Understanding California’s Energy Future Part Two:How Did Borrego Springs Become San Diego County’s “Least-Cost” Solar Basin?
David Garmon, Desert Protective Trust
San Diego County’s Regional Decarbonization Framework (RDF) identified Borrego Springs as the County’s “least-cost” location for remote, utility-scale solar generation. At first glance, that conclusion seems reasonable. Borrego Springs has abundant sunshine and broad areas of relatively flat, relatively inexpensive land. But the phrase “least cost” deserves a closer look, because it does not describe an objective characteristic of the landscape. It describes the outcome of a computer model built from a particular set of assumptions about costs, technologies, and available resources.
That distinction is important because optimization models can compare only the information they are given. If an important cost is excluded, the model cannot account for it. If a practical alternative is understated, the model treats that smaller estimate as reality. The mathematics may be flawless, yet the comparison can still be incomplete (and erroneous) because the model was never asked to evaluate all the relevant information.
The clearest example of the RDF’s problematic modeling involves the costs associated with the transmission of electricity. The RDF compared alternative decarbonization pathways and assigned only $89 million in transmission upgrade costs to the remote, industrial-scale solar generation scenario. Yet the accompanying analysis identified approximately $2.9 billion in transmission line costs that would be needed to bring large quantities of remote renewable electricity from San Diego’s deserts to its coastal communities. This enormous transmission investment was inexplicably not included in the least-cost comparison analysis.
That is not a trivial difference. A transmission investment measured in billions of dollars is part of the cost of delivering remotely generated electricity to San Diego’s major population centers. If that cost is excluded when modeling competing scenarios, the resulting ranking no longer represents the full system cost of competing strategies. Whether that omission changes the ranking of “low-cost alternatives” is precisely the kind of question policymakers must ask before relying on the model’s conclusions.
The omission of the cost of transmission was not the only concern identified by independent reviewers. The RDF documented approximately 61,000 acres—about 2.7 billion square feet—of rooftop area in San Diego County suitable for solar panels. Using the engineering conversion figures cited in the review, that area could produce more than 20,000 megawatts of rooftop solar. Yet the RDF estimated only 3,360 megawatts of rooftop solar capacity without providing an explanation for the lower figure.
Reviewers also found that parking-lot solar was largely absent from the considerations included in the RDF, even though a study cited by the RDF identified parking areas as one of the County’s largest untapped solar resources. In addition, reviewers noted the RDF relied on older and more expensive cost estimates for commercial rooftop solar despite newer, lower cost projections being available in the same National Renewable Energy Laboratory dataset referenced by the Framework.
Taken together, these issues point to a broader lesson. Optimization models do not determine truth. They determine the best answer to the question they have been asked using the assumptions they have been given. If significant transmission costs are omitted, if rooftop and parking-lot solar are understated, or if technology costs do not reflect current information, those choices can influence which alternative appears to be the “least-cost” solution.
Why This Matters
The Regional Decarbonization Framework has already shaped public discussion about the future of Borrego Springs and the proposed Golden Pacific Powerlink. Before its conclusion is used to justify industrial-scale solar development or new 500-kV transmission through Anza-Borrego Desert State Park, it is reasonable to ask whether the comparison included the full cost of remote transmission and fairly represented all practical solar resources available on rooftops, parking lots, and previously developed land. Those are not political questions. They are the questions that any sound least-cost analysis should be able to answer.