Hukseflux PVMT01 PV Module Temperature Sensor User Manual

PVMT01 is a thermal sensor designed for measuring the temperature of a PV module.
It helps in assessing the performance of PV systems by allowing users to adjust for temperature effects on module efficiency.

The sensor meets or exceeds the specifications outlined in IEC 61724-1.
The sensor features a Class A Pt1000 element connected in a 4-wire configuration for enhanced accuracy.

It is housed in a small aluminum disk, minimizing interference with bifacial modules as per IEC requirements.
The adhesive on the sensor disk is suitable for long-term outdoor use, with excellent thermal properties meeting IEC standards.

Product Usage Instructions

Place an order for the PV module temperature sensor PVMT01.
Check the package contents to ensure all components are included.

Perform a quick check to verify the integrity of the sensor upon delivery.
Learn about the stability and accuracy of the sensor. Understand how to achieve precise temperature measurements.

Explore how the sensor contributes to assessing system performance. Learn about the conversion process for resistance values to temperature readings.
Choose an appropriate location and install the sensor correctly.
Ensure proper strain relief and connection to the panel.

Connect the sensor electrically following guidelines.
Follow maintenance procedures to ensure accurate readings.

Refer to troubleshooting steps in case of issues with the sensor.

FAQ

Q: What should I do if the sensor readings are inaccurate?

A: If you encounter inaccurate readings, first ensure the sensor is properly installed and calibrated. Check for any environmental factors that may affect the readings and recalibrate if necessary.
Q: Can the sensor be used with other types of modules?

A: The sensor is designed for PV modules and may not be suitable for other types of modules due to specific design considerations.

Cautionary statements

Cautionary statements are subdivided into four categories: danger, warning, caution, and notice according to the severity of the risk.

DANGER
Failure to comply with a danger statement will lead to death or serious physical injuries.
WARNING
Failure to comply with a warning statement may lead to the risk of death or serious physical injuries.
CAUTION
Failure to comply with a caution statement may lead to a risk of minor or moderate physical injuries.
NOTICE
Failure to comply with a notice may lead to damage to equipment or may compromise the reliable operation of the instrument.

List of symbols

Quantities Symbol Unit

Voltage output U V

Temperature T °C
Electrical resistance Re Ω

Time in hours h h
Plane of Array POA W/m2

Thermal resistance Rth °C/(W/m2)

Subscripts

back of PV module BOM
PV cell CELL
sensor SEN

Acronyms

ASTM American Society for Testing and Materials
AWM Appliance Wiring Material
AWG American Wire Gauge
EN AW European Aluminium Wrought
FEP Fluorinated ethylene propylene
IEC International Electrotechnical Commission
IPA Isopropyl alcohol
ISO International Organization for Standards
TCR temperature coefficient of resistance
PV Photovoltaic
PRT platinum resistance thermometer
PR performance ratio
WMO World Meteorological Organization

Introduction

PVMT01 measures the temperature of a PV module. Assessing PV system performance, this back-of-module temperature measurement allows users to estimate and correct the performance index for the temperature dependence of module efficiency. PVMT01 meets or exceeds the specifications required by IEC 61724-1.
PVMT01 consists of a Class A Pt1000, connected in a 4-wire configuration for increased accuracy. The sensor is enclosed in a small aluminum disk. The small size minimizes the impact on bifacial modules (IEC requires obscuring less than 10 % of the surface area of any cell). The adhesive on the sensor disk is well-suited for long-term outdoor use. The adhesive has excellent thermal properties, including a total heat transfer coefficient larger than 500 W/(m2∙K) as required by IEC.
The flexible and weather-proof cable has a small diameter. For bifacial modules, this cable should be routed between the cells, as recommended by IEC. The small cable diameter not only helps to improve measurement accuracy but also helps minimize the mechanical stress on the sensor disk and on the adhesive connecting the sensor to the module. PVMT01 comes with a standard cable length of 1 m. The cable can be easily extended using an extension cable.

PVMT01 is designed for compatibility with the most commonly used data logger models. For many models, there are example programs and wiring diagrams available.

