Введение
How accurate should solar radiation measurement be? The answer depends on what the measurement is being used for. A solar resource assessment, a utility-scale PV project, and a general weather monitoring station may have very different requirements for data quality. This means there is no single accuracy value that is suitable for every solar monitoring application.
In practice, solar measurement accuracy is influenced not only by the sensor itself, but also by how it is calibrated, installed, and maintained in the field. The same is true when evaluating solar radiation sensor accuracy: a sensor specification provides important information about performance, but it does not necessarily represent the solar measurement accuracy of the complete measurement system under real outdoor conditions.
Understanding these differences helps users choose the right measurement equipment without simply selecting the sensor with the highest claimed accuracy. This guide explains what affects solar radiation measurement accuracy, how ISO 9060 classes should be interpreted, what different applications require, and how to select a suitable solar radiation sensor for reliable long-term monitoring.
Насколько точным должно быть измерение солнечной радиации?
There is no single accuracy level for every solar radiation measurement project. The requirement depends mainly on the purpose of the data. A weather station may only need reliable routine measurements, while solar resource assessment or PV performance analysis may require tighter control of measurement uncertainty.To learn more, click on “Что такое автоматическая система измерения с отслеживанием солнца?”
Оценка ресурсов солнечной энергии
Solar resource assessment relies on long-term GHI, DNI, or DHI data to characterize the available solar resource. Small measurement biases can affect the resulting solar resource estimates, particularly when data are collected over extended periods.
For this application, solar radiation measurement accuracy should be considered alongside calibration traceability, sensor stability, cosine response, spectral response, and site conditions. A well-calibrated sensor with stable field performance is generally more valuable than choosing equipment based only on a headline accuracy figure.
Мониторинг производительности PV-систем
PV monitoring uses irradiance data to evaluate energy yield and system performance. Depending on the project, measurements may include GHI or plane-of-array (POA) irradiance.
The required solar radiation measurement accuracy should be matched to the monitoring standard and the purpose of the analysis. ISO 9060 classification is useful when comparing instruments, but it should not be treated as a single overall accuracy percentage. Individual characteristics such as non-linearity, non-stability, directional response, and temperature response also matter.
Meteorological and Environmental Monitoring
For routine weather, agricultural, and environmental monitoring, the highest-performance sensor is not always necessary. The priority is usually a sensible balance between accuracy, stability, environmental resistance, maintenance, and cost.
In these applications, a properly installed and maintained sensor that provides consistent data can be more practical than an unnecessarily high-specification instrument.
What Determines Solar Measurement Accuracy?
The accuracy of a solar measurement system is not determined by the sensor specification alone. Sensor performance, calibration, installation, environmental conditions, maintenance, and data acquisition can all affect the final result. In long-term PV monitoring and solar resource assessment, even relatively small sources of error can become important when measurements are compared over months or years.
In practice, the main challenge is not simply choosing a sensor with a good datasheet specification. The measurement setup must remain suitable under the conditions in which it will actually operate. The following factors are therefore important when evaluating solar measurement accuracy in the field.To learn more, click here: Solar Measurement Mistakes: Common Errors Affecting Solar Irradiance Data Quality.
Производительность датчика
The starting point for solar radiation sensor accuracy is the performance of the sensing element and optical design. Key characteristics include non-linearity, non-stability, spectral response, temperature response, directional response, tilt response, and response time. These specifications describe different aspects of sensor behavior and should be considered together rather than reduced to a single solar measurement accuracy figure.
For a pyranometer, these characteristics determine how consistently the instrument responds as irradiance, solar position, temperature, and atmospheric conditions change. For example, directional response becomes more relevant at low solar elevations, while long-term stability is particularly important for monitoring systems expected to operate continuously for several years. For a closer look at pyranometer construction and measurement principles, see What Is a Pyranometer and How Does It Work?
Calibration and Traceability
Calibration establishes the relationship between the sensor output and a reference measurement under defined conditions. When evaluating a solar radiation sensor, a calibration certificate is useful, but buyers should also consider the calibration method, reference standard, traceability, measured sensitivity, and stated calibration uncertainty.
Calibration does not eliminate errors that may occur after the sensor is installed. Changes in sensitivity over time, installation conditions, contamination, temperature effects, and other parts of the measurement chain can contribute to the final field result. For long-term projects, maintaining calibration records and periodically checking sensor performance can help identify drift before it affects the measurement dataset significantly.
