There are generally three sources of valid solar resource data: ground measurements, ground modelling, and satellite images. We will focus on the principles and key considerations for data source selection when assessing solar resource risk.
1. Ground measurement data source
Direct measurement of solar irradiance with ground-based instruments is the first choice for obtaining data sources. Instruments that collect data require good maintenance and rigorous calibration. While the use of such high-quality ground survey data is recommended, it is rarely used near project sites. Nor is there a mandate to use this approach when analyzing solar resources to support PV project financing. However, lenders of CSP projects often require the use of ground inspection data.
The quality of measurement data is critical. Improperly maintained instruments and improperly processed measurement data can cause errors that can affect assessments. Measured solar irradiance data is difficult to trust without adequate knowledge of the quality, calibration, cleaning and maintenance history of the measuring instrument. However, a limited amount of high-quality ground measurement data can also validate and/or refine a long-term ground-based modelling data and satellite-derived data record. Similarly, poor quality ground measurements can lead to underestimated solar resource data (caused by dirt and sensor offsets), which in many cases can lead to an underestimation of the potential value of the project.
2. Ground Modeling Data Sources
Most solar resource datasets, especially in North America, including some ground-modeled irradiance data, are based on observations of cloud cover. Most long-term datasets are based on these data. The quality of ground-based modelling data can vary greatly from site to site and from year to year for a given site. The limitations of the data input or computationally generated datasets themselves pose some problems. It is important to identify and eliminate systematic errors and significant uncertainties in data.
3. Satellite data sources
Most of the solar development sites studied have satellite data sources with high spatial and temporal resolution (most data will be distributed on a 10km x 10km grid, but high-resolution data in some areas can be transmitted over the network.) Satellites can provide Data information near many sites is more valuable than ground monitoring and ground modeling methods that can only provide information about the nearest site. However, high-resolution satellite data were not available until 1998, and models were subject to considerable uncertainty in applying these data, and it was difficult for models to account for biases caused by other effects such as snow cover and surface reflections. Second-hand data sources that can be compared to satellite-derived data can greatly increase reliability and avoid significant errors.