Suggested use for PVMT01:

long-term PV system performance monitoring
module temperature measurement in PV prospecting

PVMT01 unique features and benefits:

high measurement accuracy
compliant with requirements of IEC 61724-1:2021 for Class A systems
disk adhesive rated for prolonged outdoor use

small surface area to minimise impact on bifacial modules
thin cable for routing between cells of bifacial modules
thin cable minimizes the mechanical force on the adhesive connecting the sensor to the module

easily extendable cable
ingress protection class: IP67

Ordering and checking at delivery

Ordering PVMT01
PVMT01 is supplied in packs of ten sensors, each sensor is provided with a cleaning alcohol wipe, two solar edge clips to attach the cable to the edge of the PV module and two polyester tapes to secure the sensor cable on the module. PVMT01 comes with a 1-meter cable with a connector and a sensor disk with adhesive for easy installation.

Included items
Arriving at the customer, the delivery should include:

10 x PVMT01 sensor with serial number
installation instructions

For each PVMT01 sensor:

1 x pre-saturated IPA (isopropyl alcohol) wipe per sensor
2 x solar clip per sensor

2 x polyester tape per sensor

Quick instrument check

Inspect the packing and contents for any damage. Check the sensor serial number on the cable label against the product certificate provided with the sensor.

Instrument principle and theory

PVMT01 measures back-of-module temperature for solar energy applications. The disk houses a high-accuracy Class A Pt1000. The measurement made with PVMT01 is used to correct the performance index for the temperature dependence of the efficiency of PV modules in PV system performance monitoring.

Stable and accurate
The Pt1000 is stable over a broad temperature range. It can measure back-of-module temperature accurately, also when a cable is extended to longer cable lengths than the standard 1 m cable. The 4-wire configuration eliminates the electrical resistance of the cable from the measurement and is the recommended way to connect this sensor.
The sensor is enclosed in a small aluminum disk. The compact design minimizes impact on bifacial modules (IEC 61724-1 requires obscuring less than 10 % of the surface area of any cell). The adhesive on the sensor disk is well-suited for prolonged outdoor use. The adhesive has excellent thermal properties, including a thermal conductance larger than 500 W/(m2∙K) as required by IEC 61724-1:2021.

The flexible and weather-proof cable has a small diameter. For bifacial modules, the cable is routed between the cells to minimise module shading. The small cable diameter helps improve measurement accuracy and helps minimize the mechanical stress on the sensor disk and the connector. The thin adhesive tab on the disk ensures easy installation and promotes heat transfer from the surface.
Secure the sensor cable to the module’s back sheet using polyester tape at 2 points to reduce strain on the sensor element and to keep cable temperature as close as possible to module temperature.

Attaining a high measurement accuracy
The PVMT01 measures the “back-of-module temperature”, TBOM. IEC 61724-1 recommends the use of back-of-module temperature sensors and thereby accepts TBOM as a good approximation of cell temperature, TCELL. At the same time, IEC 61724-1 explains that TBOM is not equal to TCELL and also that the measured temperature TSEN may not be equal to TBOM; certain measurement errors are accepted.
Users should carefully select and install PV module temperature sensors.
It is important to realize that sensors such as PVMT01 unless they are thermally insulated (which is not recommended), will measure a temperature TSEN between ambient air temperature and TBOM.
This means that, in the presence of solar radiation, TSEN will be lower than TBOM, which is again lower than TCELL. You may also say that measurements with poorly designed and badly installed sensors will have a higher uncertainty of “the quantity to be measured (measurand)” TBOM.
The PVMT01 is designed to optimize the measurement accuracy.

PVMT01 employs a Class A Pt1000, which keeps sensor-related uncertainties as low as possible
PVMT01’s adhesive has a very low thermal resistance

Measures that users may take to attain a high measurement accuracy:

working with PVMT01 users should connect as much of the sensor and cable to the PV panel as possible. Use tape, supplied with the sensor, to connect a cable to the panel. Using tape, the cable temperature will be close to the panel temperature.
regular inspection of the connection between the sensor and PV module.

NOTICE
Do not apply thermal insulation material to the sensor.

