• Energy Research
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International audience; The wind energy, as a kind of renewable energy resources, has the potential to replace traditional fossil fuels. However, its intermittent power output can incur frequency instability due to the instantaneous unbalance between power generation and load demand. To smooth the penetration of wind energy, this paper presents a robust cooperative load frequency control (LFC) strategy for multi-area power systems, which is a hierarchical control approach. For the low-level wind turbine control, this paper adopts model predictive control (MPC) method to achieve the rated wind power tracking. In the meantime, an improved event-triggered scheme (ETS) considering multiple historic released signals is employed to relieve the computational burden of MPC. For the high-level cooperative LFC, this paper incorporates the robust performance index in the control synthesis to suppress the impact of intermittent wind power on frequency stability. In addition, to address the underlying shift of the steady-state operating point caused by the intermittent wind power supply, this paper improves the commonly used small-signal LFC model by adding an uncertain matrix, which reasonably explains the possible change of system parameters and extends the applicability of the traditional LFC model. Simulations are done on a four-area power system, and the results verify the efficacy of the presented event-triggered scheme and the robust cooperative LFC approach. Note to Practitioners —To promote the penetration of wind energy into power systems, this work explores a robust cooperative LFC approach under multi-agent structure to ensure the stability of the system, aiming at extending the applicability of existing approaches. The proposed approach is hierarchical. At the rated wind power tracking level, the MPC is employed to handle constraints associated with actuating devices, such as heterogeneous convertors. Simultaneously, an improved ETS considering multiple historic triggered signals is integrated in the MPC to reduce the computational burden. At the power system level, the robust performance index is incorporated in the control design to smooth the impacts of intermittent wind power on frequency stability. Additionally, the study accounts for the potential shift of the steady-state operating point and improves the traditional small-signal LFC model by adding an uncertain matrix, which can better explain the variation of system parameters and is more applicable in practical power system engineering. Simulation results demonstrate that the proposed robust cooperative LFC approach can effectively maintain the system frequency within the admissible range under the high penetration of wind energy, whereas the traditional PI controller falls short in this regard.

Abstract Green hydrogen is critical for decarbonizing hard-to-electrify sectors, but it faces high costs and investment risks. Here we define and quantify the green hydrogen ambition and implementation gap, showing that meeting hydrogen expectations will remain challenging despite surging announcements of projects and subsidies. Tracking 190 projects over 3 years, we identify a wide 2023 implementation gap with only 7% of global capacity announcements finished on schedule. In contrast, the 2030 ambition gap towards 1.5 °C scenarios has been gradually closing as the announced project pipeline has nearly tripled to 422 GW within 3 years. However, we estimate that, without carbon pricing, realizing all these projects would require global subsidies of US$1.3 trillion (US$0.8–2.6 trillion range), far exceeding announced subsidies. Given past and future implementation gaps, policymakers must prepare for prolonged green hydrogen scarcity. Policy support needs to secure hydrogen investments, but should focus on applications where hydrogen is indispensable.

Companies with datacenters are procuring significant amounts of renewable energy to reduce their carbon footprint. There is increasing interest in achieving 24/7 Carbon-Free Energy (CFE) matching in electricity usage, aiming to eliminate all carbon footprints associated with electricity consumption on an hourly basis. However, the variability of renewable energy resources poses significant challenges for achieving this goal. We explore the impact of shifting computing jobs and associated power loads both in time and between datacenter locations. We develop an optimization model to simulate a network of geographically distributed datacenters managed by a company leveraging spatio-temporal load flexibility to achieve 24/7 CFE matching. We isolate three signals relevant for informed use of load flexiblity: varying average quality of renewable energy resources, low correlation between wind power generation over long distances due to different weather conditions, and lags in solar radiation peak due to Earth’s rotation. We illustrate that the location of datacenters and the time of year affect which signal drives an effective load-shaping strategy. The energy procurement and load-shifting decisions based on informed use of these signals facilitate the resource-efficiency and cost-effectiveness of clean computing—the costs of 24/7 CFE are reduced by 1.29±0.07 EUR/MWh for every additional percentage of flexible load. We provide practical guidelines on how companies with datacenters can leverage spatio-temporal load flexibility for truly clean computing. Our results and the open-source optimization model can also be useful for a broader variety of companies with flexible loads and an interest in eliminating their carbon footprint. The simulations were carried out with PyPSA — an open-source software framework for simulating and optimising modern energy system: https://pypsa.org/ All code, input data and results are published under an open license. The code to reproduce the experiments is available at GitHub: https://github.com/Irieo/space-time-optimization

With the development of the world, the energy crisis has become increasingly prominent, which has greatly affected the sustainable development of the global economy. To ease the energy crisis and move towards sustainable development, the recovery of low-grade waste heat has gained increasing attention. Through a literature tracking strategy, this report provides the current state of research on internal leakage of the scroll expander, a key component of the organic Rankine cycle system. The structure, working principle, heat transfer and expansion efficiency of the scroll expander are introduced. The types of internal leakage, calculation model of leakage, influencing factors, influencing factors and solutions are analysed in detail. The main influencing factors of internal leakage are axial clearance, radial clearance, speed, air pressure, lubricating oil and so on.

