Solar radiation sets the pace for numerous vital processes on our planet, directly impacting the climate, energy production, plant growth, and building design. Measuring this radiation is no longer just a technical matter reserved for experts; it has become a growing concern for sectors as diverse as engineering, agriculture, architecture, and even healthcare. To capture all these nuances, a wide variety of precise instruments and measurement techniques have been developed, capable of providing reliable data on the intensity, duration, and quality of the radiation reaching us from the Sun.
In this article you will discover how exactly solar radiation is measured, what types exist, what are the main instruments and sensors used and how this data is applied in everyday life, the environment, and industry. Everything explained in detail. clear, rigorous, but close manner, so that both professionals and curious people can make the most of nature's most powerful energy.
What is solar radiation and why is it so important to measure it?
La solar radiation is electromagnetic energy emitted by the Sun, which reaches Earth after passing through space and the atmosphere. It is emitted in the form of electromagnetic waves, which include ultraviolet rays, visible light, and infrared radiation, covering a very broad spectrum of wavelengths.
Measuring it is essential because determines the climate, temperature, and hydrological cycle and many activities vital to the planet and society. It also serves as the basis for the development of technologies such as photovoltaic and thermal solar energy, sustainable building design, and efficient agricultural planning.
La solar radiation provides positive physiological effects on living beings: stimulates the synthesis of vitamin D, promotes certain metabolic functions and regulates phenomena such as plant evapotranspiration. But it also has effects less wanted, such as the impact on human health (sunburn, skin cancer) and on materials (degradation, aging of plastics, paints, etc.). Therefore, Knowing its intensity, duration and spectral distribution is vital to anticipate risks, plan activities and optimize energy resources.
Solar radiation: components, spectrum and basic magnitudes
When we talk about solar radiation, we are not referring to something homogeneous. It comes to Earth in different types and components, depending on whether the energy impacts us directly, is diffusely scattered by the atmosphere or is reflected by the Earth's surface.
- Direct solar radiation: It is the one that arrives in a straight line from the Sun, without being diverted through clouds or the atmosphere. It is the most energetic and the one that, for example, is exploited by concentrated solar systems.
- Diffuse solar radiation: It is one that, after passing through the atmosphere, has been dispersed by clouds, particles and gasesIt comes from all directions, even when the sky is cloudy.
- Global solar radiation: Is the sum of the direct and diffuse that extends over a horizontal surface above the Earth. This is the most common parameter for sizing photovoltaic solar installations.
- Reflected radiation: Part of the radiation that is returned to the atmosphere or other objects from the Earth's surface, depending on the albedo (reflective power) of the terrain, snow, water, buildings, etc.
- Net radiation: Is the difference between incoming and outgoing radiation (reflected or emitted by the Earth).
As for the spectrum, the solar radiation received by the Earth It focuses mainly on three bands:
- Ultraviolet (UV): From 100 to 400 nanometers (nm), approximately 7,2% of the solar energy received.
- Visible: From 400 to 700 nm, almost half (47,2%) of solar energy is the light we perceive with our eyes.
- Infrared (IR): From 700 nm to 1 mm, the remaining 45,6%, with a strong heating effect.
La most common magnitude To express solar radiation is the irradiance, which is measured in watts per square meter (W/m²), and indicates the instantaneous power received by a surface exposed to the sun.
Customary units and methods for quantifying solar radiation
Measuring solar radiation requires knowing both the units used as recording methods most common. Some key concepts:
- Irradiance (W/m²): It is the power per unit of surface received at a given instant.
- Radiant exposure or dose: It is the energy received in a period of time, normally expressed in kilowatt-hours per square meter (kWh/m²) o megajoules per square meter (MJ/m²).
- Sunshine or sunstroke: The time during which the Sun is above the horizon and direct radiation exceeds a certain threshold (typically 120 W/m²). It is measured in hours.
In laboratories, observatories and practical applications, other units are also added such as:
- Langley (ly): 1 cal/cm² = 11,63 Wh/m²
- Calories, BTUs, lux, and microeinsteins for specific applications such as photosynthesis or visible/ultraviolet radiation.
Therefore, the measurement can be done directly —using sensors on the surface— or hint, using mathematical models and satellites that estimate average values over large areas. The choice of method depends on the level of precision required and the purpose of the analysis.
