Pyranometer FAQs

What type of Apogee pyranometer do I need?
Apogee offers silicon-cell and thermopile detector pyranometers. From a big picture perspective, the thermopile pyranometer is more accurate in all conditions than the silicon-cell models.

Generally speaking, thermopile pyranometers have a larger spectral range (this makes them more accurate in all atmospheric conditions), smaller output signal, longer response time, and are more expensive than silicon-cell detectors.

Silicon-cell pyranometers are less expensive and faster response, but errors are higher under cloudy conditions. The table below is a comparison of the general specifications for Apogee silicon-cell pyranometers and thermopile pyranometers:

Specifications Silicon-cell Detector Thermopile Detector
Calibration Uncertainty ± 5 % ± 5 %
Cosine Response ± 5 % below 75° zenith angle Less than 30 W m-2 at 80° zenith angle
Error Due to Clouds + 10 to 15 % (common to all silicon-cell pyranometer) ± 2 %
Spectral Range (50% Points) 360 to 1120 nm 385 to 2105 nm
Base Model Output Voltage 0 to 350 mV = 0 to 1750 W m-2 0 to 100 mV = 0 to 2000 W m-2
Response Time Less than 1 ms 0.5 seconds
Which Silicon-cell Pyranometer model do I need?
All SP-100, SP-200, and MP series silicon-cell pyranometers use the same silicon-cell detector. The model number you need depends on which output is compatible with your datalogger. Model numbers are listed below with their output:

SP-110-SS: 0 to 350 mV = 0 to 1750 W m-2

SP-230: 0 to 250 mV w/Heater = 0 to 1750 W m-2
*Note: The SP-230 has the same voltage output as the SP-110 but features a built in heater and Delran mounting stand for deployment in condensing or cold weather applications (e.g. frost, snow, sleet, freezing rain).

SP-212-SS: 0 to 2.5 V = 0 to 1250 W m-2

SP-215-SS: 0 to 5.0 V = 0 to 1250 W m-2

SP-214-SS: 4 to 20 mA = 0 to 1250 W m-2 *Best model for most solar inverters

SP-420: USB/software

SP-421-SS: SDI-12

SP-422-SS: Modbus RS-232 or RS-485 communication protocol

MP-100: Sensor integrated into the top of the handheld meter with digital readout

MP-200: Sensor attached to a handheld meter with digital readout

*The above ranges are standard and built to stock. If you need a larger range than what is listed please contact technical support for a quote on your specific requirement.

Which pyranometer do I need to monitor my solar panels?
For information on using Apogee pyranometers to monitor solar panels, please visit
How often should I recalibrate my pyranometer?
For maximum accuracy, we generally recommend all sensors be recalibrated every two years. You may wish to wait longer between recalibration cycles depending on your requirements. The Clear Sky Calculator may be used as a quick reference to determine if recalibration is necessary for pyranometers and quantum sensors, click here for more information on the Clear Sky Calculator. For additional information on how to send your sensor in for calibration and pricing please click here.
How do I clean my sensor?
Isopropyl (rubbing) alcohol and a Q-tip work well for cleaning the sensor area. Be careful NOT to use an abrasive cloth on the top as it will scratch the surface of the sensor. Microfiber bags work well too.
Can I add cable to my sensor?
Yes, if properly spliced, the signal from the sensor is not affected by splicing on additional cable. We have tested splicing up to 100 meters of cable. For information on how to create a proper waterproof splice, please visit our instructional webpage or watch our video.

We offer custom cable lengths of our high quality cable and splice kits that can be ordered at the time of purchase or at a later date.

How should my pyranometer be mounted?
Mount the sensor to a solid surface using the nylon mounting screw provided. To accurately measure total shortwave radiation incident on a horizontal surface, the sensor must be level. An Apogee AL-100 Leveling Plate is recommended for this purpose. To facilitate mounting on a cross arm, an Apogee AL-120 Mounting Bracket is recommended.

To minimize azimuth error, the sensor should be mounted with the cable pointing toward true north in the northern hemisphere or true south in the southern hemisphere. Azimuth error is typically less than 1 % but is easy to minimize by proper cable orientation.

