If you ask most Californians who decides where major transmission lines should be built, you’ll probably hear the same answer: CAISO. It’s an understandable assumption. Whenever a major transmission project is proposed, the California Independent System Operator is usually at the center of the discussion. Its engineers conduct reliability studies, evaluate alternatives, and publish reports explaining why additional transmission appears necessary. From the public’s perspective, it can easily appear that CAISO is the organization deciding where transmission lines should go. 

In reality, California intentionally separates responsibility among several organizations, each answering a different question. The system is designed so that no single agency decides California’s energy future. Instead, planning unfolds in stages, with each organization building upon the work of the one before it. Understanding that process is important because it explains why communities such as Borrego Springs seem to suddenly appear on planning maps—and why those maps are not the beginning of the conversation, but the result of years of earlier decisions. 

The process begins with a deceptively simple question: How much electricity will California need twenty years from now? No one can answer that question with certainty. Population changes. New technologies emerge. Homes become more energy efficient. Electric vehicles become more common. Businesses grow, while appliances and air conditioners consume less electricity than earlier generations. Each of these trends influences future demand, and each continues to evolve. It is the task of the California Energy Commission (CEC) to develop long-range forecasts that combine these and many other factors into planning assumptions that guide the next stage of the process. 

The CEC forecasts are not predictions for the future. They are the state’s best estimates, based on the information available at the time, and they are revised regularly as technology, economics, and consumer behavior change. That distinction matters because California’s planning system is designed to learn. As better information becomes available, the assumptions change, and so does the planning built upon them. 

Only after the CEC planning assumptions have been established does the California Public Utilities Commission (CPUC) begin evaluating what combination, or portfolio, of resources—utility-scale renewable generation, batteries, energy efficiency, demand response, Distributed Energy Resources, and other technologies—could reliably and economically supply California’s future electricity needs while meeting the state’s climate goals. The CPUC’s resulting “resource portfolio” then become an important input into CAISO’s work. 

CAISO’s responsibilities are different. Rather than deciding California’s climate policy or choosing among competing energy technologies, CAISO asks whether the existing transmission system can reliably support the energy future described by those planning assumptions developed by CEC and CPUC. CASIO engineers simulate thousands of operating conditions, including periods of extreme heat, equipment failures, maintenance outages, changing demand patterns, and the growing role of battery storage. If those studies identify constraints, CAISO evaluates alternatives capable of maintaining reliability, which may include upgrades to existing facilities or construction of new transmission infrastructure. 

By the time a proposed transmission project reaches the public, it is already the product of years of forecasting, resource planning, engineering analysis, and coordination among multiple agencies. That observation leads naturally to another question. If the assumptions entering the planning process change because technology changes more rapidly than expected, could the transmission needs change as well? The answer is yes and understanding why is the subject a future article in this series. 

Why This Matters 

Communities often find themselves debating the location of a proposed transmission line without first understanding the planning process that produced it. Yet transmission studies begin with assumptions about California’s future electric system. If those assumptions evolve, the transmission system needed to support them may evolve as well. Understanding that process is the first step toward participating meaningfully in decisions that will shape the future of the Anza-Borrego Desert State Park.