• Energy Research
• Closed Access close
• Restricted close
• ES close
• EU close
• Applied Energy close

The increase in installed wind power has brought a number of Grid Code areas into focus. The area of fault ride-through capability is one with serious implications for system security and thus has an impact on the allowed wind energy penetration in the network. There are several wind turbine models that can be used to study the effects of voltage dips and the corresponding wind turbine responses but these models need to be validated by comparing their results with the data obtained during field tests. This paper presents the design of a voltage dip generator that can be used to test wind turbines up to 5 MW and 20 kV. This system is able to adjust voltage dip depth and duration to the standards defined in different countries and also the fault impedance seen by the grid in order not to disturb its operation during the tests. Simulation results are validated using experimental data obtained at a laboratory-scale prototype (400 V, 90 kW). Finally, the actual 5 MW system and the results obtained during field tests are presented.

Abstract A new open-loop solar tracking system for a small-scale linear Fresnel reflector with three movements has been designed, fabricated, and simulated. The control system of the solar tracker is governed by a Raspberry Pi together with other auxiliary devices which include a Global Positioning System. The electronic control system consists of a master controller (Raspberry pi 3), 4 slave microcontrollers (Arduino), Global Positioning System module, thermocouples, laser sensors, transversal positioning sensors, and longitudinal positioning sensors. It also allows the communication between these microcontrollers based on long range wireless solutions (XBee). All the electronic circuits have been designed and constructed. The solar tracking system uses offline data. The software has been designed and developed to track the sun path using astronomical equations. In this way, the solar tracking system is able to position itself automatically using the solar position algorithm and the Global Positioning System with an accuracy of ±0.006°. The solar tracking system can be deployed automatically at any location on the Earth. The total cost of the implemented solar tracking system has been calculated. The system performance, in terms of the tracking error, annual energy, energy-to-area ratio and levelized cost of energy has been evaluated. Tracking errors smaller than 0.06 (°) are acceptable (they cause power losses smaller than 1%), whereas errors larger than 0.36 (°) start being noticeable (power losses greater than 3%). The proposed new tracking system gives 16.64% more energy, a 78.46% higher energy-to-area ratio, and a 4.62% less levelized cost of energy that the classic tracking system with one movement used in large-scale linear Fresnel reflectors.

Abstract The need to reduce both energy consumption and greenhouse gas emissions has boosted the interest in using thermoelectric generators (TEGs) as waste heat energy harvesters. High-power TEGs are usually formed by an array of commercial thermoelectric modules (TEMs). Recent studies have analyzed the effects of using different types of electrical connections between TEMs in TEGs to produce electric power, but the effects of using different thermal configurations between TEMs have not been fully examined. Here, both electrical and thermal effects have been investigated using a numerical model developed with GT-SUITE software, which has been validated with laboratory data. TEGs with a number of TEMs between 1 and 100 distributed in different patterns along the exhaust pipe have been simulated under three engine regimes. For a given TEM geometrical pattern and engine regime, results prove the existence of an optimum number of TEMs, beyond which the total extracted power decreases. A mixed spatial distribution of TEMs generates more power than either the pure series or the pure parallel topologies. Finally, a methodology is proposed to choose an appropriate pattern of TEMs for a TEG installed in a system with variable regimes. This method is applied to a mid-size automotive diesel engine.

Abstract In this paper, R32 is investigated as a replacement refrigerant for R410A. The Global Warming Potential (GWP) of R32 is only 675, 32% of that of R410Awhich has a GWP of 2088. Theoretical and experimental investigations are carried out on the performance of the condensation process within a mini-channel tube. Mini-channel heat exchangers technology allows reducing refrigerant charge and lets use flammable refrigerants. Due to the aspect ratio, high heat transfer coefficients are also registered. The experimental data recorded show that, for any given saturation temperature or refrigerant mass velocity, both the heat transfer coefficient and the frictional pressure gradient are always higher for R32. So, a numerical analysis based on the experimental data was developed to determinate which refrigerant performs better. The results of this numerical analysis show that, although at high refrigerant mass velocities R410A performs better, a given heat power can be always achieved with lower mass velocities and thus with a lower compressor power input when using R32. Therefore, it can be concluded that using R32 in a mini-channel condenser reduces the environmental impact and improves the energy efficiency of the system.

