Ackroyd & Harvey's 20 metre high sculpture is landmark presence at the gateway to the city. The work has been designed to have a low environmental impact and to harness the natural energy of Bristol's prevailing winds. The art works lighting is powered solely through solar and wind energy, and is clad with an intensive layering of thin dark grey slates. The slate is a waste material from the roofing industry. The strata-like tower supports a glazed solar canopy, from which rises a four metre high vertical axis wind turbine.