Pyranometer Sensors Explained: Which Type Is Right For Your Solar Project?

The right pyranometer sensor can make or break your solar project’s performance and profit potential. You have two main choices to measure solar radiation: thermopile pyranometers and Reference Cell Solar Irradiance Sensors. Each option works best for different uses.

Pyranometers measure global solar radiation in Watts per square meter (W/m²). They work especially well with wavelengths from about 285 to 3000 nm. Solar radiation sensors come in many types with different spectral responses, accuracy levels, and prices. Thermopile pyranometers give you high accuracy with measurement uncertainties around ±2%. But they take longer to respond (up to 30 seconds) and cost more than silicon-based options. So it’s crucial to know these differences before you buy measurement equipment for your solar setup.

What does a pyranometer measure and why it matters

A pyranometer sensor measures global solar irradiance – the total amount of solar energy that falls on a flat surface from a hemispherical (180-degree) field of view. The sensor captures both direct sunlight and diffuse radiation across the solar spectrum and converts this energy into measurable electrical signals.

Understanding solar irradiance

Solar irradiance represents the power per unit area received from the sun, measured in watts per square meter (W/m²). This measurement covers two significant components:

• Direct radiation – sunlight traveling straight from the sun to earth without interruption

• Diffuse radiation – sunlight scattered by clouds, atmospheric particles, or reflected from surrounding objects

The global irradiance (Eg↓) formula looks like this: Eg↓ = E⋅cos(θ) + Ed

E represents direct sunlight at maximum intensity, θ shows the angle between the surface normal and sun position, and Ed accounts for diffuse sunlight.

Global irradiance values typically range from 0 to 1400 W/m², though they can exceed this range when buildings or snow reflect light. Clear days at local solar noon show total irradiance between 700 and 1300 W/m², varying by latitude, altitude, and season.

The sun delivers 99.97% of all energy at earth’s surface. Solar radiation measures approximately 1,360.8 ± 0.5 W/m² at our atmosphere’s edge – a value known as the Solar Constant.

Why accurate measurement is vital for solar projects

Accurate solar irradiance data are the foundations of successful solar projects. Engineers use these measurements to find optimal site locations by assessing available solar resources, which directly affects system efficiency and energy yield.

Pyranometer sensors also help monitor operational performance. Operators can calculate a system’s performance ratio by comparing actual power output with expected output based on pyranometer readings. This ratio typically ranges from 75% to 85%. A sudden drop might signal the need for cleaning, repairs, or system fault checks.

Historical solar irradiance data helps predict potential energy yields and size PV systems properly during the design phase. The International Electrotechnical Commission standard (IEC 61724-1:2017) requires specific types and quantities of pyranometers based on plant size and category for utility-scale installations.

Measurement errors can affect financial outcomes significantly. Project bankability and investment decisions rely heavily on quality solar radiation data. A well-tuned Secondary Standard or Spectrally Flat Class A pyranometer should measure daily irradiance totals within 2% accuracy – the recommended level for most solar energy applications.

Types of pyranometer sensors explained

Pyranometer sensors come in two main types. Each type works differently and affects how they perform in applications of all sizes. You need to understand these differences to pick the right instrument for your solar project.

Thermopile pyranometers

Thermopile pyranometers use the thermoelectric effect to measure solar irradiance through temperature differences. A thermopile with multiple thermocouples sits at the core, and its active junctions lie beneath a black coating that absorbs solar radiation. These sensors generate about 10 μV per W/m² and produce outputs around 10 mV when the sun shines.

Modern thermopile designs feature one or two glass domes. The domes serve two purposes: they restrict spectral response to 300-2800 nm while keeping the full 180° field of view, and protect the sensor from convection. High-end models use a second dome that reduces instrument offsets and creates better thermal equilibrium.

Photodiode pyranometers

Silicon-cell pyranometers, as they’re also called, use semiconductor photodiodes. These photodiodes create current based on received light through the photoelectric effect. They respond faster and cost less than thermopile versions but have some key limitations. Their detection range covers only part of the solar spectrum—360-1120 nm for silicon-cell or 400-1100 nm for photodiode versions.

Spectral response differences

The way these technologies respond to different wavelengths marks a key difference between them. Thermopile sensors detect wavelengths from 300-2800 nm, which matches the full solar spectrum closely. Photodiode sensors detect a smaller range of 360-1120 nm. This selective detection leads to measurement errors when sky conditions change. Silicon-cell pyranometers show higher errors (10-15%) in cloudy weather because of this limitation.

Response time and temperature behavior

Response times vary greatly between these sensors. Silicon-cell pyranometers respond in under 1 millisecond. Thermopile models need 15-60 seconds to reach 95% of their final reading. This quick response makes photodiode sensors better at tracking rapid changes in irradiance.

Temperature response shows how sensitivity changes with ambient temperature. ISO 9060 defines it as sensitivity deviation over a 50K interval, shown as a percentage of calibration sensitivity. Class A pyranometers must keep temperature response within 2%, while Class C devices can deviate up to 8%. Thermopile pyranometers’ temperature response typically follows a third-order polynomial function.

Comparing pyranometer sensor performance

The reliability of measurements and project economics depend on how different pyranometer types perform. Several important factors need attention as you choose instruments for solar monitoring.

Accuracy and uncertainty levels

Each pyranometer class has different measurement uncertainty. Research shows that high-quality thermopile pyranometers reach uncertainties of approximately ±2.4%. Photodiode-based reference devices show higher uncertainties around ±5.0%. A Class A pyranometer can measure daily irradiance totals within ±2% with good calibration and maintenance.

