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AbstractThis paper adopts a single-period newsvendor model with supply uncertainties to be used for optimally sizing an electrical energy storage system (EESS) for an apartment house with a photovoltaic (PV) system. Hence, typical inventory cost components and supply chain characteristics are translated to the EESS application. The results show that inventory management and energy storage can be aligned. The optimal size of the EESS takes into account the total cost of the storage system including energetic losses as well as the costs for energy supply from the own energy systems and from the energy supplier.

Vortex generators (VGs) are passive flow control devices commonly employed to prevent flow separation on wind turbine blades. They mitigate the damaging fatigue loads resulting from stall while increasing lift and consequently lead to rotor torque increase. This work summarizes a research project aimed at optimizing the sectional as well as the full rotor-blade aerodynamics using VGs. The effects of chordwise position, spanwise spacing and VG size were studied with force balance measurements of a 2D wing section. Reducing the distance between adjacent VGs produced large increases in the static stall angle and maximum lift, but also resulted in a significant increase in drag as well as sharp lift excursions at angles exceeding the static stall angle. The optimal chordwise position of the vortex generators was found to be in the range of x/c = 15%–20%, where a comparatively low parasitic drag and a smooth post-stall lift curve were achieved. Particle Image Velocimetry measurements were conducted at various chordwise positions to provide insight into the interaction between adjacent streamwise vortices. The experimental aerodynamic performance curves of the optimal VG configuration were used to project their effect on wind turbine blade aerodynamics. Three different rotorblades were designed and several stall and pitch regulated wind turbine models were simulated by means of a Blade Element Momentum (BEM) code (QBlade) developed by Smart Blade GmbH. The performance of the rotorblades with and without VGs was simulated in order to assess their effect on the aerodynamic performance and loads. Finally, previously measured steady state performance curves under high-roughness conditions were used to simulate the detrimental effect of surface roughness on the performance of the aforementioned rotorblades. This allows for an estimate of the potential of the VGs to be employed as retrofit elements for performance recovery of blades with a contaminated surface.

Increasing wind capacity and capacity factors (CF) are essential for achieving the goals set by the Paris Climate Agreement. From 2010–2012 to 2018–2020, the 3-year mean CF of the global onshore wind turbine fleet rose from 0.22 to 0.25. Wind turbine siting, wind turbine technology, hub height, and curtailed wind energy are well-known CF drivers. However, the extent of these drivers for CF is unknown. Thus, the goal is to quantify the shares of the four drivers in CF development in Germany as a case. Newly developed national power curves from high-resolution wind speed models and hourly energy market data are the basis for the study. We created four scenarios, each with one driver kept constant at the 2010–2012 level, in order to quantify the share of a driver for CF change between 2010–2012 and 2019–2021. The results indicated that rising hub heights increased CF by 10.4%. Improved wind turbine technology caused 7.3% higher CF. However, the absolute CF increase amounted to only 11.9%. It is because less favorable wind turbine sites and curtailment in the later period moderated the CF increase by 2.1% and 3.6%, respectively. The drivers are mainly responsible for perennial CF development. In contrast, variations in wind resource availability drive the enormous CF inter-annual variability. No multi-year wind resource change was detected.

Abstract In many European countries the production of combined heat and power based on renewable energies is well established though the efficient and economical operation of such plants remains a challenging task. This also applies to the existing district heating network at Baden-Dattwil (Switzerland) where a conventional gas boiler is substituted by a wood-fired boiler comprising an Organic Rankine Cycle. An overall control strategy that allows fully exploring governmental incentives is therefore of paramount importance. In addition, the highly fluctuating heat demands combined with the thermal inertia of the different plant components impose demanding requirements to the control system to guarantee a stable as well as highly efficient operation. The overall control concept is successfully tested and verified by means of dynamic simulations of the overall plant with a simplified model for the district heating network. The models are implemented using the object oriented modeling language Modelica. The overall model is based on open source Modelica libraries such as ThermoCycle, Modelica Standard Library and StateGraph2 as well as on own Modelica models. The overall model is prepared to be coupled to the real plant control system which will allow virtual commissioning in the next step. This allows pre-tuning of control parameters as well as a weakness analysis which again helps to speed up the commissioning process. In General, the dynamic simulations proved to be a useful tool that deepened the insight and understanding of the plant operation at an early project phase and therefore greatly supported the making of design decisions. After commissioning, the calibrated simulation models will be used for monitoring purposes.

Photovoltaic thermal (PVT) solar collectors can be an effective solution for system output improvement. Photovoltaic thermal collectors naturally have a more expensive receiver than simpler photovo ...

A simulation program of the arc quenching process in gas circuit breakers was developed. The program calculates the thermodynamic quantities of the gas as a function of time taking into account all spaces concerned with the arc quenching process such as the puffer cylinder, the arc space and the exhaust space. The simulation program was verified by experiments carried out on two model breakers. As an important result of the simulation, a new arc quenching principle is proposed based on self-flow generation without puffer action. The feasibility of the principle was confirmed experimentally.

An empirical model of global solar irradiance (EMGSI) under all sky conditions was developed by using solar radiation and meteorological parameters at Sodankylä. The calculated hourly global solar irradiance is in agreement with that observed at the ground during 2008–2011 and at the top of the atmosphere (TOA). This model is used to calculate the global solar irradiance at the ground and its attenuation in the atmosphere due to absorbing and scattering substances in 2000–2018. The sensitivity test indicates that the responses of global solar irradiance to changes in water vapor and scattering factors are nonlinear and negative, and global solar irradiance is more sensitive to changes in scattering (expressed by the scattering factor S/G, S and G are diffuse and global solar radiation, respectively) than to changes in water vapor. Using this empirical model, we calculated the albedos at the TOA and the surface, which are in agreement with the satellite-retrieved values. A good relationship between S/G and aerosol optical depth (AOD) was determined and used to estimate AOD in 2000–2018. An empirical model for estimation of tropospheric NO2 vertical column density (VCD) was also developed and used to calculate tropospheric NO2 VCD in 2000–2018. During 2000–2018, the estimated global solar irradiance decreased by 0.92%, and diffuse irradiance increased by 1.28% per year, which is ascribed to the increases of S/G (1.73%) and water vapor (0.43%). Annual surface air temperature increases by 0.07 °C per year. Annual mean loss of global solar irradiance caused by absorbing and scattering substances and total loss are 1.94, 1.17 and 3.11 MJ m−2, respectively. Annual mean losses of absorbing and scattering global solar irradiance show negative and positive trends, respectively, and the annual total loss increases by 0.24% per year. Annual mean losses due to absorption were much larger than those due to scattering. The calculated albedos at the TOA are smaller than at the surface. The calculated and satellite-retrieved annual albedos decrease at the TOA and increase at the surface. During 2000–2018, annual means of the AOD and the tropospheric NO2 VCD increased by 8.23% and 0.03% per year, respectively.

Recently, there has been great interest in the integration of Distributed Energy Resources (DER) at the distribution level. DERs are potentially valuable providers of ancillary services such as load following and contingency reserve in distribution systems. This will require new control strategies for coordinating their system performance. One issue that has not been addressed sufficiently is the coordinated dispatch of large numbers of DERs under normal operation or system outage. In this paper, an AGC type control strategy is proposed and implemented for the real time control of DERs. Simulation results show that DERs are capable of providing load following and contingency reserve services under the proportional control mode or competitive control mode.