Main instruments for measuring solar radiation
La technological solution Solar radiation measurement encompasses a range of devices, from classic and historical models to modern electronic sensors. Each instrument is designed to capture a specific aspect (global, direct, diffuse, reflected, ultraviolet, etc.) and is selected based on the application and budget. Here are the most relevant devices:
Pyranometer: the king of global measurement
El pyranometer It is, without a doubt, the most widely used instrument for measure global solar radiation. Its design consists of a sensor—usually a thermopile or photovoltaic cell—protected under a hemispherical dome of optical glass which captures the radiation that falls from a 180-degree field of view.
The operating principle is simple: solar radiation heats the thermopileWhich generates a voltage directly proportional to the irradianceIn photodiode-based models, the photoelectric effect is responsible for the electrical signal. The dome protects the sensor from ambient conditions and filters radiation outside the range of interest.
Main types of pyranometers:
- From thermopile: They offer a wider spectral response (280 to 3000 nm), high precision and are the standard for scientific studies and calibration standards.
- Silicon cell (photovoltaic): More economical and fast answer, although their precision is lower and they are limited to shortwave radiation (360-1120 nm).
Pyrheliometer: for direct radiation
El pyrheliometer is the specialist in the measurement of direct radiation. It consists of a collimator tube with a small hole that restricts the entry of light and a sensor placed at the bottom of the tubeIt must always point perpendicular to the Sun; therefore, it is usually mounted on an automated solar tracker.
The captured radiation heats a thermopile, a bimetal or a cavity, and the The resulting measurement is also expressed in W/m²They are especially important for concentrated solar installations, materials testing, and the calibration of other instruments.
Actinograph: the continuous recording
El actinograph is a solar radiation chart recorder. It usually uses a bimetallic sensor, and its operation is based on the differential curvature of a sheet of two metals, one painted black and the other whiteThese differences are transmitted to a mechanical system that generates a continuous graph of the global radiation received throughout the day.
Its accuracy is somewhat lower than that of modern pyranometers, but its historical value in meteorology and agriculture remains relevant, especially for trend recording and long-term studies.
Campbell–Stokes Heliograph: counting hours of sunshine
Un classical instrument that is still used In many weather stations it is the Campbell–Stokes heliograph. It is a solid glass sphere which concentrates the sun's rays on a graduated cardboard band, where it burns a trace as the Sun moves across the sky. In this way, we obtain the duration of daily sunshine, or the number of effective hours of sunshine.
This data is very useful not only for climatology, but also for solar and agricultural applications, as it defines the amount of time during which direct solar radiation exceeds a certain threshold.
Net radiometer and albedometer: measuring balances and reflections
El net radiometer measure the balance of incoming and outgoing radiation at the surface, typically using two pyranometers (one upward and one downward) and two pyrgeometers (for the longwave bands). Their data are essential for energy, agricultural, and climate analysis studies.
El albedometer is, in practice, the union of two opposing pyranometers, one oriented towards the sky and the other towards the ground. They allow calculating the albedo, that is, the fraction of radiation reflected by a surface relative to the incident radiation. Its application is essential for measuring the reflectivity of snow, water, pavements, crops, and other elements.
Spectroradiometer: the detailed analysis
To determine how energy is distributed in the different wavelengths of the solar spectrum, we resort to spectroradiometer. This instrument offers detailed spectral data, allowing the study of the effects of specific radiation on materials, plants, atmosphere and biological systems.
Spectroradiometers are essential for advanced research, especially when analyzing the effects of UV radiation, photosynthesis, or the efficiency of selective solar panels.
Ultraviolet (UV) radiometer: monitoring health risks
La measurement of ultraviolet radiation It is vital for public health, agriculture, and environmental research. UV radiometers They use UV-sensitive photodiodes and optical filters to capture the UVA (315-400 nm) and UVB (280-315 nm) bands. Thanks to them, the Ultraviolet Index (UVI) and health alerts are issued at times of high risk.
Pyrgeometer: for infrared radiation
El pyrgeometer It is designed to measure the longwave radiation, mainly infrared (700 nm-1 mm), both from the night sky and from the Earth's surface itself. They work with thermopile sensors and silicon windows, allowing IR radiation isolation and monitoring of nocturnal energy exchange, dew formation, and the global radiation balance.
Satellite Instruments: A Global View
In addition to ground-based instruments, meteorological satellites equipped with specialized sensors provide a global view of solar irradiance, mapping radiation over large areas for climate and energy uses.
