Solar GIS Data: Free & Paid Sources for PV Design

Last updated: November 2026

A solar resource map can help you shortlist a site, but it cannot show every chimney, access restriction or grid constraint. Solar GIS data becomes useful when each layer has a clear purpose and its limits are recorded alongside the design.

This guide covers the layers that matter, free and paid sources, and a workflow from screening to yield modeling. It also explains why spatial resolution, time intervals and coordinate systems answer different questions.

SurgePV publishes this post and sells solar design software.

What Is Solar GIS Data?

Solar GIS data is any geospatial dataset used to evaluate, plan, or optimize a solar project. GIS stands for Geographic Information System. In solar work, GIS data is usually organized as raster grids or vector shapefiles. Each layer represents one variable tied to a location.

The core layers include:

• Solar irradiance , GHI, DNI, DHI, and GTI values across a grid
• Terrain , elevation, slope, and aspect from digital elevation models
• Land use and land cover , forests, water bodies, urban areas, agricultural zones
• Climate , temperature, wind speed, humidity, and snowfall
• Infrastructure , transmission lines, substations, roads, and property boundaries

Designers stack these layers in software like QGIS or ArcGIS Pro. The result is a suitability map. Areas with high irradiance, gentle slopes, clear land title, and nearby grid infrastructure show up as favorable. Areas inside protected zones, on steep terrain, or far from interconnection points get filtered out.

Why Solar GIS Data Matters in 2026

GIS helps teams identify what is known about a site and what still needs investigation. A resource layer, a land parcel and a utility map are different kinds of evidence; combining them does not make every layer equally accurate or authoritative.

Three practical reasons to review the data before design are:

1. Dataset versions change. A saved estimate may use a different weather period or resolution from a new download. Keep the old metadata so changes remain explainable.
2. Reviewers need traceable inputs. Record the source and assumptions before passing a yield estimate into a proposal or financial model. A named dataset is a starting point, not automatic lender acceptance.
3. Screening and detailed design need different evidence. Regional resource data can qualify a location; roof geometry and nearby obstructions need a closer assessment. Do not make a final installation promise from a screening map.

The financial importance depends on the actual project. Calculate the effect of an energy shortfall using the project’s export and self-consumption assumptions, rather than applying one generic revenue-per-kWh figure. Keep an illustrative sensitivity separate from a production forecast.

The Main Data Layers Designers Use

Not every layer matters for every project. A residential installer cares more about roof geometry and shade than about transmission-line proximity. A utility-scale developer cares more about slope, grid access, and land constraints. Here is how the layers break down.

Solar Irradiance Layers

Irradiance is the most important layer. It tells you how much energy reaches the site before any system losses.

GHI is the starting point for most flat-plate PV. DNI describes the direct beam component, while DHI describes diffuse radiation on a horizontal plane. Fixed and tracking PV calculations need an appropriate treatment of both components. Use the dataset units carefully: irradiance is power per area, while irradiation is energy per area accumulated over time.

Terrain Layers

Elevation, slope, and aspect come from digital elevation models like the Shuttle Radar Topography Mission (SRTM) or higher-resolution LiDAR. Slope affects construction cost and drainage. Aspect affects insolation on tilted ground. A south-facing slope in the Northern Hemisphere receives more direct beam radiation than a north-facing slope at the same latitude.

Terrain also feeds horizon shading. Distant hills can cut morning or evening production. The PVGIS manual documents a calculated or uploaded horizon. A terrain horizon does not replace a close-obstruction survey for the proposed array.

Land Use and Constraints

Land-use layers show forests, wetlands, water bodies, urban areas, and protected zones. These layers come from government agencies, OpenStreetMap, or commercial providers. They identify constraints that may require environmental or planning review; the responsible authority determines acceptability.

For rooftop projects, building footprints and zoning layers matter more. Some cities restrict solar on historic structures or require setbacks from roof edges.

Climate and Environmental Layers

Temperature affects module voltage and performance. Wind and snow loads affect structural design. Soiling from dust or pollen affects long-term yield. These layers come from reanalysis datasets like ERA5 or from satellite-derived products.

A common mistake is to use average temperature only. Module voltage sizing needs the coldest expected temperature, because Voc rises when it is cold. Yield modeling needs the temperature profile across the year, not just an annual mean.

Grid and Infrastructure Layers

Transmission lines, substations, roads, and parcel boundaries determine whether a site is developable. A high-resource plot may be unsuitable if a viable interconnection cannot be secured. Many GIS platforms include OpenStreetMap road data and public utility maps. Check the utility’s own records: a line shown on a map does not prove available capacity or a right to connect.

