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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 An augmented measurement uncertainty approach for CO 2 emissions from coal-fired power plants with a focus on the often forgotten contributions from sampling errors occurring over the entire fuel-to-emission pathway is presented. Current methods for CO 2 emission determination are evaluated in detail, from which a general matrix scheme is developed that includes all factors and stages needed for total CO 2 determination, which is applied to the monitoring plan of a representative medium-sized coal-fired power plant. In particular sampling involved significant potential errors, as identified and assessed by the Theory of Sampling (TOS), which also shows how these can be eliminated and/or minimised. Since coal-related CO 2 emission calculations not only require analytical results of the carbon content of coal itself but also of the by-products fly ash and bottom ash, sampling procedures of these three materials were also given full attention. A systematic error (bias) is present in the current sampling approach, which increases the present uncertainty estimate unnecessarily. For both primary sampling and analytical sample extraction steps, random variations, which hitherto only have been considered to a minor extent, have now also been fully quantified and included in the overall uncertainty. Elimination of all identified sampling errors lead to modified CO 2 determination procedures, which indicate that the actual CO 2 emission is approximately 20,000 t higher than the present estimate. Based on extensive empirical sampling experiments, a fully comprehensive uncertainty estimate procedure has been devised. Even though uncertainties increased (indeed one particular factor is substantially higher, the so-called “emission factor”), the revised CO 2 emission budget for the case plant complies with the official pre-determined uncertainty levels maxima in the EU guidelines.

The oleaginous alga Chlorella protothecoides accumulates lipid in its biomass when grown in nitrogen-restricted conditions. To assess the relationship between nitrogen provision and lipid accumulation and to determine the contribution of photosynthesis in mixotrophic growth, C. protothecoides was grown in mixo- and heterotrophic nitrogen-limited continuous flow cultures. Lipid content increased with decreasing C/N, while biomass yield on glucose was not affected. Continuous production of high lipid levels (57% of biomass) was possible at high C/N (87-94). However, the lipid production rate (2.48 g L(-1) d(-1)) was higher at D=0.84 d(-1) with C/N 37 than at D=0.44 d(-1) and C/N 87 even though the lipid content of the biomass was lower (38%). Photosynthesis contributed to biomass and lipid production in mixotrophic conditions, resulting in 13-38% reduction in CO2 production compared with heterotrophic cultures, demonstrating that photo- and heterotrophic growth occurred simultaneously in the same population.

Abstract The integration of the Photovoltaic (PV) - based Distributed Generation (DG) Systems to the conventional electrical grid is a significant issue to achieve a confidential grid operation. This study presents a novel structure for the suppression of the common-state leakage current for PV-based inverters. It investigates the real-time performance of the inverter for the grid-code compatibility of the PV-based microgrid applications. Many of the topologies have been introduced to suppress leakage currents in grid-based Photovoltaic (PV) inverters, but most of them cannot practically reach more than 95% efficiency. The number of the components, especially the switching semiconductors, including the power switches and power diodes and the current and ripples' level in the topology filter side inductors, are essential criteria for efficiency. The proposed inverter includes six power switches and two power diodes. Since different operational states, only two power components per branch of the inverter are activated a higher efficiency than the conventional H5, H6, and HERIC converters. It presents the THD equal to 1,42 for load-connection states that is considerable. This converter can also generate pure sinusoidal current and voltage waveforms for the reactive loads, especially resistive-inductive load connections that are most common in industrial applications. As a study-case, the implemented inverter was tested under different grid conditions in the laboratory, and a real-time LabVIEW-based monitoring and grid protection system was realized within the research scope. Under/over-frequency protection and under/over voltage protection were performed to provide a reliable microgrid management system for the developed inverter. According to IEEE 929-2000 threshold values for the breakers' reaction operation under the ±10% as the output threshold voltage, the converter's performance is presented. A real-time monitoring and protection system are developed, and the developed LabVIEW analyzer has done the hardware test results. THD and spectrum analysis are also investigated in the real-time domain by the developed inverter test system. In this way, the implemented inverter's grid code compatibility is investigated in real-time, and the experimental results show that the proposed inverter is reliable for PV-based microgrid applications.

