Stochastic modelling of solar irradiance on horizontal and vertical planesat a northerly location

Sunshine levels incident in the plane of a photovoltaic panel are the overr iding influence on electrical output, and modelling solar irradiance is the refore an essential step in the design and performance prediction of solar energy conversion systems. This study aims to assess the efficacy of SARIMA models and their potential for short-term prediction at a northerly latitu de. Data was collected from a monitoring site on the roof of a 5-storey bui lding at a city centre location in Newcastle upon Tyne, UK (latitude 55 deg rees N). Hourly and ten minute data relating to 13 and 15 day periods in tw o winters (1993, 1994) and two summers (1994, 1995) were utilised. Univaria te stochastic modelling, using SARIMA models, is carried out for horizontal and south facing vertical solar irradiance. Results showed that these mode ls provided a good fit for the ten minute averaged horizontal and vertical irradiance, with, on average, 82% and 85% of total variation being accounte d for respectively. Use of hourly averaged data in these models gave a subs tantial reduction in the fit. Models for the winter data were a poorer fit than for summer for both orientations. It is concluded that the SARIMA appr oach can be used to develop prediction methods and to study rapid and large changes in PV output from extensive areas of solar cladding. (C) 1999 Else vier Science Ltd. All rights reserved.