Free vs. Paid Solar GIS Data Sources

You do not always need to pay for solar GIS data. For early-stage screening and many distributed designs, free sources are sufficient. For financing and due diligence, agree the evidence and uncertainty requirements with the reviewer. Paying for a dataset alone does not make an assessment acceptable.

Global Solar Atlas

Global Solar Atlas is a useful starting point for exploring solar resource and PV potential. Distinguish a map image from a downloadable numerical layer, and inspect the metadata for the exact parameter you plan to use.

Avoid applying one resolution or coverage statement to every layer. Irradiation, modeled PV output and terrain products can have different spatial scales and assumptions. Preserve the download date, coordinate system and source description in the project folder.

For a downloadable alternative with visible product listings, Solargis’ free GIS page below lists irradiation, elevation, temperature and PV-output layers. A regional layer remains a screening input: it cannot verify the measurements of a particular roof or the status of a land parcel.

PVGIS

The JRC PVGIS user manual describes a free tool covering most parts of the world. It identifies PVGIS 5.3 as the default version and documents solar-resource outputs, PV calculations and typical meteorological year downloads.

The manual lists SARAH3 satellite data and ERA5 reanalysis among its resource databases. Availability depends on location and version. Record the selected database rather than describing all PVGIS outputs as one uniform global product.

Monthly and hourly outputs answer different questions. A monthly irradiation average is useful for seasonal screening, while a time series can support a calculation that depends on the sequence of weather. Check units and timestamps before transferring either into another tool.

NLR NSRDB

The National Solar Radiation Database is maintained by the National Laboratory of the Rockies, formerly NREL. Its download API documentation lists several products with different resolutions and coverage.

The table and chart reflect the opened NLR documentation in November 2026. Coverage differs between products, so a shorter interval is not a reason to select a dataset that does not cover the site.

Solargis

Solargis offers free GIS layers and commercial resource-assessment services. Its free maps and GIS data page lists GeoTIFF downloads for direct, diffuse and global irradiation, elevation, temperature and modeled PV potential.

For commercial work, request a scope that states the data period, coverage, uncertainty treatment, deliverable formats and permitted use. Site adaptation and measurement quality control are separate services worth discussing when local evidence is available.

Free does not mean unlicensed. Keep the attribution and reuse terms supplied with each download, especially if a map will appear in a customer-facing report. A screenshot, raw data export and derived map may have different documentation requirements.

When to Pay and When to Use Free Data

The free sources are not inferior for early work. Select a source by coverage, validation evidence, permitted use and the decision being made. A commercial provider may add support or a tailored study, but the reviewer still needs to evaluate its assumptions.

How to Use Solar GIS Data in a Design Workflow

A clean workflow prevents the most expensive GIS errors. Here is a seven-step process that works for distributed and utility-scale projects.

Step 1: Define the Project Boundary

Start with the site coordinates and a rough polygon. For rooftop projects, trace the building footprint. For ground-mount projects, use the parcel boundary or a search radius around a target point. Set your coordinate system early. Mixing EPSG:4326 with a local projected coordinate system is a common source of alignment errors.

Step 2: Pull the Base Solar Resource Layer

Download GHI and, if needed, DNI and DHI for your area. For U.S. projects, use NSRDB. For international projects, use Global Solar Atlas or PVGIS. Extract the long-term average value at your site. Note the uncertainty range if the source provides one.

Step 3: Add Terrain and Horizon Data

Import elevation data and generate a horizon profile. PVGIS documents calculated and uploaded horizon information. For nearby trees or buildings, collect the geometry needed for a separate site shading assessment. Verify the supported file formats in the tool you intend to use.

Step 4: Screen for Constraints

Overlay land use, protected areas, flood zones, and grid infrastructure. Flag areas that are undevelopable. For utility-scale projects, use proximity buffers to shortlist connection locations, then ask the utility about capacity and connection requirements.

Step 5: Run a Preliminary Yield Simulation

Import the GIS-derived irradiance and temperature data into your design tool. Model a few array configurations with different tilts, azimuths, and row spacings. Tools like SurgePV connect generation and financial modeling so you can see both energy and economics in one place.

Step 6: Validate Against Local Knowledge

Satellite-derived data can miss local conditions. A site downwind of a seasonal dust source, near a body of water with morning fog, or affected by new surrounding development may need adjustment. Talk to local installers or check nearby ground stations if available.

