Denmark

The design of future energy systems requires the efficient use of all available renewable resources. Biomass can complement variable renewable energy sources by ensuring energy system flexibility and providing a reliable feedstock to produce renewable fuels. We identify biomass gasification suitable to utilise the limited biomass resources efficiently. In this study we inquire about its role in a 100% renewable energy system for Denmark and a net-zero energy system for Europe in the year 2050 using hourly energy system analysis. The results indicate bio-electrofuels produced from biomass gasification and electricity to enhance the utilisation of wind and electrolysis and reduce the energy system costs and fuels costs compared to CO2-electrofuels from carbon capture and utilisation. Despite the extensive biomass use overall biomass consumption would be higher without biomass gasification. The production of electromethanol shows low biomass consumption and costs while Fischer-Tropsch electrofuels may be an alternative for aviation. Syngas from biomass gasification can supplement biogas in stationary applications as power plants district heat or industry but future energy systems must meet a balance between producing transport fuels and syngas for stationary units. CO2-electrofuels are found complementary to bio-electrofuels depending on biomass availability and remaining non-fossil CO2 emitters

Carbon dioxide (CO2 ) and hydrogen (H2 ) are essential energy vectors in the green energy transition. H2 is a fuel produced by electrolysis and is applied in heavy transportation where electrification is not feasible yet. The pollutant substance CO2 is starting to be captured and stored in different European locations. In Denmark the energy vision aims to use this CO2 to be reacted with H2 producing green methanol. Typically the production units are not co-located with consumers and thus the required transportation infrastructure is essential for meeting supply and demand. This work presents a novel scheme to allocate the transportation costs of CO2 and H2 in pipeline networks which can be applied to any network topology and with any allocation method. During the tariff formation process coordinated adjustments are made by the novel scheme on the original tariffs produced by the allocation method employed considering the location of each customer connected to pipeline network. Locational tariffs are provided as result and the total revenue recovery is guaranteed to the network owner. Considering active customers the novel scheme will lead to a decrease of distant pipeline flows thereby contributing to the prevention of bottlenecks in the transportation network. Thus structural reinforcements can be avoided reducing the total transportation cost paid by all customers in the long-term.

Power-to-X technologies are a promising means to achieve Denmark’s carbon emission reduction targets. Water electrolysis can potentially generate carbon-neutral fuels if powered with renewable electricity. However the high variability of renewable sources threatens the Power-to-X plant’s cost-efficiency instead favouring high and constant operation rates. Therefore a diversified electricity supply is often an option to maximise the load factor of the Power-to-X systems. This paper analyses the impact of using different power sources on the cost of production and the carbon intensity of hydrogen produced by a Power-to-X system. GreenLab Skive the world’s first industrial facility with Power-to-X integrated into an industrial symbiosis network has been used as a case study. Results show that the wind/PV/grid-connected electrolyser for hydrogen and electricity production can reduce operational costs and emissions saving 30.6 × 107 kgCO2 and having a Net Present Value twice higher than a grid-connected electrolyser. In addition the carbon emission coefficient for this configuration is 3.5 × 10− 2 kgH2/kgCO2 against 7.0 gH2/gCO2 produced by Steam Methane Reforming. A sensitivity analysis detects the optimal capacity ratio between the renewables and the electrolyser. A plateau is reached for carbon emission performances suggesting a wind/grid-connected electrolyser setup with a wind farm three times the size of the electrolyser. Results demonstrate that hydrogen cost is not competitive yet with the electricity suggesting an investment cost reduction but can be competitive with the current hydrogen price if the wind capacity is less than three times the electrolyser capacity.

Underground Hydrogen storage (UHS) is a promising technology for safe storage of large quantities of hydrogen in daily to seasonal cycles depending on the consumption requirements. The development of UHS requires anticipating hydrogen behavior to prevent any unexpected economic or environmental impact. An open question is the hydrogen reactivity in underground porous media storages. Indeed there is no consensus on the effects or lack of geochemical reactions in UHS operations because of the strong coupling with the activity of microbes using hydrogen as electron donor during anaerobic reduction reactions. In this work we apply different geochemical models to abiotic conditions or including the catalytic effect of bacterial activity in methanogenesis acetogenesis and sulfate-reduction reactions. The models are applied to Lobodice town gas storage (Czech Republic) where a conversion of hydrogen to methane was measured during seasonal gas storage. Under abiotic conditions no reaction is simulated. When the classical thermodynamic approach for aqueous redox reactions is applied the simulated reactivity of hydrogen is too high. The proper way to simulate hydrogen reactivity must include a description of the kinetics of the aqueous redox reactions. Two models are applied to simulate the reactions of hydrogen observed at Lobodice gas storage. One modeling the microbial activity by applying energy threshold limitations and another where microbial activity follows a Monod-type rate law. After successfully calibrating the bio-geochemical models for hydrogen reactivity on existing gas storage data and constraining the conditions where microbial activity will inhibit or enhance hydrogen reactivity we now have a higher confidence in assessing the hydrogen reactivity in future UHS in aquifers or depleted reservoirs.

The goals of the long-term tests were to see the impact of blends of hydrogen and natural gas on the technical condition of the appliances and their performance after several hours of operation. To do so they were run through an accelerated test program amounting to more than 3000 testing hours for the boilers and more than 2500 testing hours for the cookers. The percentage of hydrogen in the test gas was 30% by volume. Three boilers and two cookers were tested by DGC and two boilers by GWI. This report describes the test protocol the results and analysis on the seven appliances tested.

This report from the WP5 “Mitigation” provides information and test results regarding perturbations that hydrogen could cause to gas appliances when blended to natural gas especially on anatural draught for exhaust fumes or acidity for the condensates. The important topic of on-site adjustment is also studied with test results on alternative technologies and proposals of mitigation approaches.

