Analysis of the simultaneity factor in photovoltaic systems for prosumers with different consumption patterns

Abstract

Since the enactment of Law No. 14,300/2022, which updated the rules for distributed generation in Brazil, anyone who purchases a photovoltaic system connected to the grid must pay a portion of the energy tariff on the energy injected into the grid and offset. However, the energy generated during the day and consumed at the same time is exempt from any tariff, as it is not injected into the energy meter. Because of this, the so-called simultaneity factor, which represents the fraction of the energy generated that is consumed instantly by the prosumer unit (UP) itself, directly impacts the value of the energy bill and, consequently, the time to return on investment. This study aims to determine average simultaneity values ​​in UPs with different consumption patterns in the state of Tocantins and assess their impact on the time to return on investment. To this end, a case study is conducted with 86 UPs, classified into four distinct consumption profiles: Daytime, Nighttime, Full-time, and Nighttime with weekends (Nighttime+WEEKENDS).  Energy consumption and generation data are  collected at 30-day intervals over the course of a year and then processed using spreadsheets that calculated the simultaneity factor for each profile. Subsequently, a financial analysis is applied to estimate the return on investment time based on the average simultaneity rates of each consumption profile and the current tariff rules. The results indicate that UPs with predominantly daytime consumption have the highest simultaneity factors (average of 60%) and, consequently, the shortest return on investment times, although the difference between the profiles is not extremely significant. These findings reinforce the importance of considering the consumption pattern when planning photovoltaic systems.