February 3, 2025
Most of us living in the Interior West have experienced the effects of climate change firsthand. Phoenix, the region’s largest city, broiled for 113 consecutive days at temperatures 100-degrees or higher. Wildfires consumed thousands of acres of land and contributed to harmful air pollution, and drought continues to grip more than half the region.
Not only are we worried about the future of land, water, and wildlife, but there’s an increased understanding that burning fossil fuels for energy is accelerating climate change. Nearly two-thirds of voters in the West want to see a transition to 100% clean and renewable energy over the next 10 to 15 years, according to polling results from the annual State of the Rockies.
But who makes sure that renewable energy like solar and wind — and not polluting resources like coal and methane gas — are used to meet the soaring energy demands of growing populations, businesses, and industries? How do we know whether utilities are acting in our best interests when they say they need to keep coal plants running or build new fossil-fuel powered facilities? And what checks and balances are in place to ensure that the grid delivers reliable power at a reasonable cost?

Western voters support transitioning to 100% clean, renewable energy sources.
Enter, the Integrated Resource Plan
The integrated resource planning (IRP) process is the arena in which all these questions are aired out and debated to identify the best path forward. IRPs help utilities project future electricity demand and identify resources that the utility will need to meet that demand. They help determine how much of our power comes from either clean or polluting sources, and the costs of those resources — like the cost to develop and install a new solar array or to build and maintain a methane gas plant. The IRP process is one of the most significant ways we can influence the energy future of the Interior West.
For decades, WRA has worked on the IRP processes within five states in the West (Arizona, Colorado, Nevada, New Mexico and Utah) to push for the expansion of renewable energy, reduced reliance on polluting fossil-fuel power plants, and to ensure that utilities are responding to future energy demands to provide cost-effective, low risk, and clean electricity to our homes and businesses.
For a process that has such an enormous impact on our lives, IRPs are not widely understood or discussed outside of the world of energy policy. As part of our ever-evolving work, WRA helps craft effective energy policies on a state and regional level. WRA is building awareness among ratepayers, legislators and other stakeholders not only on what IRPs are and why they matter, but how the average person can get involved and have a say in our clean energy future.

How does an IRP work?
First, a note on terms: Colorado has electric resource planning, or ERPs, which are generally equivalent to the IRP processes across the Interior West. (We’ll examine Colorado’s ERP process in the second installment of this series.) And Salt River Project, a self-regulated utility in Arizona, has integrated systems planning — ISPs. To avoid any confusion, we refer to these processes collectively as IRPs throughout this blog.
State regulatory agencies, such as the Arizona Corporation Commission, require utilities to submit integrated resource plans on a fixed cycle, typically every two or three years. IRP processes differ across states in the West, but they all serve as a clear signal of where a utility is headed with its planning — if it wants to build two new 400-megawatt solar plants, for example, or keep a coal unit in operation longer than originally intended.
When some state regulatory agencies review an IRP, they can opt to disallow a resource proposed within the plan, such as a new 500-megawatt methane gas facility. Some agencies, like the Colorado Public Utilities Commission, can reject a utility’s IRP, sending much of the process back to the drawing board. How a commission reacts to an IRP filing can play a significant role when a utility seeks to raise rates by asking customers to pay for certain resources that may or may not have been approved in an IRP.
What does an IRP contain?
IRPs are complex and dense documents, often spanning more than 100 pages. Here are some key elements they contain.
Load Forecasts
In an IRP, a utility estimates how much electricity demand, or load growth, is expected over the coming years. Forecasting is both a science and art; load growth is driven by factors like population changes, economic growth, and, increasingly, the impacts of extreme weather.
With the surge in data centers needed to power the internet and AI, load growth forecasts are increasing in orders of magnitude never seen before. For example, Xcel Energy, Colorado’s largest utility, projects a staggering 5,000 to 14,000 megawatts of new generation resources that may need to come online between in just six years. (One megawatt of power provides enough electricity to serve nearly 1,100 typical homes.)
System Modeling and Expansion
In each IRP, utilities analyze the load forecast and existing resources to determine what new resources their system needs to reliably and cost effectively supply the energy needed in the coming years. Modeling is of critical importance to WRA. How a utility forecasts load growth and the cost of the resources needed to meet that growth can mean the procurement of clean energy resources, or it can mean a proposal for costly new fossil fuel infrastructure, typically a methane gas plant.
WRA will often work with data provided by utilities to conduct our own analyses of proposed IRPs. This analysis and review can help illustrate that a utility is leaning on an expensive plan that relies too heavily on fossil-fuel resources, when cleaner or more cost-effective options may be available.
Cost Assumptions
Using market data and other information, utilities identify and utilize assumptions about the costs and performance of different kinds of generation resources, such as wind, solar, or methane gas.
Resource Portfolio
As part of the resource plan, utilities will build multiple portfolios of resources which, when operated together with the existing system, can reliably meet the demand for electricity projected in the load forecast.
Preferred Portfolio
Once all the element above have been modeled and examined, utilities will typically identify one resource portfolio as its “preferred portfolio” to the relevant regulating body that they think will meet future demand in the most cost-effective and reliable way while also managing various risks.
Public Participation
To create a transparent process, advocates, experts, and other stakeholders have the opportunity to comment on the utility’s resource plan, assess the various resource portfolios and the utility’s underlying cost assumptions.
In the second part of the series, we delve more into the details of the IRP processes of Arizona, Colorado, New Mexico, and Utah, give a snapshot of what’s working in the Interior West, what changes are needed, and the work WRA is doing to lead those efforts.
Orderly, step-by-step processes aren’t always present in each state, which is why we are supporting legislation to amend the IRP process in Nevada in 2025. You can read more about that effort in the third and final part of this series.