How solar radiation sensors work: physical and technological principles
La technological basis of solar radiation sensors It varies depending on the physical phenomenon they exploit and the spectral range they wish to capture:
- Thermocouples or thermopiles: They use the thermoelectric principle: Solar radiation heats the sensor and a potential difference is generated due to the temperature variation between two dissimilar metals. It is the most precise system with the widest spectral range.
- Photodiodes and photovoltaic cells: They lean on the photoelectric effect: Incident radiation generates an electric current proportional to the light intensity. Ideal for more economical instruments, although with limited spectral response.
- Bimetallic sheets: In classical instruments such as the actinograph, the different thermal responses of two metals to radiation are exploited to record the absorbed energy.
- Optical filters and selective windows: They allow specific bands (ultraviolet, visible, infrared, etc.) to be isolated for specific applications.
In all cases, The sensors require periodic calibration using national or international standards—for example, the international solar constant of 1367 W/m²—to ensure data reliability and correct for possible deviations due to aging or dirt.
Factors affecting measurement: accuracy, calibration, and maintenance
To get reliable and comparable data It is essential to take care of several factors:
- Proper installation and orientation: An improperly leveled, tilted, or oriented sensor can significantly alter the reading. Pyranometers and most other measuring instruments should be placed horizontally and free of obstructions.
- Regular calibration: The instruments must calibrate against certified standards from time to time and whenever a possible failure is detected.
- Cleaning and maintenance: Dirt, dust, water, or insects on the sensor dome reduce accuracy and spectral response. It is recommended to regularly clean and inspect the condition of the housings and connectors.
- Thermal compensation: It is necessary to monitor the temperature of the sensor in sensitive instruments, since the ambient temperature itself can falsify the measurement.
- Protection against extreme conditions: In mountainous areas, polar regions, or deserts, sensors must be designed to withstand adverse weather conditions while protecting the electronic components.
Only in this way can we achieve that The collected values are valid for comparing different places, times and applications.
Main applications of solar radiation measurement
La information on solar radiation It plays a leading role in multiple sectors:
- Solar energy: Determining optimal areas for installing solar panels, planning and sizing photovoltaic and solar thermal systems, and monitoring facility performance and efficiency.
- Meteorology and climatology: Climate modeling, seasonal forecasting, analysis of terrestrial energy balance, studies on climate change and aquifer evaporation.
- Precision farming: Control of crop growth and development, efficient irrigation management, assessment of water and climate stress in plants.
- Public health: Monitoring and alerting against intense ultraviolet radiation, preventing diseases related to sun exposure.
- Environmental research: Air quality studies, carbon cycle modeling, monitoring the impact on materials and ecosystems.
- Bioclimatic architecture: Design of energy-efficient buildings, optimization of lighting and natural air conditioning.
Solar radiation is, in short, a transversal and essential variable in the management of territory, natural resources and daily life.
Technological advances and new trends in solar sensors
El Technological progress has significantly modernized the sectorThe most recent pyranometers and pyrheliometers feature:
- Digital sensing and wireless data transmission, integrated into automatic weather stations.
- Self-calibration and self-diagnostic capabilities to anticipate failures or deviations in the measurement.
- Miniaturization and cost reduction, which has facilitated its deployment in domestic and agricultural systems.
- Integration with satellites and big data applications, thus expanding the geographical and temporal vision of the solar resource.
- High-resolution broadband and spectral sensors for specialized measurements in energy, photosynthesis or atmospheric research.
These improvements have allowed solar measurement is more accurate, accessible and useful for decision-making.
Other forms of complementary measurement: indirect methods and modeling
In places where there are no physical instruments, solar radiation can be estimated by:
- Mathematical models: They use sunlight brightness data (sunshine hours) and empirical correlations (such as Ångström's formula) to calculate daily global radiation.
- Weather satellites: They collect radiation data over large areas and combine it with atmospheric, cloud, and aerosol information to produce radiation maps.
- Soil humidity and temperature sensors: They help estimate the impact of solar radiation on soils, crops and ecosystems.
These methods, although indirect, They are indispensable in large-scale solar planning and in the cross-validation of data obtained with ground-based sensors.
Tips for choosing and using a solar radiation meter
Select the suitable instrument it depends on several factors:
- Type of radiation to be measured: If you're only interested in global radiation, a pyranometer is sufficient. For direct radiation, a pyrheliometer is necessary. For reflected radiation, an albedometer.