Cosine and Directional Response
Solar radiation reaches the sensor from different angles throughout the day, so the instrument needs to maintain an appropriate response as the solar zenith angle changes. This characteristic is commonly evaluated through directional or cosine response, which becomes increasingly relevant when radiation arrives at a large angle from the sensor’s normal axis.
The effect is particularly noticeable around sunrise and sunset, when the sun is close to the horizon. Installation can further increase the error if the sensor is not accurately leveled. For measurements where low-sun irradiance contributes significantly to the analysis, both the sensor’s directional performance and the accuracy of its installation should be considered.
Temperature Response
Outdoor solar sensors operate through a wide range of ambient temperatures, and changes in temperature can affect sensor output. The temperature response of the instrument is therefore an important consideration when evaluating solar radiation sensor accuracy, especially for monitoring systems exposed to large daily or seasonal temperature variations.
The relevant specification is not simply the sensor’s operating temperature range. Buyers should also review how the measurement response changes across that range and whether the stated performance applies under the conditions expected at the installation site. This is one reason laboratory or room-temperature performance should not automatically be treated as representative of long-term outdoor measurements.
Спектральная характеристика
The spectrum of incoming sunlight changes with solar elevation, atmospheric conditions, clouds, and air mass. Because a sensor does not necessarily respond equally to every wavelength, its spectral response can influence the relationship between the measured value and the actual broadband irradiance.
This consideration becomes more important when comparing different detector technologies or using irradiance data for PV performance analysis. Rather than looking only at the nominal wavelength range, engineers should consider how the sensor responds across that range and whether its spectral characteristics are appropriate for the intended measurement application.
Installation and Alignment
Correct installation is essential for achieving reliable field measurements. A pyranometer used for horizontal irradiance should be accurately leveled, securely mounted, and positioned where nearby structures, equipment, or vegetation cannot introduce significant shading or reflected radiation. The mounting structure should also remain stable throughout the monitoring period.
The installation geometry should match the measurement objective. For POA irradiance, the sensor should follow the orientation and tilt of the PV surface being evaluated, while GHI measurement requires a horizontal reference. On tracking systems, the measurement arrangement may also need to account for the movement of the array. These details can have a direct effect on the quality of the collected irradiance data.
Cleaning and Environmental Conditions
Outdoor exposure can gradually affect the optical surface of a solar radiation sensor. Dust, pollen, salt deposits, snow, frost, dew, and water droplets can reduce or modify the radiation reaching the sensing element. The severity depends heavily on the local climate and site conditions, so the same maintenance interval may not be suitable for every installation.
Condensation can be particularly difficult to detect because it may occur during periods when the sensor appears clean during routine inspection. Regular inspection and cleaning, together with suitable environmental protection, help maintain consistent measurements. For projects in dusty, coastal, snowy, or high-humidity environments, the maintenance plan should be considered as part of the measurement system rather than treated as a separate operational issue.
Solar Measurement Accuracy vs Measurement Uncertainty
A sensor’s stated accuracy describes its expected performance under defined test conditions, while measurement uncertainty reflects the range of values that can reasonably be associated with the measurement result. The two terms are related, but they are not interchangeable. A specification such as ±2% should therefore not be treated as a direct statement of the uncertainty of every measurement made in the field.
For solar radiation monitoring, the final measurement can be affected by several factors beyond the sensor itself, including calibration, installation, temperature, shading, contamination, and the data acquisition system. A calibration certificate provides important information about the instrument’s calibrated performance and traceability, but calibration uncertainty is only one component of total field measurement uncertainty.
This distinction is particularly important when selecting a solar radiation sensor for long-term monitoring. Rather than comparing instruments only by a single solar measurement accuracy percentage, buyers should consider the relevant performance characteristics, calibration and traceability, installation requirements, environmental conditions, and expected maintenance. In practical terms: Sensor specification ≠ Calibration uncertainty ≠ Total field measurement uncertainty.If you’d like to learn more, click on “Что такое пиранометр и как он работает?”
ISO 9060 Accuracy Classes Explained
What Is ISO 9060?
ISO 9060:2018 provides a classification framework for instruments used to measure hemispherical and direct solar radiation. For pyranometers, the classification considers multiple performance characteristics rather than assigning one overall accuracy percentage. These include response time, offset, non-stability, non-linearity, directional response, spectral response, temperature response, and tilt response.
This means an ISO 9060 class should not be interpreted as a simple statement such as “Class A = ±1%” or “Class B = ±2%.” The class indicates whether an instrument meets defined performance requirements across several characteristics. When evaluating a solar radiation sensor, the class should therefore be considered together with the individual specifications, calibration information, installation conditions, and requirements of the measurement project.
