# The Applications and Challenges of Digital Twin Technology in Smart Grids: A Comprehensive Review
## 3 Digital Twin Technology in Smart Grids  
### Evolution of Electric Grids Towards Digital Integration  
The development of the electric grid showcases a long-standing process of innovation and technological advancement. It began with the straightforward direct current (DC) systems that [PERSON] launched in 1882 at the Pearl Street Station in New York City. This evolution has led to the intricate smart and virtual power systems that we utilize today [65]. Despite DC's limitations in transmission distance and efficiency, the transition to alternating current (AC) systems, pioneered by [PERSON] and [PERSON], allowed for more efficient transmission over long distances and set the stage for modern electricity distribution starting in 1886 [66].  
As the 20 th century progressed, as shown in Figure 5, the grid evolved into a more complex network. The first industrial microgrid, conceptualized in 1960, proposed a decentralized, reliable grid capable of autonomous operation or seamless integration with existing power infrastructure, utilizing local energy resources [67]. This concept paved the way for the Virtual Power Plant (VPP) introduced in 1997, which aggregated distributed energy resources to enhance power generation and trading within the energy market, embodying flexibility and decentralization [68].  
Figure 5: Historical moments in electric grid evolution.  
The turn of the century marked significant advancements with the start of the smart grid, defined officially in 2007 by the Energy Independence and Security Act (EISA). Utilizing digital communications technology, smart grids improved the efficiency of energy use, reliability, and integration of other renewable sources [69]. The expansion of the Internet and the proliferation of connected devices ushered in the Internet of Things (IoT) by 2012, enhancing grid management through the interconnectedness of devices [70].  
Further expanding connectivity, the Internet of Everything (IoE) was introduced, incorporating not only devices but also data, people, and processes into grid management, allowing for unprecedented integration and smarter energy management. The adoption of DTs around 2020 has enabled the simulation, analysis, and optimization of the entire energy system, boosting grid resilience and sustainability [71].  
The electric grid constitutes an extensive system that delivers electricity. The electricity generated from multiple sources is distributed to consumers over broad areas, encompassing entire countries. This expansive network facilitates the generation of power from a diverse array of resources and efficiently manages a vast array of prosumers and consumers, even those located at great distances. It provides electricity at a relatively low cost, accommodating both expected and unexpected losses while fulfilling the demand for electricity. The progression of the electric grid has seen several advancements (Figure 6), moving from the conventional electric grid (CEG) to more sophisticated systems such as the smart grid (SG), microgrid (MG), Virtual Power Plant (VPP), and the Internet of Energy, each offering improvements in efficiency, reliability, and adaptability to modern energy needs.