IEC 61724-1 Annex B states ”Temperature sensor readings may be affected by wind causing temperature readings lower than cell temperature. The application of thermal insulating tape over the sensor can be used to suppress the wind-cooling effect. For this purpose using foam resin tape with an aluminum cover layer over the temperature sensor glued to the surface of the PV module back sheet is introduced in IEC 60904-5”
Hukseflux does not agree. Sensors must not be insulated, because then the PV panel has a locally insulated backside. The local PV module temperature will then be much higher than that of the rest of the panel; so the temperature that is measured with thermally insulated sensors will no longer be representative of the module or array temperature, and be much too high.

PV system performance ratio
The performance ratio (PR) of a PV system is the ratio of measured energy to expected energy (based on measured irradiance). It offers an indication of the overall effect of losses on the system. There are many factors that impact the energy production of a solar installation. A detailed performance model may be used to predict the electrical output of the PV system as a function of meteorological conditions.
Temperature is one of the main “influence quantities” on the performance ratio.
Typical temperature dependence of a PV panel’s electrical output power is in the order of -0.3 %/°C to -0.4 %/ °C. IEC 61724-3 gives an example in Table 1 of a module power temperature coefficient of -0.35 %/°C.
IEC 61724-3 introduction states that module temperature is primarily a function of

irradiance,
ambient temperature and
wind speed

This gives seasonal variation, with higher performance ratio values in winter and lower in summer (for systems in the northern hemisphere). See Figure 2.3.1.
Also, the performance ratio generally decreases with increasing irradiance. Usually, higher irradiance leads to increasing PV module temperature and results in lower panel efficiency.
IEC 61724-1 Chapter 14 distinguishes between different temperature-corrected performance ratio parameters. For more information, refer to the standard.
By calculating the temperature-corrected performance ratio, the seasonal variation in PR can be significantly reduced.

IEC 61724-2 (via Annex A) allows two methods to determine PV cell temperature:

estimated, using a model, from measurements of POA irradiance, ambient temperature and wind speed

from direct measurements of back-of-module temperature, using a PV module temperature sensor like PVMT01

The first method is not often used, because the uncertainty of this model-based approach is relatively high. Temperature data from PVMT01 sensors can be used to perform a direct measurement.
Optionally, additional corrections may be used to calculate PV cell temperature:
IEC 61724-2 Appendix A suggests correcting for error [TCELL-TBOM]. The formula [TCELL = TBOM + POA·Rth] may be used for correction, with Rth a thermal resistance which depends on the module design and in the range of (1 to 3) x 10-3 °C /(W/m2), in °C per W/m2 POA irradiance.

PV modules have temperature coefficients in the order of – 0.35 %/K; at lower temperatures we expect PV panels to perform better. Using badly designed sensors, the measured back of module temperature will always be underestimated, leading to an underestimation of the cell temperature. At the lower temperature, we expect the panel to perform better than it actually does. The result is a lower estimate of the performance index.
We assume that the absolute error in ˚C is proportional POA irradiance, so that the error is not a constant percentage; the performance index is reduced by a higher percentage at higher irradiance levels.
In compliance testing or system commissioning, this systematic underestimation of the performance is a disadvantage for the seller of a PV system.

Converting resistance into temperature
The linear correlation between the electrical resistance of the Pt1000 and the temperature is used to measure the temperature. A temperature rise is proportional to the rise in electrical resistance.

With R Pt1000 the resistance in Ω, T the temperature in °C, and A and B the Pt1000 coefficients.

A = 3.908 × 10-3
B = -5.775 × 10-7

Specifications

Specifications of PVMT01

PVMT01 measures the temperature of the rear side surface of PV modules. It can only be used in combination with a suitable measurement system. The instrument should be used in accordance with IEC 61724-1:2021, section 9.1.
Table 3.1.1 Specifications of PVMT01 (continued on next pages).

