In this document
This article explains why accurate terrain data matters for solar project design, covering how digital elevation models (DEM) are used to derive slope, azimuth, and 360° horizon data for shading analysis. It describes the data sources patched together for Solargis's global DEM (SRTM, Viewfinder Panorama, ASTER GDEM, GEBCO bathymetry), and how detailed Digital Surface Models and manual 3D site modeling extend this for rooftop and complex-site shading analysis.
Usage in Solargis platform |
|---|
This approach is used in Solargis Prospect, Solargis Evaluate, Solargis Monitor, Solargis Forecast, S2 PV simulation, TMY and TS API data, and consultancy services. |
What terrain data Solargis provides
Solargis derives four terrain parameters for every site from a global digital elevation model: Elevation above sea level (ELE), surface slope (SLO), surface azimuth (AZI), and a 360° horizon profile (HOR). These let PV simulations account for site-specific topography – shading from surrounding hills and mountains, the optimal design of systems on inclined ground, and the atmospheric thickness that affects solar irradiance modeling.
By accounting for site-specific topography, simulations can provide precise insights into energy yields, enabling informed decision-making and maximizing the efficiency of solar installations.
Terrain parameters derived from elevation data
Thanks to the processing of digital terrain models, a comprehensive terrain characterization can be conducted for each site using data on elevation (ELE). Based on this parameter, surface slope (SLO), and surface azimuth (AZI) are calculated. These three parameters are also published as map layers in Solargis Prospect – see Prospect map layers.
On the other hand, horizon data (HOR) is generated by aggregating points from the surrounding terrain into a 360° orientation series around the site. This analysis enables the estimation of potential energy losses due to shading from nearby hills or mountains. For how the horizon profile is viewed, edited and exported in Solargis Evaluate, see Far horizon shading; for how horizon shading is applied in the optical chain, see PV simulators comparison: Irradiance modeling.
Why elevation affects solar irradiance modeling
Solargis also uses elevation above sea level to determine atmospheric thickness, which directly affects solar irradiance modeling.
When terrain data alone is not enough
Although digital terrain models such as the Solargis DEM provide detailed information globally, to do a complete shadow analysis it is necessary to include local features, buildings, and other objects. To do so, more detailed surface models and 3D modeling tools are needed.
Solar project developers usually combine terrain information with other geo-data layers like land cover and population that provide useful information for studying project feasibility – see Additional geo data.
Figure 1: Terrain elevation, slope, and aspect maps example.
The Solargis digital elevation model (DEM)
The Solargis DEM is the global elevation dataset from which ELE, SLO, AZI and HOR are derived. This section covers what a DEM is, how slope and azimuth are calculated from it, its resolution, and the source datasets it is built from.
What a Digital Elevation Model is
A Digital Elevation Model (DEM) is a 3D representation of terrain created from elevation data, offering a detailed depiction of the Earth's topography. It maps land elevation at regular intervals, typically in a grid format, providing essential insights for accurate analysis and decision-making in solar project development. The Solargis DEM described below is one such model.
How slope and azimuth are calculated
Using high-resolution DEMs, slope and azimuth data—critical auxiliary parameters to elevation—are derived through the proprietary Solargis in-house methodology. These parameters enable precise identification of flat surfaces and areas with inclinations. When an inclined surface is identified at a project site, further analysis can be conducted to determine the optimal design of the photovoltaic (PV) system, ensuring efficient and cost-effective project implementation.
Resolution of the Solargis DEM
Solargis database features DEM data at the resolution of 3 arcsec (nominally 90 m) on the land and 30 arcsec (nominally 1 km) for the sea bottom. This is satisfactory for the regional analyses of the terrain structures in the neighborhood (for example, shading from surrounding mountains or hills).
Note: The 3 arcsec (90 m) Solargis DEM is intended for regional terrain analysis, such as shading from surrounding mountains or hills. Detailed shading from local objects requires a Digital Surface Model or a manual 3D site model.
For the elevation models selectable in the Solargis Evaluate Energy system designer, see Terrain properties.
Source datasets and how they are combined
The final Solargis DEM dataset is the result of rigorous patching of a few available terrain datasets:
Dataset | Role in the Solargis DEM | Applies to |
|---|---|---|
Primary elevation source | Land areas | |
Fills gaps and corrects identified problems in the SRTM data | Lands above 60°N and below 60°S | |
Global Digital Elevation Model (ASTER GDEM) | Post-processed and implemented where the quality of SRTM and Viewfinder Panorama is insufficient | A few isolated cases |
Gridded Bathymetry Data (GEBCO) | Sea bottom elevation | Sea areas |
Solargis has also tackled many issues in elevation data along the coastline.
Modeling detailed surface objects with DSM and 3D models
Where the Solargis DEM is not detailed enough for local shading, two approaches extend it: Digital Surface Models and manual 3D site models.
Digital Surface Models for rooftop and urban shading
Where Digital Surface Model (DSM) data is available, Solargis can analyze the highest solid surfaces, including built-up structures and dense vegetation. This is particularly useful for detailed shading analyses in urban environments, such as assessing rooftop PV potential. For such analyses, a nominal resolution of approximately 10 cm or similar is recommended to ensure precision.
Manual 3D site models in Solargis Evaluate
Since achieving globally uniform solutions for detailed surface modeling is challenging, the most common approach involves creating manual 3D models for individual sites using specialized simulation software such as Solargis Evaluate. This site-specific 3D modeling is critical for solar PV projects, enabling accurate energy yield estimation, comprehensive shading analysis, and space optimization. By developing detailed 3D representations of the project site, the software assists in determining the optimal placement and configuration of solar panels to maximize energy production.
Solargis Evaluate imports site data and generates 3D terrain models, to which you can add PV modules and obstructions such as buildings or trees for shading and sun path analysis. Iterating on the design against these simulations is how layout and spacing are optimized for the site, ensuring efficient use of space and maximizing energy output.
Further reading
Hole-filled SRTM for the globe. Version 4, available from the CGIAR-CSI SRTM 90m Database Jarvis, A., H.I. Reuter, A. Nelson, E. Guevara, 2008.
Viewfinder Panorama. Jonathan de Ferranti B.A.
Global Digital Elevation Model. NASA EOSDIS Land Processes DAAC. NASA/METI/AIST/Japan Spacesystems, and U.S./Japan ASTER Science Team (2009).
GEBCO Gridded Bathymetry Data. GEBCO_2014 Grid, version 20150318.