Silicon Irradiance Sensor for PV Performance Monitoring

RS485 Modbus PV Reference Cell for Plane-of-Array Irradiance Measurement

The JW-TBQ-GJ(LC13) Silicon Irradiance Sensor is a photovoltaic reference-cell sensor developed for measuring solar irradiance in PV power plants, rooftop solar systems, module testing projects and solar weather stations.

It uses a monocrystalline silicon sensing cell with a spectral response similar to that of conventional crystalline-silicon PV modules. This allows the sensor to provide irradiance data that closely reflects the solar energy available to the monitored PV array.

With RS485 output, standard Modbus communication, built-in temperature compensation and an IP65 outdoor enclosure, the sensor can be connected to data loggers, RTUs, PLCs, SCADA systems and PV monitoring platforms.

It can operate as an independent irradiance sensor or be integrated into a complete renewable energy monitoring solution with weather sensors, module temperature sensors, communication equipment and cloud-based data management.

Product Overview

The JW-TBQ-GJ(LC13) is also commonly described as a:

• PV reference cell
• Silicon reference cell
• Photovoltaic irradiance sensor
• POA irradiance sensor
• Reference-cell irradiance sensor

Unlike a general-purpose light sensor, it is specifically designed to monitor the solar irradiance received by photovoltaic modules.

Because the sensing element is based on crystalline-silicon technology, its response to sunlight is closer to that of a crystalline-silicon PV module than the response of many broad-spectrum radiation instruments. This makes it suitable for performance comparison, operational analysis and plane-of-array monitoring.

The sensor converts the response of the silicon cell into a digital irradiance reading that can be transmitted through RS485 Modbus to a local controller or remote monitoring platform.

What Does the Sensor Measure?

The sensor measures solar irradiance incident on its sensing surface.

When installed at the same tilt angle and orientation as the PV modules, it can provide plane-of-array irradiance, commonly abbreviated as POA irradiance.

POA irradiance represents the solar energy reaching the tilted surface of the PV array. It is especially useful for comparing:

• Available solar irradiance
• Expected PV output
• Actual inverter output
• Module temperature
• System efficiency
• Performance ratio
• Irradiance loss caused by clouds or shading
• Differences between PV strings or array sections

The sensor does not directly measure PV power output. Instead, it provides an environmental reference that can be compared with electrical production data.

Why Use a Silicon Reference Cell in a PV Plant?

A PV plant cannot evaluate performance accurately using power output alone.

A reduction in generation may be caused by:

• Lower solar irradiance
• Passing clouds
• High module temperature
• Dust or soiling
• Partial shading
• Module degradation
• Inverter limitation
• String failure
• Cable losses
• Grid curtailment

By measuring irradiance close to the PV array, operators can separate changes caused by available sunlight from changes caused by equipment or operational conditions.

For example, lower output during low irradiance may be normal. Lower output under strong irradiance may indicate a system performance problem that requires investigation.

Plane-of-Array Irradiance Monitoring

The sensor is normally installed at the same inclination and azimuth as the monitored PV modules.

This installation method allows the sensing surface to receive sunlight under conditions similar to those experienced by the array.

Plane-of-array data can support:

• PV performance ratio analysis
• Yield assessment
• Inverter performance evaluation
• String comparison
• Soiling loss analysis
• Module degradation studies
• Fault detection
• O&M reporting
• Solar forecasting
• Digital twin and analytics platforms

For large solar plants with different array orientations, multiple sensors may be required.

Separate monitoring points may be considered for:

• East-facing and west-facing arrays
• Different tracker blocks
• Fixed-tilt and tracking sections
• Different module technologies
• Separate inverter zones
• Areas with different shading conditions
• Geographically distributed plant sections

How the Silicon Irradiance Sensor Works

1. Solar Energy Reaches the Sensing Cell

Sunlight reaches the monocrystalline silicon sensing surface.

2. The Cell Produces an Electrical Response

The silicon cell generates an electrical signal related to the irradiance received by the sensing surface.

3. Temperature Compensation Is Applied

The response of silicon cells changes with temperature.

The built-in temperature compensation function helps reduce measurement deviation caused by changing outdoor temperatures and improves long-term monitoring consistency.

4. The Signal Is Converted into Digital Data

The sensor electronics process the signal and convert it into an irradiance value.

5. Data Is Transmitted Through RS485 Modbus

The measured value is sent to a data logger, RTU, PLC, industrial computer or monitoring platform through the RS485 interface.

RS485 Modbus Communication

The JW-TBQ-GJ(LC13) uses RS485 communication and supports the standard Modbus protocol.

RS485 is suitable for industrial and outdoor monitoring because it supports:

• Stable wired communication
• Multi-device networks
• Long-distance field cabling
• Integration with industrial controllers
• Standard register-based data reading
• Centralized sensor acquisition

The sensor can be connected to:

• PV data loggers
• Remote terminal units
• PLC systems
• SCADA systems
• Weather station controllers
• Industrial gateways
• Edge computing devices
• Local monitoring servers
• Cloud monitoring platforms

Before system integration, confirm the communication address, baud rate, parity setting, register map and data format in the latest communication protocol document.

