Interconnection

The Opportunity

The inverter, isolation transformer, and isolation breakers for the 17 kW PV system at Pennsylvania DEP’s Cambria office building. Credit: Robb Williamson, NREL Contract Photographer. NREL Pix10999 (www.nrel.gov/data/pix)

While solar photovoltaic (PV) systems have been successfully connected to the utility grid millions of times around the world, utilities are still cautious about how these variable power sources affect safety, reliability, power quality and cost to the end user.  Utilities are also concerned about net metering, which is increasing in prevalence throughout the United States.  Variable payments to end users for their excess generation changes a utility’s business model, and a lack of useful data can make it difficult for utilities to evaluate required policies.  In addition, utility interconnection procedures differ throughout the country, which leads to inefficiencies and higher costs for installers, utilities, and solar customers.

Fortunately, these issues have been studied extensively.  There are many resources available to regulators and utilities to help identify potential solutions and facilitate the design of safe and efficient interconnection processes.

Approaches

In the United States, there are currently four major interconnection standards in effect that apply to distributed PV systems under 2 megawatts (MW):

—     California Rule 21

—     Mid Atlantic Demand Resource Interconnection Procedures (MADRI)

—     Interstate Renewable Energy Council (IREC) Model Interconnection Procedures

—     Federal Energy Regulatory Commission’s Small Generator Interconnection Procedures

A report by the Solar America Board for Codes and Standards (Solar ABCs) provides detailed review and comparison of these four sets of commonly-used interconnection procedures.  The Solar ABCs’ report determined that to provide a “suitable framework,” the IREC model standard provides the most comprehensive and effective approach to common utility concerns.

The states of California and Hawaii worked with IREC to implement enhanced interconnection procedures, including an improvement to California’s Rule 21, which specifies standard interconnection, operating, and metering requirements for distributed energy resource generators.  Both states recognized that the 15% peak load limitation for fast-track interconnection was not necessary in all situations or for all circuits.  Each state implemented eligibility criteria beyond the 15% peak load limitation, enhancing the opportunities for PV installations while still ensuring safety and reliability.  The efforts of these two states demonstrate the effectiveness of employing a uniform standard and customizing it to accommodate regionalized needs.

Benefits

Interconnection procedures are intended to provide safe, rational means to connect renewable power to the grid.  However, different regions of the United States currently have widely variable interconnection standards, which can discourage national developers and installers from pursuing PV in certain regions.  In addition, some areas of the United States have interconnection procedures that are complicated and cost-restrictive.  Developing a national interconnection standard would help alleviate these barriers through efficiency, uniformity, and economies of scale.  Even without a national standard, utilities that want to (or are required to) develop solar-friendly processes could save personnel time by adopting the IREC model standard or a similar model with appropriate regional adjustments.   Public Utility Commissions (PUCs) often open rulemaking panels and workshops when discussing interconnection rules. The IREC model standard can provide PUCs and other rule-making bodies with a proven, defensible framework for updated rules.  Uniformity in the proposed standard could also optimize the opportunity for installers to engage in the rule-making process, since they will have experience and expertise in a specific set of guidelines and can address them readily in PUC panels and workshops.

Features

Several features of the IREC model distinguish it from other interconnection procedures include:

  • Fast-track process for residential PV (inverter-based) systems (low cost, shorter time)
  • Fast-track process for systems up to 2 MW
  • Standardized agreements for different tiers
  • Insurance provisions reflective of risk
  • Accounts for interconnection to Area Networks and Spot Networks
  • External disconnect switch cannot be required at customer expense (for systems <10kW)

Successes

IREC has participated in the successful development of interconnection rules in Washington, D.C., and numerous states including California, Colorado, Florida, Hawaii, Illinois, Iowa, Maryland, Massachusetts, New Mexico, New York, North Carolina, and Utah.  The Database of State Incentives for Renewables and Efficiency (DSIRE) includes a summary of interconnection standards by state.

Education

Solar 3.0 offers PV Installation Requirements and Codes workshops and webinars that include information about interconnection standards for PV.  Check the Events Calendar to see when the next training opportunities are coming up.

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