• UNI-T UT381PV Solar Irradiance Meter front view, irradiance and dual temperature display
  • UNI-T UT381PV Solar Irradiance Meter front view, inclination and azimuth display
  • UNI-T UT381PV Solar Irradiance Meter isometric view
  • UNI-T UT381PV Solar Irradiance Meter rear view with battery cover and threaded mount
  • UNI-T UT381PV rear temperature sensor for panel surface
  • UNI-T UT381PV external temperature probe jack
  • UNI-T UT381PV Solar Irradiance Meter with included probe, bracket, case and manual
  • UNI-T UT381PV measuring irradiance on a solar module
  • UNI-T UT381PV held over a solar module
  • UNI-T UT381PV on its mounting bracket at the edge of a solar module
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UT381PV

Solar Irradiance Meter

$350.00
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Handheld solar irradiance meter for PV installers and O&M crews. Reads 0–1400 W/m², two temperatures, panel tilt and azimuth, with 12,800-record logging and Bluetooth to the iENV app.

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UNI-T UT381PV Solar Irradiance Meter

Overview

The UT381PV is a handheld solar irradiance meter for PV installers and O&M crews. A silicon PV-cell sensor reads irradiance from 0 to 1400 W/m² at ±(5.0% rdg + 5 dgts), and the same screen carries two temperatures, panel tilt and compass azimuth — the conditions a commissioning or performance check is judged against, taken at the module instead of from a weather feed.

Lay it flat on the module or clip it to the frame with the included bracket; a suction-cup probe on the backsheet adds a second temperature reading. The IP65, UV-resistant (F1) housing and 2 m drop rating suit rooftop and ground-mount work, 12,800 records log on board at intervals from 1 s to 60 min, and Bluetooth sends live readings to the iENV app for PDF/CSV reports. It's backed by UNI-T's nearly 40 years of test-meter manufacturing.

Key Features

  • Solar irradiance 0–1400 W/m² (0–500 Btu/(ft²·h)), 1 W/m² resolution, ±(5.0% rdg + 5 dgts) — natural or simulated sunlight
  • Two temperatures on screen together: built-in rear sensor (T1) and suction-cup probe (T2), −40 to 120 °C, ±1 °C from −10 to 75 °C
  • Built-in inclination sensor, −90.0° to +90.0°, ±1.5° within ±50°, with zero reset for pitched roofs
  • Compass azimuth 0–360°, ±7° with the meter held within 20° of level; field calibration
  • Audible and visual tilt alarm against a set inclination limit
  • 12,800-record memory, 1 s to 60 min recording interval, loop or stop-when-full
  • Bluetooth to the iENV app (iOS and Android) up to 100 m in open line of sight — live view and PDF/CSV export
  • IP65 UV-resistant (F1) housing, 2 m drop rating, quick-release panel bracket
  • Two AA batteries, about 95 h with Bluetooth and LED off

UT381PV Details

Irradiance at the Module

The silicon PV-cell sensor sits at the top of the meter, so the reading reflects the light arriving on the module plane when the meter lies on the glass or rides the included bracket at the frame edge. Irradiance reads 0 to 1400 W/m² at 1 W/m² resolution, or 0 to 500 Btu/(ft²·h) at the press of the UNIT button.

It measures natural sunlight in the field and simulated sunlight in the lab, so the same meter can check a rooftop string at noon and the light level on a module test bench.

UNI-T UT381PV lying on a large solar array
Laid flat on the module, the sensor reads the light on the panel plane.
× UNI-T UT381PV lying on a large solar array Laid flat on the module, the sensor reads the light on the panel plane.
UT381PV suction-cup temperature probe on the back of a solar module
T2: the suction-cup probe reads the backsheet.

Two Temperatures at Once

Module output falls as cell temperature rises, so an irradiance figure without a temperature beside it is half the story. The UT381PV shows both channels together: T1, the integrated sensor on the back of the meter, reads the panel surface when the meter sits on the module, and T2 reads the supplied suction-cup probe pressed to the backsheet.

Temperature spans −40 to 120 °C (−40 to 248 °F) at 0.1 °C resolution, ±1 °C from −10 to 75 °C. Allow about 30 seconds for a temperature reading to settle.

× UT381PV suction-cup temperature probe on the back of a solar module T2: the suction-cup probe reads the backsheet.

Tilt and Azimuth from the Same Meter

A built-in inclination sensor reads −90.0° to +90.0° at 0.1° resolution, ±1.5° within ±50°. On a pitched roof, set the meter on the roof surface and hold UNIT for 2 seconds to zero it, then place it on the module to read the panel's tilt relative to the roof.

