4.4 Hydrogen for Electricity and Heat
Today, the provision of electricity and heat is responsible for more than half of the total CO2 emissions in Germany (see chart in Section 1.2). As described in Section 4.1, the chemical energy stored in hydrogen can be converted into heat and electricity using direct combustion or fuel cell technology. If green hydrogen is used, heat and electricity are climate-neutral. In this chapter, you will learn about various use cases for which green hydrogen could become more important in this context in the future.
Hydrogen as a seasonal energy storage medium
The increase of volatile renewable energies leads to a growing demand for energy storage. In Germany, long-term storage is of particular importance, since power generation from solar and wind energy is subject to strong seasonal fluctuations here. In particular, a combination of weather events, especially occurring in winter, which reduces the energy production from solar and wind energy to a minimum for several days or weeks ("dark doldrums"), is a challenge for the security of supply in renewable energy systems.
In Germany and many other parts of Europe, gas storage is a suitable way to bridge such "dark doldrums". In the future, large quantities of green hydrogen could be stored in salt caverns, for example. In phases when wind and solar energy hardly supply any electricity due to weather conditions, the stored hydrogen could then be converted back into electricity.
In principle, both hydrogen gas turbines and fuel cell power plants can be used for the large-scale reconversion of hydrogen into electricity. Gas turbines currently used in combined cycle power plants are partly able to operate with hydrogen contents of maximum 30 % in the natural gas. Turbines that can run on pure hydrogen are not yet available in the MW power range. However, companies such as Siemens Energy and Kawasaki are working on the development of such hydrogen turbines. For the use of fuel cell power plants for the large-scale reconversion of hydrogen, the existing systems must be scaled up.
When hydrogen is converted back into electricity, part of the energy is necessarily released in the form of heat, regardless of whether turbines or fuel cells are used. This waste heat can be extracted via a water circuit and used as process heat, for heating of residential buildings (district heating) or to heat drinking water. This principle is called combined heat and power (CHP). CHP is also used in conventional natural gas and coal-fired power plants or decentralised units (in German "Blockheizkraftwerke").
In Germany and many other parts of Europe, gas storage is a suitable way to bridge such "dark doldrums". In the future, large quantities of green hydrogen could be stored in salt caverns, for example. In phases when wind and solar energy hardly supply any electricity due to weather conditions, the stored hydrogen could then be converted back into electricity.
In principle, both hydrogen gas turbines and fuel cell power plants can be used for the large-scale reconversion of hydrogen into electricity. Gas turbines currently used in combined cycle power plants are partly able to operate with hydrogen contents of maximum 30 % in the natural gas. Turbines that can run on pure hydrogen are not yet available in the MW power range. However, companies such as Siemens Energy and Kawasaki are working on the development of such hydrogen turbines. For the use of fuel cell power plants for the large-scale reconversion of hydrogen, the existing systems must be scaled up.
When hydrogen is converted back into electricity, part of the energy is necessarily released in the form of heat, regardless of whether turbines or fuel cells are used. This waste heat can be extracted via a water circuit and used as process heat, for heating of residential buildings (district heating) or to heat drinking water. This principle is called combined heat and power (CHP). CHP is also used in conventional natural gas and coal-fired power plants or decentralised units (in German "Blockheizkraftwerke").