Documentation

Documentation Methodology

Importance of terrain data

Accurate information about terrain features is important for solar project development. Below we review a few reasons why it is necessary to have reliable information on the terrain on and around the project site:

  • For utility-scale solar power plants, adequate flat areas are preferable. In more complex terrain, hills and slopes should be thoroughly analyzed and efforts required for design and engineering must not be underestimated (e.g. the row spacing of PV modules should be customized).
  • Terrain horizon helps to estimate energy losses because of shading from nearby hills or mountains
  • Elevation above sea level defines the thickness of the atmosphere above, which is an important input into the Solargis solar resource model
  • High altitudes might require the use of more resistant materials (due to UV factor)
  • On the coast or along the rivers, fundamental terrain analyses provide data about the possible risk of flooding

Elevation data

Presently, Solargis database features elevation data with a resolution of 3 arcsec (nominally 90 m) on the land and 30 arcsec (nominally 1 km) for the sea bottom. The final dataset is the result of rigorous patching of a few available terrain datasets:

  • Shuttle Radar Topography Mission (SRTM) version 4.1
    Citation: Jarvis, A., H.I. Reuter, A. Nelson, E. Guevara, 2008, Hole-filled SRTM for the globe Version 4, available from the CGIAR-CSI SRTM 90m Database (http://srtm.csi.cgiar.org)
  • Viewfinder Panoramas by Jonathan de Ferranti B.A.
    Citation: http://viewfinderpanoramas.org/
  • ASTER GDEM V2
    Citation: NASA/METI/AIST/Japan Spacesystems, and U.S./Japan ASTER Science Team (2009). ASTER Global Digital Elevation Model [Data set]. NASA EOSDIS Land Processes DAAC. doi: 10.5067/ASTER/ASTGTM.002
  • GEBCO Gridded Bathymetry Data
    Citation: GEBCO_2014 Grid, version 20150318, http://www.gebco.net

For land areas, primary dataset [1] is implemented. Dataset [2] is used to fill the lands above 60°N and below 60°S, and to fix or improve the identified problems in the dataset [1]. In a few cases of insufficient quality of [1] and [2], dataset [3] was post-processed and implemented. We have also tackled many issues in elevation data along the coastline. Finally, for sea bottom elevations, data source [4] is implemented.

Slope and azimuth data

Both parameters are calculated from terrain elevation data by Solargis approach. These are auxiliary parameters to elevation. A flat surface can be easily identified on the maps of both parameters. In case an inclined surface is identified at a project site, further analysis for optimal PV system design can be performed.

Frequently Asked Questions

Are buildings included in the Solargis terrain data and is shading from nearby objects considered?

First, let’s explain two terms:

  • DEM (digital elevation model), which should refer to a bare-earth altitude
  • DSM (digital surface model), which captures the highest solid surface (including built-up objects or even dense grown vegetation)

Solargis database features DEM terrain surface data (even though in some areas the noise from vegetation cover may be captured). The nominal resolution is 90 m, which is satisfactory for the regional analyses of the terrain structures in the neighbourhood (for example shading from surrounding mountains or hills).

For city models, DSM (digital surface model) is preferred, preferably in a sub-meter resolution. For detailed shading analyses of the roof PV, DSM model with a nominal resolution of about 10 cm or similar is recommended. Nowadays, there are no global DSM models in such high resolution available. However, there are regional activities to create country-wide products. Solargis models are capable to use high resolution data and compute solar resource and PV potential for the roofs of the entire city. However, in such case the computing capacity rises significantly, therefore such analyses are performed for limited areas.