How is renewable energy used for green hydrogen production?

Green hydrogen uses renewable electricity for water electrolysis. Electrolyzer types: Alkaline (mature, lower cost, 60-70% efficiency), PEM (faster response, higher current density, 65-80% efficiency), and SOEC (high temperature, highest efficiency 80%+, less mature). Integration options: dedicated renewables (lowest cost hydrogen), grid-connected (use renewable certificates), and direct coupling (variable operation matching renewable output). Challenges: electrolyzer cost and lifetime, hydrogen storage and transport, round-trip efficiency if reconverting to electricity, and matching variable renewable supply with electrolyzer operation. Applications: industrial feedstock, transport, and seasonal energy storage.