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Our BatchGeo world MAP shows the locations of green architecture, green building and renewable energy projects featured on Solaripedia.

Project

Solar Trees in City Gardens (Singapore)

Credits: ©2014 Solaripedia

A spectacular grove of solar trees is rooted along Marina Bay in Singapore as part of the 250-acre (101 hectares) Gardens by the Bay city park. Called Supertrees, they behave as vertical gardens - generating solar power, acting as exhaust air towers for nearby conservatories, and collecting rainwater on this island in Southeast Asia, just south of the Malay Peninsula. To generate electricity, 11 of the supertrees are fitted with solar photovoltaic systems that convert sunlight into energy to provide lighting and water technology within the conservatories below. The Supertrees are tree-like structures 80 to 160 feet (25 to 50 meters) tall, that are a fusion of the environment, creativity, and technology. They support gardens of flowering climbers, orchids, and ferns, with canopies that provide shade and shelter in the equatorial climate. Some of the Supertrees harvest rainwater and solar energy, and some are integrated with the conservatories to serve as air intake and exhaust towers that help mitigate ambient temperatures by absorbing and dispersing heat. The Supertrees even support a restaurant at the top of the tallest tree, as well as a 128-meter-long aerial walkway experience connecting several trees 22 meters above the ground.

 

Gardens by the Bay Solar Supertrees Evening

Solar Supertrees are vertical gardens in Gardens by the Bay in Singapore that are designed to mimic the ecological functions of real trees. Each structure is outfitted with an array of photovoltaic cells that collect and store solar energy throughout the day – power that’s used to illuminate the garden when the sun goes down each night. Their unique shape serves as rainwater collectors to help funnel water to fountain displays and irrigation systems. ©2014 Gardens by the Bay

The entire landscaping project was shepherded by Singapore’s National Parks Board to create a “city in a garden” rather than a garden in a city. Designed by Grant Associates (UK), the Supertrees host more than 162,900 plants comprising more than 200 species and varieties of bromeliads, orchids, ferns and tropical flowering climbers. The canopy is estimated to save 30 percent in energy consumption, compared to conventional methods of cooling. The South Bay Garden, home to the Supertrees and completed in 2009, is estimated to have cost more than $1 billion.

The integrated system of cool conservatories and ‘Supertrees’ showcase the application of sustainable energy solutions. Besides replacing the conventional air-conditioning system with a centralized district cooling system, the project applies sustainable energy solutions through the burning of biomass generated from the Gardens and other parks in Singapore. The biomass powers up the Gardens' Combined Heat and Power (CHP) system, together with photovoltaic collectors, that produce electricity for the garden’s own use. Water harvesting and storage from the ‘Supertrees’ also provide an alternative water source for irrigation.

Construction

Designed by Grant Associates (UK) with structural engineers Atelier One (UK), the Supertrees comprise four major parts including reinforcement concrete core, trunk, planting panels of the living skin, and canopy:

• Reinforced concrete core – Inner vertical structure that supports the Supertree

• Trunk – A steel frame attached around the reinforced concrete core

• Planting panels – Installed on the trunk for the planting of the living skin

• Canopy – Shaped like an inverted umbrella, the canopy was assembled and hoisted via a hydraulic jack system (with the exception of the 50m Supertree canopy assembled at its final height).

At the core of each tree is a reinforced concrete column that provides the inner vertical structure, surrounded by a steel framework that forms the trunk which spreads open at the top to form a canopy shaped like an inverted umbrella. The canopies were assembled at ground level and then hoisted via a hydraulic jack system. The structure was clad with planting panels, either on the steel skin or the concrete core, and then planted in-situ to create the living skin for each Supertree.

Biomass and Supertree Exhaust

Located close to the equator, the Gardens by the Bay use an innovative method of cooling its two large, climate-controlled conservatories that house biomes. Biomass furnaces burn horticultural waste that feeds a massive steam turbine that generates electricity on-site to enable dehumidification and cooling of the conservatories. Wilkinson Eyre Architects and Atelier One structural engineers created two different conservatories: the first, for a cool moist environment, is tall to contain an artificial mountain. The second, for a cool dry environment, is low with a large plan surface area for planting. Both biomes are situated on the Marina waterfront to avoid any obstruction (now or from future development) to ensure maximum sunlight is maintained as required for the vegetation.

To ensure the orchid flower-inspired glass conservatories -- the Cloud Forest and Flower Dome, -- operate appropriately and efficiently, several of the Supertrees are used to provide necessary exhaust. The tree cluster closest to the main entrance of the Gardens contains chimneys for the biomass furnaces whose exhaust is extensively scrubbed to ensure emissions are non-toxic. The lake edge cluster of trees contains the discharge chimneys for the liquid desiccant system. The biomes are the equivalent size of four football fields.

Together, the Supertrees allow exhaust gasses to be released at a high level, provide an outlet for steam from dehumidification and collect water and solar energy among their other uses. The huge glass gridshells of the conservatories are designed with a structural delicacy to allow maximum daylight penetration to the interior spaces for plant growth. An external arched supporting structure is carefully shaped to provide minimum negative impact on sunlight.

Mechanical Systems

Atelier Ten identified a key early ambition to use the solar energy entering the biodomes as a part of a ‘virtuous’ energy cycle. As the mechanical and electrical engineering designer, Atelier Ten developed innovative strategies for controlling conditions within the naturally hot humid environment of Singapore, while minimizing energy demand to exemplar levels and utilizing the external supertree structures coupled with liquid desiccant systems to provide cool air to the biomes.