TEMPERATURE SENSOR
Sensor type	Pt1000 Platinum resistance thermometer (PRT)
Sensor class (IEC 60751)	A
Product Description	precision 1000 Ω platinum temperature sensor
Sensor connection	4-wire, 4P male M12-A connector
Sensor housing	aluminum disk
Measurand in SI units	back-of-module surface temperature in ˚C
Rated operating temperature range Sensor and cable Connector	-40 to +150 °C -40 to +80 °C
Long-term stability	resistance drift < 0.15 ⁰C at 0 °C (after 1000 h at 300 °C) as per ISO 60751:2022
Insulation resistance	> 2 GΩ at 1 kV as per IEC 60060-1
Measurand
Uncertainty related to sensor classification	± (0.15 + 0.002\|T\|) ⁰C
Measurement resolution	≤ 0.1 °C
Achievable measurement uncertainty	± 2 °C from back-of-module surface temperature (at steady state POA 1000 W/m2) See chapter 6
Measuring current	< 1.0 mA
PVMT01 COMPLIANCE
Standard governing use	IEC 61724-1:2021 photovoltaic system performance – part 1: monitoring, section 9.1 and Appendix B
PRT standard	IEC 60751:2022
Ingress protection class	IP67 as per IEC 60529
Hazardous substances	EU RoHS2 (2011/65/EU) and EU 2015/863 amendment known as RoHS3
IEC 61724-1:2021 COMPLIANCE
IEC 61724-1:2021 compliance	meets Class A and Class B performance specifications
Number of sensors required for IEC compliance	suggested: 3 per monitoring station required: minimum 6 per PV system, depending on the size of the system
Sensor surface area for bifacial modules	sensors and wiring should obscure < 10 % of the area of any cell. A common cell size is 6 by 6 inches. The PVMT01 sensor obscures 2.1 % of such cells. A 2.5 mm diameter PVMT01 wire obscures 1.6 %. The the sum of 3.1 % is well within the IEC requirements.

PVMT01 ADDITIONAL SPECIFICATIONS
Marking	Hukseflux logo indicating front side; 1 x label at the end of the cable showing the sensor serial number
Response time (95%)	< 30 s
Recommended readout	4-wire configuration
Nominal sensor resistance	1000 Ω
MECHANICAL
Aluminum disk
Disk material	anodized aluminum, EN AW 6082
Disk diameter	25 × 10-3 m
Disk thickness	5.5 × 10-3 m
Net weight including 1 m cable	approx. 0.5 kg
Adhesive
Adhesive	3M VHB F9469PC
Adhesive material	acrylic sticker material
Adhesive thickness	0.13 × 10-3 m
Adhesive thermal conductivity	0.16 W/(m/K)
Adhesive heat transfer coefficient	> 500 W/(m²·K) as required in IEC 61724-1
ENVIRONMENT
Ingress protection rating (IEC 60529)	IP67
Maximum pressure	6 bar
UV resistance	no UV degradation
electrical insulation sensor to PV module	> 1 kV
INSTALLATION AND USE
Typical conditions of use	outdoors, at the rear side of PV modules
Product Lifetime	10 years (expected)
CALIBRATION
Calibration traceability	to SI units
Validity of calibration	if stored properly, the product retains its performance and properties for 24 months from the date of manufacture.
Requirements for recalibration	depend on the application and its requirements for measurement uncertainty. The decision is left to the user.
CABLE REQUIREMENTS
Cable length	1 m
Cable extension	maybe extended by the user to the preferred length see section 4.2 for more information

Table 3.1.1 Specifications of PVMT01.

CABLE SPECIFICATIONS
Jacket material	white TPU (thermoplastic polyurethane)
Jacket rating	-40 °C to 90 ⁰C, 3000 hours: 150 ⁰C
Wiring	4 x copper stranded wire
Conductor cross-section	0.14 × 10-6 m2 (26 AWG)
Maximum conductor resistance	134.5 mΩ/m
Cable diameter	2.5 × 10-3 m
Marking	1 x label with a serial number at the connector-end cable
Rated bending radius	static > 12.5 mm dynamic > 50 mm
CONNECTOR SPECIFICATIONS
Connector type	4P male M12-A connector (thread external, on outside of connector housing)
Requirements for the connector of the extension cable	4P or 5P female M12-A connector (thread internal, on inside of locking nut)
Connector weight	31 × 10-3 kg
Strain relief connector (IEC 61215-2)	> 40 N
Connector-rated operating temperature	-40 °C to + 80 ⁰C
SUPPLY AND PACKAGING
Supply	10 x PVMT01 in one bag
Packaging size for 10 x PVMT01	1 zip bag of (0.42 x 0.40 x 0.05) m
Gross weight for 10 x PVMT01	0.75 kg
Net weight for 10 x PVMT01	0.5 kg
Packaging size for 1 x PVMT01	1 zip bag of (0.3 x 0.2 x 0.02) m
weight for 1 x PVMT01	0.045 kg

Dimensions of PVMT01

sensor housing
adhesive with the paper release liner

cable; standard length 1 m
product label
connector

Installation of PVMT01

Site selection and mechanical installation

Table 4.1.1 Recommendations for installation of PVMT01.

