Interconnection Capacity Solutions: Right vs. Wrong Data

The biggest bottleneck for US renewable energy developers today is grid capacity. The grid is congested across the U.S., and while many projects are submitted to interconnection queues, a significant majority never see the light of day. The primary reason? Grid capacity limitations.

The US grid is managed by various regional grid operators, Independent System Operators (ISOs), and Regional Transmission Organizations (RTOs), ensuring sufficient power for all our energy needs. This includes projecting grid capacity and determining which projects to bring online to meet demand, as well as identifying necessary system upgrades to support new connections and ensure grid reliability. Each ISO and RTO has unique procedures and practices to evaluate new connections within their footprint.

Given the congestion in the grid, it is more important than ever to evaluate transmission and capacity constraints for project developers. Developers are increasingly seeking ways to model the electricity grid to determine their projects' viability prior to filing for interconnection.

It is crucial to understand grid capacity and interconnection costs to maximize project success. However, there are better and worse ways to model the grid. While there may be some value to directional analysis, it is important to realize the tradeoffs in accuracy.

The proper way to conduct this analysis is by conducting powerflow modeling studies based on each grid operator’s specific criteria to produce accurate and credible results.

This article is designed to help developers:

• ​Outline proper modeling practices that will enable maximum project success
• ​Understand different types of “capacity analysis” you may encounter in the market
• ​Outline various types of sub-par analysis and the pitfalls of using this information

Grid operators’ new power connection evaluation process

As a developer, your ultimate goal when assessing capacity is understanding how the grid operator will evaluate your project in the queue. The way to do this is by mirroring their modeling protocols to ensure that the analysis is fully aligned. In order to mimic their process, the first step is to understand their methodology. Best practice is to only evaluate capacity solutions that mirror their approach.

Accurate insights into interconnection capacity across various substations and transmission lines are crucial for making informed decisions early and at the least possible cost.

Grid operators’ new power connection evaluation process

Grid operators meticulously evaluate new power connections by thoroughly examining the electrical system. Here's the process:

1. 1.Simplified computer models of the entire power grid, referred to as base cases, are created. These models simulate how the actual grid might respond in various scenarios and aid in planning for new connections.
2. 2.Computer programs designed for power grids (such as TARA, PSS/E, and Powerworld) are employed to test these models.
3. 3.The normal operation of the grid (N-0/base case conditions) and potential breakdowns (contingency condition or N-1) are evaluated.
4. 4.Models for both present and future scenarios are developed, considering new power plants (queue), decommissioning of old power plants (retirements), anticipated power consumption (load), and modifications to the power grid (planned upgrades).
5. 5.The impact of new connections on the grid under both normal and problematic conditions is analyzed.
6. 6.Plans for projects to address any existing or potential issues are created to ensure an uninterrupted power supply.

While each grid operator follows this general process, the detailed steps vary greatly from one grid operator to another. It is necessary to follow both this general process as well as the detailed technical steps of each grid operator to model their grids effectively.

These methods can determine system capacity, identify potential constraints, and calculate upgrade costs necessary to ensure system reliability when assessing new project interconnections. The only accurate way to evaluate capacity is by adhering to the same procedures employed by region-specific grid operators when they assess new connections within their area.

Understanding the different types of capacity solutions

Aligning capacity assessments with the grid operator's methodology is a best practice, offering the most reliable insights. However, alternative methods exist to provide capacity and interconnection insights for the market. It's crucial to recognize that these analyses are primarily directional and, if not applied correctly, could pose costly risks that might jeopardize project success.

Model type 1: historical capacity data

Historical capacity data documents previous requests to connect new power projects to the grid in a specific region, capturing project details, study results, and outcomes. This data aids in understanding past trends and the progression of the interconnection queue.

However, it offers limited insight into current or forecasted capacity, as the electrical grid is a dynamic entity in constant flux. Grid operators look at changes like new generation coming online, retiring existing resources, transmission upgrades, and shifts in load patterns as they all significantly impact power flow and available capacity at any given moment.

Historical capacity data in use

By analyzing historical data spanning several years, specific trends can be identified to predict regional future load growth, aiding the load forecasting process. With this forecasting in hand, new generators can use it to initiate their site selection process, aligning with the anticipated baseline increase in load demand.

