An autonomous photovoltaic system sizing program for office applications in Africa

A spreadsheet tool and underlying model was developed to aid non-expert users in sizing off- or on-grid photovoltaic systems with battery back-up for office applications in Africa. The tool offers the user a number of choices which help in the decision process. The model is based on the concept of energy equivalence and extended by taking into account non-ideal behaviours of photovoltaic system components, modelled as efficiency deviations. The spreadsheet tool uses freely available data, such as PV system component manufacturer's data sheets, as well as climatic data from the NASA SSE database. The irradiation data on the plane-of-array is calculated for the chosen location using the well established HDKR irradiation model. The obtained irradiation and energy output were compared to free services from Soda-is and the HOMER sizing software. The predicted energy output comparison of identical off-grid photovoltaic systems per location for two sites in Africa were within 14% of the value given by HOMER. A performance ratio-equivalent efficiency was calculated as part of the model. This intuitive approach to photovoltaic system sizing reduces the learning curve for non-expert users. The predicted performance ratio-equivalent efficiency can be used as a predictive analytic tool for grid-connected and off-grid photovoltaic systems.