Location	mount the sensor on the rear side of the module. IEC 61724-1 recommends selecting a location at the center of a cell close to the center of the module, avoiding boundaries between cells. do not place the cable and/or connector in direct sunlight.
Location – bifacial modules	wiring/cable should be routed in between cells when possible.
Site selection	before mounting, clean the back of the PV module with the provided IPA wipe. Allow all cleaned surfaces to dry completely before proceeding.
Adhesive mounting	an adhesive layer covers the back of the aluminum disk. To mount the sensor, remove the paper release liner and place the disk on the back of the PV module. Press the disk firmly for a few seconds to ensure good bonding of the sensor to the surface.
Mechanical mounting / thermal insulation	there should be no dust, dirt, or other debris between the sensor and the PV module.
Attachment of the cable/strain relief	for mechanical stability, to avoid exerting too much force on the sensor and to keep cable temperature as close as possible to module temperature, attach the sensor cable with strain relief with the provided solar clips and polyester tape. Two clips and two tapes are provided with every sensor.
Performing a representative measurement	IEC 61724-1:2021 requires a minimum of 6 PVMT01 sensors per PV system, depending on the size of the system as per IEC 61724-1. Suggested by IEC: 3 per monitoring station.
Long cable lengths	Cable extension is possible by using a connector matching the PVMT01 connector and an extension cable. Placement of extension cable inside a rugged conduit is advisable for longer cable lengths, especially in locations subject to digging, mowing, traffic, animals, etc.

Clean the rear side of the PV module with the provided pre-saturated IPA wipe.
Remove the protective release liner on the back from PVMT01.
Stick the PVMT01 on the rear side of the PV module, according to IEC 61724-1. Press the disk firmly for a few seconds to ensure good bonding of the sensor to the surface.

Place 2 x polyester tape strain relief to hold the cable in place.
Attach 2 x solar edge clips on the PV module frame.
Guide the PVMT01 cable through the tie-wrap.

Tighten the tie-wrap and cut off the excess.
Connect the M12 connector to extend the cable.

Cable extension
PVMT01 is equipped with one cable containing four wires and a 4P male M12-A connector. The standard cable length is 1 m. The cable can be extended to a preferred length by the user, using a cable with a matching 4P female M12-A connector. A 5P (5-pin) will also fit. Keep the distance between the data logger and the sensor as short as possible. Cables may act as a source of distortion by picking up capacitive noise. In an electrically “quiet” environment the PVMT01 cable may be extended up to 20 meters, if needed even longer to 100 m.

Please consider the following when extending the cable:

use high-quality shielded connectors to ensure high measurement accuracy
connect the cable shield to the data logger cabinet ground to reduce electrical noise

match the wire cross-section of the extension cable with the sensor cable or use a larger cross-section to avoid a large voltage drop in a 2-wire configuration
extension cable must be suited for outdoor use.

Cable and connection specifications are summarised below.

In many cases, the extension cable will be the readily available standard 5 pin M12-A.
In that case, the connection will be as in the table below.

Table 4.2.1 Extension cable and connector connections

Connecting the cable shield is optional. There is no through connection to PVMT01 housing.

NOTICE
Always use a shielded extension cable and connect the cable shield to the ground.

Table 4.2.1 Preferred specifications for cable extensions of PVMT01.

