Eternal Sun, a Netherlands-based provider of solar panel testing equipment, has sold an 80% stake to Bolster Investment Partners. Eternal Sun develops flash and steady-state simulators used by manufacturers and research institutions in over 60 countries. Eternal Sun systems are designed to measure peak output and long-term performance, including for next-generation technologies such as perovskite solar cells. Eternal Sun also provides quality control services, including import testing and factory audits for developers and importers. Eternal Sun was founded in 2011 and acquired Spire Solar in the United States in 2016 and SunChine in China in 2022. According to Bolster Investment Partners, the acquisition is intended to support Eternal Sun’s international expansion, product development, and operational scaling through organic growth and strategic acquisitions.