HOMER can model two popular types of photovoltaic (PV) arrays: flat panel and concentrating. Flat panel PVs are common and are lower in cost compared to the higher cost, higher performance concentrating PV arrays. Concentrating PV arrays have reached above 40% efficiency in commercial installations. An efficiency of 15% is typical of flat panel PV arrays.
Since CPVs use optics to focus solar irradiation, they generally also require active tracking to follow the sun. Only direct solar radiation incident normal to the surface of the panel is collected, in contrast to flat panel PVs that can capture radiation striking the panel at a range of angles. This irradiance of flat panel PV is calculated using the solar global horizontal irradiance (GHI) which includes direct and indirect radiation. Concentrating PV uses the direct normal irradiance (DNI) solar resource that only includes the portion of solar that can be captured by CPV.