4.4 Hydrogen for Electricity and Heat
| Site: | Hamburg Open Online University |
| Course: | Green Hydrogen |
| Book: | 4.4 Hydrogen for Electricity and Heat |
| Printed by: | Gast |
| Date: | Saturday, 23 November 2024, 10:35 AM |
Description
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.
Generation of process heat
Process heat describes heat that is used for the production, further processing or refinement of products. The provision of process heat is therefore primarily relevant for industrial processes and could be considered part of this sector too.
Almost all products of daily use contain materials or components whose production requires high temperatures. While some areas of industry, such as food processing or mechanical engineering, largely require process heat at a temperature level of below 500 °C, there are other areas, such as glass and ceramics production or the processing of stones and soils, that need high-temperature heat in the range between 500 and 3,000 °C. This high-temperature heat accounts for around two-thirds of the total process heat demand in industry and is currently provided predominantly by fossil fuels.
In addition to energy sources such as biomass or renewable electricity, also green hydrogen can be used to provide process heat, especially at a high-temperature level, in a climate-neutral way. For this purpose, the hydrogen can be combusted directly in appropriate burners or heating boilers. Under certain circumstances, the use of high-temperature fuel cells (SOFC) is also possible, which at least enable the provision of heat at a temperature level of up to 700 °C.
Almost all products of daily use contain materials or components whose production requires high temperatures. While some areas of industry, such as food processing or mechanical engineering, largely require process heat at a temperature level of below 500 °C, there are other areas, such as glass and ceramics production or the processing of stones and soils, that need high-temperature heat in the range between 500 and 3,000 °C. This high-temperature heat accounts for around two-thirds of the total process heat demand in industry and is currently provided predominantly by fossil fuels.
In addition to energy sources such as biomass or renewable electricity, also green hydrogen can be used to provide process heat, especially at a high-temperature level, in a climate-neutral way. For this purpose, the hydrogen can be combusted directly in appropriate burners or heating boilers. Under certain circumstances, the use of high-temperature fuel cells (SOFC) is also possible, which at least enable the provision of heat at a temperature level of up to 700 °C.
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").
Heat supply for buildings
In Germany, about 75 % of the heat supply for public and private buildings is currently provided by natural gas. Due to the long life cycles of heating systems, gas is likely to remain a central energy source in the building sector in the medium to long term. Furthermore, existing buildings in urban areas in particular are difficult to convert to alternative, low-CO2 heating systems such as electric heat pumps.
The application of green hydrogen is an option to replace fossil natural gas and to reduce greenhouse gas emissions in the building sector. For instance, hydrogen can be mixed with natural gas and burned in gas condensing boilers connected to the pipeline network. Provided the necessary adaptation of the infrastructure (e.g. pipelines and heating systems), a gradual increase in the proportion of hydrogen in natural gas is conceivable.
In addition to the co-combustion of hydrogen in gas condensing boilers, the use of hydrogen can also take place in stationary, decentralised fuel cell heating systems for domestic energy supply. Especially in the case of a complete conversion of the gas grid or certain districts to hydrogen, such fuel cell heating systems can be a reasonable alternative to gas condensing boilers. The electricity generated by the fuel cells in addition to the heat (keyword: combined heat and power) can either be used to supply the households themselves or fed into the grid. Fuel cell heating systems are already offered by various suppliers and are mostly based on PEM fuel cells.
The application of green hydrogen is an option to replace fossil natural gas and to reduce greenhouse gas emissions in the building sector. For instance, hydrogen can be mixed with natural gas and burned in gas condensing boilers connected to the pipeline network. Provided the necessary adaptation of the infrastructure (e.g. pipelines and heating systems), a gradual increase in the proportion of hydrogen in natural gas is conceivable.
In addition to the co-combustion of hydrogen in gas condensing boilers, the use of hydrogen can also take place in stationary, decentralised fuel cell heating systems for domestic energy supply. Especially in the case of a complete conversion of the gas grid or certain districts to hydrogen, such fuel cell heating systems can be a reasonable alternative to gas condensing boilers. The electricity generated by the fuel cells in addition to the heat (keyword: combined heat and power) can either be used to supply the households themselves or fed into the grid. Fuel cell heating systems are already offered by various suppliers and are mostly based on PEM fuel cells.