With urban density increasing, heliostats are providing opportunities for architects to change the way they design buildings and spaces and overcome traditional development objections based on resulting overshadowing or poor solar access.
Solar access is an early planning stage assessment carried out while developments are still at 'block massing' stage. This is typically the exploration of how major building geometry changes (overall size/orientation/location) significantly impact on the site and surrounds.
This stage is where architects will define a building's height or shape in relation to areas where solar access must be protected, such as town squares and parks, or maximized, such as child care centres and laneways.
This is typically explored through an overshadowing study which explores the impact of the building geometry considering the seasonal variations in the path of the sun.
The use of Heliostat daylighting systems for architectural purposes is an emerging technology which is creating opportunities to control sunlight on a large scale. The systems feature motorised mirrors that track the sun and redirect the sunlight to predetermined targets. Heliostats have not previously been used specifically to address solar access concerns of councils and this represents a significant opportunity for future application.
“The effectiveness of a heliostat system is primarily driven by the total surface area of mirrors in the installation. The more heliostats you install the more sunlight you can reflect,” said Tim Phillips, managing director of Kennovations, the industrial design company behind the heliostat system at One Central Park in Sydney; a world-first with respect to its sheer size and application.
The effectiveness of a heliostat system is often measured using two quantifiable parameters: average illumination per square metre (measured in lumens), and the total area affected by reflected light.
“Heliostat technology has the capability to control both of these parameters,” explained Phillips. “You can disperse the amount of available sunshine, or you can intensify it if required dependent on site specific objectives.”
Analysis of how effective the technology can be is completed utilising simulation and modelling at the same early planning stage as solar access in general. This analysis can be used to determine how well a heliostat system can support a development proposal, therefore reducing the likelihood of a planning objection based on limited solar access.
Each project has its own value proposition. The potential for a heliostat system to improve a site design needs to be evaluated in terms of specific building geometry and the resulting overshadowing issues, or objections to a design resulting in inadequate solar access.
Opportunities for heliostats currently being explored indicate significant potential for high rise developers to more than double previously acceptable tower heights based on the specification of the technology.
These gains would be directly related to the capability of the technology to reinstate solar access to parklands, providing access to the amenity of sunlight on a level comparable to current levels.
Other opportunities relate not to solar access directly but average reflected light levels experienced by residents in high density towers. The provision of supplementary sunlight to balconies and windows will enable the current design limitations of towers to be revisited, offering architects the ability to visualise new shapes and forms.
“The amenity of natural light is increasingly valuable in urban environments. Heliostats can enable architects and developers to challenge traditional building methodologies,” said Phillips. “By addressing solar access and shadowing concerns we can achieve higher density living in urban environments without compromising on the quality of the living experience.”
Although the solar contribution delivered by the heliostat system at the award-winning One Central Park was not necessary in order for council to approve the east tower height, the additional lighting provided to the podium area was acknowledged by council as a positive during the planning stage.
The system here is made up of 40 motorised heliostats (on the West Tower roof) and 320 reflective mirror panels (on the East Tower cantilever) which capture and redirect sunlight into the retail spaces and landscaped terraces.
The architect, Jean Nouvel, wanted to achieve a 'dappled light' effect, akin to that one would experience under a tree canopy, rather than harsh edged reflections or a direct sunbeam. The dappled effect is amplified in the retail area by running water on the atrium glass roof, resulting in a dynamic experience.
The controlled delivery of natural light improves the living experience for residents and visitors to the site. In the park or by the pool, people can sit in a single reflection for long periods of time in an area that would otherwise be shaded by buildings, or be subject to transient sunshine.
So what’s next for the technology?
“Installations with specific solar performance requirements,” said Phillips. “Whereby we are going to be contracted to deliver a quantifiable measure of light as a result of councils approving developments based on the use of the technology.”
The potential of the technology, he concluded ‘may only be limited by the imagination of the architect.’