What: Huge solar PV array Where: Rotterdam Centraal station
In the enormous commercial development of Rotterdam’s central station and the surrounding area, it was quickly realised that Sybold van Ravesteyn’s 1957 station hall, pedestrian tunnel and open platforms, each with their own canopy, were plainly not capable of meeting
current standards. They were also not of the stature worthy of a major European transport hub.
Hence, after Benthem Crouwel won the international competition for the station’s redesign, came its proposal not only for an enormous new station hall to the south, but for a northern platform zone that did away with the makeshift external canopies. In 2015 these were replaced with a huge, 250m wide state-of-the-art glazed roof, creating an impressive sense of scale for the station.
Architect Jan Benthem says the idea of turning Rotterdam Centraal into one of the largest PV rooftop installations in Europe was originally an afterthought.
‘The design of the glass roof was already complete when the project manager of the railway company suggested actively doing something with the expanse of the roof itself,’ he recalls, ‘which is when we happily suggested using it as a vast solar collector.’
The upshot of this light bulb moment was the installation of more than 130,000 solar cells across 10,000m2 of the 28,000m2 roof. The cells have all been strategically placed to ensure that neighbouring tall buildings do not have a detrimental effect on the efficiency of the solar array.
As it stands, the cells can reduce the station’s total carbon emissions by 8%, and generate 320MW of electricity a year.
Benthem says the application of solar cells to the glass helped mitigate the transition from the darker station hall into the relative brightness of the platform area. ‘We needed to reduce the transparency anyway to reduce glare, so the coating of the roof was as much about daylight control as it was generating power,’ adds Benthem.
With the efficacy of the PV array dependent upon the cleanliness of the glass, the roof facade maintenance strategy was fundamental to the whole proposal: the apex of each roof pitch has an integral rail, to accommodate manual cleaning from a bogey running along between pitches.
At platform level the roof is supported by powerful steel structural trees, and the dappled effect created by the PV cells overhead only adds to the sense of walking beneath a verdant canopy.
The array might have been conceived by accident but it is bound into the bigger myth of the roof’s design, says Benthem: ‘Its shadows are beautiful to behold.’
Rotterdam Centraal’s remodelling is so radical one needs to remember it is a refurbishment rather than a new build. The original costings only budgeted for upgrading the platforms and canopies in the railway yard behind the new station hall. But Benthem Crouwel had a much bigger vision and looked to indigenous techniques to achieve it.
‘The Dutch are expert greenhouse builders,’ says Jan Benthem, ‘and they have got costs down to about €200/m2. We thought if we adapted these techniques, it would be feasible to build a single massive roof for the same amount as the basic upgrade.’ Key to this was merging stakeholder interests, split between station hall and railway yard, into a single budget. This allowed value engineering of the station’s south hall to transfer directly into the north railway yard budget.