As the deployment of grid-connected solar photovoltaic (PV) systems has increased, so too has the desire to track the installed cost of these systems over time and by location, customer type, system characteristics, and component. This report helps to fill this need by summarizing trends in the installed cost of grid-connected PV systems in the United States from 1998 through 2010, with preliminary data for 2011, and includes, for the first time, installed cost trends for utility-sector PV. The analysis is based on installed cost data for approximately 116,500 behind-the-meter (i.e., residential and commercial) and utility-sector PV systems, totaling 1,685 megawatts (MW) and representing 79% of all grid-connected PV capacity installed in the United States through 2010. It is essential to note at the outset the limitations inherent in the data presented within this report. First, the cost data are historical, focusing primarily on projects installed through the end of 2010, and therefore do not reflect the cost of projects installed more recently (with the exception of a limited set of results presented for behind-the-meter projects installed in the first half of 2011); nor are the data presented here representative of costs that are currently being quoted for prospective projects to be installed at a later date. For this reason and others (see Text Box 1 within the main body of the report), the results presented herein likely differ from current PV cost benchmarks. Second, this report focuses on the up-front cost to install PV systems; as such, it does not capture trends associated with PV performance or other factors that affect the levelized cost of electricity (LCOE) for PV. Third, the utility-sector PV cost data presented in this report are based on a small sample size (reflecting the small number of utility-sector systems installed through 2010), and include a number of relatively small projects and "one-off" projects with atypical project characteristics. Fourth, the data sample includes many third party-owned projects where either the system is leased to the site-host or the generation output is sold to the site-host under a power purchase agreement. The installed cost data reported for these projects are somewhat ambiguous –in some cases representing the actual cost to install the project, while in other cases representing the assessed "fair market value" of the project.2 As shown within the report, however, the available data suggest that any bias in the installed cost data reported for third party-owned systems is not likely to have significantly skewed the overall cost trends presented here. The report separately describes cost trends for behind-the-meter PV systems and utility-sector systems.