Gray Hydrogen, High Costs, and the Real Emissions of SunLine’s Fuel Cell Fleet - CleanTechnica

The article from CleanTechnica examines SunLine Transit Agency’s extensive, multi-decade efforts to develop and operate a hydrogen fuel cell bus fleet in western California. Since around 2000, SunLine has continuously invested in hydrogen production and fueling infrastructure, cycling through various technologies including electrolyzers, reformers, and liquid hydrogen stations. Despite being a small agency with supportive regulators and a willingness to innovate, SunLine’s experience reveals a pattern of repeated system rebuilds, upgrades, and replacements rather than a stable, mature hydrogen ecosystem. The agency’s hydrogen refueling infrastructure evolved through four major generations—from early pilot electrolyzers to reformers, a large PEM electrolyzer station in 2019, and a liquid hydrogen station added in 2024—highlighting ongoing challenges in reliability, capacity, and fueling speed. Financially, SunLine has spent approximately $27 million (adjusted to 2026 dollars) on hydrogen refueling infrastructure to support a fleet of about 31-32 buses. This