April 26


A Comprehensive Overview of Solar Resource Analysis

By hacheng1@gmail.com

April 26, 2023

In this article, you will learn about the basics of solar resource analysis, including its definition and importance, as well as types and units of solar radiation. The factors that affect solar resource quality, like geographic location, seasonal variations, and weather conditions, will be discussed. You will also explore different solar resource assessment methods, such as on-site measurements and satellite data, and commonly used software tools for solar resource analysis. Finally, the article will touch upon the applications of solar resource analysis in energy system planning, such as grid integration, policy making, and spatial planning for solar energy development.

Solar Resource Basics

Definition and Importance of Solar Resource Analysis

Solar resource analysis refers to the study and evaluation of the availability, distribution, and intensity of sunlight at a given location. Understanding solar resources is crucial for designing, installing, and operating solar energy systems effectively. This information helps system planners, developers, researchers, and policymakers make informed decisions about the appropriate size, placement, and configuration of solar installations to maximize energy production while minimizing costs and environmental impacts.

Types of Solar Radiation: Direct, Diffuse, and Global

There are three primary types of solar radiation that solar resource analysts need to consider: direct, diffuse, and global radiation.

Direct radiation, also known as beam radiation, is the sunlight that travels in a straight line from the sun to the Earth’s surface without being scattered or absorbed by the atmosphere. Direct radiation is the primary source of energy for most solar energy systems, such as photovoltaic (PV) panels and concentrated solar power (CSP) systems.

Diffuse radiation is sunlight that has been scattered by the atmosphere, clouds, and other particles before reaching the Earth’s surface. Diffuse radiation typically has lower intensity compared to direct radiation but contributes to the overall solar resource received by certain solar technologies, such as solar thermal collectors.

Global radiation refers to the total amount of solar energy received at the Earth’s surface, including both direct and diffuse components. Global radiation measurements are essential for determining the total solar resource available in a location.

Units of Measurement for Solar Energy

The most common unit of measurement for solar energy is the watt per square meter (W/m²). This unit is used to express the intensity or irradiance of solar radiation at a given location. Other units include kilowatt-hours per square meter (kWh/m²), which represents the total amount of solar energy received over a specific period (e.g., daily or monthly). Solar resource analysts also use various other metrics to describe solar resources, such as the duration of sunshine hours, the solar zenith angle (the angle between the sun and a point directly overhead), and solar elevation angle (the angle between the sun and the horizon).

Factors Affecting Solar Resource Quality

Geographic Location

Several geographic factors influence the quality and quantity of solar resources available in a location:

Latitude and Longitude: As one moves closer to the equator, the intensity of solar radiation increases, leading to higher overall solar resource potential. Similarly, sunlight hours increase as one moves towards the poles during the summer and decrease during the winter.

Altitude: Higher altitude locations tend to have stronger solar resources due to reduced atmospheric interference and lower air density. This results in a higher percentage of direct solar radiation reaching the Earth’s surface.

Seasonal and Time-of-Day Variations

Solar resources fluctuate throughout the year and the day due to changes in the Earth’s tilt, rotation, and orbit around the sun. These variations affect the angle and duration of sunlight received at a location, leading to changes in solar irradiance and energy production potential. Understanding seasonal and time-of-day variations is critical for optimizing the output and efficiency of solar energy systems.

Weather and Climate Factors

Weather and climate play a significant role in determining solar resource availability. Cloud cover, humidity, temperature, and other meteorological factors can affect the levels of direct, diffuse, and global solar radiation received at a location. Areas with consistently clear skies and low humidity tend to exhibit higher solar resource potential, while regions with frequent cloud cover or high humidity may experience reduced solar energy production.

Topography and Surrounding Environment

The topography, including features such as hills and valleys or man-made structures such as buildings and vegetation, can significantly influence solar resource availability. Shadows, reflections, and shading from surrounding objects can impact the amount of sunlight received by solar energy systems, affecting their overall performance and output.

Solar Resource Assessment Methods

On-Site Measurements

Accurate on-site measurements are critical for assessing solar resources in a specific location. Instruments used for these measurements include:

Pyranometers and Pyrheliometers: These devices measure global and direct solar irradiance, respectively, and are typically mounted on weather stations or standalone solar monitoring stations.

