Achievements in Photovoltaic Technologies within the Next Decades

Solar-cell efficiency is the portion of energy in the form of sunlight that can be converted via photovoltaics into electricity by the solar cell. The efficiency of the solar cells used in a photovoltaic system in combination with latitude and climate determines the annual energy output of the system. Usually solar panels are exposed to sunlight for longer than this in a given day but the solar irradiance is less than 1000 W/m2 for most of the day. A solar panel can produce more when the Sun is high in Earth's sky and produces less in cloudy conditions or when the Sun is low in the sky. The Sun is lower in the sky in the winter. Several factors affect a cell's conversion efficiency including its reflectance thermodynamic efficiency charge carrier separation efficiency charge carrier collection efficiency and conduction efficiency values. Because these parameters can be difficult to measure directly other parameters are measured instead including quantum efficiency open-circuit voltage (VOC) ratio and § Fill factor. Reflectance losses are accounted for by the quantum efficiency value as they affect external quantum efficiency.