The compass reads azimuth 0 to 360°, ±7° with the meter held within 20° of level; tilt it further and the display shows "---". Steel racking, rails and the module frame pull a compass, so take the azimuth reading clear of the panel and any metal, pointing the tip the way the module faces. The compass indicates magnetic north and can be recalibrated in the field.

UT381PV display showing irradiance, inclination and azimuth
Irradiance, tilt and azimuth on one screen.
× UT381PV display showing irradiance, inclination and azimuth Irradiance, tilt and azimuth on one screen.
UT381PV tilt alarm LED lit
The LED and buzzer flag an angle outside the set limit.

Tilt Alarm for Racking Checks

Set an inclination limit from the meter's menu or the app, and the UT381PV sounds its buzzer and flashes its three-color LED whenever the measured angle falls outside it. Working down a row of tables, the alarm flags an off-angle module without anyone reading the display.

The LED and buzzer can each be switched off for quiet or long-term logging work.

× UT381PV tilt alarm LED lit The LED and buzzer flag an angle outside the set limit.

Logging and the iENV App

The meter stores 12,800 records at a recording interval you set from 1 second to 60 minutes, and it can either loop over the oldest data when memory fills or stop and hold what it has. Short intervals capture fast-moving cloud cover; long ones cover a day or more of site data.

Over Bluetooth, the iENV app for iOS and Android shows live readings and trend charts, sets the recording interval, mode, alarm and tilt limit, and exports PDF or CSV reports. The link reaches up to 100 m in open line of sight. The UT381PV can also send its irradiance and temperature readings over Bluetooth to a compatible UNI-T PV I-V curve analyzer.

iENV mobile app showing UT381PV irradiance, temperature, direction and tilt
The iENV app: live readings, trend and report export.
× iENV mobile app showing UT381PV irradiance, temperature, direction and tilt The iENV app: live readings, trend and report export.
UT381PV clamped to a solar module frame with the mounting bracket
The quick-release bracket holds the meter at the module edge.

Built for Rooftops and Racking

An IP65 rating and a 2 m drop rating cover rain, dust and the occasional fall from a module table. The housing uses a specialized anti-UV (F1) material that resists the aging and cracking long sun exposure causes in ordinary plastics.

The quick-release bracket clamps the meter to a module frame for hands-free logging, and a 1/4-inch threaded hole on the back takes standard mounting hardware. Two AA batteries run it for about 95 hours with Bluetooth and the LED off, and auto power-off after 30 minutes idle can be switched off for long recordings.

× UT381PV clamped to a solar module frame with the mounting bracket The quick-release bracket holds the meter at the module edge.

Applications

PV Installation, Commissioning and O&M

  • Record irradiance and module temperature at the moment an I-V curve, string or insulation test is taken, so results can be judged against the conditions they were measured in.
  • Verify tilt and azimuth against the design drawings before racking is signed off, and use the tilt alarm to check a whole row quickly.
  • Log irradiance through the day to separate a weather-driven drop in output from a fault.
Ground-mount solar array
PV plant installation and maintenance.
× Ground-mount solar array PV plant installation and maintenance.
Weather-monitoring masts in an open field
Site assessment and meteorological monitoring.

Site Assessment and Lab Testing

  • Log irradiance on a prospective site at 1 s to 60 min intervals to support resource assessment before a system is built.
  • Check the light level on a module test bench or under a solar simulator, with the probe on the device under test.
× Weather-monitoring masts in an open field Site assessment and meteorological monitoring.

Agricultural and Environmental Monitoring

  • Track sunlight and temperature in greenhouses, agrivoltaic plots and field research sites, with records exported to CSV for analysis.
Crops growing in a greenhouse
Agricultural and environmental monitoring.
× Crops growing in a greenhouse Agricultural and environmental monitoring.

Accessories & In the Box

Included

  • UT381PV Solar Irradiance Meter
  • Suction-cup temperature probe
  • Solar panel mounting bracket
  • Carrying bag
  • 2 × AA batteries
  • User manual, safety guide and download operation guide

Frequently Asked Questions

What units does the UT381PV display?

Irradiance in W/m² (0–1400) or Btu/(ft²·h) (0–500), switched with the UNIT button. Temperature reads in °C or °F.

Can I use it under a solar simulator?

Yes. The UT381PV measures irradiance from natural or simulated sunlight.

Why does the compass show "---"?

The azimuth reading needs the meter within 20° of level. Hold it flat, away from the module frame, racking and other metal, with the tip pointing the way the panel faces.

How do I measure panel tilt on a pitched roof?

Place the meter on the roof surface and hold UNIT for 2 seconds to zero it, then set it on the module to read the panel's tilt relative to the roof.

Which app does it use?

iENV, on the App Store and Google Play. It connects over Bluetooth up to 100 m in open line of sight and exports PDF and CSV reports.