The notion of connecting small generating units with the power system has received a lot of interest. Such distributed generation (DG) is critical in strengthening the capacity of major generating power plants to meet rising electricity demand. Unlike main power options, DG may be readily attached and removed from the network, allowing for greater flexibility. Economic savings through reduced power losses, increased system reliability and better power quality are just a few of the advantages of properly built and managed DG plants.
Nevertheless, higher DG penetration without harmonization among generating units may result in increased grid power losses, unattractive voltage profiles, inefficient protection device performance and a mismatch between real power usage and generation. As a result, distributed energy resources units must be accessible to the system operator in order to ensure the most cost-effective functioning of the main power system.
Introduction
The adverse effects of uncontrolled DG penetration are the driving force behind the emergence of virtual power plant (VPP) concepts. VPP technology denotes the grouping of DG units, storage devices connected to a specific cluster, and controlled loads into a single conceptual entity (single power plant) in charge of controlling the flow of electrical energy inside the cluster as well as in exchange with the main system. Previously, distributed energy resources were deployed in a "fit and forget" manner and were inaccessible to system operators. VPP combines all distributed energy resources into a single body, allowing them to have system accessibility, controllability and market influence in the same way as transmission-connected generators.
Architecture
VPPs contain three key components: energy storage systems, distributed energy resources and information and communication technology (ICT).
Energy storage system
The energy storage system and its components play a critical role in removing the gap between generation and demand, particularly where stochastic (variable) generation is prevalent. Energy storage elements in VPPs can store energy during off-peak hours and then feed it back during peak hours. It can also shift the output power of wind turbines and solar panels all through the day and in the most efficient way possible. The energy storage system can be categorized based on its intended use, such as whether it is supplying power or energy. For example, supercapacitors are power-supplying energy storage systems and compressed air energy storage systems are energy suppliers.
Distributed energy resources
Distributed energy resources may include controllable loads or distributed generators integrated with the main power grid. DG inside VPP grounds may be categorized depending upon the generating capacity, the kind of the principal power source, their owner and their operational nature. The generating capacity can be small-, medium- and large-scale units. The small-scale units are bound to be connected with VPPs, however, medium- and large-scale units have free will and can choose if they want to be integrated with VPPs to secure optimal revenue stability. Depending upon the type of power sources, there may be distributed generators that use renewable energy sources and are known as photovoltaic array-based generators or wind-based generators.
The ownership of distributed generators also defines their duties. For example, commercial, residential and industrial owners use distributed generators to provide some or all of their load demand in their own facilities. Similarly, distributed generators operated by utilities are utilized to help with the main grid supply deficit and are sometimes referred to as public distributed generators. In terms of operational nature, DG systems may be stochastic in nature if based on photovoltaics or wind energy because they are dependent on a changing input resource, making the output power vary accordingly. To address this problem, such distributed generators are provided with battery storage so that the output power may be controlled.
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ICT technologies
The ICT system's heart is the energy management system. It controls the working of other VPP components using bidirectional communication technologies. In general, the energy management system is responsible for gathering data on the status of each component within the VPP; forecasting the key sources of renewable energy and their production power; controlling the flow of power between VPP components; load forecasting and management; and controlling the working of storage systems, controllable loads and DG. All this is done in accordance with a certain aim such as minimization of power losses or electricity prices or improvement of power quality.
Conclusion
A VPP is a comparatively recent but appealing concept that requires much research in order to be implemented. Generally, it combines energy sources of different types with energy storage devices and communication technologies in order to optimize the operation of a power system. This article introduces the concept of VPPs, their components and the relationship between its key elements. VPPs are the future and their engagement in other energy service markets, such as carbon trading, auxiliary services and so on can be a significant contribution.