Abstract The Danish city Frederikshavn is aiming at becoming a 100% renewable energy city. The city has a number of energy resources including a potential for off-shore wind power, waste and low-temperature geothermal energy usable as heat source for heat pumps producing district heating. In this article, a technical scenario is described and developed for the transition of Frederikshavn’s energy supply from being predominantly fossil fuelled to being fuelled by locally available renewable energy sources. The scenario includes all aspects of energy demand in Frederikshavn i.e. electricity demand, heat demand, industrial demand as well as the energy demand for transportation. The locally available energy resources are deliberated and an energy system is designed and analysed with an energy systems analysis model on an aggregate annual level as well as on an hourly basis. Particular attention is given to the use of geothermal energy in the area. It is shown, that the use of geothermal energy in combination with an absorption heat pump shows promise in a situation where natural gas supply to conventional cogeneration of heat and power (CHP) plants decreases radically.

Abstract This article presents a model of natural ventilation of buildings at the stage of design and a consequence of the behaviour of the occupants. An evaluation is made by coupling multizone air modelling and thermal building simulation using a deterministic set of input factors comprising among others climate, local environment, building characteristics, building systems, behaviour of occupants and heat loads. Selected deterministic input factors are varied to generate additional information applied in an optimization loop. With that, it is found that the optimal solution depends to a great extent on the possibility of optimization of the behaviour of occupants, and to a lesser extent on the design of the building.

Abstract There is a variety of solar-based energy system designs for buildings. Although these systems are economically profitable, reducing the energy cost of the buildings over time, their penetration has not been that impressive yet due to their high initial cost. In this study, an energy system comprising a few PVT panels (without any batteries) and a heat storage tank is proposed and investigated for smart buildings with two-way interactions with both heat and electricity grids. Removing the battery from the system would result in a sharp reduction of the cost of the system and, thereby, will make incentives for the end-users to adopt the solution. This novel system will not only supply the buildings’ real-time electricity and domestic hot water needs but also will compensate for a significant portion of the buildings’ energy expenses by selling the surplus generations to the electricity and heat networks. The dynamic model of the proposed system is comprehensively analyzed from thermodynamic and economic points of view using TRNSYS software. Additionally, defining the overall annual exergy efficiency, and the total product cost as the objective functions, optimization of the design and size of the system employing the TRNOPT tool has been done. It is shown that the optimized system results in 16.7 €/MWh and 7.7 €/MWh lower energy costs for electricity and heat of the buildings compared to when the buildings’ demand is only supplied by heat and electricity grids.

Abstract Any kind of Wave Energy Converter (WEC) requires information on how optimize the device in terms of hydraulic performances and structural responses. This paper presents results on wave loading acting on an innovative caisson breakwater for electricity production. The Seawave Slot-Cone Generator (SSG) concept is based on the known principle of overtopping and storing the wave energy in several reservoirs placed one above the other. Using this method practically all waves, regardless of size and speed are captured for energy production. In the present SSG setup three reservoirs have been used. Comprehensive 2D and 3D hydraulic model tests were carried out at the Department of Civil Engineering, Aalborg University (Denmark) in the 3D deep water wave tank. The model scale used was 1:60 of the SSG prototype at the planned location of a pilot plant at the west coast of the Kvitsoy island (Stavanger, Norway). The analyses of hydraulic model tests have identified the main shapes assumed by wave surfaces at the breakwater and respective spatial and temporal pressure distributions. The influence of wave obliquity and multidirectionality is also described by loading reduction factors referred to the case of long-crested head-on wave attack. Pressure measurements were compared with the prediction method made for caisson breakwaters with sloping top. These results suggest to use the experimental data as design pressures since the design criteria of traditional maritime structures may be not satisfactory for designing innovative breakwater as SSG.