Voltage Regulation Performance of Centralized and Decentralized Solar PV in Weak Radial Distribution Networks: A Multi-Voltage Case Study of the Zaria System

Abstract

The increasing penetration of solar photovoltaic (PV) systems presents both opportunities and operational challenges for weak radial distribution networks, where voltage regulation is often constrained by long feeder lengths and limited control infrastructure. This paper presents a simulation-based comparative assessment of centralized and decentralized solar PV integration in the Zaria Area distribution network, Nigeria. A detailed utility-based network model was developed in PSS®SINCAL, and steady-state load flow analyses were conducted under three scenarios: base-case operation, centralized PV integration via a 50  MW plant connected at the transmission–distribution interface, and decentralized PV deployment distributed across selected medium and low-voltage buses. Voltage profiles were evaluated at the 33  kV, 11  kV, and 0.415  kV levels. The results show that centralized PV integration improves upstream voltage conditions and reduces overall undervoltage severity but offers limited support at electrically remote feeder ends. In contrast, decentralized PV deployment provides superior end-of-line voltage improvement across all voltage levels due to localized generation and reduced feeder loading. These findings demonstrate that, for weak radial distribution networks, decentralized PV integration is more effective for improving customer-side voltage quality, while centralized PV remains advantageous for bulk power injection and upstream voltage support. The study provides practical planning insights for distribution utilities considering high PV penetration under weak grid conditions.