Energy-positive commercial building with DualSun panels – Lyon (FR)

  • 2018
  • Lyon, France
  • Power output : 7kWp + 9,35kWh
  • Panels : 25 hybrids

DualSun participated in this ambitious project to renovate and transform a commercial building to be energy-positive (in other words, to generate more energy than it consumes).

KTR France, a manufacturing leader in the transmission, braking, and cooling sector over the past 50 years, had this vision to transform this building built in the 1970s where it would relocate its headquarters. The building, which is located in Lyon, France, was previously an energy sink, and now is energy-positive. Better yet, the building achieved 2020 ratings for new buildings !

To transform its building to be energy-positive, KTR chose the 2SOL system, deployed for the first time in France. 2SOL comes from the French words for solar and ground: énergie solaire avec stockage au sol (ground). The geothermal storage of solar thermal energy takes place 150m underground!

The solar installation is part of a 2SOL geothermal system, which is the first to be installed in France.  M. Campesi, head of Diagonale Concept, the engineering firm that managed the project, plans to duplicate this exemplary system all over France.


Learn more about 2SOL

2SOL is a geothermal project that optimizes solar energy for the winter. The DualSun solar panels generate hot water in the summer and inter-season months, the excess energy which is stored in the ground, and used in the winter months when the solar panels do not generate enough heat. A water-water heat pump completes the system, and the electricity generated from the DualSun solar panels is used in part to power the heat pump. 2SOL is an extremely well-designed system to optimize solar energy production.

“I appreciate the technical support and presence of the DualSun team during the installation process. The building and connected and in several months, the first monitoring results will demonstrate the measured performance of the DualSun panels.”




KTR is the first commercial building renovated to be energy-positive with thermal and electric energy storage. Marc Campesi is head of the engineering firm that designed the project. His company was selected for the global renovation project, and following the installation, we got to ask him a few questions.


Please present yourself

I’m a highly engaged participant for sustainable cities. I’m a professional who believes that it is possible to combine human and economic development with respect for the environment. I design and realize living and working spaces for more than 20 years. My clients are private companies, industrial groups, and organizations that are looking to renovate or build their offices with an eco-responsable approach. I am located between Lyon and Paris with a multi-disciplinary team that includes engineers, architects, interior-designers, ergonomic specialists, and landscapers in order to offer my clients quality turnkey services.


Can you explain the history of this project ?

The KTR group is a world leader in mechanical transmission. In 2017, KTR France purchased a 900m2 building just outside of Lyon with the plan to move its headquarters. As the building dates from the 1970s, this acquisition was a real opportunity for Pierre Martin, CEO of KTR France, to concretely pursue an eco-responsable approach for the company.

The global renovation project presented to KTR France by Diagonale Concept includes a strong capacity of innovation on the part of KTR. This unique project is an energy-positive renovation project. The building is already going towards energy-independence over the past months, thanks to self-consumption of the electricity and geothermal energy storage at over 150 meters in depth.

How is the DualSun installation used in the the global energy system?

The installation of DualSun panels is a central part of the energy system: the electricity generated is used in the building and to power the heat pumps, the heat generated in the summer and inter-season months is stored underground for use in the winter months.


Why install DualSun solar panels ?

The double production of the DualSun panels particularly interested me. Above 25°C, the electrical efficiency of traditional photovoltaic panels slowly decreases. The presence of a water circulating behind the PV panels allows to cool the cells in the hot summer months and increase their efficiency, and simultaneously produce a large quantity of solar hot water. This solar heat is transferred to geothermal storage 150m underground.


How did you discover DualSun ?

I discovered DualSun by the eOspace Lyon club, which unites local actors involved in sustainable cities. The Swiss engineering firm Amstein&Walthert which is located in Lyon is very active with the club and collaborated with Diagonale Concepte for the KTR project. Amstein&Walthert is at the origin of the 2SOL concept which integrates the DualSun technology to produce solar energy which is stored in geothermal storage.


How did the installation go ?

The panels are relatively simple to install. Setting the correct parameters requires experienced professionals with the support of DualSun. The only difficulty is that the installation requires two experts, for the photovoltaic component, and for the thermal component. Innovation is never entirely smooth from the get-go, but overall, the installation process went very well.


Would you recommend DualSun ?

Yes. Even the installation has only been operational for several weeks. I really appreciated the technical support and presence of DualSun during the installation process. The building is connected and in several months, the first results will demonstrate the measured performance of the DualSun panels.

Technical information

Characteristics KTR headquarters
Number of panels 25 DualSun hybrid panels
Power output 7kWp + 9,35kWh
Rooftop installation Flat-roof installation, south / south-east facing, 10° angle
Thermal system 2SOL (solar + geothermal), electric booster
Photovoltaic system Self-consumption in the building and for the electric car charging stations (FIX EVO TILT system)