Inter-system time lag due to clouds in an urban PV ensemble

This paper presents a short term (<; 1 hour) in situ global horizontal irradiance (GHI) forecasting method without the use of external weather data. This forecasting method is based on the relative temporal shift (time lag) of measured GHI, or GHI-fluctuations time series of pairs of photovoltaic (PV) systems that are influenced by the same cloud(system) sequentially. Additionally, in combination with measured weather data an estimation of cloud height can be made. The cloud height can prove useful when whole sky cloud images are interpreted for forecasting purposes.