Photovoltaic electricity is most commonly generated using roof panels. But there is considerable additional potential for using other constructions that up to now has been seldom exploited. The solar fold-out roof from dhp technology (in Zizers, Canton of Graubünden) is deployed over treatment tanks in sewage plants to generate renewable energy.

The idea of installing PV modules over the treatment tanks of a wastewater treatment plant (WWTP) might initially raise a few eyebrows, but there is more to it than meets the eye: WWTPs offer vast surface areas that can be used to generate solar power. What’s more, the electricity produced can immediately be used locally. “We can re-use the surface area required for the infrastructure installation to generate renewable energy, thereby making a significant contribution to the energy transition,” says Gian Andri Diem, co-founder and joint managing director of dhp technology.

The company has developed a support structure that uses cables to enable the photovoltaic modules to fold out over built surfaces and fold up again when required. This makes it possible for large PV solar power systems deployed over WWTP’s treatment tanks to generate maximum outputs ranging from 150 to several thousand kilowatts and then to be safely stowed away whenever operational imperatives or bad weather dictate. In Switzerland there are 800 WWTPs, and in the European Union overall there are 80’000. Market surveys have shown that one in three WWTPs are in principle suitable for installing fold-out solar roofs.

And it is this potential that the 20-strong team at dhp technology AG, founded in 2015, wants to tap into. Encouraged by a successful pilot scheme at the Chur WWTP, five other Swiss sewage treatment plants have committed to installing fold-out solar roofs. In 2019, the EU’s Horizon 2020 SME Instrument programme began backing the market introduction of this idea in Europe. This is a major boost for dhp technology, because the company covers the entire value-added chain from planning through to manufacture and installation, and industrialising the necessary processes for export markets is a huge challenge for them.

The idea of fold-out solar roofs dates back to 2012, when Franz Baumgartner, a professor and PV expert at Zurich University of Applied Sciences in Winterthur (ZHAW) and Arthur Buechel from Liechtenstein developed a cable-based system for deploying photovoltaic modules. Gian Andri Diem then joined forces with mechanical engineer Andreas Hügli to take up the idea and develop the technology further to make it market-ready.