Abstract We present a mathematical model to diagnose HVAC systems in buildings based upon the analysis of a small number of ambient state variables. In particular, the equations of the model accurately fit recorded data of temperature, relative humidity and carbon dioxide concentration in different workplaces. For validation, data were obtained under different conditions and with different sensors. In particular, we designed and fabricated a wireless sensor that measures and transmits data to a remote device and we also applied our model to data collected using a commercial sensor. For each case, information was obtained that could be used to understand and predict the evolution of ambient variables that impact thermal comfort and energy consumption in buildings. The tools presented here can thus be of great interest to achieve affordable, smart energy-efficient buildings, while adhering to environmental laws and comfort for work spaces.

Abstract A Microgrid (MG) Energy Management System (EMS) is a vital supervisory control to make decisions regarding the best use of the electric power generation resources and storage devices within this MG. This paper presents an operational architecture for Real Time Operation (RTO) of an islanded MG. This architecture considers two different parts including Central Control Unit (CCU) and MG Testbed. CCU implements an EMS based on Local Energy Market (LEM) to control a MG. In order to reach this objective, this unit executes Day Ahead Scheduling (DAS) and Real Time Scheduling (RTS). Regarding DAS, a Modified Conventional EMS (MCEMS) based on LEM (MCEMS−LEM) algorithm has been proposed to find out hourly power set-points of Distributed Energy Resources (DERs) and customers. LEM is also presented in MCEMS−LEM to obtain the best purchasing price in Day-Ahead Market (DAM), as well as to maximize the utilization of existing DER. With regard to RTS, it must update and feedback the power set-points of DER by considering the results of DAS. The presented architecture is flexible and could be used for different configurations of MGs also in different scenarios. Simulations and experimental evaluations have been carried out using real data to test the performance and accuracy of the MG testbed. This paper aims to operate the MG in islanded mode, ensuring uninterruptable power supply services and reducing the global cost of generated power. Results demonstrate the effectiveness of the proposed algorithm and show a reduction in the generated power cost by almost 8.5%.

Abstract This work addresses the potential for waste energy recovery from exhaust gases in a diesel passenger car mounted in a chassis dynamometer. The New European Driving Cycle was followed, while recording relevant operating variables. Tests were performed under three temperature conditions, and exergy analysis was included to find the potential of exhaust gases to produce useful work at six points in the exhaust system. Results include mean temperature at each point, as well as the energy quality index, which was lower than 33%, meaning that less than one-third of the energy of exhaust gases can be converted into useful work in a recovery system. In general, the highest exergy losses were found in the muffler. Although the greatest recovery potential corresponds to the highest temperature of gases, environmental regulations for vehicles restrict waste energy recovery to be performed downstream after-treatment devices, which, in the present work, was the outlet of the diesel particle filter. Temperature of gases at this location varied in the range 115–320 °C, and potential fuel saving varied between 8% and 19% for the complete driving cycle.

A distributed energy system is a multi-input and multi-output energy system with substantial energy, economic and environmental benefits. The optimal design of such a complex system under energy demand and supply uncertainty poses significant challenges in terms of both modelling and corresponding solution strategies. This paper proposes a two-stage stochastic programming model for the optimal design of distributed energy systems. A two-stage decomposition based solution strategy is used to solve the optimization problem with genetic algorithm performing the search on the first stage variables and a Monte Carlo method dealing with uncertainty in the second stage. The model is applied to the planning of a distributed energy system in a hotel. Detailed computational results are presented and compared with those generated by a deterministic model. The impacts of demand and supply uncertainty on the optimal design of distributed energy systems are systematically investigated using proposed modelling framework and solution approach.