The displacement conditioning arrangement causes the air at the top of the biomes to be significantly warmer than the design temperature at low level, particularly in periods of high solar gain. Air is extracted from the top of the Flower Dome and is returned through an underground tunnel to the adjacent Silver Supertree cluster where it becomes the supply air for the desiccant regenerator equipment. The temperature and dryness of this extracted air increases the efficiency of the system and effectively means that there is an indirect solar energy component to the regeneration process. The Supertrees also house photovoltaic panels that generate enough power on an annual basis to power the lighting on the Supertrees.

As part of the Masterplan development and implementation process, Atelier Ten developed sustainability implementation plans to cover all areas of environmental sustainability potentially affected by the development, with holistic ideas of sustainability woven throughout the project. Benchmarking of the sustainability initiatives was achieved through Singapore’s Building & Construction Authority (BCA) Green Mark scheme, achieving a Platinum rating for the conservatories (see below).

The Conservatories

The two Conservatories replicate the cool-dry climate of the Mediterranean and semi-arid sub-tropical regions and the cool-moist climate of the Tropical Montane region. They house a diverse collection of plants that are typical in other parts of the world and are of high conservation value.

Working out how to cool the conservatories was a two-fold process. First was managing the solar gain while balancing the horticultural requirements. The project team developed a retractable shading device for the glass- and steel-arched gridshells, combined with high-performance glazing that lets in more light than heat to keep the cooling loads in check. Second was working out how to use fresh air to cool the conservatories without wasting energy.

The innovative solution was to use large quantities of liquid desiccant to help dehumidify the air in the biomes. The process absorbs moisture from the air, evaporated it outside the conservatories, and recycling the desiccant. The primary heat source used to evaporate the water comes from a superheated steam biomass boiler that drives the CHP system. Another energy-saver is the strategy of cooling only the lower levels – thermal stratification –thus reducing the volume of air to be cooled. Ground cooling by chilled water pipes cast within the floor slabs enables cool air to settle at the lower occupied zone while the warm air rises and is vented out at high levels. The primary energy source for the entire development is 5,000 tons of waste wood per month three million trees in Singapore’s streets and parks.

For the plants to flourish, the necessary light levels in the conservatories was determined to be 45,000 lux for more hours than at the benchmark Eden Project. In comparison, a typical office requires about 500 lux. Singapore is humid, but it’s also often overcast and when not overcast, it’s bright and allows almost too much light in, according to Atelier Ten.

The facades use double glazed units with a low-e coating on the inner face of the outer pane minimizes solar heat gain, allowing 65% of the incidental daylight through to the interior, but only 35% of the solar heat. The sensor-operated, automated external shading system was developed with structural engineer Atelier One to restrict the amount of direct sunlight into the interior comprises of an engineered shading fabric of a triangular shape that varies in size, the maximum span being 21 feet by 30 feet (7m x 10m). The responsive skin is described by the architects as, “like a series of sails unfurling from the primary supporting structure of the conservatory.” Each triangle unfurls from one arch to another and, when completely rolled out, the shading system resembles a giant pinecone. These retractable sails open automatically to provide shade to the plants when it gets too hot.

Water

The Gardens by the Bay use a lake system that encompasses two main lakes – the Dragonfly Lake and Kingfisher Lake – designed to be an extension of the Marina Reservoir. The system incorporates key ecological processes and acts as a natural filtration system for water from the Gardens’ catchment, helping to provide aquatic habitats for biodiversity of wildlife such as dragonflies. Water run-off from within the Gardens is captured and treated in filter beds of aquatic reeds and wetlands before being discharged into the reservoir and/or used in the irrigation system for the Gardens. This assists the natural process of reducing water flow and filtering sediments. Islands of aquatic plants and reed beds absorb nutrients such as nitrogen and phosphorus, helping to minimize algal bloom, promoting improved better water quality. The variety of aquatic plants provides habitat for fish and dragonflies, both of which help control mosquito breeding.

Green Building Certification

The Gardens by the Bay conservatories achieved platinum accreditation by Singapore’s Green Mark green building rating program (equivalent to Breeam). Key sustainable features include:

• Estimated energy savings: 16,800,700 kWh/yr; estimated water

savings: 741,539 m 3/yr.

• Spectrally selected glass with a motorized shading system.

• Biomass cogeneration energy system with absorption chiller.

• Thermal stratification, displacement ventilation and slab cooling.

• Liquid desiccant system.

• Photovoltaics.

• Natural water filtration using the lake.

• Earth control measures with turbidity curtain.

Wilkinson Eyre Architects 

Grant Associates

Atelier One Structural Engineers 

Atelier Ten Mechanical Electrical Engineers 

Building & Construction Authority (BCA) Green Mark 


Documents

  Gardens by the Bay Structural Award Submission (3,086 kb)

  Gardens by the Bay Greenhouse Engineering by Atelier Ten (1,175 kb)

  Singapore's Supertrees Article from Ingenia 2014 (498 kb)

  Gardens by the Bay Structural Steel Award 2013 (3,086 kb)


Resources

Atelier Ten Mechanical Electrical Engineers (UK)

Atelier One Structural Engineers (UK)

Gardens by the Bay (Singapore)

Grant Associates Landscape Architects (UK and Singapore)

Green Building Product Certification (Singapore)

BCA Green Mark (Singapore)