The uncertainty calculations use a 95% confidence level. This means the true value has only a 5% chance of falling outside the stated range. The uncertainty figure plays a crucial role in bankability assessments and affects the calculated returns on investment.

Cost and maintenance factors

Pyranometer prices vary based on type. Class A pyranometers cost more than Class B or C models.

The total cost of ownership depends on:

• Calibration requirements (every 2 years for IEC compliance)

• Cleaning frequency (weekly for Class A systems)

• Ventilation and heating systems

Class A monitoring needs weekly cleaning and yearly recalibration to maintain high accuracy. Large solar projects face considerable operational expenses due to this maintenance schedule.

Standards and certifications (ISO 9060, IEC 61724-1)

ISO 9060:2018 puts pyranometers into three accuracy categories: Class A, B, and C. Each class has maximum calibration uncertainties: ±1.2% for Class A, ±1.5% for Class B, and ±2.4% for Class C.

IEC 61724-1 also defines monitoring system classes (A, B, C) with specific pyranometer requirements. Class A monitoring systems need heated and ventilated pyranometers that get cleaned weekly.

Integration with data loggers and systems

Solar monitoring works best with compatible data acquisition systems. Good data loggers should provide accuracy equal to 1 W/m² (10 μV). This prevents measurement quality from dropping.

New pyranometer systems often use digital outputs with Modbus RTU protocol over RS-485. This makes integration easier. IEC standards suggest logging every 3 seconds at least and storing 1-minute averages for the best data collection.

Choosing the right pyranometer for your solar project

Your project’s requirements and constraints will determine which pyranometer you should choose. Here’s what you should know about sensors that work best for different solar applications.

Small-scale residential systems or Agricultural and environmental monitoring

Homeowners who install solar systems care more about affordability than perfect precision. Silicon-cell pyranometers give good performance that meets most homeowners’ needs while staying economical. These sensors help track simple system performance and spot major issues like panel deterioration or excessive soiling. ES-S228A models work well for rooftop installations. A single well-placed sensor is enough because residential systems usually cover small areas with uniform conditions.

Utility-scale PV plants

Solar farms need detailed monitoring solutions. Industry standards require Class A pyranometers that meet IEC 61724-1 specifications for utility-scale installations. The ES-S228T has become the standard choice for large installations with over 65,000 units deployed worldwide.

Budget vs. precision trade-offs

Each higher pyranometer class doubles the measurement accuracy, from C to B to A. In spite of that, this precision costs more—both in money and upkeep. Class A instruments need weekly cleaning and regular recalibration. Several Class B or C instruments might give better results than one poorly maintained Class A device in places where maintenance is difficult. Your choice should balance upfront costs with long-term expenses based on your accuracy needs and available maintenance resources.

Conclusion

Choosing the Right Tool for Solar Success

Your specific project requirements, budget limits, and performance goals will guide your pyranometer choice. This piece explores how these vital sensors measure global solar irradiance. These measurements are the foundations of successful solar installations.

Technology makes a big difference in measurement quality. Thermopile sensors give you better spectral response (300-2800 nm) and accuracy (±2%). They take longer to respond and cost more. Photodiode options react faster and are more affordable but lose accuracy, especially in changing weather.

The decision goes beyond technical specs. You need to balance your upfront costs against future operational expenses. This includes how often you’ll need calibration and what maintenance you’ll do. Standards like ISO 9060:2018 and IEC 61724-1 help you match sensor capabilities to your project’s needs.

The size of your project determines which sensor fits best. Small home installations work well with affordable silicon-cell pyranometers. Large utility-scale plants need Class A thermopile sensors with full monitoring systems. Farms often require special wavelength coverage that matches what plants need for photosynthesis.

A great pyranometer only works well when it’s properly maintained and connected to the right data systems. Clean it regularly, calibrate it on schedule, and log data correctly. These steps ensure accurate readings throughout your solar project’s life.

These insights will help you pick the right measurement equipment for your solar installation. The right pyranometer lets you assess solar resources, verify system performance, and achieve a soaring win.

Contact us and discuss the selection with us.

FAQs

Q1. What are the main types of pyranometer sensors? There are two primary types of pyranometer sensors: thermopile pyranometers and photodiode (silicon-cell) pyranometers. Thermopile sensors offer higher accuracy and broader spectral response, while photodiode sensors are faster and more cost-effective.

Q2. How accurate are pyranometer measurements? Accuracy varies by sensor type and class. High-quality thermopile pyranometers typically achieve uncertainties of about ±2.4%, while photodiode-based devices show higher uncertainties around ±5.0%. Class A pyranometers can measure daily irradiance totals within ±2% with proper calibration and maintenance.

Q3. What factors should I consider when choosing a pyranometer for my solar project? Consider your project’s scale, budget, required accuracy, maintenance capabilities, and specific application needs. Also, factor in the sensor’s spectral response, response time, temperature behavior, and compatibility with your data acquisition system.

Q4. How often should pyranometers be calibrated and maintained? For IEC compliance, pyranometers typically require calibration every 2 years. Class A monitoring systems need weekly cleaning and annual recalibration. Regular maintenance is crucial for ensuring accurate measurements, especially for high-precision instruments.

Q5. Are expensive pyranometers always better for solar projects? Not necessarily. While higher-class pyranometers offer greater precision, they also require more maintenance. In some cases, multiple lower-class sensors might provide better overall performance than a single neglected high-end device, especially in large-scale projects or low-maintenance scenarios.