Data from the Department of Energy’s National Renewable Energy Laboratory (NREL) shows the cost of Solar PV systems varies by the size of the systems. Costs for homeowners have a wide range based on specific project details. Costs can vary due to project-specific fees like mounting costs, tax incentives, installer overhead costs, permitting, and interconnecting with the grid. Although cost differs across the United States generally the costs have declined in recent years for both utility-scale and homeowner projects. Utility-scale projects have the lowest unit costs from 1.06 per watt to 1.113 in 2018. PV residential system costs have also declined. Data from the NERL shows that at a residential scale the price per watt has on average declined from over $7 in 2010 to under $3 in 2018.