Satellite

Satellite Imagery


WorldView-3 imagery (worldview3.digitalglobe.com):

WorldView-3 is a commercial Earth observation satellite owned by DigitalGlobe (acquired by Maxar in 2017). It was launched on 13 August 2014. WorldView-3 collects panchromatic imagery of 0.31 m resolution, eight-band multispectral imagery with 1.24 m resolution, shortwave infrared imagery at 3.7 m resolution, and CAVIS (Clouds, Aerosols, Vapors, Ice, and Snow) data at 30 m resolution. It has an average revisit time of < 1 day and is capable of collecting up to 680,000 km2 per day. This satellite was used because the images it collects currently have the highest spatial resolution (31 cm) that is commercially available.


The following rooftop information, required to assess technical solar PV, was extracted from the WorldView-3 stereoscopic image pairs of the two cities (Ho Chi Minh City and Da Nang): outline or footprint; height; surface area, slope and orientation; type (flat, two-sided, four-sided, with or without obstructions, etc.); and shading (from surrounding buildings). Rooftop category (residential, public and industrial/commercial) was obtained from a local government-produced land use map for the individual cities.


Landsat-8 imagery (landsat.usgs.gov/landsat-8):

The Landsat 8 satellite, launched in February 2013, images the entire Earth every 16 days. It is the latest in a continuous series of land remote sensing satellites that began in 1972. Data collected by the instruments onboard the satellite are available to download at no charge from EarthExplorer, GloVis, or the LandsatLook Viewer within 24 hours of acquisition. Landsat-8 provides moderate-resolution imagery, from 15 meters to 100 meters, of Earth’s land surface and polar regions. Landsat 8 operates in the visible, near-infrared, short wave infrared, and thermal infrared spectrums. It captures more than 700 scenes a day.


Global Solar Atlas Data


The Global Solar Atlas (globalsolaratlas.info), provided by the World Bank Group, was used as the source of solar irradiation data at ground level. Three parameters were extracted from the Atlas: global solar irradiation received on a horizontal surface (GHI); global solar irradiation on a surface with an inclination angle equal to the latitude and oriented to the south (optimal surface, GOPTA); and solar irradiation on a tilted surface according to rooftop slope and azimuth (GTI). This allowed calculating the solar irradiation received by each rooftop (or part of it) according to its slope and aspect, in addition to the solar irradiation received by equivalent horizontal and optimal surfaces.


Definitions


Peak Capacity Yearly average of PV power that is expected to be generated, at solar noon, at a given site (a rooftop or a Commune) on a horizontal surface (unit = MW).
PV Optimal Yearly amount of energy, converted by a PV system into electricity, that is expected to be generated at a given site (a rooftop or a Commune) on a south-oriented surface with a slope equal to latitude (unit = MWh/year).
PV Tilted Yearly amount of energy, converted by a PV system into electricity, that is expected to be generated at a given site (a rooftop or a Commune) on a surface having the same slope and orientation as the rooftops (unit = MWh/year).
PV Horizontal Yearly amount of energy, converted by a PV system into electricity, that is expected to be generated at a given site (a rooftop or a Commune) on a horizontal surface (unit = MWh/year).
PV Optimal/m2 Yearly amount of energy, converted by a PV system into electricity, that is expected to be generated at a given site on an optimal surface, per square meter (unit = kWh/m2/year). This value is useful for determining the size of the PV systems to be installed.
Rooftop Area Total surface area of a rooftop, as calculated from the footprint that was extracted from the WorldView-3 imagery. Helps eliminate rooftops with surface area that is under the minimum threshold.
Suitable Area Subtracts from the Rooftop Area the surface area corresponding to shading, obstructions, and a 1-m maintenance buffer around the PV systems. At the Commune and country levels, it corresponds to the sum of all suitable rooftop areas (unit = km2).
% Suitable Area Corresponds to : ( Suitable Area / Rooftop Area ) x 100
Panel Efficiency The efficiency of a photovoltaic system is the ratio of conversion of the received solar energy into electrical energy. Values of PV panel efficiency range between 0.16 and 0.26 (news.energysage.com/what-are-the-most-efficient-solar-panels-on-the-market).
PV System A photovoltaic system, also PV system or solar power system, is a power system designed to supply usable solar power by means of photovoltaics. It consists of an arrangement of several components, including solar panels to absorb and convert sunlight into electricity, a solar inverter to change the electric current from DC to AC, as well as mounting, cabling and other electrical accessories to set up a working system (en.wikipedia.org/wiki/Photovoltaic_system).
PV Calculator Calculates total amount of energy (Wh) over an entire year on the basis of selected roof characteristics (surface area, type of PV system (horizontal, latitude or tilted) to be installed.

About the base layer


The basemap tiles are requested through the Google maps JavaScript API. These tiles are used in agreement with the Google Maps/Google Earth APIs Terms of service. IMPORTANT NOTE: The different base layers available in this application are used ONLY for visualization. The imagery one sees inside Google Earth is different from the images that were used for this project and might be older. This means that some buildings might not appear in the imagery provided by Google Earth since they were built after the image acquisition, but do appear in the WorldView-3 imagery used in this project. That explains why some rooftop markers appear at locations where it seems like there are no buildings. Similarly, buildings might also have been destroyed since the acquisition of the Google Earth imagery and no rooftop marker appears on them since they no longer exist in the more recent imagery.