| Work Detail |
An international research team has developed an index-based remote sensing method to observe trends in the global development of water-based photovoltaics. They found that China currently accounts for 80% of the total installed capacity worldwide. A research group led by scientists at Tianjin Normal University in China has used satellite imagery to reveal the rapid development of water photovoltaics (WPV) globally over the past 20 years. WPV comprises both floating photovoltaic systems and photovoltaic plants installed on fixed structures in shallow waters. For this task, the team developed an index-based remote sensing method, which they called the Normalized Difference Photovoltaic Index (NDPI). Index-based methods are mathematical formulas that identify terrain features based on spectral indices, calculated using different bands of light captured by satellites. “Compared to traditional thresholding and machine learning approaches, index-based methods are based on the universal characteristics of target objects, offering greater adaptability to variations in environmental conditions,” the researchers noted. “Furthermore, index-based methods provide faster and more flexible solutions for mapping and updating WPV information, as they respond directly to the spectral characteristics of target objects. Furthermore, WPV arrays, typically located over water surfaces, are less susceptible to environmental disturbances compared to land-based PV plants.” To create their NDPI method, the researchers analyzed 5,000 sites around the world using Google Earth. The samples were divided into five land cover types: bare soil, impervious surface, vegetation, water, and photovoltaic. According to the image analysis, solar panels reflect more shortwave infrared (SWIR) light than most surfaces and less visible and near-infrared (NIR) light than land or water. From these findings, the team was able to design formulas that detect solar panels above water. The method was then verified on more than 1,000 WPV installations, achieving accuracy (OA) for spatial distribution and installation date of 0.935 and 0.927, respectively. “Overall, WPV installation dates showed high accuracy, with user precision (UA), producer precision (PA), and F-score values ??above 0.9 for all years except 2012 and 2013,” they noted. Once the method was verified, the scientists applied it to 2023 images from the European Space Agencys (ESA) Sentinel-2 MSI satellite sensor. Using 2000-2023 images from NASAs Landsat satellite, the team tested the NDPI for installation date trends. “The global WPV area reached 589.14 km² in 2023. Notably, global WPV growth accelerated significantly after 2015, with an annual growth rate of 56.06 km² per year, nearly ten times that of the 2000–2015 period (5.98 km² per year),” the results show. “WPV development has been particularly rapid in Asia, driven mainly by China. In 2023, the WPV area in China reached 472.92 km², accounting for more than 80% of the global total.” The analysis revealed that Asia is the largest contributor to global WPV, accounting for over 97% of the WPV area, followed by North America at 1,569%, while all other continents account for approximately 1% combined. While China is the largest contributor, with a WPV area of ??472.92 km², Thailand and Vietnam emerge as key areas, each exceeding 20 km². “In China, policy support has significantly accelerated the development of WPV, with the WPV area increasing from 104.89 km² in 2016 to 472.92 km² in 2023,” they noted. “Apart from China, the WPV area in Vietnam also grew from 6.17 km² in 2017 to 24.24 km² in 2023, and the WPV area in Thailand nearly tripled year-on-year through 2023. In Europe and North America, WPV areas also continue to show an upward trend, with a significant acceleration between 2005 and 2009.” At the conclusion of their research, the team stated that they estimate global installed WPV capacity at 21.18 GW, with projections suggesting it could reach 35.64 GW by 2030. Their findings were presented in “ Satellite images reveal rapid development of global water-based photovoltaic over the past 20 years,” published in the International Journal of Applied Earth Observation and Geoinformation . |
