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