracks across the country.

A second research programme, dedicated to connecting alternate current (AC) lines to the solar supply, is also on the cards. This would be a more expensive undertaking, but would also provide a much bigger market for the technology, as AC electrified lines dominate the UK and European networks. But both researchers seem optimistic.

“From our point of view as a climate change charity, we’re very excited about this, because it supports a modal shift and more journeys taking place by rail, particularly electrified rail,” Murray says.

“The big prize here is that it is a means to support subsidy-free renewable energy deployment in the UK,” he says.