Modeling Methods for Capturing System Interactions of Combined Technologies: A Study of PV + Battery

Abstract

The costs of solar photovoltaics (PV) and batteries have been decreasing in recent years, leading to increasing installations of them-both independently sited and colocated solar PV and battery systems-and growing interest in how the technologies can interact with the electric grid at greater deployment levels. Given the increasing deployment of these technologies, it is important to understand the value and limitations of battery storage for the grid as well as potential value of colocating battery storage and PV, particularly within the realm of future system planning. However, representing the dynamic nature of these technologies to accurately capture their potential values is challenging within capacity expansion models (CEMs) given their typical formulation as a linear program. Interactions between variable renewable technologies, such as PV, and storage resources are nonlinear and thus novel approaches must be developed to robustly capture the interactive effects of these technologies.This report presents methodological developments to represent more fully the value and limitations of combined (i.e., installed in the same model year and region) PV and battery installations (PV + battery) in CEMs using the Resource Planning Model (RPM), which cooptimizes capacity investments, transmission investments, and reduced-order dispatch in the Western Interconnection of North America through 2045. We use RPM to simulate the evolution of the generation and transmission system under two core scenarios-a baseline scenario and a high renewable deployment scenario-coupled with sensitivities assuming low and midline PV and battery cost projections. When incorporating PV + battery systems, it is important that CEMs adjust their methodology to accurately capture both the firm capacity combined technologies can provide and their ability to reduce expected curtailment. We find that without adjustments for the inherent nonlinearities, PV + battery systems are undervalued in linear CEMs. The interactions between these technologies have an increasing impact on CEM expansion decisions as solar deployment rises. vi This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.