WECC and CAISO: Interconnection Windows & FCDS Pathways 

As the energy landscape across the U.S. West evolves, developers and asset owners face two important opportunities to advance generation and storage projects in the WECC and CAISO regions. 

Here’s what you need to know: 

Utilities Open 2025 Interconnection Windows 

Utilities across the western U.S. are preparing to open their 2025 Generation Interconnection Request Windows, offering a critical opportunity to meet growing load demands from sectors like transportation electrification, data centers, and hydrogen production. 

With demand expected to surge, these windows allow you to interconnect a range of new generation resources to meet future energy needs. 

What to Plan for: 

Many utilities are now requiring electromagnetic transient (EMT) models as part of your Interconnection Request data package submission. Developing these models takes time – and if started late, may exceed the typical 45-day window. Each utility has its own EMT model testing and validation requirements, so it’s essential to start early to avoid delays or invalid submissions. 

Key 2025 WECC Interconnection Window Dates 

Add Energy Storage in CAISO and Obtain FCDS

 If you own or operate an existing wind or solar facility in CAISO, you now have a unique opportunity to add battery energy storage (BESS) and pursue Full Capacity Deliverability Status (FCDS). 

Here’s how it works: 

• Submit a material modification request to CAISO (or your Participating Transmission Owner [PTO] if operating under a Wholesale Distribution Access Tariff). 
• Initially, the BESS will be treated as an Energy-Only resource. 
• The BESS may then become eligible for Transmission Plan Deliverability (TPD) based on the timing and structure of your modification request. 

Deadlines to watch: 

• Submit by August 29, 2025, to qualify for TPD in: 
• Group A: If your project has an executed Power Purchase Agreement (PPA). 
• Group B: If your project is shortlisted for a PPA. 
• After August 29, 2025, projects will only qualify under the new “Commercial Operation” Group, requiring BESS to reach commercial operation before TPD allocation is considered. 

Structuring the addition: 

• BESS can be added as a co-located facility with a separate resource ID using an Aggregated Capacity Constraint framework. 

How EPE Can Help 

At EPE, we help clients like you: 

• Navigate interconnection processes across WECC utilities 
• Optimize timelines for EMT model development and submission 
• Maximize deliverability opportunities for your CAISO projects 
• Stay ahead of shifting regulatory requirements 

Contact our interconnection experts today and learn how we can help position your projects for success in WECC and CAISO markets.