Eternal Sun

Eternal Sun operates as a specialized manufacturer and service provider in the solar energy sector, focusing on equipment that tests the performance and reliability of photovoltaic (PV) panels. The company was founded in 2011 as a spin-off from the Delft University of Technology in the Netherlands by Chokri Mousaoui and Stefan Roest. The founders' journey began during their time at university, where Roest developed a new type of solar panel for his graduation project and, out of necessity, created a solar simulator to test it. This invention formed the basis of the company. Roest, who serves as CTO, holds a Master's degree in Sustainable Energy Technology and was the team leader for the winning Nuon Solar Team at the 2007 World Solar Challenge.

The firm's business model centers on two primary streams: the sale of high-end solar simulation equipment and the provision of PV testing services. Its clientele includes leading solar panel manufacturers, R&D laboratories, and project developers worldwide. The product line features both steady-state solar simulators, crucial for long-term and precise testing of next-generation technologies like perovskite, and flash simulators, which use a flash of light to measure a panel's maximum power output. These systems are designed to help clients accurately determine a solar panel's power output and price, and to ensure quality control throughout the manufacturing supply chain. The company also offers quality inspection services, such as import tests and factory inspections, with testing facilities in key locations like Rotterdam, Valencia, China, and India.

A significant milestone occurred in 2016 when Eternal Sun acquired the solar simulator business of the US-based Spire Corporation, a move that expanded its product range and provided greater access to the Asian market. This led to the rebranding as Eternalsun Spire in 2019. Over the years, the company has secured multiple rounds of funding to fuel its global expansion and product development, including from Belgian family fund Vermec NV and the ABN AMRO Energy Transition Fund. In 2019, co-founder Chokri Mousaoui sold his shares. Most recently, in 2025, Bolster Investment Partners acquired a majority stake to support further growth and international expansion, followed by the acquisition of German competitor WAVELABS.

Keywords: solar simulator, photovoltaic testing, PV module testing, solar panel quality assurance, solar energy equipment, PV reliability, Chokri Mousaoui, Stefan Roest, Eternalsun Spire, Delft University of Technology spin-off, steady-state simulator, flash simulator, perovskite testing, solar R&D, solar panel certification, IEC 61215, energy yield measurement, PV manufacturing, solar cell measurement, light soaker, solar panel inspection services