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The renewable energy zone (REZ) process is a proactive approach to transmission system planning that supports investment in large-scale transmission expansion and renewable energy development. The REZ process consists of six steps:

 Overview of the REZ Transmission Planning Process

Figure. Overview of the REZ transmission planning process


1. Define the REZ Vision and Process
An effective REZ process should be consistent with applicable laws and regulations to ensure that the designation of a REZ has legal weight and that decision makers have the authority to approve and implement transmission system investments.

The REZ process scope defines the geographic boundaries and the renewable energy resources of interest (such as wind and solar) for the planning activity. These decisions, made together with energy sector stakeholders, may include government priorities and data availability. Additionally, the lead entity may work with stakeholders to publish a REZ process design document that describes the steps, responsibilities, deliverables, timelines, and goals in detail.

2. Conduct Renewable Energy Resource and Technical Potential Assessments
REZ process work continues by identifying the available energy resources and their technical potential. A systematic and transparent technical analysis is used to map the resource quality, topography, and land-use categories for the entire geographic area covered by the planning activity. The goals of this step are to estimate the renewable energy technical potential and to screen out areas with poor resources or obvious limitations on development. The result is a set of initial study areas capable of supporting high levels of clean energy development. Next, economic considerations can help further filter areas based on factors such as the cost of electricity generation, distance to roads, and distance to transmission system infrastructure.

Reliable, robust, and validated data are a critical input to this step to ensure that the REZ process drives informed planning and investment in the clean energy sector. This data supports mapping and visualization of renewable energy resources, technical and economic potential analyses, and power system modeling activities.

Tools such as the Renewable Energy Data Explorer can help identify and visualize potential REZs through the evaluation of accessibility and feasibility (technical potential) and energy resource quality. Find more information on Renewable Energy Data Explorer and other tools on the REZ Tools and Templates page.

3. Select Candidate Zones
Not all areas that contain excellent renewable energy resources will be attractive to private-sector renewable energy developers for reasons that may not be captured by energy resource and technical potential assessments. In this step, private-sector developers demonstrate their interest in the pre-screened areas to ensure REZs are commercially attractive for development. This increases the likelihood of cost recovery for transmission system investments based on evidence from private developers that REZs would be developed and transmission connections utilized.

4. Assess Transmission Development Options
The same set of REZs can be connected to the rest of the grid in several different ways. This step develops various options for transmission enhancements to cost-efficiently connect candidate zones to load. A series of transmission planning studies—including production cost, load flow, and stability analyses—help identify the option that best meets all the criteria for new renewable energy development while minimizing infrastructure costs.

5. Formalize the Final Transmission Development Plan
Before selecting the final transmission plan, the appropriate authorities (such as the regulatory authority) may need to ensure compliance with additional reliability, social welfare, environmental and other requirements. The final transmission order documents the selected plan and authorizes implementation of the decisions made throughout the REZ process.

6. Upgrade and Expand Transmission Systems
This final step involves the coordinated implementation of the approved transmission enhancements and the development of identified REZs. Where a significant transmission system overhaul is necessary and limited by financing constraints, the outputs, time horizon, and/or scale of a REZ process can be tailored to consist of a staged investment and development approach.

7. Outcomes of the REZ Transmission Planning Process
Successfully implementing the REZ process enables integrated transmission expansion and renewable energy development—helping to cost-effectively increase the share of solar, wind, and other renewable energy resources in the power system.

Ultimately, the REZ process is a proactive transmission planning approach that aids policymakers and planners in achieving renewable energy goals while meeting increased electricity demand and providing cost-effective power generation by scaling-up renewable energy development.


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The following quick reads provide additional information to topics relevant to the REZ process.

Renewable Energy Zones: Delivering Clean Power to Meet Demand
Sep 20, 2018 · File

Renewable Energy Zones: Delivering Clean Power to Meet Demand

The Renewable Energy Zone (REZ) is a concept that has emerged as a transmission planning tool to help scale up the penetration of solar, wind, and other resources on the power system. This document gives an overview to the critical steps necessary to implement a REZ process. These steps include: reviewing the regulatory environment on transmission planning; performing a resource assessment; screening the resources for potential for development; formalizing an input process for developers; performing an economic analysis for potential REZ areas; designating the REZs; and finally planning and commissioning transmission to the REZs.

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Technical Potential Assessment for the Renewable  Energy Zone (REZ) Process: A GIS-based Approach
Aug 15, 2018 · File

Technical Potential Assessment for the Renewable Energy Zone (REZ) Process: A GIS-based Approach

Geographic Information Systems (GIS)-based energy resource and technical potential assessments identify areas capable of supporting high levels of renewable energy (RE) development as part of a Renewable Energy Zone (REZ) Transmission Planning process. This document expands on the REZ Process to aid practitioners in conducting GIS-based RE resource and technical potential assessments. The REZ process is an approach to plan, approve, and build transmission infrastructure that connects REZs - geographic areas that have high-quality RE resources, suitable topography and land-use designations, and demonstrated developer interest - to the power system. The REZ process helps to increase the share of solar photovoltaic (PV), wind, and other resources while also maintaining reliability and economics.

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Transmission Planning Studies for the Renewable Energy Zone (REZ) Process
Sep 19, 2018 · File

Transmission Planning Studies for the Renewable Energy Zone (REZ) Process

Transmission planning studies help power system planners determine how they can best supply load with renewable energy. The early steps of the REZ process result in the identification of multiple candidate REZs. Many potentially feasible transmission expansion and upgrade options may exist to deliver the electricity from these zones to load. Knowledge of the location and target installed capacity of each candidate REZ allows power system planners to conduct transmission planning studies that identify the costs, benefits, and reliability impacts associated with various transmission line additions, equipment upgrades, and new substations and transformers. Furthermore, such studies help identify the lowest-cost, preferred transmission enhancement (upgrade and/or expansion) option that meets reliability and other system requirements.

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