1. Interconnection Procedures

As explained in Chapter III.A, the manner in which export is managed is likely to be a critical aspect of interconnection review for many ESS in the coming years. Furthermore, it is likely that a significant number of all future interconnection applications to the distribution system are going to include an energy storage component. For this reason, it is important that interconnection procedures be updated to more clearly and deliberately address what types of export controls are safe and reliable and can therefore be proposed as part of an interconnection application without triggering the need for additional customized review.

Relying on customized review of the export controls for each and every interconnection application is a significant barrier for ESS. Customized review deprives applicants of the certainty they need to design an application to meet utility and distribution system requirements from the start. Customized review also requires additional utility time and resources for each application. Most importantly, however, as discussed in the preceding sections, there are a number of export control methods that are already widely accepted for use. Those that are newer, like PCS and the configured power rating, can also be trusted because they rely on equipment whose functionality has been certified. Non-standard types of export control equipment will continue to need customized review, but it is reasonable to update interconnection procedures to identify a list of acceptable methods that can be trusted and relied upon by both the interconnection customer and the utility.

A section on acceptable export control methods provides a foundation upon which other important interconnection rule and process changes can be made that ensure that ESS are screened and studied safely and efficiently. As discussed further in Chapter IV, in order to screen and/or study projects, utilities need to know, with confidence, how much the proposed project will export. In most states today, the existing approach is that the utility assumes the project will export the full nameplate (or combined nameplate) of the DER equipment. In order to evaluate a project as exporting anything less than the full combined nameplate, a utility must have clear information, and confidence, in the manner in which the DER limits export. This confidence can be achieved by providing a pre-approved list of methods which are considered acceptable.

This Toolkit recommends that interconnection procedures include a distinct section defining acceptable export methods and provides model language that states can use. The model language can be incorporated into all different styles of interconnection procedures with only minor modifications.

The model language, which is provided in the following Chapter III.E.2, accomplishes the following things:

  • It establishes that if an applicant uses one of the export control methods specified in its application, then the Export Capacity specified in the application will be used by the utility for evaluation during the screening and study process. It also makes clear that the Export Capacity identified in the application will be considered a limitation in the interconnection agreement.
  • It identifies six different acceptable export control methods. The methods identified are those described above in Chapter III.C and III.D and in Table 1[3]  below. The methods are organized by whether they can be used for non-export, limited-export, or for both (as shown in the following table). Settings and response times are identified where necessary.
  • It also includes a seventh export control option that allows for the use of any other method (beyond the six specifically identified methods), so long as the utility approves its use. In other words, this provision allows for customized review of any export control methods that do not meet the criteria of one of the six pre-identified acceptable methods.

Table 1. Acceptable Export Control Methods

* ANSI((The American National Standards Institute (ANSI) is a private non-profit organization that oversees the development of voluntary consensus standards for U.S. products and services. ANSI accredits standards developed by others that ensure consistency in product performance and conformance with testing protocols.)) device numbers are listed in parentheses, as defined by IEEE C37.2 IEEE Standard Electrical Power System Device Function Numbers, Acronyms, and Contact Designations.

2. Recommended Language

In order to recognize the controllable nature of ESS in interconnection review, PCS should be included in the list of eligible export controls, and the limits set by the PCS should be considered as enforcing the Export Capacity. Having a certified PCS allows smaller systems to incorporate a limit without an additional extensive review process. It is reasonable to require utilities to rely on the capabilities of certified devices. Some systems may be made up of components from different manufacturers, which are more challenging to certify through a Nationally Recognized Testing Laboratory (NRTL). Therefore, some allowance for non-certified PCS, which the utility agrees meets the export control requirement, should also be provided for. Assurance for non-certified systems may be provided through other utility evaluations, potentially including field testing.

The early interconnection rules incorporating PCS (such as Hawaii Rule 22 and California Rule 21) included detailed technical requirements. As of this writing, the technical requirements in those rules are now out of alignment with the way PCS is defined and tested per the UL CRD. This can be problematic for the evaluation of equipment since the certification will not match the rule’s required capabilities. To maintain alignment, most detailed technical requirements should defer to the UL CRD and UL 1741, and any high-level performance requirements in interconnection rules should align fully with the UL CRD and UL 1741.