Ground-based Radiometers: These instruments measure solar radiation at various wavelengths (e.g., UV, visible, and infrared) to provide detailed information about atmospheric effects on solar resources.

Data Collection and Quality Control: Ensuring the accuracy and reliability of on-site measurement data is essential for reliable solar resource assessment. This requires regular calibration, maintenance, and quality control procedures for the monitoring equipment.

Remote Sensing and Satellite Data

Remote sensing and satellite data are increasingly used for solar resource assessment and mapping in conjunction with on-site measurements. Key aspects include:

Global Meteorological Satellite Services: Several satellite services, such as the National Oceanic and Atmospheric Administration (NOAA) and the European Space Agency (ESA), provide solar resource data covering the entire globe.

Advantages and Limitations of Satellite Data: Satellite data has the advantage of providing continuous coverage of large areas, but their accuracy can be affected by factors such as atmospheric disturbances or sensor limitations.

Climate and Reanalysis Models

Climate and reanalysis models are essential tools for predicting and assessing solar resource availability:

Global and Regional Models: Climate models simulate atmospheric conditions and generate long-term estimates of solar resources at global, regional, and local scales.

Validation and Uncertainty Assessment: Comparing model outputs with on-site measurements and satellite data is crucial to validate the accuracy and reliability of climate and reanalysis models. The assessment of uncertainty helps in identifying potential errors and limitations in these models.

Tools and Software for Solar Resource Analysis

Geospatial Mapping and Solar Potential Tools

Geospatial mapping tools help visualize solar potential and other pertinent data in a specific location on a map. These tools are particularly useful during the initial stages of solar project planning, as they can provide information on solar radiation, land use, rooftop potential, and other variables relevant to solar energy systems.

Some popular geospatial mapping tools for solar resource analysis include:

  1. Google Project Sunroof: This tool uses 3D aerial imagery and machine learning to estimate rooftop solar potential at a specific location, taking into account factors such as rooftop area, shading, and changes in solar irradiation throughout the year.
  2. Global Solar Atlas: Developed by the World Bank Group, this web-based tool provides solar resource data for any location in the world. It combines satellite data and on-site measurements to estimate global, direct, and diffuse solar radiation, as well as historical time series and aggregated data for various time scales.
  3. U.S. National Renewable Energy Laboratory (NREL) Solar Prospector: This tool provides renewable energy data, including solar resource data, to assist with renewable energy project siting and implementation. It includes data layers on various factors that affect solar energy production, such as solar insolation, land use, and terrain.
  4. European Commission’s Joint Research Centre (JRC) – Solar Photovoltaic Geographical Information System (PVGIS): This online tool is designed to assess solar electricity production at a specific location. It uses historical solar radiation data and a photovoltaic model to provide an estimate of energy output for a given photovoltaic system.

Popular Solar Resource Assessment Software

PVGIS (Photovoltaic Geographical Information System)

PVGIS, developed by the European Commission’s Joint Research Centre (JRC), is an online tool that provides estimates of solar energy production for any location in Europe, Africa, and Asia. The tool uses a database of solar radiation data to calculate the amount of energy a photovoltaic system will generate at a specific site. PVGIS considers factors such as the type of PV technology, system orientation, and shading.

System Advisor Model (SAM)

The System Advisor Model (SAM) is a free, comprehensive performance and financial model designed by NREL to facilitate decision-making for renewable energy projects, including solar photovoltaic (PV), concentrating solar power (CSP), and solar water heating systems. SAM can simulate a wide range of technologies and financial structures and provides estimates of energy production, cash flows, and other performance metrics. In addition to solar resources, SAM can also model wind, geothermal, biomass, and conventional power systems.


RETScreen is a clean energy management software program developed by the Canadian government’s CanmetENERGY laboratory. The software allows users to determine the viability of proposed renewable energy projects by comparing the energy production, greenhouse gas reductions, and life-cycle costs of different technologies. Users can input location-specific solar resource data to estimate the potential energy production of a solar power plant.

Software for Solar Simulation and Energy Production Prediction


PVSyst is a leading solar simulation software that estimates the energy production of PV systems based on specific project parameters. The software uses various solar resource datasets to calculate solar irradiance at a given site and takes into account the PV system’s design features, such as module type, system orientation, and shading. PVSyst also provides detailed simulations of PV system performance, including expected monthly and annual energy production and component temperatures, as well as a comprehensive financial analysis tool.


