Eternal Sun welcomes Bolster Investment Partners as majority shareholder to push growth, technology development and further professionalization
The Hague, May 7, 2025
A strategic partnership with Bolster Investment Partners
Eternal Sun, a global leader in solar simulators for photovoltaic testing, proudly announces that Bolster Investment Partners has acquired an 80% stake in the company. They acquire the stake of Vermec and ABN AMRO Sustainable Impact Fund, who invested in the start and scale-up phases of Eternal Sun and have grown the company to the mid-size market segment. Bolster’s focus is on companies that have a leadership position in niche markets, a perfect match to Eternal Sun and its team.
The next step in sustainable growth
After leading the winning Nuna Solar Car Team of TU Delft in 2007 Stefan Roest founded the company in 2011. Since then Eternal Sun has grown into a global provider of advanced solar testing equipment. Founder and CTO Stefan Roest: “Our technology is essential for accurately determining the performance and thus value of solar panels, this plays a critical role in the development and scaling of next-generation technologies such as tandems and perovskite”.
In addition to innovative flash and steady-state solar simulators, Eternal Sun offers inspection services for large-scale importers and solar project developers. Roest: “Thanks to our deep expertise, flexibility, and focus on customization, we continue to lead in a rapidly evolving market”.
Scaling with vision and purpose
After earlier growth supported by Vermec and ABN AMRO SIF, Eternal Sun is ready for its next chapter. CEO Florian van Rijn van Alkemade:
“We grew as a scale-up, and now we welcome an investor focused on scaling mid-sized companies. We are very proud of our continuous and uninterrupted growth track in what have sometimes been difficult market conditions. It provides proof of how we’ve strategically diversified our business in recent years. It is also a great tribute to our team, we could not have reached these milestones without their continued enthusiasm and drive”
CCO Erik Bentschap Knook adds:
“We're playing in the solar industry’s Champions League. Our clients are the most advanced PV developers in the world. We work with them to enable a fast deployment of new technologies like tandem and perovskite, we see a bright future for Eternal Sun.”
Partnering for long-term success
This partnership with Bolster marks a major milestone. Beyond capital, Bolster provides strategic support to accelerate Eternal Sun’s buy-and-build strategy, international expansion, and operational growth.
Mark van Rijn, Managing Partner at Bolster:
“The global leadership position of Eternal Sun, combined with its innovation capabilities, creates a unique position. The solar testing market is growing rapidly, driven by new technologies and energy independence trends. Eternal Sun is exceptionally well-positioned, and we look forward to working with their strong and visionary team.”
For more information
Eternal Sun – Florian van Rijn van Alkemade: +31 6 30936144
Bolster Investment Partners – Mark van Rijn: +31 20 226 30 88
About Eternal Sun
Eternal Sun is a global leader in solar panel testing technology. With its advanced simulators and inspection services, the company supports manufacturers, laboratories, and developers in over 60 countries. Operating from six locations in four countries, Eternal Sun continues to set the standard in the solar testing industry through innovation and expertise.
About Bolster Investment Partners
Bolster Investment Partners is a long-term investor focused on exceptional Dutch companies with proven business models. Bolster supports entrepreneurs in realizing their full potential through equal, strategic partnerships.
