- Extruded foil layers are highly transparent & resistant to chemicals
- Such a smooth surface, that rain can clean it
- Completely recyclable
A recently installed carport roof at Munich’s waste management company AWM is composed of air-filled foil cushions made from ETFE (Ethylene Tetra Fluoro Ethylene) material. The foil, which is made from 3M Dyneon ETFE, is so transparent that a photovoltaic system integrated into the foil cushions can generate up to 140,000 kWh of electrical energy per year. The roof is designed to withstand large snow loads, and requires virtually no maintenance due to the very smooth surface of the foil. A rain shower is sufficient to clean it.
Extruded foils: no use of plasticisers and 100% recyclable
The roof is made up of 220 three-layer foil cushions each measuring 3.30 metres by 10.40 metres. The foil layers, Nowoflon ET 6235 Z extruded by Nowofol Kunststoffprodukte GmbH & Co. KG, are made from Dyneon ETFE which does not require the use of plasticisers and is 100% recyclable. The foils are highly transparent and almost universally resistant to chemicals.
Integrated solar cells protected from the weather
The foils allow more than 90 per cent of the sunlight to pass through. This is important because 12 flexible solar cells are mounted on the middle foil layer of each cushion, protected from the effects of the weather. A photovoltaic system covering 3,200 square metres has a peak output of around 140 kW and provides 1,000 kWh/kwp of electrical energy per year, on average. The surfaces of the solar cells are protected by highly transparent UV resistant Nowoflon ET 6235 Z film both on the front and backsides. In order to achieve a permanent bond to the cells, Nowofol put a special coating onto the ETFE films. This combination of ETFE cushions with ETFE covered photovoltaic cells provides weldability of the system. The solar modules, together with the printed lower foil layer, contribute to shading the carport in the summer, protecting it from exposure to excessive sunlight.
As thin as a human hair
Each of the curved foil cushions of the carport comprises an aluminium frame in which three layers of foil are held. The load-bearing upper and lower foil layers are 250 micrometres thick. The middle foil layer is the thickness of a human hair, around 100 micrometres. The cushions are given their characteristic shape using compressed air, which also ensures a high level of stability. Under normal weather conditions, the pressure in the cushions is 300 pascals which is around 0.2% of the pressure in a car tyre. In the event of a storm or snowfall, the pressure is increased to a maximum of 600 pascals. This is sufficient to safely support a load of up to 600 kilograms of snow per square metre. The blowers generating the compressed air are designed with dual redundancy so that even if two blowers were to fail, pneumatic support would be maintained. Even in the case of a failure of the entire pressure supply, the high loads specified would be held by the foils, which have a very high tensile strength.
The design of the roof was realised by Munich architectural firm Ackermann & Partner and construction carried out by Taiyo Europe. In total, the foil design weighs 720 tonnes less than a glass roof of the same size.