Distributed generation | EPFL Graph Search

Distributed generation, also distributed energy, on-site generation (OSG), or district/decentralized energy, is electrical generation and storage performed by a variety of small, grid-connected or distribution system-connected devices referred to as distributed energy resources (DER). Conventional power stations, such as coal-fired, gas, and nuclear powered plants, as well as hydroelectric dams and large-scale solar power stations, are centralized and often require electric energy to be transmitted over long distances. By contrast, DER systems are decentralized, modular, and more flexible technologies that are located close to the load they serve, albeit having capacities of only 10 megawatts (MW) or less. These systems can comprise multiple generation and storage components; in this instance, they are referred to as hybrid power systems. DER systems typically use renewable energy sources, including small hydro, biomass, biogas, solar power, wind power, and geothermal power, and incr

Harvesting the ﬂexibility of energy communities from a DSO perspective

Antoine Zürcher

As non-controllable power sources, photovoltaics can create overvoltage and overloading in low voltage (LV) distribution feeders during periods of high generation and low demand. This is usually prevented passively by limiting the penetration level of PV to very conservative values, even if the critical periods rarely occur. Alternatively, one can use active power curtailment techniques, reducing the amount of active power injected by the PV inverters. In this way, it is possible to prevent overvoltage of the network buses and overloading of the network lines. This study investigates an approach for controlling the PV power generated in the town of Rolle, Switzerland, equipped with a large number of rooftop PV systems. Simulations of a one year period with typical solar irradiance and load proﬁles are conducted to assess the quantity of PV generation that needs to be curtailed to avoid violated constraints. A comparison between the economical loss of the curtailed power and the economical cost of the reinforcement of the grid to reach a safe operation of the network is proposed. This allows to give the distribution system operator an overview of which method is economically proﬁtable. The study shows that the curtailment of the PV systems is less proﬁtable than reinforcing the network.

2020

EPFL's District Heating Heat Pump - Performance Analysis for DIfferent Working Fluids

Sylvain Clément

The present case study is multi-criteria performance analysis of EPFL’s heat pump for different working fluids. The heat pump is based on a 2-stage vapour compression cycle which is modelled using the software Belsim VALI for 7 low-GWP refrigerants. The simulation of the heat pump over different typical periods allowed to estimate the yearly mean COP of the heat pump. R-600a, R-600 and R-717 are the refrigerants showing the higher thermal efficiencies (COP = 5.5-5.7) and thereby also the higher environmental and economical performances. According to the TEWI indicator, the leakages of low-GWP refrigerants are negligible compared to the CO2-eq. emissions from the electricity generation. The decrease in the isentropic efficiency when the heat pump does not work at its maximum capacity strongly affect the COP. Therefore it is recommended to implement a heat storage system to increase the number of operating hours without isentropic efficiency decrease.

2021

Distribution management system including dispersed generation and storage in a liberalized market environment

Elvira Kägi-Kolisnychenko

Distribution systems are now fundamentally changing. This is due to the fact that a lot of small size dispersed generation units (DG) are expected to be installed at the distribution level, that is, in the medium voltage (MV) and low voltage (LV) networks [1.1]. The problems arise from the current design features of distribution networks, which were not supposed to include energy sources. At this level, until now, the energy is bought from the wholesale market, transported through a transmission system and delivered to the customers through a distribution system. This primary objective is compatible with the arborescent operational network configuration, the conditions of protection and security assessment design, the wire characteristics, and also the type of customer service. Since the distribution grid is used strictly in open-loop mode and has no energy sources, the currents are unidirectional and consequently the top-down centralized management model is the strait-forward choice. With the introduction of dispersed energy resources, the network may need reinforcement and the grid protection schemes should be adapted to bidirectional energy flows [1.1, 1.2]. In this case, the amount of information to be treated centrally would grow considerably [1.3], due to the number of generation equipments inserted into the grid. Large amounts of data would need to be collected, treated simultaneously and provided quickly for further processing. The presence of stochastic energy sources and the reliance on the communication system could compromise the centralized grid operation and the security of supply. In this respect, the decentralized approach is adopted in this study to both energy management planning (day-ahead) and on-line operation. The decentralized energy management system is built using a multi-agent approach. This approach allows for the simultaneous integration of competition and collaboration among the actors. It is characterized by a high flexibility and robustness, while using minimum data exchange. Since generation sources at the MV/LV level are of relatively small capacity, their generation is normally consumed locally. This specificity and the arborescent topology (feeders with laterals) tend to create zones containing some local generation corresponding to local energy needs. The multi-agent approach is thus applied to clusters of active distribution networks at two levels: intrazonal and interzonal, based on an original definition of zones. This framework offers a partial autonomy to each cluster and allows for parallel optimization and for cooperation among several independent entities. The decentralized approach was successfully applied to several distribution network problems, such as: unit commitment and dispatch, voltage profile control and supply restoration after a blackout. It seems however evident from this study that an appropriate centralization degree should be preserved in order to maintain an adequate system operation.

EPFL2009

Distribution management system including dispersed generation and storage in a liberalized market environment

Elvira Kägi-Kolisnychenko

EPFL2009