For enabling export controls more broadly, interconnection procedures should be revised to include the following model language. For interconnection procedures based on SGIP, this section replaces SGIP Section 4.10 titled Capacity of the Small Generating Facility (section 4.10.1 would remain). In interconnection procedures that use a level-based approach (like IREC’s Model), this section would fit best in a section on general requirements that applies to all projects regardless of the review level (such as section IV of IREC’s 2019 Model).

Section 4.10 – Export Controls

4.10.2 If a DER uses any configuration or operating mode in subsection 4.10.4 to limit the export of electrical power across the Point of Interconnection, then the Export Capacity shall be only the amount capable of being exported (not including any Inadvertent Export). To prevent impacts on system safety and reliability, any Inadvertent Export from a DER must comply with the limits identified in this Section. The Export Capacity specified by the interconnection customer in the application will subsequently be included as a limitation in the interconnection agreement.

4.10.3 An Application proposing to use a configuration or operating mode to limit the export of electrical power across the point of interconnection shall include proposed control and/or protection settings.

4.10.4 Acceptable Export Control Methods Export Control Methods for Non-Exporting DER Reverse Power Protection (Device 32R)

To limit export of power across the point of interconnection, a reverse power protective function is implemented using a utility grade protective relay. The default setting for this protective function shall be 0.1% (export) of the service transformer’s nominal base Nameplate Rating, with a maximum 2.0 second time delay to limit Inadvertent Export. Minimum Power Protection (Device 32F)

To limit export of power across the point of interconnection, a minimum import protective function is implemented using a utility grade protective relay. The default setting for this protective function shall be 5% (import) of the generating unit’s total nameplate capacity, with a maximum 2.0 second time delay to limit Inadvertent Export.  Relative Distributed Energy Resource Rating

This option requires the DER facility’s nameplate capacity to be so small in comparison to its host facility’s minimum load that the use of additional protective functions is not required to ensure that power will not be exported to the electric distribution system. This option requires the DER facility’s nameplate capacity to be no greater than 50% of the interconnection customer’s verifiable minimum host load during relevant hours over the past 12 months. This option is not available for interconnections to area networks or spot networks. Export Control Methods for Limited-Export DER  Directional Power Protection (Device 32)

To limit export of power across the point of interconnection, a directional power protective function is implemented using a utility grade protective relay. The default setting for this protective function shall be the Export Capacity value, with a maximum 2.0 second time delay to limit Inadvertent Export.  Configured Power Rating

A reduced output power rating utilizing the power rating configuration setting may be used to ensure the DER does not generate power beyond a certain value lower than the nameplate capacity. The configuration setting corresponds to the active or apparent power ratings in Table 28 of IEEE Std 1547-2018, as described in subclause 10.4. A local DER communication interface is not required to utilize the configuration setting as long as it can be set by other means. The reduced power rating may be indicated by means of a Nameplate Rating replacement, a supplemental adhesive Nameplate Rating tag to indicate the reduced Nameplate Rating, or a signed attestation from the customer confirming the reduced capacity.  Export Control Methods for Non-Exporting DER or Limited-Export DER   Certified Power Control Systems

DER facilities may use certified Power Control Systems to limit export. DER facilities utilizing this option must use a Power Control System and inverter certified per UL 1741 by a nationally recognized testing laboratory (NRTL) with a maximum open loop response time of no more than 30 seconds to limit Inadvertent Export. NRTL testing to the UL power control system certification requirements decision shall be accepted until similar test procedures for power control systems are included in a standard. This option is not available for interconnections to area networks or spot networks.   Agreed-Upon Means

DER facilities may be designed with other control systems and/or protective functions to limit export and Inadvertent Export if mutual agreement is reached with the Distribution Provider.((SGIP includes the term “Transmission Provider” in place of “Distribution Provider” in its model interconnection procedure language because it was adopted as a pro forma for transmission providers under FERC jurisdiction. However, states typically change it to “Distribution Provider” or another term when applicable.)) The limits may be based on technical limitations of the interconnection customer’s equipment or the electric distribution system equipment. To ensure Inadvertent Export remains within mutually agreed-upon limits, the interconnection customer may use an uncertified Power Control System, an internal transfer relay, energy management system, or other customer facility hardware or software if approved by the Distribution Provider.


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