Distributed Energy Resources Affected Systems Study (DER AFS) Process

The DER AFS process begins with simplified technical screening: a transmission owner (TO) considering the amount of DER net injection and MISO verifying net injection before screening for changes in line loading levels. DER dispatch assumptions, the amount of DER considered to be injecting under peak and shoulder peak, follow existing MISO practices outlined in MISO Business Practice Manuals (BPM). MISO proposes reviewing DER impacts at a substation-level of granularity.

Should a DER or group of DER at a particular substation trigger screening criteria, MISO will include all DER at that substation in the next cycle of DER AFS studies. Existing DER will be included in the model to the extent that MISO is provided modeling information. MISO will perform studies with quarterly periodicity for the initial implementation. MISO will perform steady state voltage and thermal analysis for all DER included in the study. Voltage and thermal constraint criteria will align with existing MISO business practices.

DER Affected System Study Cycles occur on a quarterly basis. Key milestones, timelines, and dates are listed below.

DER being studied through DER AFS shall be submitted via email to DER-AFS@misoenergy.org.

The information shall be submitted in accordance with BPM-015, Section 8.3.2.3. The below template shall be submitted to describe the aggregate DER to be screened.

DER AFS data exchange template

Aligned with MISO’s objective for a practical and effective process transparency, MISO will post the below information to be publicly available and updated with each DER AFS cycle. The information will be reported for each DER Substation included in screening or study activities.

·        Transmission Owner

·        Total Studied DER Amount (MW)

·        Date of last MISO Screen

a.         (a) 1% Screen (Pass/Fail)

b.         (b) Net Injection (0 – 5 MW) Screen (Pass/Fail)

c.          (b) Net Injection (greater than 5 MW) Screen (Pass/Fail)

·        Ongoing AFS (Y/N)

·        Total Pending DER in current DER AFS

·        Number of completed DER AFS Studies

·        Upgrades Identified (Y/N)

While DER interconnection is wholly State-jurisdictional at this time, MISO’s offers guidance on how Electric Distribution Companies (EDCs) and Relevant Electric Retail Regulatory Authorities (RERRAs) could view implementation. As a general matter, MISO suggests RERRAs examine how MISO’s DER AFS may fit within existing State-jurisdictional affected system study interconnection practices and to what extent practices may need to be adapted or developed.

MISO expects the MISO DER AFS screening and study process to be triggered by new DER interconnection requests. Existing DER should be included for purposes of screening and study, but MISO’s DER AFS process transition does not equate to a MISO request to evaluate all existing DER Substations that might exceed the new criteria. Consistent with MISO’s understanding of common RERRA interconnection practices, existing DER is “grandfathered” using the interconnection requirements that were in place at the time of interconnection.

In terms of which new DER applications might be included in MISO’s first DER AFS cycle, MISO suggests EDCs and RERRAs consider a cutoff point associated with state-Jurisdictional steps such as application deemed complete, EDC screening, or the EDC’s distribution system impact study. These DER interconnection process steps often feed into transmission studies and affected systems studies and may be an appropriate demarcation point that does not require DER interconnection customers to move backwards, or pause, within the relevant interconnection process. MISO anticipates that DER Substations that trigger MISO’s screening criteria will also trigger EDC distribution impact studies.

Since MISO DER AFS reports will address impacts at the DER Substation level, EDCs and RERRAs may need to document to allocate costs arising from impacts. MISO understands cost allocation principals are likely in place across many RERRAs’ jurisdictions. However, a decision may be necessary to reaffirm and/or clarify application of existing principles (e.g., “cost causer pays”) or consider new principles such as allocating costs a pro rata share.

Growing DER interconnections with distribution systems across the MISO footprint necessitates a more formal process to consistently and effectively evaluate DER transmission system impacts. MISO views DER impacts on the transmission system as another form of an affected system study, a practice MISO carries out regularly at the regional electric system seams (e.g., MISO seam with Southern Power Pool).

MISO led a stakeholder process throughout 2022 to develop refined Distributed Energy Resource (DER) Affected System study (AFS) procedures and technical criteria to evaluate potential reliability impacts for new DER interconnection requests, while accounting for the aggregate DER already interconnected. The five meetings covered different DER topics MISO and produced presentation materials, stakeholder feedback, and MISO responses (Table 1).

Table 1: Summary of MISO IPWG DER topics in 2022

MISO uses a definition of DER that includes only resources capable of injecting power into an electric system, such as solar or storage. Controllable load is not included in the definition and is out-of-scope for MISO’s DER proposals.

MISO intentionally limits its process proposals to an AFS perspective and does not aim to address state-jurisdictional processes; MISO’s Federal Energy Regulatory Committee Order 2222 proposed technical review practices; broader DER modeling issues; or DER market participation.