Renewable Energies from Renewable Raw Materials

The ecological footprint of the photovoltaic industry is often smaller than that of conventional energy sources. Photovoltaic systems do not produce any harmful emissions during operation and thus contribute significantly to reducing air pollution and greenhouse gas emissions. However, when considering the entire life cycle of solar modules—from raw material extraction to production, use, and disposal—weak points become apparent.

Current photovoltaic modules consist of glass, polymers, metals, and silicon-based solar cells. The extraction of raw materials, especially silicon, can be harmful to the environment. In addition, the individual components are rarely returned to the raw material cycle. At the end of their average operating phase and service life, which currently stands at 20 to 25 years, old PV modules are a waste product that contains valuable materials that are difficult to separate, for which there is currently no solid recycling concept. Most of the components are currently either incinerated or “downcycled” into low-quality products. Approaches that involve manufacturing the materials used from renewable raw materials and simultaneously reintegrating them into the cycle could make the solar industry even greener.

This is where the “E² – E-Quadrat” project, funded by the German Federal Ministry for Economic Affairs and Climate Protection (funding code 03EE1114), comes in. A team from Fraunhofer CSP, in collaboration with NOVO-TECH GmbH, developed and tested materials that are both highly reliable over the long term in all weather conditions and fully recyclable.

“The project addressed all phases of a PV module's life cycle: from manufacturing using renewable raw materials, through the actual operating phase, to material recycling and return to the recycling cycle at the end of its service life,” says Ringo Köpge, research associate in the “PV Modules, Components, and Manufacturing” group at Fraunhofer CSP and project manager.

The 380-watt solar module, which was developed as a “bio-module prototype” within the project, has four distinctive features compared to conventional modules. The module frame has a high wood content. This can be completely recycled at the end of the module's service life and reintroduced into module production. The cell connections of the module were not joined with lead-containing solders, as is standard practice, but with an electrically conductive adhesive containing silver particles, which serves as a connector between the wires and the cells. Currently, only around three to four percent of modules on the global market are lead-free. The rear cover of the module consists of a film made from 30 percent recycled polyethylene terephthalate (PET). The ethylene vinyl acetate (EVA) film, which is used as a transparent plastic layer in the production of solar modules and serves as an encapsulation material for the cells, consists of 60 percent bio-based “sugar cane ethylene.” Currently, only EVA from fossil raw materials is used in the modules, which must be recycled or disposed of.

The team at Fraunhofer CSP subjected the individual components to various tests, including accelerated aging, heat, humidity, and temperature change tests. It was shown that every component used meets the latest module standards. The results will enable the CO₂ footprint to be improved in the future through the use of renewable raw materials and the recycling of energy-intensive raw materials (silicon cells). With the proof that biopolymers are also suitable for use in photovoltaics, they can be used for a variety of other complex outdoor applications in the future.