Class A, Class B and Class C
ISO 9060 classes provide a practical way to distinguish instruments with different levels of performance. Class A represents the highest performance category, while Class B and Class C provide progressively less demanding performance levels. The appropriate choice depends on how the irradiance data will be used, how much measurement error the project can tolerate, and whether a specific monitoring standard or contractual requirement applies.
For example, a long-term solar resource assessment project may justify Class A instrumentation because data consistency and measurement quality are important over the entire monitoring period. Many routine PV and meteorological applications can use Class B when its individual specifications meet the project requirements, while Class C can be appropriate for basic monitoring. The important point is to select the class based on the measurement objective rather than automatically choosing the highest available class.
| Classification | General Performance Level | Typical Application Consideration |
| Class A | Highest performance category | Solar resource assessment, research, high-quality irradiance monitoring, demanding PV applications |
| Class B | Intermediate performance category | Routine PV monitoring, meteorological stations, general solar radiation measurement |
| Class C | Basic performance category | General-purpose monitoring and applications with less demanding data requirements |
How to Choose the Right ISO 9060 Class?
Start with the measurement purpose, not the sensor class. If the data will be used to characterize solar resources, support bankable project studies, compare long-term irradiance data, or evaluate PV performance where measurement quality is critical, a higher-performance Class A instrument may be appropriate. For routine operational monitoring, weather stations, and applications where moderate measurement performance is sufficient, Class B may provide a more practical balance between performance and cost. Class C should be considered when the measurement objective does not require tighter performance.
The class is only the first filter. Before purchasing, check the specific performance characteristics relevant to the site and measurement parameter, along with calibration uncertainty, traceability, temperature response, directional response, non-stability, installation requirements, environmental protection, and maintenance needs. A Class B sensor with appropriate calibration and a well-controlled installation can be more suitable for a particular project than a higher-class instrument that is poorly matched to the application or operating environment.
What Accuracy Do Different Solar Applications Need?
The required solar measurement accuracy depends mainly on how the irradiance data will be used. Solar resource assessment and high-quality PV performance monitoring generally require stronger control of sensor performance, calibration, and long-term stability, while routine meteorological, agricultural, and general monitoring can use a more application-specific approach. The goal is not to select the highest-rated sensor in every case, but to choose a measurement system that provides sufficient data quality for the intended purpose.
| Приложение | Solar measurement accuracy Priority | Recommended Approach |
| Оценка ресурсов солнечной энергии | Очень высокий | High-performance sensor with reliable calibration and traceability |
| Мониторинг производительности PV-систем | Высокий | Appropriate ISO 9060 class matched to the monitoring requirements |
| Utility-Scale PV Monitoring | Высокий | Standard-compliant sensor and measurement setup |
| Метеорологический мониторинг | Medium–High | Sensor selected according to the required observation quality |
| Сельскохозяйственный мониторинг | Средний | Fit-for-purpose accuracy with good outdoor stability |
| General Solar Monitoring | Средний | Balanced solution based on accuracy, reliability, and cost |
Main Specifications to Compare When Selecting a Solar Radiation Sensor
When selecting a solar radiation sensor, buyers should compare more than the advertised accuracy value. The most relevant specifications describe how the sensor performs under different irradiance levels, solar angles, temperatures, spectral conditions, and long-term outdoor operation. Calibration information and data output should also be checked to ensure the sensor can be integrated and maintained properly within the measurement system.
| Технические характеристики | Почему это важно |
| Calibration & Uncertainty | Shows how the sensor response is established and how reliably the measurement can be traced to a reference standard. |
| Non-Stability | Indicates how sensor performance changes over time, which matters for long-term monitoring. |
| Non-Linearity | Shows whether the sensor maintains consistent response across its measurement range. |
| Directional Response | Determines how accurately the sensor measures radiation at different solar angles. |
| Temperature Response | Indicates how temperature changes can affect sensor output in outdoor conditions. |
| Спектральная характеристика | Shows how the sensor responds across the solar spectrum and affects measurement consistency under changing atmospheric conditions. |
How to Improve Solar Radiation Measurement Accuracy?
Improving solar measurement accuracy is not simply a matter of choosing a sensor with a tighter specification. In a field installation, the sensor, calibration, mounting, environmental conditions, maintenance, and data acquisition system all contribute to the final measurement result. A practical approach is to match the instrument to the measurement objective first, then control the factors that can introduce additional error during operation.If you would like to learn more, click on “Преимущества слежения за солнцем при измерении радиации.”