Typical Technical Specifications

Technical specifications should be confirmed using the latest datasheet before procurement.

For engineering projects, please also confirm:

• Irradiance measurement range
• Resolution
• Response time
• Operating temperature range
• Storage temperature range
• Cable length
• Connector type
• Modbus register map
• Sensor dimensions
• Mounting-hole dimensions
• Calibration method
• Calibration documentation
• Surge and lightning protection requirements

Silicon Irradiance Sensor vs Pyranometer

A silicon irradiance sensor and a pyranometer both measure solar irradiance, but they use different sensing technologies and serve different project needs.

A silicon sensor is often preferred when the project needs an economical, fast-response irradiance reference closely related to crystalline-silicon PV module behavior.

A thermopile pyranometer may be more suitable when the project requires:

• Broad-spectrum solar radiation measurement
• Meteorological reference data
• Compliance with a specified pyranometer class
• Research-grade irradiance monitoring
• Comparison between different PV technologies
• Higher-level calibration traceability

JW-IoT also provides a Class A Pyranometer Solar Radiation Sensor with RS485 Output, a Solar Radiation Sensor Class C for 2000 W/m² Monitoring and a Photoelectric Total Solar Radiation Sensor for RS485 Irradiance Monitoring.

The correct sensor should be selected according to the required accuracy, spectral response, project standard, budget and monitoring purpose.

Silicon Reference Cell vs PV Module Power Data

A silicon reference cell measures incoming solar irradiance.

PV electrical monitoring measures:

• DC voltage
• DC current
• DC power
• AC output
• Inverter efficiency
• Energy yield

These measurements should not replace one another.

The irradiance sensor shows how much solar energy was available. The electrical monitoring system shows how much energy the PV system produced.

Comparing the two datasets helps operators evaluate whether the plant is converting available solar energy into electricity efficiently.

Performance Ratio Monitoring

Performance Ratio, or PR, is commonly used to evaluate normalized PV plant performance.

A simplified project-level comparison uses:

• Measured irradiance
• Installed PV capacity
• Actual energy output
• Module temperature
• Monitoring period
• System losses

The silicon irradiance sensor provides the solar irradiance input required by many PR monitoring systems.

For reliable analysis, irradiance data should be synchronized with:

• Inverter data
• Meter data
• Module temperature
• Ambient temperature
• Wind conditions
• Alarm records
• Plant availability
• Curtailment periods

Incorrect sensor installation or poor maintenance can directly distort PR results.

Installation Guidelines

Install at the Same Tilt as the PV Array

For plane-of-array measurement, the sensor should match the tilt angle and azimuth of the PV modules being monitored.

Even a small angular difference can create measurement differences, especially when the sun is low.

Avoid Shading

Do not install the sensor where it may be shaded by:

• Module frames
• Mounting structures
• Cables
• Junction boxes
• Railings
• Nearby sensors
• Vegetation
• Buildings
• Tracker components

The sensing surface should receive the same unobstructed sunlight as the monitored modules.

Select a Representative Location

The installation point should represent the operating conditions of the target PV array.

Avoid unusual locations affected by:

• Local reflections
• Permanent shading
• Excessive dust accumulation
• Water runoff
• Heat exhaust
• Snow drifting
• Uneven cleaning

Large plants may require several measurement points.

Keep the Sensing Surface Clean

Dust, sand, pollen, bird droppings, salt spray and water stains can reduce the measured irradiance.

The sensor should be inspected and cleaned as part of the PV plant’s regular maintenance schedule.

For soiling studies, make sure the cleaning method is consistent with the monitoring objective.

Protect the Cable

Route the RS485 cable through suitable conduit or cable trays.

Avoid:

• Sharp bends
• Loose connections
• Long unsupported cable sections
• Direct contact with hot module backsheets
• Water accumulation at connectors
• Parallel installation beside high-power cables without suitable separation

Use surge and lightning protection where required by the project design.

Record Installation Information

Document:

• Sensor serial number
• Installation date
• GPS location
• Array section
• Tilt angle
• Azimuth
• Cable length
• Modbus address
• Data logger channel
• Calibration information
• Maintenance history

This information is important for troubleshooting and long-term data traceability.

Front-Side and Rear-Side Installation

The current product configuration supports installation on the PV panel surface or rear side.

The selected method should match the monitoring objective and mounting accessory.

Front or Plane-of-Array Position

This position is generally used when the sensing cell must directly receive the same sunlight as the PV module surface.

The sensor should not create shading on the active module area.

Rear-Side Mounting Structure

Rear-side mounting may refer to fixing the sensor bracket to the back or frame of the module while keeping the sensing surface oriented toward the sky.

The sensing surface itself should remain unobstructed and aligned with the module plane.

Do not install the active sensing surface facing downward unless the application specifically requires reflected or rear-side irradiance measurement and the product configuration supports it.

Application Scenarios

Utility-Scale PV Power Plants

The sensor can be installed in fixed-tilt or tracking solar plants to support:

• Irradiance monitoring
• Performance ratio analysis
• Inverter-zone comparison
• O&M diagnostics
• Yield assessment
• Fault investigation

Rooftop Solar Systems

For commercial and industrial rooftop PV, the sensor can provide a local irradiance reference for comparing expected and actual system output.

