# Effects of On-Site PV Generation and Residential Demand Response on Distribution System Reliability
## 1 Introduction  
### Motivation and Background  
Power system reliability can be evaluated as one of the most important factors in the operation, planning, and design process of the utility network and sometimes state-regulated area. This complicated architecture including numerous different types of loads, transformers, substations, switching components, and long transmission lines targets to supply hundreds of millions of electricity consumers' daily needs in a reliable fashion. The North American Electric Reliability Corporation (NERC), one of the most widely-known institutions, has provided a definition for reliability as [1]_\"the ability to meet the electricity needs of end-use customers even when unexpected equipment failures or other factors reduce the amount of available electricity\"_. Additionally, from European energy providers' viewpoint, European Network of Transmission System Operators (ENTSO-E) provided the widely-known definition as _\"a general term encompassing all the measures of the ability of the system,generally given as numerical indices, to deliver electricity to all points of utilization within acceptable standards and in the amounts desired\"_[1]. Recently, increasing environmental concerns and growing demand paved the way for expanding the portion of renewable-based energy systems on the generation side, ensuring reliable, sustainable, and resilient power grid operation [2]. In order to reduce greenhouse gas emissions, there have been great attempts and incentives within the context of signing protocols by most of the countries. Among them, Malta and Sweden target to increase the installed renewable energy resources (RESs) capacity respectively by 10% and 49% [3]. The European Council has agreed on the 2030 climate and energy framework, including targets and policy objectives. Particularly, reducing greenhouse gas emission at least by 40% compared to the level of 1990, increasing renewable energy consumption rate at least 32%, and improving energy efficiency level by 32.5% are the key targets for 2030 [4]. According to the Renewable Energy Roadmap (Remap) 2030 [5], the world's biggest energy consumer, China, is aiming to increase the share of renewables in the power sector from 20% to 40% by 2030. It is obvious that it requires a market reform as well as significant growth in transmission and grid capacity. There are many types of renewable energy resources in the energy sector, such as wind, solar, hydro, and biomass [5]. Among them, photovoltaic (PV) generation is accepted as one of the most prominent sources, and its globally installed capacity is increasing day by day considering technological developments and economic achievements, especially for implementing at the scale of distributed generation (DG). This green resource can be installed at a large-scale in utility facilities or at a small-scale at the end-users' premises with the aim of meeting the local demand. It is to be highlighted that grid-connected units can play a key role in system operation, especially in case of failures in any part of the system and in providing reliability improvement by decreasing unsupplied power. From the other perspective, demand side has also witnessed spectacular changes in its architecture, e.g., prosumers (consumers also with on-site production facilities) with flexible loads are strongly encouraged to alter their load profiles for the purpose of accomplishing particular objectives such as load leveling, reliability enhancement, and voltage regulation within the paradigm of smart grid. Unlike the conventional network operation in which expanding generating capacity means to increase reserve margin and reliability factor [6], modern structure turns its perspective from the power supply side to the demand side.