First performance analysis of a silicon-cell microcontroller-based solar radiation monitoring system

Abstract

This paper demonstrates the operation of a low-cost silicon pyranometer in combination with a self-designed low-power microcontroller-based data acquisition system for monitoring global horizontal solar radiation. The performance and behaviour of this low-cost silicon-cell microcontroller-based data acquisition system (SIMBADAS) are studied on the basis of experimental instantaneous global horizontal solar radiation data obtained between January and October 1997. This measurement system operates unattended, collecting and storing data at 10 min intervals. Data from the SolData silicon-cell pyranometer ( SolData, 1989) are collected via an on-chip A/D converter and stored in non-volatile memory. Only unprocessed data are stored in memory. Quality control and data analysis are done off-line to minimize system cost and complexity. At the end of each data collection period, the acquired data are transmitted to a computer through the RS232 serial port for subsequent analysis. Digital correction of the signal by means of an auto-correction procedure is then done as the data are retrieved by the computer. This paper also presents initial calibration results where the SIMBADAS was compared against the first class reference, the Eppley (PSP) precision spectral pyranometer. Data covering an almost complete range of atmospheric conditions in Harare has been used to develop calibration coefficients for this silicon-based system. Field tests and comparisons with the Eppley pyranometer have shown that the accuracy of the SIMBADAS measurement system is fairly good, typically ±13 W/m 2 except during partly cloudy days in which readings could be vastly different. This error is acceptable for a lot of applications and comparable to other similar methods developed so far.