A team of researchers from Japan and Indonesia used satellite data to study variations in solar radiation across the Asia-Pacific region and conclude which areas would be best suited for future installations.
August 29, 2024 Patrick Jowett
Researchers from Chiba University in Japan and Indonesia's Bandung Institute of Technology have used solar radiation data to gain insights into the best locations for future solar power plants in the Asia-Pacific region.
The research paper, “Solar irradiance variations in the Asia-Pacific region: spatial and temporal perspectives towards active utilization of solar energy,” published in the July issue of Solar Energy, investigates the variations in solar irradiance in terms of spatial and temporal heterogeneity.
The study used solar radiation data from Japan's geostationary satellites Himawari-8 and -9, and Amaterass, a tool that estimates solar radiation using an ultra-fast computational method with neural networks based on a radiative transfer model. The resulting data covers the year 2022 at 10-minute intervals and has a spatial resolution of 0.04 degrees, or about 4 km. The researchers also used a digital surface model to understand the changes in solar radiation at different altitudes.
Research leader Professor Hideaki Takenaka said the assessment based on spatiotemporal data “revealed characteristics that were not achievable with traditional approaches that rely on simple long-term averages or a typical meteorological year as representative solar radiation data.”
Each region was divided into 0.2 degree × 0.2 degree, or approximately 20 km × 20 km, to determine its nonuniformity. The nonuniformity of solar irradiance in the Asia-Pacific region was calculated to be approximately 0 to 135 W/m2.
The authors explain that solar nonuniformity exhibits seasonal variation, but that closer to the equator the variation in solar radiation over time is smaller than at higher latitudes, mainly due to the influence of precipitation and cloud activity, while at higher altitudes the nonuniformity is greater due to more active clouds, with the oceans showing the smallest nonuniformity.
The paper also calculated the probability of an umbrella effect caused by clouds (umbrella index) to be around 0 to 0.34 throughout the year. The researchers observed that the umbrella index is higher in summer than in winter at high latitudes. Notable seasonal variations were observed on the Tibetan Plateau, a vast plateau where eight countries from Central, South and East Asia intersect. The region had the lowest umbrella index from July to August compared to other seasons.
By taking into account both the non-uniformity and umbrella effect index, the researchers were able to advise on where future solar panels would be suitable. “The best locations for installing solar power plants are those with low non-uniformity and umbrella effect hours,” the research paper states. “Under these conditions, solar radiation in this region can be very high throughout the year due to low cloud cover. In the study area, 5.76% meets these conditions. Based on the results, these conditions are found in deserts and coastal areas at high altitudes.”
The scientists also found that 4.43 percent of the study area had low heterogeneity values but high umbrella effect, making it the least suitable for solar photovoltaic installations.
The researchers also assessed the performance of over 1,900 existing solar power plants using annual and seasonal data. The analysis found that most of the existing solar power plants are located in areas with low solar uniformity and very low umbrella effect time index. Such locations account for 39.17% of the total study area. However, a significant portion of the existing power plants were found to perform suboptimally from June to August due to the umbrella effect caused by clouds. The researchers advised that these areas should not rely entirely on solar power to meet increased demand during these months.
In discussing the optimal form for future solar power plants, the research paper concludes that more widely distributed solar power generation is superior to more localised efforts, and highlights rooftop solar power as a key way to achieve increased stability of solar energy supply to the power grid.
“Based on the spatial and temporal characteristics of solar radiation, we suggest that by distributing small-scale solar power generation systems over a wide area, rather than relying on large-scale solar power plants, it should be possible to reduce the rapid fluctuations in solar power output,” Takenaka said. “It should be noted that these conclusions are drawn from meteorological and climate studies, not from an engineering perspective.”
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