King’s Cross station at end of solar timetable
Millions of people a year will have the opportunity to see the solarPV installation at King’s Cross station in London. Ken Sharpe looks behind the scenes of this very special project.
Exploiting renewable energy for a major railway terminus in central London presents limited opportunities. For King’s Cross station, the terminus for trains from cities such as Leeds, York, Newcastle, Edinburgh and Aberdeen, the setting has particular problems. It is in an urban area with a dense network of Underground lines serving the station — so ground-source heat pumps are a non-starter. What it does have, however, is a huge roof spanning eight long platforms — providing an ideal prospect for a major solarPV installation.
Factor in the extensive 6-year refurbishment of the station which has seen the construction of a new main passenger concourse and the restoration of the Grade 1 listed roof dating from the 1880s, and you have an ideal opportunity for integrating a solarPV installation into the overall project.
The Grade 1 listing of the roof meant that English Heritage and conservation planners were closely involved in all aspects of the restoration. Consequently, the solar installation is rather special. All the detailed design, specification and supply of key components for the PV system and the DC electrical installation was undertaken by Sundog Energy, working for main contractor Kier, in collaboration with Network Rail.
The £1.3 million projects comprises 1392 panels that form part of the two massive barrel-vaulted glass roofing structures. They have an output of 240 kW and are expected to generate 175 MWh of electricity a year.
The custom-made glass-laminate solarPV units were made by Romag in the north east of England and installed by roof-glazing specialist ESB Services. AC electrical works were carried out by the rail division of NG Bailey. All the work of refurbishing the roof and installing the solarPV system was carried out with the station fully functional — a major challenge in itself.
One special feature of the panels is that they are of blast-proof glass as an anti-terrorist measure. The panels are also required to pass light down to the station platforms below, so the solar cells are installed between the glass sheets to allow for this. The structure of the roof also casts shadows on the panels as the Sun moves round during the day, so the solar cells are kept away from the edge of the panels — especially the top edge. Further protection against shading is provided by a diode that disconnects a panel if it is in shadow so as not to affect the rest of the panels in the string.
One area that is particularly susceptible to shadows is near the clock tower at one end of the roof.
Such concerns and the structure of the roof itself limited the output that could be installed.
The panels are divided into 128 string circuits, usually 10 panels to a string, which are in turn run into 22 string combiner boxes. DC cables ranging in length from 125 to 260 m deliver the electricity to the plant room, which is towards one end of the station. The thickness of these cables varies according to the distance they run
In the plant room are 22 Fronius IG Plus inverters of various sizes. Most of them deliver 3-phase AC electricity and are rated at 12 kW. Most of the string groups have the same number of panels, but there are a few with less. Some inverter boxes deliver 2-phase electricity and some single phase. 3-phase electricity is fed back to the station switch room 80 m away and can also be fed to the grid — though this is unlikely to happen given the electrical demand of the station.
Looking up at the roof from below, the panels are discreet and integrate with the aesthetics of the new roof. Some of the string boxes can be picked out if you know what you are looking for. However, the cable runs are carefully concealed by the ironwork of the roof and the glazing bars.
Martin Cotterell, founder and director of Sundog Energy, summarises the project. ‘King’s Cross has been a fantastic project to work on — but also a labour of love. The sheer scale of the installation has presented many major technical and aesthetic design challenges from day one, and there has been no margin for error as the work had to be undertaken whist the station remained fully operational. We are very proud of our involvement as we believe the project combines the very best in modern design, technical excellence and sustainability with the grace of one of the UK’s most iconic Grade 1 listed buildings.’
And a final word from the managing director of Romag, Phil Murray. ‘As one of the few companies equipped to manufacture this type of PV, Romag is proud to be associated with this flagship project and is even prouder to have manufactured the bespoke panels here in the UK.’