- Accuracy and spectral range required: For research or calibration, opt for thermopile sensors with superior optical quality. Residential applications can use more economical photovoltaic models.
- Maintenance and ease of use: Make sure the equipment allows for easy cleaning and that calibration is accessible or automated.
- Support and compatibility: Look for instruments with technical support, clear manuals, and data compatible with energy management or meteorology systems.
It is always recommended go to distributors with experience and a proven reputation, since the quality and reliability of measurements depends largely on the robustness of the instrument and after-sales service.
Practical comparison between the most used instruments
To make your decision easier, here is a summary table with the main characteristics of the usual teams:
| Instrument | radiation type | Principle | Precision | typical application |
|---|---|---|---|---|
| Pyranometer (thermopile) | Global (direct + diffuse) | Thermal difference | High | Weather stations, solar studies, calibration |
| Pyranometer (photodiode) | Global (shortwave) | Photoelectric effect | Media | Residential solar installations, rapid monitoring |
| Pyrheliometer | Direct | Collimator + thermopile/bimetal | High | Research, solar concentration systems |
| Actinograph | Global | Bimetallic sheet | Middle-low | Historical record, agricultural studies |
| Heliograph | Sunlight (sunlight hours) | Optical sphere | Variable | Climatology, agricultural planning |
| Albedometer | Reflected / Albedo | Two pyranometers | High | Environmental studies, energy efficiency |
| Net radiometer | Total balance | Four sensors (two short, two long) | High | Meteorology, energy research |
| UV radiometer | Ultraviolet | UV photodiode + filter | High | Health, atmospheric research |
| Pyrgeometer | Infrared (long wave) | Thermopile + window Yes | High | Night balance, terrestrial energy |
Remember that the Correct choice improves decision making, safety and efficiency in any application where solar radiation plays a key role.
Typical errors in solar radiation measurement and how to avoid them
Not everything is as simple as just installing the sensor and that's it. Some common mistakes that can distort the results are:
- Poor leveling of the instrument: A deviated sensor can underestimate or overestimate irradiance.
- Unwanted shadows or reflections: A nearby antenna, branch or building may alter the measurement.
- Accumulated dirt: Dust, water or insects on the sensor dome impair the spectral response.
- Insufficient calibration: Using uncalibrated instruments or instruments with expired standards prevents comparability and reliability.
- Do not compensate for temperature: Some sensors vary their response with ambient heat.
The best way to avoid them is Scrupulously follow the manufacturer's recommendations and perform maintenance and calibrations according to use and installation.
Environmental and social impact of measuring and using solar radiation
El harnessing solar radiation It is one of the major bets towards a cleaner and more sustainable planet. However, the Large solar installations also entail environmental challenges, such as intensive land use, the management of potentially toxic materials in panels, water consumption in thermal plants, or the alteration of habitats.
La Accurate measurement of solar radiation helps optimize the design and location of solar plants, minimizing its footprint and maximizing environmental and social benefits. It also enables the development of more efficient and cleaner technologies, ensuring that the energy transition is carried out in the most responsible manner possible.
Reliable measurement is also a pillar for comply with international regulations and plan a sustainable energy future for all.
Case studies, interesting facts and future trends
Some interesting examples of advanced solar metering:
- Weather stations in extreme environments: Equipment capable of withstanding high mountain or polar zone conditions, with protected sensors and self-diagnostic systems.
- National and international solar monitoring networks: Synchronized and accessible data for governments, businesses, and researchers.
- Application in precision agriculture: Sensors that combine radiation and humidity data to adjust irrigation and fertilization in real time.
- Implementation in smart cities: Real-time radiation monitoring to optimize energy consumption and provide UV alerts to the population.
The future will bring smarter, more compact and connected sensorsThe integration of artificial intelligence and the fusion of data from multiple sources (ground sensors, satellites, weather models) will make it possible to anticipate trends and further optimize energy use and environmental protection.
Know How solar radiation is measured and what instruments are used It's key to maximizing the use of solar energy and protecting the environment and human health. From classic pyranometers and heliographs to advanced modern spectroradiometers and UV sensors, each provides invaluable information for different sectors. Accurate and reliable measurement is the first step toward optimizing the use of solar energy, ensuring human well-being, and moving toward a sustainable and resilient energy model, adapted to the challenges of the present and the future.