Select the Right Sensor and Calibration Level
Sensor selection should start with the parameter being measured—such as GHI, DHI, DNI, or POA irradiance—and the data quality required by the project. ISO 9060 classification provides a useful basis for comparing pyranometer performance, but buyers should also review calibration uncertainty, non-stability, directional response, temperature response, and spectral characteristics. For DNI measurements, the pyrheliometer and tracking system need to be considered as one measurement setup rather than as separate components.
Calibration records are equally important. A suitable calibration certificate should identify the calibration method, reference standard, traceability, and applicable uncertainty. For long-term monitoring, the expected calibration interval and the sensor’s stability over time should also be considered. A high-performance sensor with clear traceability provides a stronger basis for comparing data between sites and identifying changes in measurement performance.
Install and Maintain the Sensor Correctly
Even a well-calibrated sensor can produce poor field data if it is installed incorrectly. The sensor should be properly leveled and securely mounted, with the installation orientation matched to the measurement objective. The site should also be checked for shading, reflected radiation, nearby obstructions, and other conditions that can affect the sensor’s exposure to the sky. For long-term outdoor stations, the mounting structure must remain stable throughout seasonal temperature and weather changes.
Routine maintenance is part of solar measurement accuracy, not just equipment care. Dust, pollen, bird droppings, dew, frost, and condensation can change the optical response of the sensor surface. Inspection and cleaning should therefore follow the site’s environmental conditions rather than a fixed schedule alone. In areas with frequent condensation, frost, or heavy soiling, appropriate ventilation, heating, or environmental protection may be necessary to keep measurements usable.
Monitor Data Quality Over the Operating Period
Reliable solar measurements also require attention to the data acquisition chain. The sensor output, cable connections, data logger, power supply, sampling interval, and data processing should be checked as part of the measurement system. Sudden offsets, unrealistic values, flat-line data, or unusual differences from nearby reference measurements can indicate problems that may not be visible from the sensor itself.
For long-term PV monitoring and solar resource assessment, periodic data validation is particularly useful. Comparing the sensor with a suitable reference instrument, reviewing long-term trends, and retaining calibration and maintenance records can help distinguish real changes in irradiance from measurement problems. This is often more valuable in practice than relying on the sensor’s nominal accuracy figure alone.
How to Choose a Solar Radiation Sensor for Your Project?
The first step is to define what needs to be measured and how the data will be used. GHI, DHI, DNI, POA irradiance, and albedo are not interchangeable measurements, and each may require a different sensor configuration. For example, GHI and POA measurements normally use a pyranometer, while DNI measurement requires a pyrheliometer with a suitable tracking system. The required measurement interval and whether the data will be used for resource assessment, PV performance analysis, research, or general monitoring should also be established before comparing sensor models.
Once the measurement objective is clear, compare the specifications that have a direct effect on the quality of the intended data. ISO 9060 classification provides a useful starting point, but the individual performance characteristics should still be reviewed, particularly when measurements will be used for long-term analysis or project verification. Calibration documentation, traceability, spectral response, directional response, temperature response, and long-term stability can reveal differences between instruments that are not obvious from a single solar measurement accuracy figure.
The final decision should also account for the actual installation and operating environment. A sensor installed at a dusty utility-scale PV site may require different protection and maintenance provisions from one used in a controlled research station. Output type and data logger compatibility should be confirmed before purchase, especially for systems using RS485, Modbus, or other digital interfaces. For long-term projects, replacement parts, cleaning requirements, calibration arrangements, and technical support are practical considerations that can affect the reliability and total cost of the measurement system over several years.
Заключение
Good solar measurement is not simply about choosing a sensor with the highest accuracy rating. The right choice depends on what you need to measure, how the data will be used, and the conditions where the sensor will operate. A sensor that works well for a general weather station may not be the right choice for long-term PV performance monitoring or solar resource assessment.
In actual projects, sensor class, calibration, installation, environmental conditions, tracking, maintenance, and data checking all have a role in the final data quality. Paying attention to these details from the beginning can help reduce avoidable measurement errors and make the collected data more consistent and useful over time.
Yantai Sensor provides solar radiation measurement solutions for PV monitoring, meteorological observation, solar resource assessment, and other outdoor applications. We can help match the sensor type, performance level, and measurement configuration to your project requirements. Свяжитесь с нами to discuss the right solar radiation measurement solution for your application.
