Electrolysers and fuel cells are two machines that store electricity as hydrogen. An electrolyser is a machine that uses electricity to split water into hydrogen and oxygen. A fuel cell does the opposite: it combines hydrogen with oxygen from the air and produces electricity and water. Together they let electricity be stored as hydrogen and used again.
The electrolyser has two electrodes in water. Electric current passes between them. Hydrogen gas collects at one electrode and oxygen at the other. If the electricity comes from wind or sun, the hydrogen is called green hydrogen. A good electrolyser needs about 50 to 55 kilowatt-hours of electricity for each kilogram of hydrogen. The electrodes use catalysts, materials that speed up the reaction without being used up.
Take, for example, a 1 MW electrolyser next to a solar park in Kutch, Gujarat. At noon, when power is cheap, it makes about 18 kg of hydrogen in an hour. A tank holds the hydrogen. At night a fuel cell, or a company that needs hydrogen for making fertiliser, uses it. Wind turbines can supply an electrolyser as well.
Who buys the hydrogen? In India, most hydrogen is made today from natural gas, and used in fertiliser plants and oil refineries. Green hydrogen can replace that gas-based hydrogen. The government's National Green Hydrogen Mission supports this. A fuel cell is also used for vehicles and for backup power, since it runs silently and produces only water.
Hydrogen loses more energy than a battery, because only part of the original electricity comes back. So a battery energy storage system is better for a few hours of storage, and hydrogen is considered for long storage or for industry. Electrolysers are built from advanced materials.