Rainer Duttmann

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.

Improved hydrological model parametrization for climate change impact assessment under data scarcity — The potential of field monitoring techniques and geostatistics

According to current climate projections, Mediterranean countries are at high risk for an even pronounced susceptibility to changes in the hydrological budget and extremes. These changes are expected to have severe direct impacts on the management of water resources, agricultural productivity and drinking water supply. Current projections of future hydrological change, based on regional climate model results and subsequent hydrological modeling schemes, are very uncertain and poorly validated. The Rio Mannu di San Sperate Basin, located in Sardinia, Italy, is one test site of the CLIMB project. The Water Simulation Model (WaSiM) was set up to model current and future hydrological conditions. The availability of measured meteorological and hydrological data is poor as it is common for many Mediterranean catchments. In this study we conducted a soil sampling campaign in the Rio Mannu catchment. We tested different deterministic and hybrid geostatistical interpolation methods on soil textures and tested the performance of the applied models. We calculated a new soil texture map based on the best prediction method. The soil model in WaSiM was set up with the improved new soil information. The simulation results were compared to standard soil parametrization. WaSiMs was validated with spatial evapotranspiration rates using the triangle method (Jiang and Islam, 1999). WaSiM was driven with the meteorological forcing taken from 4 different ENSEMBLES climate projections for a reference (1971-2000) and a future (2041-2070) times series. The climate change impact was assessed based on differences between reference and future time series. The simulated results show a reduction of all hydrological quantities in the future in the spring season. Furthermore simulation results reveal an earlier onset of dry conditions in the catchment. We show that a solid soil model setup based on short-term field measurements can improve long-term modeling results, which is especially important in ungauged catchments.

Simulation of future groundwater recharge using a climate model ensemble and SAR-image based soil parameter distributions — A case study in an intensively-used Mediterranean catchment

We used observed climate data, an ensemble of four GCM-RCM combinations (global and regional climate models) and the water balance model mGROWA to estimate present and future groundwater recharge for the intensively-used Thau lagoon catchment in southern France. In addition to a highly resolved soil map, soil moisture distributions obtained from SAR-images (Synthetic Aperture Radar) were used to derive the spatial distribution of soil parameters covering the full simulation domain. Doing so helped us to assess the impact of different soil parameter sources on the modelled groundwater recharge levels. Groundwater recharge was simulated in monthly time steps using the ensemble approach and analysed in its spatial and temporal variability. The soil parameters originating from both sources led to very similar groundwater recharge rates, proving that soil parameters derived from SAR images may replace traditionally used soil maps in regions where soil maps are sparse or missing. Additionally, we showed that the variance in different GCM-RCMs influences the projected magnitude of future groundwater recharge change significantly more than the variance in the soil parameter distributions derived from the two different sources. For the period between 1950 and 2100, climate change impacts based on the climate model ensemble indicated that overall groundwater recharge will possibly show a low to moderate decrease in the Thau catchment. However, as no clear trend resulted from the ensemble simulations, reliable recommendations for adapting the regional groundwater management to changed available groundwater volumes could not be derived.

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.

Driving factors of temporal variation in agricultural soil respiration

Investigations of diurnal and seasonal variations in soil respiration support modeling of regional CO2 budgets and therefore in estimating their potential contribution to greenhouse gases. This study quantifies temporal changes in soil respiration and their driving factors in grassland and arable soils located in Northern Germany. Field measurements at an arable site showed diurnal mean soil respiration rates between 67 and 99 mg CO2 m–2 h–1 with a hysteresis effect following changes in mean soil temperatures. Field soil respiration peaked in April at 5767 mg CO2 m–2 day–1, while values below 300 mg CO2 m–2 day–1 were measured in wintertime. Laboratory incubations were carried out in dark open flow chambers at temperatures from 5°C to 40°C, with 5°C intervals, and soil moisture was controlled at 30%, 50%, and 70% of full water holding capacity. Respiration rates were higher in grassland soils than in arable soils when the incubating temperature exceeded 15°C. The respiration rate difference between them rose with increasing temperature. Monthly median values of incubated soil respiration rates ranged from 0 to 26.12 and 0 to 7.84 µg CO2 g–1 dry weight h–1, respectively, in grassland and arable land. A shortage of available substrate leads to a temporal decline in soil respiration rates, as indicated by a decrease in dissolved organic carbon. Temporal Q10 values decreased from about 4.0 to below 1.5 as temperatures increased in the field. Moreover, the results of our laboratory experiments confirmed that soil temperature is the main controlling factor for the Q10 values. Within the temperature interval between 20°C and 30°C, Q10 values were around 2 while the Q10 values of arable soils were slightly lower compared to that of grassland soils. Thus, laboratory studies may underestimate temperature sensitivity of soil respiration, awareness for transforming laboratory data to field conditions must therefore be taken into account.