In addition to orienting the cable to point toward the nearest pole, the sensor should also be mounted such that obstructions do not shade the sensor.

*Solar applications: Many of our solar customers inquire about if they should mount their sensor horizontally or in the plane-of-array. Because most applications are verifying panel efficiency/panel soiling we recommend the plane-of-array, however, every application is different and some may require horizontal installation.

Can I use my pyranometer under water?
Absolutely. We have quite a few customers that purchase our sensors for continuous deployment in underwater applications such as marine biology and hydrology. The SP-series pyranometer sensors are completely sealed and watertight and the cable can be submerged underwater as well.
Caution: The MP-series handheld meters cannot be submerged (the screen is splash resistant). The sensor head and cable of the MP-200 can be submerged.
How can I use a voltmeter to determine readings from my SP-110 or SP-230 pyranometer?
The SP-110 is considered to be self-powered and has been calibrated to 5.0 W m-2 per mV. Using a voltmeter with a mV setting allows for better resolution. Connect the positive lead of the voltmeter to the red wire of the pyranometer and the negative lead of the voltmeter to the black wire of the pyranometer. Once you are reading the mV output from the sensor, multiply this reading by 5.0. This will give you the W m-2 output from the sensor, also known as irradiance.
How do I get data off my meter?
Handheld Meter Video Guide
The AC-100 communication cable accessory is used to download saved measurements from any of our handheld meters. This USB cable includes a built-in circuit board to convert voltage levels to be compatible with the meters-normal USB to micro-USB cables will not work. The AC-100 also comes with a flash drive that includes the necessary computer software, drivers, and instructions. If you already have the AC-100 and just need the software files please click here.
Do I need to order a sensor to go with my meter?
Do I need to order a sensor to go with my meter?
No. All Apogee meters (MO, MP, MQ, and MU series) either have sensors built into the meter or attached via two meters of cable. If you order a sensor only (SI, SO, SP, SQ, and SU series) you will need to have your own datalogger (or, depending on the sensor, a voltmeter) to collect information form the sensor.
Can I add cable to my meter?
Although it is possible to splice additional cable to the separate sensor, note that the cable wires are soldered directly into the circuit board of the meter. Care should be taken to remove the back panel of the meter in order to access the board and splice on the additional cable, otherwise two splices would need to be made between the meter and sensor head. Click here for further details on how to extend sensor cable length.
I received an error code on my meter. How do I fix it?
Error codes will appear in place of the real-time reading on the LCD display and will continue to flash until the problem is corrected. For steps on completing a fix please refer to the manual.
Err 1: Battery voltage out of range. Fix: replace CR2320 battery and perform master reset.
Err 2: Sensor voltage out of range. Fix: perform master reset.
Err 3: Not calibrated. Fix: perform master reset.
Err 4: CPU voltage below minimum. Fix: replace CR2320 battery and perform master reset.
What kind of battery does my meter take?
The meter takes a CR2320 coin cell battery.
What should I do if my meter becomes non-responsive or experience abnormalities?
A master reset can be performed that may correct the problem. *Note: a master reset will erase all logged measurements from memory.

First press the power button so that the LCD display is activated. While still powered, slide the battery out of the holder, which will cause the LCD display to fade out. After a few seconds slide the battery back into the holder. The LCD display will flash all segments and then show a revision number. This indicates the master reset was performed and the display should return to normal.

Is each logged or sampled reading time stamped?
No – user should record the starting time when the meter is placed in LOG mode and take note of time when sampled readings are taken.
How many readings will the meter take in LOG mode?
When in LOG mode the meter will power on/off to make a measurement every 30 seconds. Every 30 minutes the meter will average the sixty 30 second measurements and record the averaged value to memory. The meter can store up to 99 averages and will start to overwrite the oldest measurement once there are 99 measurements. Every 48 averaged measurements (making a 24 hour period), the meter will also store 99 integrated daily totals in moles per meter squared per day (mol m-2 d-1).
How many measurements can I take in SMPL mode?
When in SMPL mode press the sample button to record up to 99 manual measurements (a counter in the upper right hand corner of the LCD display indicates the total number of saved measurements).
My USB sensor is no longer working after performing an automatic update. How do I fix this?
Please email with the model number and serial number for your sensor.