State policy incentives for solar power have grown significantly in the past several years. This paper examines the effectiveness of policy incentives to increase residential solar PV capacity. County-level solar adoption data and controls for demographic characteristics, solar resources, and pro-environmental preferences are used to estimate a model of residential solar adoption. Empirical findings show that financial incentives, solar-specific mandates, and loan financing programs are important drivers of residential PV capacity growth. Incentives that reduce the up-front cost of adoption and that are subject to low uncertainty are found to have the largest impact. Results also point to a significant positive relationship between hybrid vehicle sales and residential PV capacity growth, indicating the importance of pro-environmental preference as a predictor of solar PV demand.