Researchers from Japan’s Chiba University and Indonesia’s Institut Teknologi Bandung have used solar irradiance data to gain insights on where best to locate future solar power plants across the Asia Pacific.
The research paper, “Solar irradiance variability around Asia Pacific: Spatial and temporal perspective for active use of solar energy,” published in the July edition of Solar Energy, investigates solar irradiance variability in terms of spatial and temporal heterogeneity.
The study used solar irradiance data from Japanese geostationary satellites Himawari-8 and Himawari-9 and Amaterasss, a tool that estimates solar irradiance using an ultra-high-speed calculation method with neural networks based on a radiative transfer model. The data obtained covered 2022 within 10-minute intervals, with a spatial resolution of 0.04 degrees, or approximately 4 km. The researchers also used a digital surface model to understand solar irradiance variation at different altitudes.
Professor Hideaki Takenaka, the research lead, said that the evaluations based on spatiotemporal data “revealed characteristics that would’ve been impossible to achieve using a traditional approach that relies on simple long-term averages or typical meteorological year as a typical solar irradiance data.”
Each region was divided into 0.2 degrees × 0.2 degrees or approximately 20 km × 20 km to determine its heterogeneity. The solar irradiance heterogeneity in the Asia Pacific was calculated at around 0 to 135 W/m2.
The paper explains that solar heterogeneity exhibited seasonal variability, but locations near the equator experienced lower fluctuations in solar irradiance over time when compared to higher latitude regions, largely due to the effects of rain and cloud activity. Meanwhile, sites with higher elevations had higher heterogeneity because of high cloud activity, while the ocean recorded the smallest heterogeneity.
The paper also calculated the probability of an umbrella effect caused by clouds, known as the umbrella effect index, at approximately 0 to 0.34 across the year. The researchers observed a higher umbrella index in high-latitude locations during summer than in the winter. A significant seasonal change was noted in the Tibetan Plateau, a vast, elevated plateau across the intersection of eight central, south and east Asian countries. This area had the lowest umbrella index when compared to other seasons from July to August.
Considering both heterogeneity and the umbrella effect index allowed the researchers to advise on where future solar panels would be well suited. “An excellent location for installing a solar power plant has a low heterogeneity and umbrella effect time,” the research paper says. “Under these conditions, solar irradiance in the region has a very high potential throughout the year due to low cloudiness. In the target area, 5.76% have these conditions. Based on the results, these conditions are found in the desert and coastal regions of high altitudes.”
The scientists also found that 4.43% of the area studied has low heterogeneity values but a high umbrella effect, and therefore the most unsuitable for solar installations.
The researchers also assessed the performance of over 1,900 existing solar plants using annual and seasonal data. This analysis found most existing solar power plants are located in very low umbrella effect time indices in areas of low solar heterogeneity. Such locations account for 39.17% of the overall studied area. However, a significant portion of existing plants were found not to perform optimally from June to August, due to the umbrella effect caused by clouds. The researchers advised these zones should not rely entirely on solar power to meet increased demands during these months.
In a discussion of the most optimal format for future solar power plants, the research paper concludes more widely distributed solar energy generation is superior to more localized effort and highlights rooftop solar as a key way to achieve an increase in the stability of solar energy supply to the grid.
“Based on the spatial and temporal characteristics of solar irradiance, we suggest that it should be possible to suppress rapid fluctuations in solar power generation output by distributing small photovoltaic systems over a wide area rather than relying on large solar power plants,” Takenaka said. “Worth noting, these conclusions come from weather and climate research, not an engineering perspective.”
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