Frank Dethlefsen

Impacts of the use of the geological subsurface for energy storage: an investigation concept

New methods and technologies for energy storage are required to make a transitionto renewable energy sources; in Germany this transition is termed “Energiewende”. Subsurface georeservoirs, such as salt caverns for hydrogen, compressed air, and methane storage or porous formations for heat and gas storage, offer the possibility of hosting large amounts of energy. When employing these geological storage facilities, an adequate system and process understanding is essential in order to characterize and to predict the complex and interacting effects on other types of subsurface use and on protected entities. In order to make optimal use of georeservoirs, a comprehensive use planning of the subsurface is required that allocates specific uses to appropriate subsurface locations. This paper presents a generic methodology on how subsurface use planning can be conducted and how its scientific basis can be developed. Although synthetic, realistic scenarios for the use of the geological underground for energy storage are parameterized and numerically simulated, accounting for other kinds of subsurface use already in place. From these scenario analyses, the imposed coupled hydraulic, thermal, mechanical and chemical processes, as well as mutual effects and influences on protected entities are assessed and generalized. Based on these, a first methodology for large-scale planning of the geological subsurface considering different surface and subsurface usage scenarios may also be derived.

Energy storage in the geological subsurface: dimensioning, risk analysis and spatial planning: the ANGUS+ project

New techniques and methods for energy storage are required for the transition to a renewable power supply, termed “Energiewende” in Germany. Energy storage in the geological subsurface provides large potential capacities to bridge temporal gaps between periods of production of solar or wind power and consumer demand and may also help to relieve the power grids. Storage options include storage of synthetic methane, hydrogen or compressed air in salt caverns or porous formations as well as heat storage in porous formations. In the ANGUS+ project, heat and gas storage in porous media and salt caverns and aspects of their use on subsurface spatial planning concepts are investigated. The optimal dimensioning of storage sites, the achievable charging and discharging rates and the effective storage capacity as well as the induced thermal, hydraulic, mechanical, geochemical and microbial effects are studied. The geological structures, the surface energy infrastructure and the governing processes are parameterized, using either literature data or own experimental studies. Numerical modeling tools are developed for the simulation of realistically defined synthetic storage scenarios. The feasible dimensioning of storage applications is assessed in site-specific numerical scenario analyses, and the related spatial extents and time scales of induced effects connected with the respective storage application are quantified. Additionally, geophysical monitoring methods, which allow for a better spatial resolution of the storage operation, induced effects or leakages, are evaluated based on these scenario simulations. Methods for the assessment of such subsurface geological storage sites are thus developed, which account for the spatial extension of the subsurface operation itself as well as its induced effects and the spatial requirements of adequate monitoring methods.

Development of a 3D Online Planning Tool for the Evaluation of Potential Underground Energy Storage Areas in S.-H.

We would like to present a GIS-based 3D online planning tool for underground energy storage. Its aim is to provide a basis for a pre-selection of possible sites for thermal, electrical, and substantial underground energy storages. The primary task of the proposed tool is to assist local authorities when dealing with the security of energy supply regarding the safe subsurface energy storage in the German state of Schleswig-Holstein. Taking into account as many of the relevant input factors as possible, the tool aims to suggest appropriate sites for setting up a selected kind of underground energy storage. The data base incorporates the current situtation as well as different energy related future scenarios. The system is implemented as an online 3D server GIS environment, with no software needed to be installed on the user side. The results, representing areas potentially suitable for underground energy storage, are visualized as interactive 3D graphics and 2D maps in the browser. They can be downloaded in Geomodelling and GIS file formats for integration into an existing workflow.

Parameterizability of processes in subsurface energy and mass storage

The numerical simulation of scenarios is a promising approach when quantifying the potential hydraulic, thermal, geomechanical, and chemical effects of subsurface energy and mass storage. Particularly, the coupling of processes is a strong point in numerical simulations. This study defines the geoscientific parameter demand as well as the demand for process understanding for simulating subsurface energy and mass storage, describes the existing numerical codes to conduct the simulations, provides generally valid parameter values, and emphasizes on discussing parameters where only few values exist. In this context, it is exemplified that the parameterizability of the regarded processes is determined by an uncertainty in parameter values (variability or aleatory uncertainty) as well as in the understanding of processes (epistemic uncertainty) as it was suggested by Walker et al. (Integr Assess 4:5–17, 2003). The study categorizes the knowledge about parameter values and processes into these uncertainty groups and exemplarily evaluates the impacts of the uncertainties. Using this approach illustrates the concepts needed for calculating prediction errors of numerical scenario simulations, such as sensitivity analyses in the case of statistical data uncertainty and laboratory or field studies in the case of scenario uncertainties.

Utilization of a 3D webGIS to support spatial planning regarding underground energy storage in the context of the German energy system transition at the example of the federal state of Schleswig-Holstein

When decarbonizing a state-wide energy system by introducing a growing share of renewable energies, underground energy storage can help to deal with fluctuating electric grid feed-in from renewables like wind power. Since besides energy storage other subsurface usages can claim or effect possible scarce suited underground spaces and interact with other usages at the surface, subsurface spatial planning is a growing field of interest for state authorities and in science now. Combining two-dimensional surface geodata on concerned fields like regional planning and energy infrastructure with three-dimensional geological data into one coherent data model could therefore support spatial planners in identifying and locating underground entities suited for energy storage. In this paper, a volumetric grid-based concept to integrate two- and three-dimensional geodata into one coherent data framework is implemented, including available data sets on geology, energy infrastructure and existing spatial plans. Missing spatial data on regional electric energy production and heat energy demand are derived from available primary data. Upon this data basis, a self-developed open source-based 3D webGIS prototype is utilized to identify and visualize potential underground spaces for a compressed air energy storage use case scenario at the example of the federal state of Schleswig–Holstein in North Germany. A first basic and a subsequently extended query via the 3D webGIS on the developed data model provide spatial information on search domains for potential energy storage sites in salt rock structures that could be integrated into emerging subsurface spatial planning.

Geochemical Effects of Millimolar Hydrogen Concentrations in Groundwater: An Experimental Study in the Context of Subsurface Hydrogen Storage

Hydrogen storage in geological formations is one of the most promising technologies for balancing major fluctuations between energy supply from renewable energy plants and energy demand of customers. If hydrogen gas is stored in a porous medium or if it leaks into a shallow aquifer, redox reactions can oxidize hydrogen and reduce electron acceptors such as nitrate, FeIII and MnIV (hydro)oxides, sulfate, and carbonate. These reactions are of key significance, because they can cause unintentional losses in hydrogen stored in porous media and they also can cause unwanted changes in the composition of protected potable groundwater. To represent an aquifer environment enclosing a hydrogen plume, laboratory experiments using sediment-filled columns were constructed and percolated by groundwater in equilibrium with high (2-15 bar) hydrogen partial pressures. Here, we show that hydrogen is consumed rapidly in these experiments via sulfate reduction (18 ± 5 μM h-1) and acetate production (0.030 ± 0.006 h-1), while no methanogenesis took place. The observed reaction rates were independent from the partial pressure of hydrogen and hydrogen consumption only stopped in supplemental microcosm experiments where salinity was increased above 35 g L-1. The outcomes presented here are implemented for planning the sustainable use of the subsurface space within the ANGUS+ project.