Rate Analysis of Two Photovoltaic Systems in San Diego

Analysts have found increasing evidence that rate structure has impacts on the economics of solar systems. This paper uses 2007 15-minute interval photovoltaic (PV) system and load data from two San Diego City water treatment facilities to illustrate impacts of different rate designs. The comparison is based on rates available in San Diego at the time of data collection and includeproportionately small to large demand charges (relative to volumetric consumption), and varying on- and off- peak times. Findings are twofold for these large commercial systems: 1) transferring costs into demand charges does not result in savings and 2) changes in peak times do not result in a major cost difference during the course of a year. While lessons learned and discussion on ratecomponents are based on the findings, the applicability is limited to buildings with similar systems, environments, rate options, and loads.