Albedo and Solar Power: What You Should Know

What is albedo? 

Albedo definition: Albedo is a measure of the reflectivity of a surface, defined as the ratio of reflected solar radiation to the total incoming solar radiation. It quantifies a surface’s ability to reflect sunlight and is commonly referred to as the reflection coefficient. Albedo values range from 0 to 1, where 0 represents a perfectly absorptive surface (no reflection) and 1 represents a perfectly reflective surface (all incident radiation is reflected).

Albedo is influenced by surface characteristics such as color, texture, and material composition, and is a critical parameter in fields such as climatology, remote sensing, and solar energy. It is typically determined through direct radiometric measurements or satellite observations, often supported by physical and statistical models.

In practical terms, lighter-colored surfaces (e.g., snow, sand, or white roofing) exhibit high albedo and reflect more solar energy, while darker surfaces (e.g., dark soil) have low albedo and absorb more energy, leading to higher surface temperatures. This principle is evident in everyday life, for example, dark clothing absorbs more heat under sunlight compared to light-colored clothing, due to differences in albedo.

Albedo also plays an important role in solar energy. Albedo is especially important with regard to bifacial solar panels that capture sunlight on both sides. Surfaces with higher reflectivity, like snow, enhance energy production by reflecting more light onto the panels. In contrast, dark soil absorbs light, reducing panel efficiency. Designers often choose reflective ground materials to boost performance after weighing up the relative cost vs improved solar output.

Types of albedo that affect solar design

In solar energy and climate modeling, black-sky, white-sky, and blue-sky albedo represent different scenarios of solar radiation reflection under varying atmospheric conditions:

• Black-sky albedo (also known as direct-beam albedo) describes the reflectivity of a surface under clear skies with direct sunlight only, excluding diffuse light. 

• White-sky albedo, by contrast, assumes entirely diffuse illumination, such as under completely overcast skies, and measures how a surface reflects light scattered from all directions. 

• Blue-sky albedo is a weighted combination of both, representing real-world conditions that include both direct and diffuse sunlight. 

These distinctions are highly relevant in solar panel system design. Understanding how the ground and surrounding surfaces reflect solar energy under different sky conditions helps optimize panel placement, ground cover materials, and energy yield predictions in various climates.

What are the surfaces with the highest and lowest albedo for solar radiation?

When designing a photovoltaic (PV) plant, the type of ground surface plays a crucial role in determining how much solar radiation is reflected, particularly for bifacial modules. Surfaces with the highest albedo include snow-covered ground, white gravel, and light-colored sand, all of which can reflect over 60–80% of incoming solar radiation. 

These high-reflectance surfaces significantly enhance the rear-side irradiation of bifacial panels. In contrast, dark soils such as clay, loam, or organic-rich topsoil typically exhibit low albedo values (often below 20%) and absorb most of the solar energy, reducing reflected light available to the panels. 

Even among dry soils, albedo can vary: sandy soils tend to reflect more than moist, compacted, or vegetated soils. Selecting or modifying ground surfaces to increase albedo, through artificial ground coverings or site grading, can therefore be an effective strategy to boost energy yield in bifacial PV systems.

Albedos of other surfaces include:

• Bare ground: 20%

• Bare soil: 17%

• Grass: 25%

• Dry Grass: 30%

• Sand: 36%

• White pebbles: 58%

• Snow: 65%

Measuring albedo

Scientists use a variety of methods to gather data on how different land surfaces and other areas reflect sunlight and solar radiation:

• Ground-based measurements: Instruments placed directly on the ground measure the reflectance of specific surfaces, such as snow covered areas, forests, or urban regions. These ground-based measurements are vital for validating satellite data and for studying the detailed properties of different surfaces, including how factors like vegetation, snow, or soil moisture affect albedo. This is the most common method used in solar plants.

• Laboratory measurements: In controlled laboratory settings, scientists analyze samples of materials, such as soil, sand, or artificial surfaces, to determine their reflectance properties. These experiments help researchers develop accurate models of albedo and predict how different materials will behave when exposed to sunlight and other forms of radiation.

• Aerial measurements: Instruments mounted on aircraft can measure the reflectance of surfaces from above, covering regional scales that are difficult to access from the ground. Aerial measurements are especially useful for studying remote or large areas, such as the Arctic or vast forests, and for capturing seasonal changes in albedo.

• Satellite measurements: Satellites orbiting the earth capture detailed images and data on the reflectance of land surfaces, oceans, and even clouds. These satellite observations allow scientists to calculate albedo values for various areas across the globe and monitor changes in surface reflectance over time, providing a big-picture view of how the earth’s climate is evolving.

How to improve albedo in your PV plant

Improving ground albedo is a practical way to enhance the performance of bifacial photovoltaic (PV) systems by increasing the amount of reflected sunlight reaching the rear side of the panels. One effective method is using light-colored gravel, which offers high reflectivity, durability, and low maintenance. 

Maintaining short, healthy grass can provide moderate albedo while also controlling soil erosion, though its reflectivity is lower than gravel and seasonal changes can affect performance. In colder regions, natural snow cover offers exceptionally high albedo (often over 80%), significantly boosting energy yield during winter months, though accumulation on panels must be managed. 

Other strategies include applying white or reflective ground coatings, using engineered reflective membranes, or selecting naturally reflective soils. The choice of albedo-enhancing materials should consider site-specific factors like climate, maintenance costs, and land use regulations.

Determine your albedo data with RatedPower

There are three different ways to determine albedo data using RatedPower, which you can find in the Energy tab.

The first option allows you to choose a yearly fixed albedo value based on ground type. The second allows you to use monthly data from the MODIS NASA satellite. The third offers data from NASA Power.

RatedPower provides detailed albedo data for in-depth analysis and system optimization. You can also create your own albedo values using the Createalbedo button, allowing you to set a fixed value for the year or input monthly data.

How to simulate with bifacials in RatedPower