Solar Prize 2025: Solar roof on a listed farmhouse

The award recognises the exemplary integration of the photovoltaic system into the historic building fabric. It is in line with BKW's PV strategy presented in April 2024, which specifically promotes sustainable energy solutions. Frédéric Palli, Managing Director Region Central & Photovoltaics Division at BKW Building Solutions, says: “This shows that high-quality and practical solutions are also possible for special challenges such as listed buildings. Monument preservation and solar energy are not mutually exclusive; rather, they can make a joint contribution to the energy transition.”

The expert jury was impressed by the quality, innovation and contribution of the residential construction project to promoting renewable energies and reducing CO2 emissions. The PV system was said to have been particularly carefully coordinated with its surroundings. The project represents a new generation of solar installations that convincingly combines efficiency, aesthetics and sustainability.

The installation meets the highest heritage protection requirements and makes a significant contribution to the energy supply of the entire neighbourhood. With 665 PV modules in a subtle brown colour, the installation achieves an output of around 70 kWp and produces approximately 70,000 kWh of electricity per year – enough to supply several households with local solar power.

The historic farmhouse, built in 1754, now serves as an energy centre: the solar energy generated supplies both the building itself and adjacent new builds on the site. The sustainable overall concept is complemented by geothermal probes, mineral insulation, natural ventilation, and high-quality densification with community-promoting spaces and soil unsealing.

Victor Nichanian, Project Manager at Solstis, adds: “We are proud to have implemented a solution together with the various stakeholders that is impressive both aesthetically and in terms of energy efficiency – and thus creates real added value for the neighbourhood.”

Frédéric Palli from BKW Building Solutions also emphasises that the award is recognition of the fact that Solstis installs high-quality and innovative renewable energy systems – and has been doing so for over 30 years.

7 questions for the people responsible at Solstis

What makes this project in Crissier special from your point of view – both technically and architecturally?

Victor Nichanian: Architecturally, the building fits perfectly into the neighbourhood, as the aerial photographs show: the integration of the solar roof tiles is unobtrusive, aesthetically very successful, and the original roof structure has been preserved. On the technical side, it was crucial to coordinate the various trades well – from the carpenter to the tinsmith and the electrician. This resulted in a customised installation with electrified roof windows and a self-consumption community that makes optimal use of the solar power produced on site.

What challenges are involved in installing a photovoltaic system on a listed building?

Victor Nichanian: There were many discussions between the developer, the client, the architects and the municipality in order to find the best possible solution from an aesthetic point of view – with the right colour and within a reasonable budget. It was particularly important to preserve the roof beams from 1754. Together with the timber construction engineer, we developed a concept that respects the historic structures while perfectly integrating the solar roof tiles.

Were the PV modules manufactured or adapted specifically for this project? Why was the decision made to use brown modules?

Stéphane Krattinger: We proposed three shades of brown from the manufacturer's catalogue: Terracotta Rust, Terracotta and Earth Brown. The authorities ultimately opted for earth brown, because it blends most harmoniously into the roofscape, even though this shade was not technically the strongest. The tile format (985 x 875 mm) was also deliberately chosen to come as close as possible to the appearance of traditional roof tiles.

What role do the choice of colour and material aesthetics play in the acceptance of such installations in historic districts?

Stéphane Krattinger: Municipalities are increasingly demanding a terracotta look for solar roof tiles, particularly in regions such as Lavaux, where conventional solar panels are not permitted at all.

How are local residents and the municipality responding to the project?

Stéphane Krattinger: As the roof is clearly visible in the neighbourhood and the surrounding area, the installation is perceived as a great success and as a remarkable example of architectural integration. There was a real wow effect throughout the entire district – across all generations.

How did the collaboration with the architectural and engineering firms go?

Victor Nichanian: The collaboration was extremely constructive, particularly with the architectural firm Fiona Pia Architectes – from the initial cost estimate through to commissioning. Several quotation variants had to be prepared in order to meet the client’s requirements, with different tile types and sizes. Once the model had been chosen and the contract awarded, a meeting took place with the timber construction engineer to integrate the tiles into the overall roof renovation concept. The integration of ten roof windows in the same size as the tiles, positioned at strategic points on the roof surface, presented a particular challenge. These meetings resulted in precise roof truss plans, enabling integration to the nearest centimetre.

What was your personal highlight of this project?

Victor Nichanian: Accompanying the project from A to Z was at times demanding and challenging, but above all educational and fascinating! One of the best moments for me was the first drone flight over the installation – first during assembly and then after completion. At that moment, we realised how successful the installation was and how beautiful the tile colour looks in both cloudy and sunny weather.

Stéphane Krattinger: It is a real pleasure to work with architects who demonstrate a spirit of innovation! We love exceptional projects like this, which allow our planning office to find the best possible integration solution for a listed building dating from 1754. In short: an outstanding result with terracotta solar roof tiles manufactured in Switzerland and custom-made roof windows.

Expert network

As an installation and technology provider with its expert network, BKW Building Solutions is able to supply customers with solutions and components that are coordinated, customised, mutually compatible and continuously expandable. With this approach, future trends and changing needs are no obstacle to a successful transition to an environmentally friendly future.

The Swiss Solar Prize has been awarded annually since 1990 by the Swiss Solar Agency – in cooperation with the Swiss Federal Office of Energy (SFOE), SwissEnergy and other partners.

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