SOLAR Roof at London

By Lorna Sharpe

Solar modules in the glazed roof at King's Cross
Credit: Sundog Energy

One of the UK’s largest and most complex building-integrated solar electricity systems has been officially switched on at King’s Cross railway station in London.

The solar glazing on the main train shed will have a peak output of 240kW and is expected to generate around 175,000kWh of electricity each year, saving over 100 tonnes of CO₂ emissions and meeting up to 10 per cent of the station’s electricity needs.
Photovoltaic (PV) cells that convert sunlight directly into electricity are integrated into 1,392 glass laminate units that form part of two massive new barrel vaulted glass roofing structures spanning the main platforms of the Grade 1 listed building, covering more than 2,300 square metres.
The £1.3m solar PV installation is part of a six-year redevelopment programme for King’s Cross station that has included renovation of the 1880s trainshed roof and replacement of yellowing glass-fibre panels to let in more daylight and create a better environment for station users.
All the detailed design, specification and supply of key components for the PV system and the DC electrical installation were undertaken by Sundog Energy, working to the main contractor Kier, in collaboration with Network Rail.
Sundog’s founder and technical director, Martin Cotterell, said the PV design was complex, having to take account of a Victorian roof structure that faces east and west, multiple sources of shading, difficulties with cable routing and finding a suitable location for the inverters, and the need to ensure access for maintenance.
The blast-proof glass-laminate solar PV units were custom-made in north-east England by specialist PV manufacturer Romag and installed by roof glazing specialist ESB Services. Fronius supplied the inverters, and AC electrical works were carried out by the rail division of NG Bailey, which also installed dimmable high-bay lighting as part of the same project.
DC cabling has been concealed as far as possible. Junction boxes are located under cells, with cable running alongside ironwork and through glazing bars to string combiner boxes on the access walkway.
Ronnie Kennah, Kier Construction mechanical and electrical manager, explained that making the link between the roof cabling and the inverter room was particularly challenging. The original plan was to locate the main cables out of sight in the roofspace of the station’s Eastern Range Buildings - but that would have required installation of a crash deck, bringing in a crane and arranging a road closure just for the deliveries. Instead, after negotiations with English Heritage, it was agreed to drop the cabling down to ground level and run it along one of the platforms. “We’ve gone from a 150-metre run to 80 metres,” said Kennah. “The voltage drop is less, it was quicker to install, safer - and it saved a lot of money.”
Simon Matthews, senior project manager for Kier Construction, praised the open and collaborative way in which the various challenges had been dealt with. “The switch-on of the PV system is the culmination of a massive effort by the project team, working with specialists in the renovation and refurbishment of the structure, using innovative methods that have allowed the works to be undertaken above the live station.”
Those innovative methods included construction of a massive moveable scaffold deck hung from the roof structure so that work could progress without obstructing the platforms below, as well as installation of a temporary roof before the old roof covering was removed, to maintain weatherproofing.
Martin Cotterell concluded: “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 and there has been no margin for error as the work had to be undertaken whist the station remained fully operational.”