London’s green-rooted sculpture to inspire urban renewables

Green energy generator, sculpture and educational project rolled into one, the London Oasis is a public display of renewables adapted for an urban environment. Environmental services engineer Becci Taylor, who helped make the project a reality, outlines the range of cutting edge technologies involved.

The passer-by could hardly fail to be intrigued by the London Oasis installation: a 12m tall steel ‘tree’ on Clerkenwell Green which, at night, dramatically pulses with light. Its reactive nature – designed to respond to external stimuli – is another enticement. Investigating further, the surprised city-dweller might wonder about the intertwining wires and hose pipes, the equipment in the transparent cylinders, or the mysterious happenings in the centre of the trunk.

The London Oasis project has been driven by the desire of the architect, Laurie Chetwood, to stimulate emotion and to intrigue and uplift the spirit of the city-dweller. The beauty of this project is not simply that it aims to do so sustainably, but that it wears these technologies proudly. With its highly visible systems, the Oasis inspires the observer with the potential to harvest energy from the environment, incorporating new generation photovoltaics, a fuel cell, a wind turbine and rain water harvesting. Engineering design has included numerous specialists, including Arup.

The integration of renewable power technologies certainly strikes a chord with the 10% on-site renewable power generation planning requirement being introduced by many boroughs. It demonstrates how sustainable technologies can positively contribute to the look of a project and become an architectural feature.

The installation is built on a human scale. It was never intended to be a power station. Instead, it provides value by demonstration and stimulates thought about sustainable principles, reinforced by a form analogous to nature. It functions as a larger-than-life schematic, with educational value: one might talk a school child through the concept of energy cycles and the use of natural resources using the installation as a giant example.

Flexible renewables for urban living

The branches of the tree are dressed with 12m² of new-generation, thin-film photovoltaics (PVs) which can generate about 500 Wp. Thin-film PVs are made from a single amorphous silicon layer on a plastic substrate and hence can easily be produced in large quantities for a variety of applications. They are used for their flexibility and light weight (about a quarter of traditional PVs), demonstrating the potential for customisable, seamless integration into urban forms – particularly in building integrated applications. Polymer-based PVs are also tougher, more durable and safer to use than conventional glass-based crystalline silicon PV modules, and the energy payback is lower than with conventional PV technologies. Less raw material is used and it is almost all recyclable.

The branches of the London Oasis open and close with the sun, like giant petals on screw jacks, generating energy to charge the batteries and protecting the structure at night. The thin-film PVs work well in low light conditions and are therefore ideal for use in the UK.

At the top of the structure is a vertical axis wind turbine. This is included to demonstrate the aesthetic potential of such turbines, which are ideal for integration into urban environments. It aims to convey the important message to the public (and planners) that renewable technologies are to be embraced as positive elements of our environment. The energy-generation potential is dependent on its location and design, the first London Oasis uses a drag type turbine which operates best at low wind speeds and is easier to control. It is expected to generate approximately 250kWh per year – on a more exposed site, the benefits of a larger, lift type turbine could be realised.

A 1kW methanol-fuelled hydrogen fuel cell is also used to charge the batteries. Within the unit, liquid methanol is reformed into pure hydrogen and therefore eliminates the need for the storage of compressed gas on site. The fuel cell can be run on sustainable fuels such as bio-diesel. It is a totally portable and self-contained unit which starts with the switch of a button and generates continuously rated power, making it ideal for a large number of off grid applications. The project shows that such fuel cells are inherently safe and can be used in the public arena.

Visible amongst the ‘roots’ of the tree, providing some of the weight for stability, is a bank of eight 12V batteries which is charged from all or any one of the energy technologies. This has the potential to operate without maintenance for several years. At the end of life the supplier will recycle up to 95% of their material: this is driven by the value of the materials within the batteries. An Energy System Control Module interconnects all the components of the energy system, providing electrical protection and data logging.

Energy for relaxation

At the base of the ‘trunk’ are five pods which provide individual tranquil spaces, drawing inspiration from the Mayor’s environmental strategy for London. Filtered air is supplied to the pods and sounds and images are streamed to the occupant – a feature which the participating public have been enjoying.

The transparent body, or trunk, promotes heat generation which can draw air through the pods to create an upward draft cooling effect. The potential for electricity generation using this effect is demonstrated as the warm air can assist the rotation of the turbine at the top of the ‘chimney’. The branches are profiled to funnel rain water to a lower storage tank which is used for irrigation of the planted garden. Water is also stored as a feature and to demonstrate its potential as a thermal mass for warming and cooling applications.

Light show

At night the entire structure is transformed into a narrative light sculpture. 350 strands of broken glass side-emitting fibres are carefully threaded through the water zone to create a stream of light, analogous to the harvesting of natural resources into energy. Colour-changing side-glow fibres are handcrafted as intertwining vines, whilst a matrix of 40 light emitting diodes spirals up the ‘trunk’ to generate lightning pulses which interact with people passing by. As the ‘branches’ close at the end of each day, the entire structure is bathed in an ultraviolet light finale.

While the showcase at the London Architecture Biennale was dramatic and saw Clerkenwell Green filled with people, one can imagine the London Oasis as a refuge from the busy, noisy, polluted city. Imagine escaping from the centre of the city and entering the pod to discover a tranquil, relaxing space – where you can sit and contemplate, and connect the power that lights the beacon that attracted you, drives the soothing air and plays the calming sounds with the photovoltaic-dressed branches, wind turbine and fuel cell.

The London Oasis website is at

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