• Energy Research
• The Research Council of Norway close
• Frontiers in Energy Research close

The exponential rise of renewable energy sources and microgrids brings about the challenge of guaranteeing frequency stability in low-inertia grids through the use of energy storage systems. This paper reviews the frequency response of an ac power system, highlighting its different time scales and control actions. Moreover, it pinpoints main distinctions among high-inertia interconnected systems relying on synchronous machines and low-inertia systems with high penetration of converter-interfaced generation. Grounded on these concepts and with a set of assumptions, it derives algebraic equations to rate an energy storage system providing inertial and primary control. The equations are independent of the energy storage technology, robust to system nonlinearities, and rely on parameters that are typically defined by system operators, industry standards, or network codes. Using these results, the authors provide a step-by-step procedure to size the main components of a converter-interfaced hybrid energy storage system. Finally, a case study of a wind-powered oil and gas platform in the North Sea demonstrates with numerical examples how the proposed methodology 1) can be applied in a practical problem and 2) allows the system designer to take advantage of different technologies and set specific requirements for each storage device and converter according to the type of frequency control provided.

Support schemes like the Feed-in-Tariff (FiT) have for many years been an important driver for the deployment of distributed energy resources, and the transition from consumerism to prosumerism. This democratization and decarbonization of the energy system has led to both challenges and opportunities for the system operators, paving the way for emerging concepts like local energy markets. The FiT approach has often been assumed as the lower economic bound for a prosumer’s willingness to participate in such markets but is now being phased out in several countries. In this paper, a new pricing mechanism based on the Levelized Cost of Electricity is proposed, with the intention of securing profitability for the prosumers, as well as creating a transparent and fair price for all market participants. The mechanism is designed to function on a Distributed Ledger Technology-based platform and is further set up from a holistic perspective, defining the market framework as interactions in a Cyber-Physical-Social-System. Schemes based on both fixed and variable contracts with the wholesale supplier are analyzed and compared with both the conventional FiT and to its proposed replacement options. The results show a cost reduction for the consumers and a slight loss in revenue for the prosumers compared to the FiT scheme. Comparing it to the actual suggested replacements to the FiT, however, it is clear that the pricing mechanism proposed in this study provides a substantial increase of benefits for both prosumers and consumers.

Flow field designs for the bipolar plates of the proton exchange membrane fuel cell are reviewed; including the serpentine, parallel, interdigitated, mesh type or their mixtures, furthermore 2D circular and 3D tubular geometries, porous, fractal, and biomimetic flow fields. The advantages/disadvantages and tendencies from field optimizations are discussed. The performance of each flow field design is compared to the conventional serpentine flow field. Good flow field plates give uniform gas distributions, low pressure drop for transport, and sufficient rib area to provide high electronic conductivity. A good field should also prevent water condensation, remove water efficiently, and provide sufficiently high moisture content in the membrane. The demands on design are sometimes contradictory. Future work should aim for a flow field geometry and topology that produces uniform gas delivery at a low pressure-drop, and at the same time has an optimal channel shape for better water removal. It is concluded that for an area-filling gas distributor, the developments should aim to find a flow field in accordance with minimum entropy production, making an emphasis on multi-criteria optimization methods.

Methanol syntheses at low temperature in a liquid medium present an opportunity for full syngas conversion per pass. The aim of this work was to study the role of solvents polarity on low-temperature methanol synthesis reaction using eight different aprotic polar solvents. A “once through” catalytic system, which is composed of Cu nanoparticles and sodium methoxide, was used for methanol synthesis at 100°C and 20 bar syngas pressure. Solvent polarity rather than the 7–10 nm Cu (and 30 nm Cu on SiO2) catalyst used dictated trend of syngas conversion. Diglyme with a dielectric constant (ɛ) = 7.2 gave the highest syngas conversion among the eight different solvents used. Methanol formation decreased with either increasing or decreasing solvent ɛ value of diglyme (ɛ = 7.2). To probe the observed trend, possible side reactions of methyl formate (MF), the main intermediate in the process, were studied. MF was observed to undergo two main reactions; (i) decarbonylation to form CO and MeOH and (ii) a nucleophilic substitution to form dimethyl ether and sodium formate. Decreasing polarity favored the decarbonylation side reaction while increasing polarity favored the nucleophilic substitution reaction. In conclusion, our results show that moderate polarity solvents, e.g., diglyme, favor MF hydrogenolysis and, hence, methanol formation, by retarding the other two possible side reactions.

