研究目的
To determine errors in two calibration approaches [non-adjusted linear calibration and adjusted calibration] in estimating solar global irradiance using SiPs under outdoor conditions over the course of a year.
研究成果
The study concluded that calibrations accounting for solar zenith angle and temperature effects improved global irradiance estimates, especially for older sensors. The best calibration periods for the Lincoln NE location were identified as spring or late summer. The findings suggest that future calibrations could be improved by accounting for the diffuse component of radiation under cloudy conditions.
研究不足
The study was limited by the need for a wide range of temperatures and solar zenith angles for accurate calibration, which requires a year of calibration data. Monthly calibrations were recommended but may not fully account for seasonal variations. Additionally, the effect of sensor age on calibration accuracy was noted, with older sensors showing more variability.
1：Experimental Design and Method Selection:
The study involved the deployment of 16 silicon photodiode pyranometers (SiPs) and two secondary standards (precision spectral pyranometers, PSPs) to measure incident global irradiance over a 5-year period. The methodology included both non-adjusted linear and adjusted calibration approaches to account for solar zenith angle and sensor age effects.
2：Sample Selection and Data Sources:
Data were collected from the sensors mounted on an aluminum plate on the roof of a nine-story building to avoid ground reflectance and shading. The sensors were maintained and cleaned according to manufacturer recommendations, and data were quality checked for errors.
3：List of Experimental Equipment and Materials:
Equipment included 16 LI-COR model LI-200 SiPs, two Eppley precision spectral pyranometers (PSPs), a temperature and relative humidity probe (HMP45C-L Campbell Scientific, Inc.), and a data logger (model CR3000, Campbell Scientific).
4：Experimental Procedures and Operational Workflow:
Measurements were taken every 5 seconds, averaged over a 10-minute period, and stored. Calibrations were performed using clear sky days identified through a MATLAB-based program, with adjustments for solar zenith angle and temperature effects.
5：Data Analysis Methods:
Data were analyzed using regression techniques to estimate calibration coefficients and standard errors (SE) to evaluate the performance of the calibration approaches.
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