Strategic Application of Underground Storage Potential for Energy Decarbonization
Battery technologies, until they advance to offer higher storage capacities, cannot entirely replace fossil fuel-based power generation in meeting future energy demands. Consequently, supplementing intermittent renewable sources will require the storage of natural gas and hydrogen. Other technologies, such as compressed air energy storage — which is currently in the pipeline — hold immense potential for meeting variations in seasonal energy demand.
Subsurface energy storage plays a critical role in facilitating the transition to sustainable energy sources. Many renewable energy generation methods, such as wind and solar power, exhibit fluctuations over short periods and across peak and off-peak demand seasons. As a result, reliable energy provision relies on effective energy storage solutions. The storage of substantial quantities of gases, including natural gas (NH4), hydrogen (H2), and carbon dioxide (CO2), in suitable underground geological formations will gain increasing importance as the energy transition progresses.
Natural gas storage is an established global industry. Over the years, countries with underground storage potential have used this mechanism to store natural gas when market prices and demand for gas are low in the summer, and then utilize it in the winter or during periods of higher energy demand. It is also one of the most widely used concepts for nations to achieve energy security, which is one of the three core dimensions of the energy trilemma (i.e., a framework by which a balance of energy price, sustainability, and security of a country is achieved). Currently, Germany ranks as the highest country in the world with enormous storage facilities, following Ukraine, Russia, and the US. Germany boasts gas storage fields for injection and production of approximately 23 billion cubic meters, estimated to have a retrieval rate of around 255 terawatt-hours worth of gas, meeting over half of the country’s gas demand in the winter. Such extensive capacities underscore the critical role that natural gas storage plays in maintaining energy security and regulating supply and demand fluctuations.
Carbon capture and storage (CCS), on the other hand, is a proven technology, not only at a pilot scale but also at a commercial scale, that is viable for cleaning up anthropogenic CO2 emissions and limiting global temperature rise to 1.5 degrees above its pre-industrial revolution level. Currently, more than 40 Mt of CO2 is sequestered annually, with the figure scaling up to gigatons per year by 2050. This technology not only isolates CO2 emissions from the atmosphere but is also an essential requirement for sustainable hydrogen production. For instance, the primary source of hydrogen today is steam methane reforming (SMR), a process through which blue hydrogen is produced. This process involves breaking down methane into hydrogen and carbon dioxide. The hydrogen produced through this method is called blue hydrogen, and the resulting carbon dioxide, if not permanently sequestered underground, will contribute to global warming.
Hydrogen — in both blue and other forms — serves as an alternative fuel in the energy transition due to its high energy density by mass. The energy content of 1 kg of hydrogen is approximately equivalent to 3 kg of gasoline. Unlike natural gas, hydrogen production varies by season. For example, large-scale production of green hydrogen, which is produced through the electrolysis of water using renewable electricity, depends on the availability of renewable energy sources characterized by seasons of sun, wind, etc. Additionally, the price of natural gas could also determine the quantity of blue hydrogen produced. In essence, intermittent hydrogen production necessitates large-scale storage solutions to store excess hydrogen produced during off-peak demand seasons for reuse during periods of high demand, in a cyclical manner. The same principle applies to blue hydrogen, which is produced in large quantities when prices are low during seasons of low natural gas demand. Enormous storage space is required for storing these large volumes, and the subsurface, with its unlimited storage capacity, is the ideal candidate to provide this capacity.
As contributions from renewable energy sources increase in the global primary energy mix, electricity from centralized thermal generating plants is being replaced by components that constitute renewable sources for power generation. To maintain equilibrium between load demand and power supply, energy storage solutions need to be deployed. One suitable technology is compressed air energy storage (CAES). CAES, an evolving technology with over four decades of history, is operated by charging and discharging air into and from an underground store — usually salt caverns, aquifers, or other suitable geological formations — using surplus electricity available during off-peak demand periods. This stored air can later be used to feed the grid during peak demand seasons. In locations where CAES is deployed, hundreds of megawatts of electricity can be conserved, and usage time can be shifted to periods of high demand. An operational example of a CAES plant is the McIntosh plant located in Alabama, USA, with an installed capacity of 110 MW.
Overall, the recent Russia-Ukraine war has further exacerbated the challenges faced by countries with insufficient domestic production or those relying on foreign gas imports, especially European countries characterized by excessive gas demand that surpasses immediate supply. This situation underscores the strategic imperative of large-scale energy storage. The incident serves as a reminder of the vital role that storage infrastructure plays in ensuring not only the smooth functioning of energy markets but also energy security.
August 15, 2023
Nuruddeen Inuwa Aminu (nuruddeeninuwa4@gmail.com) is a master's student in Subsurface Energy Systems at Heriot-Watt University, Edinburgh