HelioScope is an advanced solar design and performance modeling software that combines 3D CAD modeling and solar simulation into a single, easy-to-use platform. It enables users to efficiently design and compare different PV system layouts and configurations while taking into account solar resources, shading, and other site-specific factors. HelioScope’s integrated solar simulation engine provides accurate energy production estimates based on the project’s design and location, allowing users to optimize their solar projects to maximize energy production and return on investment.

Solar Resource Applications in Energy System Planning

Grid Integration of Solar Energy Systems

Solar resource analysis plays a critical role in determining the optimal integration of solar energy systems onto the energy grid. Accurate solar resource data allows grid operators and utilities to plan for the impact of solar energy on the grid, including distribution and transmission upgrades, load forecasting, and system balancing. Solar resource analysis can also assist in determining the suitability of various solar technologies, such as PV or CSP, and their integration with energy storage systems for improved energy system flexibility and reliability.

Energy System Modelling and Impact Analysis

Solar resource data is essential for the development of accurate and robust energy system models. These models provide insights into the potential of solar energy to contribute to long-term energy system decarbonization and can be used for scenario analysis and policy evaluation. Understanding the availability and distribution of solar resources helps in evaluating the potential impacts of large-scale solar energy deployment, such as land use changes, environmental impacts, and social acceptance.

Spatial Planning for Solar Energy Development

Spatial planning is critical for the sustainable development of solar energy projects, as it helps identify the most suitable locations for solar development based on factors, including solar resources, land use, environmental constraints, and grid infrastructure. Solar resource analysis is essential for spatial planning, helping to identify areas with high solar potential and low environmental or land use conflicts. Along with geographic information systems (GIS), solar resource data can be used to generate solar resource maps, which can assist in the identification of priority areas for solar energy development and inform land use or zoning regulations.

Renewable Energy Policy and Support Mechanisms

Accurate solar resource data is vital for the establishment of effective renewable energy policies and support mechanisms. Policy-makers can utilize solar resource analysis to set realistic targets and develop appropriate support mechanisms, such as feed-in tariffs or auctions, tailored to the prevailing solar resource conditions. Solar resource data can also help identify potential barriers to solar energy deployment, such as grid integration challenges, and inform policies or regulatory measures to address these challenges.

Frequently Asked Questions

What is the purpose of performing a solar resource analysis?

A solar resource analysis evaluates the potential for solar energy generation in a specific area. This assessment provides valuable information on the long-term energy production, site suitability for solar power installation, and helps optimize system design for maximum efficiency.

What factors are considered when conducting a solar resource analysis?

Several factors, such as solar irradiance, topography, land use, temperature, and shading objects, are taken into account when determining solar energy potential. The analysis combines historical meteorological data with field measurements to produce an accurate representation of the solar resource for the selected site.

What is the significance of Global Horizontal Irradiance (GHI) and Direct Normal Irradiance (DNI) in solar energy analysis?

Global Horizontal Irradiance (GHI), or total received solar radiation, and Direct Normal Irradiance (DNI), or direct sunlight beams, are crucial metrics for determining the potential of solar energy generation. Higher levels of GHI and DNI indicate greater solar resource availability, thereby increasing the feasibility and efficiency of a solar power installation.

How is the tilted plane irradiance calculated during solar resource analysis?

Tilted plane irradiance accounts for the solar radiation received at various tilt angles and orientations of the solar panels. To calculate the tilted plane irradiance, experts combine the incident solar radiation, reflecting the inclination and orientation, with the surrounding diffuse radiation. This process helps optimize the panel placement for maximum energy output.

Why is the use of solar resource analysis software essential during the planning stage of solar power installations?

Solar resource analysis software utilizes advanced algorithms for accurate solar radiation estimation and detailed site suitability analysis. It saves time and resources, streamlines the decision-making process, and maximizes system efficiency by optimizing panel orientation and detecting potential shading issues.

What are the benefits of implementing a solar resource analysis for homeowners and businesses?

Undertaking a solar resource analysis helps homeowners and businesses identify the feasibility of solar installations, estimate long-term energy production, and maximize system efficiency. It evaluates potential cost savings, allows informed decision-making, and contributes to smarter, more sustainable energy use.


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