Data sampling speed versus energetic measurement errors in photovoltaic system monitoring

Abstract

To measure solar irradiation and photovoltaic array output energy, measuring accuracy cannot be guaranteed unless the data sampling interval is appropriately selected. From this viewpoint, actual irradiance had been measured by comparatively high speed sampling of 1 to 4 seconds for 44 months and the daily errors of numerical integral has been estimated for various step sizes. Approximation formulae of the error versus the step size have been statistically obtained as well as their probability density function covering /spl plusmn/4/spl sigma/. Finally a nomograph is presented to decide an appropriate sampling interval. A concluding example shows that the deviating component of the error exceeding /spl plusmn/1% can happen once for every 1 month or 6 months if the step size is selected as 105 seconds or 65.5 seconds, in each of which the total error becomes -0.0485/spl plusmn/1% or -0.0336/spl plusmn/1% including an average error component.