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9

Magazine for Organic & Printed Electronics

T

he cooperative

research project

FLEX-G started

on 1 June 2017 under

the federal construction

technology initiative named

ENERGIEWENDEBAUEN

funded by the German

Federal Ministry for Eco-

nomic Affairs and Energy

(BMWi). The main goal of

the research project is to

investigate technologies

for the manufacturing of

translucent and transparent

membrane roof and façade

elements with integrated

optoelectronic components. The focus lies

on a switchable total energy transmittance

(often referred to as the solar factor or

solar heat gain, and “g-value” in Europe)

and on flexible solar cell integration to

significantly contribute to both energy

saving and power generation in buildings.

Solar modules and a variety of energy

management systems are well established

in small and large buildings to optimise

their energy balance both by generat-

ing electrical energy and by minimising

required power for heating, ventilation

and air conditioning (HVAC). A major trend

in modern architecture is the use of large

transparent and translucent façade and

roof elements to make time spent in these

buildings more pleasant due to bright and

spacious rooms and appearance. When

made of glass, these façades and roofs

are functionalised with heat reflecting

coatings to minimise their “g-value”.

Limitations of glass

However, glass is not bendable enough

to apply it to vaulted surfaces as design

element in representative buildings such as

airports, stadiums, event halls or shop-

ping malls. Furthermore, its high weight

limits the use for large area roofs or

façades without massive, expensive and

design-limiting supporting structures. For

these applications, fluoropolymers such

as ethylene tetrafluoroethylene (ETFE) are

an alternative to glass, providing a long

lifetime and resistance to weathering.

In contrast to glass, fluoropolymers

are difficult to handle in thin-film coating

processes. For this reason, roof and façade

elements of membranous material are as

yet rarely functionalised with energy-saving

features such as thermal shielding layers or

integrated solar modules. Until now, it was

not feasible to optimise the energy budget

of buildings featuring membrane roof and

façade surfaces. A consortium of nine indus-

trial and research partners has been formed

to change that situation by functionalising

fluoropolymer web surfaces with optoelec-

tronic components through thin film coating

techniques. The project coordinator, Dr John

Fahlteich, summarises the research plans as

follows: “Membrane façade and roof ele-

ments will be functionalised with electro-

chromic films which allow switching of the

transmission of visible light and thermal radi-

ation by applying an electrical voltage. The

energy required for that is made available

through flexible organic solar cells. Within

the project FLEX-G, we aim to develop

dynamic processing and deposition tech-

niques in a way that they are applicable not

only for flexible, membrane based building

envelopes but also for glass-based systems.”

Economical, efficient,

high throughput

Within the project duration of 3-years,

FLEX-G will investigate processes that allow

the deposition of electrochromic layer stacks

directly on an ETFE film surface. The flexibil-

ity of the film enables the use of economi-

cal, efficient and high throughput roll-to-roll

(R2R) fabrication processes. Finally, a 36m²

large ETFE membrane roof prototype will

demonstrate both the electrochromic com-

ponents for switching the total solar energy

transmittance and the flexible organic solar

cells for electrical power generation.

With integration of flexible optoelec-

tronic components on vaulted building

envelopes FLEX-G will contribute con-

siderably to reducing the primary energy

consumption of buildings. This is also in-line

with the goal of the German federal govern-

ment to reduce primary energy consump-

tion in Germany to up 50% by 2050.

The FLEX-G research programme is a

joint effort of Fraunhofer FEP (Dresden),

ISC (Würzburg), and IAP (Golm), as well

as Hochschule für Technik Stuttgart,

Coatema Coating Machinery GmbH,

Hightex GmbH, Lamilux Heinrich Strunz

GmbH, Heliatek GmbH, ROWO Coating

GmbH, EControl Glas GmbH & Co. KG,

and Nowofol Kunststoffprodukte GmbH.

Smart buildings are investigated by the joint research programme

FLEX-G (photo: Hightex GmbH)

Optimising the

energy balance

FLEX-G project investigates smart buildings through innovative

membrane roofs and façade