• Energy Research
• Restricted close
• US close
• GB close
• VBN close

This paper proposes a decision tree (DT) based systematic approach for cooperative online power system dynamic security assessment (DSA) and preventive control. This approach adopts a new methodology that trains two contingency oriented DTs on daily basis by the databases generated from power system simulations. Fed with real-time wide area measurements, one DT about measurable variables is employed for online DSA to identify potential security issues and the other DT about controllable variables provides online decision support on preventive control strategies against those issues. A cost effective algorithm is adopted in this proposed approach to optimize the trajectory of preventive control. The paper also proposes an importance sampling algorithm on database preparation for efficient DT training for power systems with high penetration of wind power and distributed generation. The performance of the approach is demonstrated on a 400-bus, 200-line operational model of western Danish power system.

Abstract Nitrous oxide (N2O) is an important long-lived greenhouse gas and precursor of stratospheric ozone-depleting mono-nitrogen oxides. The atmospheric concentration of N2O is persistently increasing; however, large uncertainties are associated with the distinct source strengths. Here we investigate for the first time N2O emission from terrestrial vegetation in response to natural solar ultra violet radiation. We conducted field site measurements to investigate N2O atmosphere exchange from grass vegetation exposed to solar irradiance with and without UV-screening. Further laboratory tests were conducted with a range of species to study the controls and possible loci of UV-induced N2O emission from plants. Plants released N2O in response to natural sunlight at rates of c. 20–50 nmol m−2 h−1, mostly due to the UV component. The emission response to UV-A is of the same magnitude as that to UV-B. Therefore, UV-A is more important than UV-B given the natural UV-spectrum at Earth's surface. Plants also emitted N2O in darkness, although at reduced rates. The emission rate is temperature dependent with a rather high activation energy indicative for an abiotic process. The prevailing zone for the N2O formation appears to be at the very surface of leaves. However, only c. 26% of the UV-induced N2O appears to originate from plant-N. Further, the process is dependent on atmospheric oxygen concentration. Our work demonstrates that ecosystem emission of the important greenhouse gas, N2O, may be up to c. 30% higher than hitherto assumed.

The production of glucoamylase (GAM) by Aspergillus niger B1, a genetic transformant containing an additional 20 copies of the homologous glucoamylase gene (glaA) was studied in nutrient (maltodextrin)-limited chemostat and nutrient-excess pH auxostat cultures. In these culture systems the specific production rate of GAM increased with dilution rate and reached a maximum (up to 15.0 mg GAM [g biomass]-1 h-1) when A. niger B1 was grown at its maximum specific growth rate in pH auxostat culture, indicating that GAM is a growth-associated product. The appearance of spontaneous morphological mutants was observed in all continuous flow cultures grown at pH 5.4, with a light brown mutant always displacing the parental strain. However, no morphological mutants were observed in cultures grown at pH 4.0. Further, when A. niger B1 was grown in pH auxostat culture, the specific production rate of GAM was 31% higher at pH 4.0 than at pH 5.4. Southern blot analyses showed that some morphological mutants (including the light brown mutant) isolated from a pH auxostat culture had lost copies of the glaA genes.

Abstract Sustainable infrastructures need technologies that do not cause climate or environmental degradation. The only long-term sustainable solution to global warming in terms of both environmental and economic mitigation is renewable energy generation for stationary and transportation infrastructures. The papers in this special issue review some of the major technology and economic approaches to sustainable infrastructures. They specifically address the issue of sustainable energy and transportation systems, i.e. energy generation for vehicles and the relation to the stationary supply of electricity and heating. In order for communities, regions, nations and international communities to become sustainable, they must make energy into integrated infrastructures that use hybrid technologies. This chapter reviews and summarizes many of the points made in the volume to that end: sustainable infrastructures for power generation and transportation. The key is to consider the true costs for energy in terms of well to wheels and how the developing technologies for renewable energy power generation can be leveraged or made into hybrid systems that are cost-effective and sustainable. The series of articles begin to get into such as an approach for sustainable energy systems.

Abstract Reasonable energy storage capacity in a high source-to-charge ratio local power grid can not only reduce system costs but also improve local power supply reliability. This paper introduces the capacity sizing of energy storage system based on reliable output power. The proposed model is formulated to determine the relationship between the power capacity and wind energy loss, considering the wind curtailment loss and traditional energy power uncertain reserve. The non-parametric kernel density estimation is adopted to estimate the confidence intervals of wind power prediction error and fluctuation ranges of the actual output of a wind farm under different confidence degrees. The actual historical data of scenery resources in a certain area is used to verify the feasibility of the proposed method. The simulation shows the large-capacity energy storage, the reliable output power of the microgrid wind ensures the feasibility of day-ahead generation plans.

Six hydrothermal liquefaction experiments on Nannochloropsis salina and Spirulina platensis at subcritical and supercritical water conditions (220–375 °C, 20–255 bar) were carried out to explore the feasibility of extracting lipids from wet algae, preserving nutrients in lipid-extracted algae solid residue, and recycling process water for algae cultivation. GC–MS, elemental analyzer, FT-IR, calorimeter and nutrient analysis were used to analyze bio-crude, lipid-extracted algae and water samples produced in the hydrothermal liquefaction process. The highest bio-crude yield of 46% was obtained on N. salina at 350 °C and 175 bar. For S. platensis algae sample, the optimal hydrothermal liquefaction condition appears to be at 310 °C and 115 bar, while the optimal condition for N. salina is at 350 °C and 175 bar. Preliminary data also indicate that a lipid-extracted algae solid residue sample obtained in the hydrothermal liquefaction process contains a high level of proteins.

This paper describes a method of initialising dynamic wind turbine models in power-system simulations. The method uses grid-status information to initialise the grid-connected wind turbine model. The goal is to start a power-system simulation in a stationary state, without unnecessary transient behaviour at the beginning of the simulation. Correct initialisation is necessary to reach quickly the steady state of the grid-connected wind turbine, before a real transient on the grid occurs. Consequently, the dynamic performance of the system can be independently and accurately evaluated. The method presented considers wind turbines with directly grid-connected induction generators, with constant or variable blade angle (passive stall control, blade angle control or active stall control). These aspects apply to both constant and variable speed wind turbines. The investigation is performed in the commercial dedicated power-system simulation-tool DIgSILENT. Attention is especially drawn to the initialisation of the non-electrical parts of the wind turbine. The suitability of this initialisation strategy is illustrated by an example.

This paper defines and compares two strategies for integrating intermittent renewables: SuperGrid and SmartGrid. While conventional energy policy suggests that these strategies may be implemented alongside each other, the paper identifies significant technological and socio-economic conflicts of interest between the two. The article identifies differences between a domestic strategy for the integration of intermittent renewables, vis-a-vis the SmartGrid, and a cross-system strategy, vis-a-vis the SuperGrid. Policy makers and transmission system operators must understand the need for both strategies to evolve in parallel, but in different territories, or with strategic integration, avoiding for one strategy to undermine the feasibility of the other. A strategic zoning strategy is introduced from which attentive societies as well as the global community stand to benefit. The analysis includes a paradigmatic case study from West Denmark which supports the hypothesis that these strategies are mutually exclusive. The case study shows that increasing cross-system transmission capacity jeopardizes the feasibility of SmartGrid technology investments. A political effort is required for establishing dedicated SmartGrid innovation zones, while also redefining infrastructure to avoid the narrow focus on grids and cables. SmartGrid Investment Trusts could be supported from reallocation of planned transmission grid investments to provide for the equitable development of SmartGrid strategies.