PV Weather Stations

The sensor can be combined with:

• Ambient temperature and humidity sensors
• PV module temperature sensors
• Wind speed and direction sensors
• Rain gauges
• Atmospheric pressure sensors
• Data loggers
• Communication gateways

Explore more radiation sensors for complete solar and weather monitoring projects.

PV Module Testing

The sensor can support comparative testing of:

• Individual PV modules
• Different tilt angles
• Different module technologies
• Cleaning methods
• Cooling methods
• Mounting configurations
• Shading conditions

Solar Farm Operation and Maintenance

O&M teams can compare irradiance and production data to identify:

• Unexpected output loss
• Inverter underperformance
• String-level abnormalities
• Soiling-related loss
• Shading events
• Sensor faults
• Data synchronization problems

Distributed PV Monitoring

The compact RS485 structure makes the sensor suitable for distributed systems that require multiple irradiance monitoring points connected to local gateways or centralized platforms.

Renewable Energy Research

The sensor can be used in applied research involving:

• PV efficiency
• Irradiance variability
• Module temperature
• Solar forecasting
• Soiling loss
• Cloud effects
• Energy yield models

Complete PV Monitoring System

A complete PV environmental monitoring system may include:

1. Silicon irradiance sensor
2. PV module temperature sensor
3. Ambient temperature and humidity sensor
4. Wind speed sensor
5. Wind direction sensor
6. Rain gauge
7. Soiling monitoring sensor
8. All-sky camera
9. Data logger or RTU
10. RS485 communication network
11. 4G, Ethernet or LoRaWAN gateway
12. Cloud monitoring platform
13. API or SCADA integration
14. Surge and lightning protection

JW-IoT’s Renewable Energy Monitoring portfolio includes solar farm environmental monitoring, rooftop solar monitoring, floating solar monitoring, PV plant weather stations and IoT-based PV monitoring systems.

Data Quality and Common Installation Errors

Reliable irradiance data depends on more than sensor specifications.

Common causes of inaccurate readings include:

• Incorrect tilt angle
• Wrong azimuth
• Partial shading
• Dirty sensing surface
• Loose wiring
• Incorrect Modbus settings
• Voltage drop
• Wrong register interpretation
• Sensor and inverter clock mismatch
• Poor installation location
• Different cleaning conditions between the sensor and modules
• Using one sensor for multiple array orientations
• Missing calibration records

Data should be validated after installation by comparing:

• Sensor output during clear-sky conditions
• Nearby irradiance instruments
• PV power trends
• Module temperature
• Expected solar position
• Historical site data

Maintenance Recommendations

Regular Inspection

Check the sensor for:

• Surface contamination
• Mechanical damage
• Loose brackets
• Cable wear
• Corrosion
• Water ingress
• Connector damage
• Unexpected shading

Cleaning

Clean the sensing surface with a suitable soft, non-abrasive method.

Do not use sharp tools or harsh chemicals that may damage the optical or sensing surface.

Data Validation

Review the data for:

• Flat-line readings
• Sudden offsets
• Unrealistic nighttime values
• Repeated communication loss
• Differences from nearby sensors
• Unexplained deviation from PV output

Calibration

Calibration requirements depend on the project standard, contractual requirements and required measurement uncertainty.

Confirm the recommended calibration interval and available documentation before ordering.

How to Select the Correct Irradiance Sensor

Choose a silicon irradiance sensor when:

• The project mainly monitors crystalline-silicon PV modules
• Plane-of-array irradiance is required
• Fast operational monitoring is important
• Multiple monitoring points are needed
• RS485 Modbus integration is preferred
• Project cost must be controlled
• The sensor will support PR and O&M analysis

Consider a thermopile pyranometer when:

• Broad-spectrum measurement is required
• The project specifies a pyranometer class
• Meteorological reference measurements are needed
• Calibration traceability has higher priority
• Different PV technologies must be compared
• The project requires research-grade radiation data

Ordering Information

To recommend the correct configuration, please provide:

• Project application
• Installation country
• PV plant capacity
• PV module technology
• Fixed-tilt or tracker system
• Number of array orientations
• Number of monitoring points
• Required irradiance range
• Required accuracy
• Communication protocol
• Cable length
• Data logger or SCADA type
• Calibration requirements
• Quantity
• Expected delivery date

Why Choose JW-IoT?

JW-IoT provides sensors and system integration support for solar PV and renewable energy monitoring projects.

Available project support includes:

• Irradiance sensor selection
• PV weather station configuration
• Module temperature monitoring
• RS485 Modbus integration
• RTU and data logger configuration
• 4G and Ethernet communication
• Cloud platform connection
• API and SCADA integration
• OEM and private-label service
• Installation guidance
• Remote technical support

Request a Quotation

For pricing, technical documents, Modbus protocol information and project configuration support, please provide your PV plant type, monitoring points, communication requirements, cable length and quantity.

Contact JW-IoT for product selection and quotation

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