Solar photovoltaic (PV) panels are devices that directly convert sunlight to electrical energy, which contributes significantly to renewable power in California. Dust deposition on the surface of solar PV panels is inevitable in residential applications, which can significantly lower the efficiency of solar PV panels. In this project, we investigate the size distributions of surface dust at two residential locations in the United States of America (USA) and the impact of surface coverage on PV panels. It is found that dust on residential PV surfaces differs from that in ambient air in terms of the mean size. The mean dust size at the two residential sites is about 100 micrometers, with a few large observed particles of 0.5-1 mm, likely arising from residential activities such as traffic, landscaping, and gardening. We also find that the size distributions of the surface dust can be well described by the log-normal distribution, which is popularly used to model ambient dust, and by a literature empirical correlation. The PV performance loss due to surface coverage is experimentally measured using a well-defined coverage method of screen layers. This indicates that the impact of surface coverage on PV power is more significant at the initial stage of dust deposition. The relationship discovered in this study between surface coverage and PV power loss is consistent with the literature data using artificial dust.  Correlations and theories are established to evaluate the power loss due to dust coverage on PV surface.