An electrolyser uses electrical energy to split water into hydrogen and oxygen. A plant includes electrolysis cells as well as power electronics, water treatment, cooling, gas separation and safety systems. Different designs include alkaline, proton-exchange membrane and solid-oxide electrolysers.
Electrolyser capacity is commonly reported in megawatts of electrical input. That number is not the same as annual hydrogen output. Production depends on operating hours, conversion efficiency, electricity availability and planned downtime. A large plant running rarely can make less hydrogen than a smaller plant running steadily.
Electricity is usually a major operating cost. Renewable projects must manage variations in wind or sunlight and may need grid connections, storage or a different operating strategy. Stack lifetime, replacement schedules and water quality also influence the total cost of hydrogen.
When evaluating a project, check whether its stated capacity is proposed, ordered, installed or operating. Ask for expected kilograms produced per year and the assumptions behind that estimate, not only the headline megawatt rating.