Although hydrogen is actually a colorless gas, the term "green hydrogen" has been coined to describe hydrogen that is produced by splitting water into its constituent elements hydrogen and oxygen using electrolysis with electricity obtained from sunlight, wind, or other renewable sources, thereby resulting in very low or zero carbon dioxide emissions.
Nearly all hydrogen is currently produced using fossil fuels, and green hydrogen still accounts for less than one percent of total world output because electrolysis is extremely energy intensive. However, the share of green hydrogen is expected to increase as the cost of electricity from renewable sources continues to drop and the demand for hydrogen as a fuel continues to grow.