Target: SDG 7.1 By 2030, ensure universal access to affordable, reliable and modern energy services.

●  Background

Electricity shortage is the primary energy challenge faced by developing countries, with about 733 million people worldwide still lacking access to electricity in 2020. Access to electricity is an SDG 7 indicator reflecting electricity penetration, and timely and accurate data, which is of practical importance to its universal achievement. At present, global access to electricity data is mainly obtained using statistical surveys, which suffer from untimely data updates, uneven data quality levels, poor data comparability between different countries, uneven quality levels, non-spatialized data, and missing data in some developing countries. In response to these issues, this study develops a 500 m resolution data set of electrification conditions in BUAs in the world in 2014 and 2020. It proposes a new method for the remote sensing monitoring of electrification in BUAs, analyzes its global spatial distribution and change, and addresses the problems of missing data and untimely updates of existing electrification rates in some countries. It improves the global monitoring capacity of electrification conditions in BUAs, and provides data to inform the formulation of targeted power supply strategies.

●  Data

■  European Union Global Human Settlement Layer (GHSL) datasets. https://ghsl.jrc.ec. europa.eu/download.php?ds=bu.

■  NPP-VIIRS night images of the year. https://eogdata.mines.edu/nighttime_light/annual/v20/.

■  World Bank data on access to electricity by country. https://data.worldbank.org/indicator.

●  Method

This study presents a new method for remote sensing monitoring of the electrification status of BUAs. The method is based on the significant difference in night light brightness values between electrified and unelectrified BUAs, using European Union global built-up data (Corbane et al., 2018), randomly selecting image elements from non-BUAs as samples from unelectrified areas, and randomly selecting image elements from BUAs as samples from electrified areas from countries with 100% electrification, to construct a sample library, all of which are verified by all samples visually verified by high-resolution remote sensing images. Two-thirds of the samples were randomly selected from the sample pool and classified using the threshold method based on the night light histograms of the samples (Elvidge et al., 2021). The threshold value at which the classification accuracy of the electrified and unelectrified samples was highest was selected as the classification threshold, and the percentage of unelectrified BUAs was calculated for each country worldwide. Finally, the classification results were validated for accuracy using the remaining one-third of the samples in the sample pool (Gao et al., 2022a). More than 10,000 samples were involved in the accuracy validation, and the quality of the product was checked based on the judgment accuracy of the random samples. In this study, the method was used to produce a global data set of the remote sensing monitoring of electricity access in BUAs for 2014 and 2020.

●  Results and analysis

Based on global 500 m resolution NTL remote sensing data, a remote sensing monitoring method was proposed (Gao et al., 2022a), by which the electrification of global build-up areas in 2014 and 2020 was monitored. Based on a global test of over 10,000 random sample points, the product has an accuracy of 98.10%. The areas where errors arise are mainly located in rural areas with small floor areas, mainly due to the low resolution of the remote sensing data. Their spatial distribution and temporal variation patterns were analyzed for the purpose of assessing global progress in achieving SDG 7.1.1 access to electricity.

Africa and Asia, especially Sub-Saharan Africa, have the largest unelectrified BUAs in the world. The world’s unelectrified BUAs were mainly found in Africa and Asia in 2020 (Figure 4.1), with 76% of the 20 countries having the largest share of unelectrified BUAs located in Sub-Saharan Africa. Achieving the SDG 7 indicator of access to electricity for all globally will require additional and greater international support for developing countries.

Global electrified BUAs increased notably from 2014 to 2020. Global electrified BUAs increased from 96.95% to 98.68%, by 29,108.62 km², from 2014 to 2020 (Figure 4.2). According to the Global Power Plant Database of the World Resources Institute, in this period, the share of unelectrified BUAs decreased in 117 countries (regions), thanks to the construction of 415 power stations. In contrast, only 17 power stations were constructed in the 18 countries, with the largest increase in the share of unelectrified BUAs.

More than half of the countries (regions) where unelectrified BUAs increased notably are in fragile and conflict environments. 32 countries (regions) saw their unelectrified BUAs increase, by more than 0.1% in 18 of them. Six of these 18 countries were in medium- to high-intensity conflict (World Bank, 2022), one had a fragile social environment, three experienced armed conflicts (riots), and five were in economic recession due to the COVID-19 pandemic. Thus, political unrest, armed conflicts, and economic recession are among the main reasons behind the increases in unelectrified BUAs.

Highlights

●  A global remote sensing monitoring method for buildings and a global remote sensing data set for 2014 and 2020 were provided to support global electrification policies and investment decisions.

●  The electrified BUAs increased significantly around the world. 29108.62 km² of such areas were added globally in 2020 compared to 2014, raising their share by 1.73 percentage points. 117 countries (regions) experienced substantial increases in electrified BUAs; more than half of the countries (regions) experiencing decline were in fragile and conflict environments.

●  Discussion and outlook

This study focuses on indicator SDG 7.1 energy supply, and proposes a remote sensing monitoring method for the global electrification status of BUAs based on remote sensing data of NTLs, creating a global 500 m resolution remote sensing monitoring data set of building electrification status for 2014 and 2020, which can quickly, timely and accurately monitor the global electrification status of BUAs and improve the monitoring capability of the global electrification degree, and can provide global electrification policy making.

Developing countries may address their energy shortages by building new power plants, and renewable energy should be the focus of this endeavor. Most of the unelectrified BUAs in the world are found in developing countries. 117 countries (regions) have seen a reduction in unelectrified buildings due to the construction of power plants. Developing countries are suggested to vigorously develop renewable energy, such as solar and wind energy, because those renewable energies are widely available and easy to develop and use.

Further improvement in the capacity of Big Earth Data to support SDG 7 progress is needed, and more big data infrastructure for SDGs should be constructed. The Big Earth Data technology has the potential of global application for SDG 7.1 monitoring, in support of global SDG 7 monitoring. However, due to the limited spatial resolution of satellite remote sensing data, there is still room for improvement in some of the assessment results. In the future, a constellation of satellites for sustainable development should be developed to further enhance the supporting capacity of Big Earth Data for SDGs.