Applied Solar Energy Pub Date : 2021-05-04 , DOI: 10.3103/s0003701x20060043 N. Herrera , S. Orozco , M. Rivero , R. Loera , C. Alvarez
Abstract
Among the different available technologies to estimate and forecast solar irradiance, total sky imagers are a suitable option for short-term horizons (less than 30 min). For this purpose, cameras are able to capture images at high speed (less than a second), depending on hardware and configuration, while solarimetric measurements are restricted to the characteristic response time of pyranometers, that varies from 15–60 s, depending on its quality. This difference in sampling time may lead to asynchronous data logging. As a result, two data sets with different sampling time are obtained. A close look into specialized literature showed a lack of evidence on data synchronization of reported results. Thus, the existence of asynchronous data is a plausible assumption. The main objective of this study is to investigate the effect of considering two different approaches in which data can be treated for the estimation of the solar irradiance and clearness index. For this purpose, two data sets are available: solar irradiance with a sampling time of 1 min, and sky images taken at 5 s intervals. Image acquisition system is based on a fisheye camera and a cost-effective and portable device. In one approach solar irradiance is interpolated to image time, and in the second approach, extracted image data is interpolated to solar irradiance time. For each case, solar irradiance and clearness index estimation is based on a multiple linear regression with two different number of features extracted from sky image processing. To evaluate these models, the mean bias error, root mean square error and the mean absolute percentage error were used. Obtained results shows that using different approaches to process data of measurements may lead to errors of 6.2% for the solar irradiance and 3% for the clearness index.
中文翻译:
异步数据处理对通过天空影像估算太阳辐照度和净度指数的影响
摘要
在估算和预测太阳辐照度的各种可用技术中,总的天空成像仪是短期视界(少于30分钟)的合适选择。为此,根据硬件和配置,照相机能够高速(不到一秒)捕获图像,而日光法测量则限于日光强度计的特征响应时间,视响应时间而定,该时间范围为15-60 s,具体取决于其质量。采样时间的这种差异可能导致异步数据记录。结果,获得了具有不同采样时间的两个数据集。对专业文献的仔细研究表明,缺乏关于报告结果的数据同步的证据。因此,异步数据的存在是一个合理的假设。这项研究的主要目的是研究考虑两种不同方法的效果,在这些方法中可以使用数据来估计太阳辐照度和净度指数。为此,可以使用两个数据集:采样时间为1分钟的太阳辐照度和以5 s间隔拍摄的天空图像。图像采集系统基于鱼眼镜头和具有成本效益的便携式设备。在一种方法中,将太阳辐照度插值到成像时间,在第二种方法中,将提取的图像数据插值到太阳辐照度时间。对于每种情况,太阳辐照度和净度指数估算均基于具有从天空图像处理中提取的两个不同数量特征的多元线性回归。为了评估这些模型,平均偏差误差 使用均方根误差和绝对百分比均值误差。获得的结果表明,使用不同的方法处理测量数据可能会导致太阳辐照度误差为6.2%,净度指数为3%。