Capturing The Sun: Integrating Heliostats Into Buildings

one central park

One Central Park

Heliostats, typically found on giant solar farms, are utilised for the production of concentrated solar power, usually to generate electricity. The mirrored devices turn in conjunction with the movement of the sun so as to keep reflecting sunlight toward a predetermined target.

Now, engineers and designers are starting to use smaller versions in building designs to improve daylighting and heating.

Nowhere is this being done more dramatically than at the One Central Park project in Sydney, jointly developed by Fraser Property and Sekisui House and designed by acclaimed French architect Jean Nouvel.

The $600 million complex, which includes 593 apartments across the two towers in a mix of studio, one, two and three-bedroom apartments, plus 14,000 square metres of retail space, will see a monumental cantilever extending from the taller tower.

one central park lighting

Heliostats Plan

The cantilever will house a panoramic terrace and a theatrical public artwork: a innovative system of fixed and motorized mirrored panels. The heliostat will capture sunlight and reflect it down onto the landscaped terraces, extending the central parkland at the heart of the new precinct into the green building.

At night, the heliostat will be transformed by French lighting artist Yann Kersale, theatrically and colourfully illuminating the towers.

The system comprises a 110-tonne reflector steel frame, lifted 100 metres above Sydney’s Broadway, 42 Sun Tracking Heliostats on the rooftop and 320 Reflector Panels suspended beneath the main cantilever, each with nine LED clusters within the surface.

According to Frasers Property Australia chief executive officer Guy Pahor, plans to integrate a heliostat into the development had been “30 months in the making” and ”meticulously and painstakingly orchestrated.”

With the weight of the reflector frame needing to perfectly counterbalance with the East tower, lifting it into place was an extremely complex process.

one central park interior

Genzyme Center, Cambridge, Massachusetts

“This is a delicate and scientific exercise in precision engineering,” said Watpac Construction NSW state manager Ric Wang. The next task will be to fix 320 large mirrored panels to the reflector frame.

At the end of last year, developer Highbury Focus4 lodged a planning application with Melbourne City Council proposing the use of heliostats to reflect daylight into the narrow gap between their project and an existing apartment block.

In its application, the developer said the seven proposed heliostats would be designed in a ”leaf” shape to make them aesthetically pleasing.

This was believed to be the first time heliostats had been proposed in a residential setting in Melbourne, as developers look for innovative ways to enable high-rise buildings on small CBD sites. In the only other example of the use of heliostats in Melbourne, they reflect light into the public atrium of the commercial building at 161 Collins Street.

one central park light

Genzyme Center Heliostats

Internationally, the sun-deprived village of Viganella in the Italian Alps installed a heliostat to redirect light in winter and they have been used in buildings such as the historic Reichstag building in Berlin, the Puente Hills Mall in California and the corporate headquarters of Genzyme Corporation in Cambridge, Massachusetts, where heliostats on the roof direct sunlight into its 12-storey atrium.

It has been suggested that small heliostats, placed on building rooftops, could be used like a solar power tower system, using the sun’s power to heat and cool a building or to provide input for thermal industrial processes such as processing food. The system could have the potential to be more reliable and cost-effective than a solar power tower plant, partly because it would not sacrifice 80 per cent of the power collected in the process of converting it to electricity.

Conventional heliostats themselves, though, are still expensive and the challenge for engineers if they are to become more commonplace is to find commercially cost-effective designs that use fewer, lighter materials while also working as efficiently as traditional designs.

Alternative proposals, including silvered polymer reflectors and aluminized reflectors, have failed due to delamination of the protective coatings, reduction in solar reflectivity over long periods of sun exposure, and high manufacturing costs.

By Justin McGar
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