The installation of photovoltaic (PV) equipment is governed by a number of industry codes and standards. Electrical contractors need to be aware of the codes and standards to ensure a safe and functional PV installation. This article will briefly discuss the National Electrical Code (NEC) requirements as well as The Institute of Electrical and Electronics Engineers Inc. (IEEE) interconnection standards.

National Electrical Code

Even though PV arrays produce low-voltage direct current (DC) power, PV systems can be hazardous if not installed correctly and are therefore addressed in the NEC. In almost all applications, the low-voltage DC power produced by the PV array is converted to standard alternating current (AC) voltages to serve building loads and may also be interconnected with the utility grid through the building's service entrance.

Chapter 6 addresses special equipment and includes Article 690: “Solar Photovoltaic Systems.” Article 690 covers the wiring of the PV arrays as well as the installation of inverters and controllers. The method for determining the minimum conductor sizes and overcurrent device ratings throughout the PV system based on the characteristics of the PV panels, inverters and other equipment is provided Part II. Part III states the requirements for the location, rating and installation of disconnect switches throughout the PV system. Parts IV and V address PV-system wiring methods and grounding. Interconnection with the building's distribution system and ultimately the utility grid is covered in Part VII. Part VIII addresses the installation of storage batteries and chargers.

Article 705-“Interconnected Electric Power Production Sources”-applies to PV systems that are interconnected to other power sources such as the serving electric utility's system or on-site generator.

Interconnection standards

Connecting the facility's PV system to the serving utility's system provides a number of potential advantages to both the facility's owner and utility. A grid-connected PV system allows power to flow to and from the building depending on the building load at any instant relative to the amount of power being produced by the PV system. Excess power can be sold to the utility at a predetermined rate or exchanged for utility power when the facility has a power deficit such as at night. PV system output usually tracks utility demand. Its peak output occurs midday when the utility experiences its peak demand and the cost of utility power production is highest. A grid-connected PV system can also eliminate the owner's need to install expensive battery banks or backup generators that have ongoing operating and maintenance costs, which will make the PV system a less attractive investment.

A major barrier to grid-connected PV has been the lack of standards for interconnecting the facility's PV system with the utility's system. Different utilities, even with adjacent service areas, often have different policies and requirements for connecting on-site distributed generation to their systems. Two standards have been developed by the IEEE aimed at standardizing the requirements for interconnecting PV systems with the serving utility's system:

o 1547-2003: Standard for Interconnecting Distributed Resources with Electric Power Systems

o 929-2000: Recommended Practice for Utility Interface of Residential and Intermediate Photovoltaic (PV) Systems

IEEE Standard 1547 establishes recommended practices for interconnecting distributed generation technologies with the electric grid. The goal of these recommended practices is to promote the use of alternative energy sources and make connecting to the utility grid economical for the building owner.

IEEE Standard 929

IEEE Standard 929 specifically addresses the interconnection of photovoltaic systems generating 10 kilowatts or less to the utility grid but can be applied to PV systems of any size. Many utilities require that small- to medium-sized PV systems comply with the same interconnection requirements that apply to very large rotating generators such as those found in industrial cogeneration. These requirements are not practical for PV systems and can be a roadblock to PV installation. IEEE Standard 929 simplifies the PV system interconnection with the utility grid with the objective of safety for linemen, safeguarding the utility's equipment and protecting the utility customer. The use of PV inverters that comply with IEEE Standard 929 reduces the cost of meeting interconnection requirements and helps remove another barrier to widespread PV use.

This article is the result of a research project investigating the investigating the potential of the emerging PV market for the electrical contracting firm being sponsored by The Electrical Contracting Foundation Inc. The author would like to thank the foundation for its support. EC

GLAVINICH is an associate professor in the Department of Civil, Environmental and Architectural Engineering at The University of Kansas and is a frequent instructor for NECA’s Management Education Institute. He can be reached at 785.864.3435 or [email protected].