Insights from satellite data pave the way for better solar power generation

Given the ongoing energy crisis and the threat of climate change, the use of renewable energy sources has quickly become a global necessity. Although our options are varied, solar energy appears to be our best bet – experts estimate that it could be our main source of energy long before the turn of the century.

Despite its clear advantages, solar energy generation also has some limitations. Similar to wind, solar radiation in a given region can vary rapidly depending on weather conditions, leading to fluctuations in electricity production. These fluctuations not only pose a problem for electricity grids, but also mean that energy demand cannot always be met. Therefore, a clear understanding of the potential fluctuations in solar radiation in time and space is crucial to determining the optimal locations for solar power plants.

With this in mind, a research team led by Associate Professor Hideaki Takenaka of the Center for Environmental Remote Sensing at Chiba University set out to expand our knowledge of solar radiation over the Asia-Pacific region.

In their latest study, published in Solar energy in July 2024, they conducted an in-depth analysis of solar irradiance data collected by geostationary satellites. Other team members included Kalingga Titon Nur Ihsan of the Graduate School of Science and Engineering and Atsushi Higuchi of the Center for Environmental Remote Sensing, both from Chiba University, and Anjar Dimara Sakti and Ketut Wikantika of the Center for Remote Sensing at Institut Teknologi Bandung.

The data for the analysis came from Himawari-8 and Himawari-9, two Japanese satellites that collect high temporal and spatial resolution images over the Asia-Pacific region. The researchers used solar radiation data from AMATERASS, obtained from a quasi-real-time analysis of solar radiation synchronized with observations from geostationary satellites.

They were developed by Dr. Takenaka and colleagues to accurately estimate solar irradiance through high-speed radiative transfer calculations using neural networks. AMATERASS operation began in July 2007, and the analysis data have been continuously archived for over 16 years. These data have been made publicly available by Chiba University, CEReS DAAC (Distributed Active Archive Center), downloaded 186,465,724 times, and used in various research and Japanese national projects.

Using this technology, the team was able to estimate the variability of solar radiation in terms of spatial and temporal heterogeneity. Simply put, they calculated how drastically solar radiation varies in space and time by analyzing solar radiation data every ten minutes on a 20 km x 20 km grid.

Their analysis revealed interesting facts about solar radiation in the region. For example, the team found that solar radiation near the equator varied less over time due to rainfall and cloud activity than in higher latitude regions. In addition, higher-altitude regions showed greater heterogeneity due to higher cloud activity. The area around the Tibetan Plateau showed strong seasonal variations in the strength of the “umbrella effect,” which indicates how much solar energy is reflected back into space.

“Our analyses based on spatiotemporal data have revealed properties that could not have been achieved using a conventional approach that relies on simple long-term averages or TMY (Typical Meteorological Year) as typical solar radiation data,” says Dr. Takenaka.

In addition to these findings, the research team evaluated the performance of over 1,900 existing solar power plants using annual and seasonal data. They found that the production of a large proportion of these plants is suboptimal from June to August due to screen effects caused by clouds. This means that the most affected areas should not rely entirely on solar energy to meet the increased demand during these months.

Finally, the researchers also investigated the optimal format for future solar power plants and concluded that a more widespread distribution of solar energy would be superior to more localized generation.

“Due to the spatial and temporal characteristics of solar radiation, we believe that it should be possible to suppress rapid fluctuations in solar power generation by distributing small photovoltaic systems over a large area rather than relying on large solar power plants,” explains Dr. Takenaka.

“Notably, these conclusions come from weather and climate research rather than from an engineering perspective.” One way to realize this vision could be the use of solar panels on rooftops, which is a growing trend in many countries.

Overall, the findings of this study will help us plan the short- and long-term future of solar power generation in the Asia-Pacific region, promote sustainable energy technologies, and support our fight against climate change.