Anthropogenic influence on rates of aeolian dune activity within the northern European Sand Belt and socio-economic feedbacks over the last ~2500 years

In North-Western Europe, Pleistocene sand sheets have been reactivated during phases of Holocene deforestation and agricultural land use. Although there are temporal overlaps between anthropogenic activity and sand sheet reactivation, the root cause and subsequent feedbacks between aeolian activity and societal response remain largely unknown. Here, we seek to establish cause and effect by examining the detailed co-variation in both timing and magnitude of aeolian and anthropogenic activity through the quantification of Holocene dune sediments in combination with archaeological and pollen records. These records indicate a series of complex phases of aeolian activity followed by landscape stabilization, which we attribute primarily to changing patterns of human impact. We find that a steady increase in dune deposition rates in the Medieval Period corresponds to an increase in settlement activity and deforestation (~AD 1000–1500). At their peak, Medieval deposition rates were 3.4 times larger than during the late Pleistocene, the period experiencing the most favourable natural conditions for aeolian sediment transport. Prior to the Medieval Period, relative land-surface stability (represented by a depositional hiatus) persisted from the late Pleistocene until the Roman Iron Age Period (AD 0–400). Deforestation to fuel iron production had minor impact on aeolian activity, as indicated by the lowest recorded deposition rate (0.12 ± 0.02 t/ha/a). Following the Medieval Period peak in deposition rates, aeolian activity diminished rapidly and coincided with the abandonment of nearby human settlement. This sequence of events provides evidence of a direct positive feedback in which Medieval agricultural overexploitation favoured aeolian activity that rendered the landscape practically unworkable for cropping agriculture. Based on our findings and a comprehensive review of Northern European sand belt activity, we interpret a very high sensitivity of aeolian activity to past and present human impact and argue that unsustainable land-use practices have been the cause for widespread settlement abandonment.

Functional dependencies of soil CO2 emissions on soil biological properties in northern German agricultural soils derived from a glacial till

Agricultural soil CO2 emissions and their controlling factors have recently received increased attention because of the high potential of carbon sequestration and their importance in soil fertility. Several parameters of soil structure, chemistry, and microbiology were monitored along with soil CO2 emissions in research conducted in soils derived from a glacial till. The investigation was carried out during the 2012 growing season in Northern Germany. Higher potentials of soil CO2 emissions were found in grassland (20.40 µg g−1 dry weight h−1) compared to arable land (5.59 µg g−1 dry weight h−1) within the incubating temperature from 5°C to 40°C and incubating moisture from 30% to 70% water holding capacity (WHC) of soils taken during the growing season. For agricultural soils regardless of pasture and arable management, we suggested nine key factors that influence changes in soil CO2 emissions including soil temperature, metabolic quotient, bulk density, WHC, percentage of silt, bacterial biomass, pH, soil organic carbon, and hot water soluble carbon (glucose equivalent) based on principal component analysis and hierarchical cluster analysis. Slightly different key factors were proposed concerning individual land use types, however, the most important factors for soil CO2 emissions of agricultural soils in Northern Germany were proved to be metabolic quotient and soil temperature. Our results are valuable in providing key influencing factors for soil CO2 emission changes in grassland and arable land with respect to soil respiration, physical status, nutrition supply, and microbe-related parameters.

Estimation of Soil Material Transportation by Wind Based on in Situ Wind Tunnel Experiments

Abstract 25% and 40% of territory of Hungary is moderate to highly vulnerable to deflation. However, precise estimates about the soil loss and related losses of organic matter and nutrients due to wind erosion are missing in most cases. In order to determine magnitudes of nutrient masses removed at wind velocities that frequently occur in SE Hungary, in-situ experiments using a portable wind tunnel have been conducted on small test plots with an erosional length of 5.6 m and a width of 0.65 m. The wind tunnel experiments have been carried through on a Chernozem which is typical for this region. In order to compare the effects of soil coverage on the masses of blown soil sediment and adsorbed nutrients, two soil surface types have been tested under similar soil moisture und atmospheric conditions: (1) bare soil (dead fallow) and (2) bare soil surface interrupted by a row of maize plants directed downwind along the center line of the test plots. The results of our experiments clearly show that a constant wind velocity of 15 m s-1 (at a height of 0.3 m) lasting over a short time period of 10 minutes can already cause noticeable changes in the composition and size of soil aggregates at the top of the soil surface. Due to the grain size selectivity of the erosive forces the relative share of soil aggregates comprising diameters > 1 mm increased by 5-10% compared with the unaffected soil. Moreover it has shown that short time wind erosion events as simulated in this study can result in erosion rates between 100 and 120 g m-2, where the erosion rates measured for bare soils are only slightly, but not significantly higher than those of the loosely vegetated ones. Soil samples taken from sediment traps mounted in different heights close to the outlet of the wind tunnel point to an enrichment of organic matter (OM) of about 0.6 to 1 % by mass referred to the control samples. From these findings has been calculated that the relocation of organic matter within short term wind erosion events can amount to 4.5 to 5.0 g OM m-2. With the help of portable field wind tunnel experiments we can conclude that our valuable, high quality chernozems are struck by wind erosion mainly in drought periods.

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.