What are Tilt and Orientation Factor (TOF) and Total Solar Resource Fraction (TSRF)?

When using the NREL TMY3 weather model (US only), the SunEye can display solar resources relative to the optimum at that location. The terms TOF and TSRF are displayed as an alternative to solar access. These terms are defined as follows: – Tilt and Orientation Factor   (TOF). TOF is the solar insolation at the actual tilt and orientation divided by the insolation at the optimal tilt and orientation, expressed in percent.   – Total Solar Resource Fraction   (TSRF). TSRF is the ratio of insolation available accounting for both shading and the specific tilt and orientation of the surface, divided by the total insolation available assuming no shade and assuming the surface is at the optimal tilt and orientation. TRSF is expressed in percent, according to the following equation: TSRF = Solar Access x TOF.