How much impact does tilt have on a fixed grid-tied array? In Raleigh, North Carolina, on a roof with slope of 25° (a roof pitch between 5:12 and 6:12), a flush-mounted 3 kW array will produce about 3,916 kWh per year. The same size array tilted close to latitude (in this case, 35.9°) would produce about 3,937 kWh per year—a production difference of 21 kWh. Of course, if the array tilt was adjusted throughout the year, the production numbers would increase.
For example, a monthly adjustment to each month’s optimum angle would result in 4,139 kWh per year. A quarterly adjustment to optimum tilt would result in 4,127 kWh per year, a 4.8% increase over the fixed-tilt array. Generally, only off-gridders who need to squeeze every winter watt-hour out of their systems are willing to go to these lengths, which can add up to 10% to their system’s winter production.