Risk analysis of islanding of photovoltaic power systems within low voltage distribution networks home > publications > reports >
Last updated: 27 December 2002

Authors: Cullen, Neil (1)
Thornycroft, Jim (2)
Collinson, Alan (3) 		Risk analysis of islanding of photovoltaic power systems within low voltage distribution networks
Organizations: Freelance Consultant, Hillside House, Swindon, UK SN1 3QA (1)
Halcrow Group Ltd, Burderop Park, Swindon, UK SN4 0QD (2)
EA Technology, Capenhurst Technology Park, Chester, UK CH1 6ES (3)
Type: Report IEA  PVPS Task 5
Reference: IEA  PVPS T5-08: 2002
Date of issue: March 2002
Details: 21 p.: figures, graphs; with references and appendices
Download: Open or download this report as PDF document (805 kB)
Available from: Task 5 members or Operating Agent of Task 5
Abstract: It is generally accepted that grid interconnection of photovoltaic (PV) power generation systems enables effective utilization of the generated power from PV. However, technical requirements of both the utility power system grid and the PV system must be satisfied to ensure the safety of the PV operator and the reliability of the utility grid. Clarifying the technical requirements for grid interconnection and solving the problems are therefore very important issues for the widespread application of grid-connected PV systems. The requirements for grid-connected systems are closely related to the configuration and operational regime of the power distribution system, which are often country-specific. However, one of the technical issues of concern that is common to all network operators around the world is that of islanding.
  The purpose of this study was to apply formal risk analysis techniques to the issue of islanding of photovoltaic power systems within low voltage distribution networks. The aim was to perform a first pass calculation to determine the additional level of risk that islanding could present to the safety of customers and network maintenance staff. In the event of a loss of mains supply, grid-connected PV systems are required to automatically disconnect from the grid in order to prevent the network from islanding. This study has identified the reliability required of the islanding detection and control systems and their installation, based on standard procedures for developing a safety assurance strategy.

The main conclusions from the study are:

  • The “benchmark” risk that already exists for network operators and customers is of the order of 10-6 per year for an individual person
  • The risk of electric shock associated with islanding of PV systems under worst-case PV penetration scenarios to both network operators and customers is typically <10-9 per year
  • Thus, the additional risk presented by islanding does not materially increase the risk that already exists as long as the risk is managed properly
  • Loss of mains (LOM) protection functionality provides additional safety, up to a point:
    • An inverter’s designed safety integrity level (SIL) affects the level of risk
    • The quality of the installation and any subsequent maintenance will also affect the risk
  • There is a need to inform and educate both network operators and customers about the implications of the use of PV as an embedded micro-generator, as PV systems become more widespread.
It is recommended that:
  • Since LOM functionality is included in many PV inverters already, it is appropriate to maintain this requirement, but emphasis should be put on simple, robust, verifiable and costeffective solutions (e.g: software-based).
  • The findings of this report should be:
    1. incorporated into the training and education programmes of network operators and PV system installers
    2. reviewed by appropriate interconnection standards working groups
    3. publicized in appropriate professional institutional journals and subjected to thorough public peer review
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