Connector	4P (or 5P) M12-A, with an outside thread on the connector body, use a female connector (4P or 5P) with an internal thread on the locking nut for connecting to the sensor connector
Wire	4 x or 5 x copper, 24 AWG, stranded wire
Extension sealing	make sure connectors are well connected and sealed against humidity ingress
Wire configuration	cable resistance can cause significant errors. To counter such errors, a 4-wire configuration readout is the best configuration, especially for long cable lengths. Using a 4-wire connection will eliminate errors due to cable resistance. The PT1000 is equipped with 4 wires; 1 and 2 at one end, 3 and 4 at the other end. The principle relies on the fact that a known current [I] is fed in through wire 1, through the Pt1000, and out through wire 3 at the opposite end. Two additional wires, 2 and 4 are used to measure the voltage drop [V] across the Pt1000. These wires do not carry any current because the voltage measurement circuit has a very high electrical resistance. Therefore there is no voltage drop across these measurement wires 2 and 3. The wires 1 and 3 may show a voltage drop but the current remains constant. So Pt1000 resistance simply is [V/I].
Conductor resistance	< 0.09 Ω/m (24 AWG)
Extension cable	always use a shielded extension cable.
Length	cable length should be as short as possible, we recommend the total cable length should be less than 100 m
Cable cladding/ outer mantle	with specifications for outdoor use (for good stability in outdoor applications)

Strain relief & cable to panel connection

PVMT01’s cable must be properly strain-relieved, and the cable temperature must be kept as close as possible to the module temperature. To accomplish this, PVMT01 comes with two solar clips and two polyester tapes per pack.
Recommended is to fasten the solar edge clips at the following locations:

above the sensor
next to the cable connector

Use (extra) cable ties to secure the cable to the solar clips.
Recommended is to fasten the polyester tape at the following locations

near the sensor
± 20 cm along the cable, use as little tape as possible.

Electrical connection
PVMT01 must be connected to a measurement and control system, typically a so-called data logger. The Pt1000 is a standardized type of temperature-sensitive resistor. To use a PRT, its electrical resistance must be measured. The resistance is measured by applying a small excitation voltage or current. To prevent heating of the PRT, care must be taken to apply only low-power excitations. Most commonly used data logger systems have preprogrammed functions to calculate the temperature from a temperature-sensitive resistance. For more information, refer to the user manual of the data logger used.
PVMT01 can be read out in a 2-wire or 4-wire configuration. The 2-wire configuration accuracy decreases, relative to the 4-wire, as a function of the cable length. The 4-wire configuration eliminates the electrical resistance of the cable from the measurement and is the most accurate way to measure this sensor.
Figure 4.4.1 shows the circuit diagram for a 2-wire configuration. When possible, connect the two wires at each end of the PRT to reduce resistance.

Figure 4.4.2 shows the circuit diagram for a 4-wire configuration. A 4-wire configuration is recommended. For extension, always use a shielded cable.

NOTICE
Putting more than 5 Volt across any of the sensor wires may lead to inaccurate readings or permanent damage to the sensor.

Maintenance and troubleshooting

Recommended maintenance and quality assurance
PVMT01 requires minimal maintenance. Unreliable measurement results are detected by scientific judgment, for example by looking for unreasonably large or small measured values.
Table 5.1.1 Recommended maintenance of PVMT01.

MINIMUM RECOMMENDED PVMT01 MAINTENANCE
	INTERVAL	SUBJECT	ACTION
1	1 month	data analysis	compare measured data to maximum possible/maximum expected temperatures and to other measurements nearby, for example, nearby stations or redundant instruments. Also, historical seasonal records can be used as a source for expected values. Look for any patterns and events that deviate from what is normal or expected. For analysis: use nighttime data of cloudy nights with high windspeeds (> 3 m/s) without rain/snow: under these conditions, all measured temperatures of ambient air temperature, and panel temperature should be the same.
2	1-year	inspection	inspect the sensor for wear and damage, cable quality, inspect correct attachment to the PV panel, correct fitting of connectors, and inspect the location of installation. Check electrical connections at the data logger.
3	10 years	lifetime assessment	judges if the instrument will be reliable for the next years, or if it should be replaced.

Troubleshooting

Table 5.2.1 Troubleshooting for PVMT01.

