Power-to-gas stores renewable electricity by using an electrolyzer to produce hydrogen from water.
When wind or solar generation exceeds immediate demand, an electrolyzer can use that electricity to split water into hydrogen and oxygen. The hydrogen may then be stored, transported, used directly in industry, burned for heat, or converted back into electricity in a fuel cell or turbine.
Power-to-gas is a form of sector coupling because it links the electricity system with gas networks, transport, heating, and industrial processes. Some projects add carbon dioxide to hydrogen to produce synthetic methane or other fuels; this is often called power-to-methane or power-to-liquid, depending on the product.
The method is not perfectly efficient: converting electricity into hydrogen and later back into electricity loses energy. Its advantage is long-duration or seasonal storage, since hydrogen can potentially be stored for much longer than batteries. It should not be confused with ordinary electrolysis used without an electricity-storage purpose.