With the constant increase in variable renewable energy production in electricity and district heating systems integration with the gas system is a way to provide flexibility to the overall energy system. In the sustainable transition towards a zero-emission energy system traditional natural gas can be substituted by renewable gasses derived from anaerobic digestion or thermal gasification and hydrogen. In this paper we present a methodology for modelling renewable gas options and limits on biomass resources across sectors in the energy optimisation model Balmorel. Different scenarios for socio-economic pathways to emission neutral electricity and district heating systems in Denmark Sweden Norway and Germany show that a renewable based energy system benefits from a certain percentage of gas as a supplement to other flexibility options like interconnectors. Especially upgraded biogas from anaerobic digestion serves as a substitute for natural gas in all scenarios. Allocating only 10% of available biomass to the electricity and district heating sector leads to full exploitation of the scarce biomass resource by boosting biogas and syngas with hydrogen. The need for renewable gasses is highest in Germany and least in Norway where hydro-power provides flexibility in terms of storable and dispatchable electricity production. The scenarios show that a required ‘‘late sprint" from fossils to achieve a zero-emission energy system in 2050 causes (1) significant higher accumulated emissions and (2) a system which strongly relies on fuels also in an emission free system instead of stronger integration of the electricity and district heating systems through electrification as well as stronger integration of the power systems across countries through interconnectors.

To enhance renewable energy (RE) generation and maintain power balance energy storage systems are of utmost importance. This research introduces a cutting-edge Power-to-Hydrogen (PtH) framework that harnesses hydrogen as a clean and versatile energy storage medium. The primary focus of this study lies in optimizing power flow within a microgrid (G) equipped with RE and energy storage systems considering various factors such as RE generation power demand battery charge cycles and operational costs. To achieve the optimal balance between power generation and consumption a sophisticated mathematical solution is devised. This solution governs the charging and discharging patterns for both battery and electrolyzer ensuring a harmonious power equilibrium. The use of short-term forecasting further refines the optimization process adapting the parameters based on anticipated RE sources and load requirements. To fine-tune the power management solution for day-to-day operations an artificial neural fuzzy inference system (ANFIS)-based shortterm prediction model is employed. The predictive analysis provides confidence intervals for crucial aspects including power generation demand battery charging cycles and hydrogen generation. This facilitates precise cost estimation across various hydrogen and heat price ranges. the proposed PtH optimization framework offers an efficient approach to balance power generation and consumption in Gs driven by RE sources and energy storage. To validate the proposed approach numerical simulations are performed based on data from wind and solar farms load requirements and cost of energy. The results show that the proposed energy management strategy significantly reduces operational costs and optimizes PtH generation while maintaining power balance within the microgrid (G). The predictive approach helps fine-tune the optimization process improving efficiency and cost-effectiveness. The research convincingly demonstrate the economic advantages of adopting hydrogen as an energy storage medium paving the way for a cleaner and more sustainable energy future.

This paper presents a comprehensive review of existing explosion mitigation techniques for tunnels and evaluates their applicability in scenarios of hydrogen tank rupture in a fire. The study provides an overview of the current state of the art in tunnel explosion mitigation and discusses the challenges associated with hydrogen explosions in the context of fire incidents. The review shows that there are several approaches available to decrease the effects of explosions including wrapping the tunnel with a flexible and compressible barrier and introducing energy-absorbing flexible honeycomb elements. However these methods are limited to the mitigation of the action and do not consider either the mitigation of the structural response or the effects on the occupants. The study highlights how the structural response is affected by the duration of the action and the natural period of the structural elements and how an accurate design of the element stiffness can be used in order to mitigate the structural vulnerability to the explosion. The review also presents various passive and active mitigation techniques aimed at mitigating the explosion effects on the occupants. Such techniques include tunnel branching ventilation openings evacuation lanes right-angled bends drop-down perforated plates or high-performance fibre-reinforced cementitious composite (HPFRCC) panels for blast shielding. While some of these techniques can be introduced during the tunnel's construction phase others require changes to the already working tunnels. To simulate the effect of blast wave propagation and evaluate the effectiveness of these mitigation techniques a CFD-FEM study is proposed for future analysis. The study also highlights the importance of considering these mitigation techniques to ensure the safety of the public and first responders. Finally the study identifies the need for more research to understand blast wave mitigation by existing structural elements in the application for potential accidents associated with hydrogen tank rupture in a tunnel.

Optimized operation of wind/hydrogen systems can increase the system efficiency and further reduce the hydrogen production cost. In this regard extensive research has been done but there is a lack of detailed electrolyzer models and effective management of multiple electrolyzers considering their physical restrictions. This work proposes electrolyzer models that integrate the efficiency variation caused by load level change start–stop cycle (including hot and cold start) thermal management and degradation caused by frequent starts. Based on the proposed models three operational strategies are considered in this paper: two traditionally utilized methods simple start–stop and cycle rotation strategies and a newly proposed rolling optimizationbased strategy. The results from daily operation show that the new strategy results in a more balanced load level among the electrolyzers and a more stable temperature. Besides from a yearly operation perspective it is found that the proposed rolling optimization method results in more hydrogen production higher system efficiency and lower LCOH. The new method leads to hydrogen production of 311297 kg compared to 289278 kg and 303758 kg for simple start–stop and cycle rotation methods. Correspondingly the system efficiencies for the new simple start–stop and cycle rotation methods are 0.613 0.572 and 0.587. The resulting LCOH from the new method is 3.89 e/kg decreasing by 0.35 e/kg and 0.21 e/kg compared to the simple start–stop and cycle rotation methods. Finally the proposed model is compared with two conventional models to show its effectiveness in revealing more operational details and reliable results.