Step 7: Document the Data Source and Assumptions

Keep a source record with every yield assessment. Include the dataset name, version, resolution, time period and published uncertainty, where available. This transparency protects you during review and helps with project handoff.

Common Mistakes When Using Solar GIS Data

Even good data produces bad results when misused. Check these failure modes before using a map value in a design.

Using Long-Term Averages for Interannual Variability

A long-term average does not describe the spread between individual years. Review a multiyear series and its uncertainty where the financial decision needs downside estimates. A Pxx value is a probability-of-exceedance estimate and needs a documented uncertainty method; it is not simply a chosen discount to an average.

Ignoring Local Shading

Read the layer methodology to identify its horizon treatment. Regional layers generally cannot resolve the individual neighboring building, tree or new construction project that affects a particular array. Always pair resource data with a site-specific shade analysis.

Mixing Coordinate Systems

Different coordinate systems can align correctly when the GIS applies the right transformation. The QGIS projection guide explains on-the-fly reprojection and the difference between assigning a coordinate reference system and transforming coordinates. Incorrectly assigning the source system can place a layer in the wrong location; changing its label alone does not transform the data.

Applying Global Data Without Regional Validation

Free global datasets are validated against ground stations, but station density varies. In data-scarce regions, satellite estimates may drift. If you are designing in a region with few weather stations, discuss an uncertainty assessment or a measurement campaign with the technical reviewer. Short-term measurements also need quality control and a method of relating them to long-term conditions.

Forgetting Temperature and Soiling

GHI is only half the story. A site with high irradiance and high temperature may produce less than a cooler site with moderate irradiance, because module output drops as cells heat up. Dust, pollen, and snow also reduce yield and must be modeled.

Solar GIS Data and SurgePV Design Workflows

A useful design workflow keeps the site information, proposed layout and energy estimate tied to the same revision. Before choosing software, establish which inputs you need to import and what evidence must remain visible to a reviewer.

SurgePV’s published scope includes 3D roof modeling, array layout, shading analysis, energy-yield modeling, financial modeling and proposal generation. It does not publish a blanket promise of automatic GIS ingestion or a guaranteed data-to-proposal turnaround. Demonstrate the required formats and workflow on a representative site before relying on them.

The energy and financial workflow is relevant once the resource assumptions are documented. Keep local tariff, load and cost inputs separate from the irradiance data so a change in one source can be traced through the proposal.

Next Steps for Your GIS Data Review

Start with a source suited to the decision, record its limitations and add the evidence missing from the regional map. Check coordinate systems, local shading and site constraints before turning a screening result into a design commitment.

For your next project, retain a small data register alongside the design: layer name, provider, version, license, resolution, units, coordinate system and date downloaded. Add a note explaining why each layer is suitable for its intended use. This makes the handoff useful even when another engineer uses a different GIS application.

Bring that register to a SurgePV project walkthrough to discuss how the reviewed site inputs fit your layout, yield-modeling and proposal process.

Frequently Asked Questions

What is solar GIS data?

Solar GIS data is geospatial information used to plan photovoltaic systems. Resource, terrain, climate and constraint layers support different decisions. Keep each layer’s source and limitations with the design.

Which solar GIS data sources are free?

PVGIS, NSRDB and Solargis’ free GIS page provide publicly accessible solar-resource information. Check coverage, download format and reuse terms for the selected product. Access to a map does not imply that every underlying dataset has the same license.

What is the difference between GHI, DNI and DHI?

GHI describes total irradiance on a horizontal plane, DNI the direct beam normal to the sun, and DHI diffuse irradiance on a horizontal plane. PV models use these components to estimate radiation on the array. Check whether a downloaded value represents instantaneous power or accumulated energy.

How accurate is satellite-based solar GIS data?

Accuracy depends on the dataset, location, period and validation method. Spatial resolution alone is not an uncertainty estimate. Use published validation evidence and review local conditions before applying a resource value to a project.

Can I use solar GIS data for residential rooftop design?

Yes, as the regional resource input rather than a complete roof survey. Roof dimensions, nearby obstructions and mounting assumptions still need site-specific evidence. A coarse resource grid cannot resolve individual chimneys or trees.

What resolution do I need for solar GIS data?

The required resolution depends on the decision and the feature being represented. Regional resource screening and local roof geometry need different datasets. Review both spatial resolution and the time interval before importing the data.

How do I import solar GIS data into design software?

Check the receiving tool’s supported formats and units before importing a dataset. Preserve coordinate-system metadata, timestamps and source details. Verify a small sample against the original data before using the imported results in a proposal.