General	make sure spare sensors are available on-site. inspect the quality of installation and attachment of the sensor to the PV panel. inspect the sensor for any damage. inspect if the connectors are properly attached. check for possible moisture intrusion in connectors check the connection of extension cables to the data logger look if neighboring sensors work exchange extension cables with those of nearby sensors that work. decouple the sensor from the extension cable and put a spare sensor in its place.
The sensor does not give any signal	a quick test of the instrument can be done by using a handheld multimeter. check the electrical resistance of the sensor at the connector. Measure between pins 1-3 or 2-4. See Figure 4.2.1. Use a multimeter at the lowest range larger than 1000 Ω. Measure the sensor resistance. The typical resistance of the wiring is 0.13 Ω/m. Typical resistance should be the typical sensor resistance of 1000 Ω plus 0.26 Ω for the total resistance of two wires (back and forth) of each 1 m. Infinite resistance indicates a broken circuit; zero or low resistance indicates a short circuit. measure the electrical resistance of the sensor at the connector between pins 1-2 and 3-4. See Figure 4.2.1. Use a multimeter in the 100 Ω range. Measure the wire resistance. The typical resistance of the wiring is 0.13 Ω/m. Typical resistance should be the total resistance of two wires (back and forth). Infinite resistance indicates a broken circuit. connect the extension cable. Repeat the 2 measurements.
If the temperature signal is unrealistically high or low	check the cable condition to look for cable breaks. check the Pt1000 measurement by replacing it with a 1000 Ω resistor with a 4-wire connection. The result should be 0 °C. for analysis: use nighttime data of cloudy nights with high windspeeds (> 3 m/s) without rain/snow: under these conditions, all measured temperatures of air temperature, and panel temperature should be the same.
The sensor signal shows unexpected variations	to check the presence of strong sources of electromagnetic radiation (radar, radio) or switching of high-power equipment. check the condition of the sensor cable. check if the cable is not moving during the measurement. check the condition of the connector.

Appendices

Appendix on uncertainty evaluation
There is no general consensus on the uncertainty evaluation of back-of-module temperature measurements. IEC 61724-1 does not give an estimate of the total measurement uncertainty, implicitly recognizing that this depends on sensor design and environmental factors such as POA. The user should make his assessment. Table 6.1.1 summarises the main contributions to the uncertainty budget of the entire measurement from TCELL to the TBOM as used for calculating PV performance indices.

Table 6.1.1 Uncertainty budget of PV module temperature measurements; the accepted uncertainty under IEC 61724-1 compared to PVMT01 performance.

	UNCERTAINTY BUDGET	COMMENT	IEC 61724 ACCEPTANCE	PVMT01 SPECIFICATION
[#]	[contribution]	[description]	[interval]	[interval]
1	TBOM-TCELL	depends on the composition of the module and is often assumed to be proportional to POA	expected: (1 to 3) °C at 1000 W/m2	N/A
2	PRT	sensor accuracy class	requirement: ± 1 °C	< ± 0.5 °C -40 °C to +150 °C
3	\|TSEN – TBOM \|	depends on multiple factors is often assumed to be proportional to POA	no requirement	< 2 °C at 1000 W/m2 POA (nominal)
3.1	the thermal resistance of adhesive	is often assumed to be proportional to POA Uncertainty is included in TSEN – TBOM	requirement: < 2 x 10-3 K/(W/m2)
	the thermal resistance of adhesive		requirement: < 2 x 10-3 K/(W/m2)	< 0.2 x 10-3 K/(W/m2)
4	non-uniformity	over a PV power plant the module temperature is variable	not quantified	N/A
5	electronics	measurement uncertainty of the electronic measurement system	not mentioned	N/A
6	recalibration	in case a sensor is not stable, recalibration is needed to keep uncertainty within the required limits	requirement: the sensor is replaced or recalibrated as per the manufacturer’s requirements	no requirements