Sodium-ion battery is a promising alternative to lithium-ion battery because of its abundant raw material resources, low price, and high specific capacity. Amorphous carbon materials (hard carbon) have micropores and impurities, facilitating the intercalation of sodium ions to form "quasi-metallic sodium," resulting in a high sodium storage capacity and a low sodium storage potential. Consequently, hard carbon is one of the most widely studied negative electrode materials. It can be prepared from biomass by thermochemical conversion and has the advantages of large specific capacity, low cost, good cycling stability, and renewability. This review focuses on Patents and thesis research in the hard carbon materials based on biomass. Firstly, the preparation methods of hard carbon, including precursor selection, pretreatment, drying methods, and carbonization processes, are summarized. Secondly, the effects of precursor composition and heteroatom doping structure and properties of hard carbon are examined, and the changes in carbon material pores during the activation process, as well as the selection of optimal drying method, pyrolysis temperature, carbonization temperature, activator dosage, and additive, are discussed. Thirdly, the impact of preparation methods on hard carbon's cost, efficiency, and stability is briefly summarized, and the relevant improvement measures and prospects are proposed. Finally, some insights are provided into preparing high-performance biomass-based anode materials for sodium-ion batteries.

The average revenue, or market value, of wind and solar energy tends to fall with increasing market shares, as is now evident across European electricity markets. At the same time, these markets have become more interconnected. In this paper, we empirically study the multiple cross-border effects on the value of renewable energy: on one hand, interconnection is a flexibility resource that allows to export energy when it is locally abundant, benefitting renewables. On the other hand, wind and solar radiation are correlated across space, so neighboring supply adds to the local one to depress domestic prices. We estimate both effects, using spatial panel regression on electricity market data from 2015 to 2023 from 30 European bidding zones. We find that domestic wind and solar value is not only depressed by domestic, but also by neighboring renewables expansion. The better interconnected a market is, the smaller the effect of domestic but the larger the effect of neighboring renewables. While wind value is stabilized by interconnection, solar value is not. If wind market share increases both at home and in neighboring markets by one percentage point, the value factor of wind energy is reduced by just above 1 percentage points. For solar, this number is almost 4 percentage points.

The relationship between climate and human evolution is complex, and the causal mechanisms remain unknown. Here, we review and synthesize what is currently known about climate forcings on African landscapes, focusing mainly on the last 4 million years. We use information derived from marine sediment archives and data-numerical climate model comparisons and integration. There exists a heterogeneity in pan-African hydroclimate changes, forced by a combination of orbitally paced, low-latitude fluctuations in insolation; polar ice volume changes; tropical sea surface temperature gradients linked to the Walker circulation; and possibly greenhouse gases. Pan-African vegetation changes do not follow the same pattern, which is suggestive of additional influences, such as CO2 and temperature. We caution against reliance on temporal correlations between global or regional climate, environmental changes, and human evolution and briefly proffer some ideas on how pan-African climate trends could help create novel conceptual frameworks to determine the causal mechanisms of associations between climate/habitat change and hominin evolution.

In order to solve the problems of slow reaction rate and large reactor volume of traditional urea hydrolysis to ammonia, the urea catalytic hydrolysis was studied in this paper. The bimetallic solid catalyst TiO2@Al2O3 was synthesized firstly, in which the mesoporous ?-Al2O3 was selected as substrate and the TiO2 was inserted into the active site. The solid catalyst was characterized by Raman spectroscopy and transmission electron microscopy, and the intermediates were qualitatively detected by liquid NMR H-spectroscopy and C-spectroscopy, which was combined with density functional theory calculations to analysis the mechanism of the bimetallic solid catalyst. Then, the kinetic and thermodynamic properties of the urea catalytic hydrolysis by solid catalyst were investigated on a batch reactor and a continuous operation pilot plant. The kinetic parameters of the catalytic hydrolysis reaction were measured, and the influences of different catalysts on the hydrolysis reaction temperature, energy consumption and variable load response time were researched. The bimetallic solid catalyst proposed in this study can solve the problems of phosphorus-containing wastewater discharge and insufficient active sites of traditional catalysts, and will provide significant reference to the research of urea catalytic hydrolysis to ammonia for flue gas denitrification.