Over the past decade, Na-ion batteries (NIBs) have gained a substantial interest within the research community and relevant industry. NIBs are now emerging as a cost-effective and sustainable alternative to modern Li-ion batteries (LIBs). Similar to the parent LIB technology, NIB requires a new set of materials, which can boost battery capacity without sacrificing cycling stability, rate capabilities, and other performance targets. In NIB chemistry, anodes have received less attention compared to cathode chemistry, leaving hard carbon as a primary anode material, although its intercalation/adsorption mechanism limits the allowed number of Na-ions. Promising alternative groups of anodes are materials that undergo the combined conversion and alloying reactions (i.e., conversion-alloying anodes), due to the beneficial high theoretical capacity and good cycling stability. The conversion reaction in conversion-alloying anodes can be either reversible or irreversible, each possessing its advantages. However, the complexity of their operating mechanism(s) severely impedes their development. The present mini-review provides a survey of the recent developments of conversion-alloying-type anode materials for Na-ion batteries discussed in the context of their operation mechanism(s). Considering the chemical complexity of the conversion-alloying materials, the suggestions and guidance on characterization are provided along with theoretical considerations.

Solar mapping can contribute to exploiting more efficiently the solar energy potential in cities. Solar maps and 3D solar cadasters consist of visualization tools for solar irradiation analysis on urban surfaces (i.e., orography, roofs, and façades). Recent advancements in solar decomposition and transposition modeling and Light Detection and Ranging (LiDAR) scanning enable high levels of detail in 3D solar cadasters, in which the façade domain is considered beside the roof. In this study, a model chain to estimate solar irradiation impinging on surfaces with different orientations at high latitudes is developed and validated against experimental data. The case study is the Zero Emission Building Laboratory in Trondheim (Norway). The main stages of the workflow concern (1) data acquisition, (2) geometry detection, (3) solar radiation modeling, (4) data quality check, and (5) experimental validation. Data are recorded from seven pyranometers installed on the façades (4), roof (2), and pergola (1) and used to validate the Radiance-based numerical model over the period between June 21st and September 21st. This study investigates to which extent high-resolution data sources for both solar radiation and geometry are suitable to estimate global tilted irradiation at high latitudes. In general, the Radiance-based model is found to overestimate solar irradiation. Nonetheless, the hourly solar irradiation modeled for the two pyranometers installed on the roof has been experimentally validated in accordance with ASHRAE Guideline 14. When monthly outcomes are considered for validation, the east and the south pyranometers are validated as well. The achieved results build the ground for the further development of the 3D solar cadaster of Trondheim.

Carbon capture and storage (CCS) is an inevitable action to achieve CO2 emission reduction targets including becoming net-zero by 2050. Increased efforts are therefore required to identify suitable locations for large-scale CO2 storage. In addition to large aquifers, shut down oil and gas fields in the North Sea are logical candidates for offshore large-scale CO2 storage because of their proven storage capacity, reliable caprock integrity, established infrastructure, and public acceptance. However, in some cases, old and legacy wells are subject to high uncertainties in their integrity, and they can compromise CO2 containment in such reservoirs. On the Norwegian Continental Shelf (NCS), such wells are numerous even outside of oil and gas production areas, i.e., legacy wells affecting aquifers. Therefore, there is a clear need for reliable and cost-effective technologies for well integrity evaluation and remediation. This paper discusses a workflow for screening, monitoring, and remediation of legacy wells. In a first stage, the screening of the Horda Platform areas suggested the need for integrity investigation for the exploration well 32/4-1 T2, drilled into the Alpha structure of the Smeaheia fault block if CO2 is stored in the structure. Our initial well screening of drilling documentation indicates that the well is not suitable to be reused for CO2 injection and geophysical monitoring is recommended. In a second stage, a numerical representation of the well architecture is built including realistic geological setting. We evaluate the sensitivity of non-invasive low-frequency electromagnetic monitoring to corrosion levels in the casing. Numerical end-member simulations of assuming casing corrosion of different degrees by changing material conductivity are performed. Results comparing different corrosion scenarios with a base case (no corrosion) give an above noise signal at receiver locations enabling to separate the different cases. Comparison of the gained electrical fields at seafloor suggests that well casing corrosion monitoring should be possible. Finally, the electrochemical deposition potential of the Sognefjord Formation water is analyzed, revealing depositional potential for portlandite, which might be useful for cement remediation. We recommend such an analysis for all legacy wells penetrating candidate reservoirs for future CO2 or hydrogen storage.