Takeaway

Historical data can be beneficial for identifying trends, but relying on it as a method to determine future capacity can be misleading and potentially more detrimental than having no data at all. While it offers insights into past trends, these may not hold true for the future. Ultimately, this study does not provide clarity on how your project would be evaluated under the conditions pertinent to your interconnection year. Given the variance from how a project will actually be evaluated, it is important to consider this information minimally insightful and far from the accuracy required to make any investment decisions.

Model type 2: simplified capacity models (e.g., 8-Bus Capacity Modeling)

The 8-bus capacity model offers a simplified depiction of a power system, utilizing just eight electrical buses (nodes) to examine power flow and capacity. This model incorporates representative generators, loads, and transmission lines arranged in a specific topology. Although it is considerably less intricate than real-world systems, which may contain hundreds or thousands of buses, it facilitates basic power flow analysis.

Simplified capacity models in practice

These models are frequently used for educational purposes to illustrate fundamental power system concepts or in high-level screening studies where detailed precision is not essential. The results yield a general insight into the system's behavior within the constraints of the simplified network configuration.

Takeaway

Due to its highly aggregated nature, an 8-bus model offers limited accuracy for real-world interconnection studies and provides no specific insight into the complexities and constraints of a particular region's actual grid. Interconnection capacity is influenced by factors beyond the immediate vicinity of a Point of Interconnection (POI), such as interface limits, which define the power flow limits between regions. Once again, all of these factors come into play in grid operator’s project evaluation modeling practices.

Labeling this as an “interconnection study” is misleading, as it offers an extremely limited perspective of the grid. Grid operators will not perform this type of study on a project in its queue. Power flow analysis is non-linear, meaning that distant POIs can affect the behavior of every other POI. Given the high complexity of the real grid's interconnections, adopting an approach that mirrors real-world conditions, rather than relying on a simplified 8-bus or n-bus model, is advisable to achieve greater success when integrating into the grid.

While simplified modeling is actual powerflow modeling, unlike historical analysis, it lacks the breadth of a comprehensive study like the grid operator will conduct. Given this, the analysis should be considered highly directional with material variances from real-world values.

Model type 3: full powerflow-based interconnection studies – the gold standard

A full power flow-based study is an in-depth computer analysis utilizing a comprehensive grid model to assess how connecting a new power source or large load impacts the electrical system. This model closely aligns with the methodologies employed by grid operators, incorporating base cases, N-1 contingencies, industry-standard modeling software, and considering factors such as upgrades, dropouts, retirements, and assumptions used by the grid operator.

This thorough evaluation helps identify any necessary upgrades to maintain grid reliability and safety with the new connection. These studies must be conducted using the same region-specific assumptions and guidelines that each grid operator applies in their own interconnection evaluations.

Full powerflow-based interconnection studies in practice

Modeling future capacity at a specific node or bus at a substation provides developers with a substantial advantage. By understanding the projected capacity and constraints at these precise points, developers can effectively preview how their proposed projects will be evaluated by the grid operator. This foresight enables more strategic site selection, ensuring projects are positioned in locations where they are most likely to receive approval and successful interconnection. Thanks to this gold standard — risks associated with project development are significantly reduced.

PVcase Prospect offers this gold standard in full powerflow-based interconnection studies. By providing developers with the ability to model future capacity at a specific node or bus, PVcase Prospect delivers a substantial advantage, enabling more strategic site selection and allowing developers to effectively preview how their proposed projects will be evaluated by the grid operator. Thanks to this unparalleled level of insight, the risks associated with project development are significantly reduced, ensuring projects are positioned for approval and successful interconnection.

Takeaway

This is the only truly accurate method for understanding how the grid operator will evaluate your project and conducting effective due diligence. While it is complex, time-intensive, and requires deep analysis, it faithfully mirrors the actual evaluation process.

What’s next?

PVcase Prospect's Capacity feature provides comprehensive N-1 powerflow-based interconnection studies. These studies utilize the latest base cases, industry-standard modeling software, and assumptions that replicate how each ISO/RTO evaluates the grid within their respective regions. With geo-located data seamlessly integrated into the PVcase Prospect platform, you can identify Points of Interconnection (POIs) with ample capacity right from the beginning of your site selection process, enabling you to confidently progress from site origination to operation.

Don’t let your projects end up in the shade — download the e-book “Capacity analysis — why PVcase Prospect wins,” to get a glimpse into features that move early-stage projects forward.

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