Ad 1: Table A1 of IEC 61724-2 and IEC 61724-1 clause 9.1 note 1 mention thermal resistances between cell and back-of-module of (1 to 3) x 10-3 °C /(W/m2), in °C per W/m2 POA irradiance. This means 1 to 3 °C difference TCELL – TBOM at a POA of 1000 W/m2. Table A1 gives a value of 3 x 10-3 °C /(W/m2), in °C per W/m2 POA irradiance for the most common “open rack” glass-cell-glass modules and glass-cell-polymer modules.
An independent estimate by Hukseflux leads to an estimate in the order of 0.6 °C, so much lower than the IEC estimate of 3 °C, at 1000 W/m² POA irradiance for both module types:
Glass-cell-glass modules typically use 2 glass plates, each of 2 mm thick. A glass-cell-polymer module typically has a 3 mm thick glass plate and a 0.3 mm thick polymer sheet. Both have 2 glue layers of approximately 0.2 mm each. The silicone PV cell material has negligible thermal resistance. Glass thermal conductivity is approximately 1 W/(m·K), and polymer and glue are both 0.2 W/(m·K). Assuming that silicon absorbs 60 % of incoming solar irradiance, reflects the rest and that 20 % of the incoming solar irradiance is converted to electrical power, we estimate that 40 % is converted to heat. We estimate for both panels thermal resistances between the cell and the combined 2 surfaces of 1.5 x 10-3 °C /(W/m2). The thermal resistances between the cell and the back-of-module are 3 and 2.5 x 10-3 °C/(W/m2), with the lower thermal resistance for the polymer back sheet. However, with 40 % heat conversion and assuming the heat going in two directions, the net effect estimated by Hukseflux is in the order of 0.6 °C at 1000 W/m2 POA irradiance for both module types.
Ad 2: for the temperature sensor IEC 61724-1, clause 9.1 accepts ± 1 °C or better. Class A platinum resistance temperature sensors are a factor 2 better. The uncertainty specification is ±(0.15 + 0.002·| TSEN |), which is ± 0.45 °C at 150 ° C.
Ad 3: IEC 61724-1 does not give an estimate of the total measurement uncertainty of the TBOM measurement, implicitly recognizing that this depends on sensor design and environmental factors such as POA and wind direction. The error resulting from 3.1, the thermal resistance of the adhesive, is one of the contributors to the uncertainty of the TBOM measurement.
Ad 3.1: for the adhesive IEC 61724-1, clause 9.1 accepts a minimum of 500 W/(K m2) thermal conductance, which is equal to a maximum of 2 x 10-3 °C /(W/m2) thermal resistance. Assuming that silicon absorbs 60 % of incoming solar irradiance, reflects the rest and that 20 % of the incoming solar irradiance is converted to electrical power, we estimate that 40 % is converted to heat. Taking a 50-50 distribution of heat flux between the front and rear of the solar module, this means a contribution to the difference TBOM – TSEN at a POA of 1000 W/m2 of 0.4 °C. For a maximum irradiance of 1500 W/m2, this contribution is of the same order as what IEC 61724-1 calls “on the order of approximately 1 °C”.
Ad 4: the variability of module temperatures is mentioned in IEC 61724-1, clause 9.1
“module temperature varies across each module and the array. Temperature sensors shall be placed at representative locations to capture the range of variation, and allow determination of an effective average.” Also, the required minimum of 3 sensors per measurement station (table 2 of IEC 61724-1), is meant to make it possible to determine a meaningful average. Under given solar conditions, important factors in the variability of module temperature are panel orientation, and exposure of the module to wind, i.e. local wind speed and direction.
Ad 5: consult the electronics manual to estimate the contribution of the measurement by the electronics to the uncertainty budget.
Ad 6: modern temperature sensors have a good record of stability. The decision to replace or recalibrate after a certain time interval of use is left to the user.
Ad 1, Ad 3: these errors are caused by thermal resistances and all contribute to a measured temperature that is lower than cell temperature (unless sensors are thermally insulated, which is exceptional).
They are often assumed to be proportional to POA. However, accurately correcting for these errors is not easy because at a certain POA, the distribution of heat losses between the front and rear sides of a PV module may change. This distribution depends on the exposure of the panel to wind, in particular wind direction.

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Documents / Resources

	Hukseflux PVMT01 PV Module Temperature Sensor [pdf] User Manual PVMT01 PV Module Temperature Sensor, PVMT01, PV Module Temperature Sensor, Temperature Sensor, Sensor
	Hukseflux PVMT01 PV Module Temperature Sensor [pdf] Installation Guide PVMT01 PV Module Temperature Sensor, PVMT01, PV Module Temperature Sensor, Module Temperature Sensor, Temperature Sensor, Sensor
	Hukseflux PVMT01 PV Module Temperature Sensor [pdf] User Manual PVMT01, PVMT01 PV Module Temperature Sensor, PVMT01, PV Module Temperature Sensor, Temperature Sensor, Sensor

References

User Manual

Hukseflux PVMT01 PV Module Temperature Sensor

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