Blog - K&Z

PV Module IV Curve: A Definitive Guide to Understanding Solar Performance

divyamaria.sunil@otthydromet.com (Divya Maria Sunil) — Tue, 14 Apr 2026 11:12:33 GMT

A PV module IV curve is one of the most powerful tools available for understanding how a photovoltaic module actually performs under real‑world conditions. More than a theoretical plot, the IV (current-voltage) curve reveals how current and voltage interact — and whether measured output reflects true system health or hidden performance losses.

For solar engineers, O&M teams, EPCs, and asset owners, PV module IV curve analysis plays a critical role in performance validation, fault detection, commissioning assurance, and long‑term reliability.

This guide explains what a PV module IV curve is, how to interpret it, what it reveals about system behavior, and why accurate environmental measurement is essential for meaningful analysis.

What is a PV module IV curve?

A PV module IV curve (current–voltage curve) is a graphical representation of the electrical behaviour of a photovoltaic module under illumination. Often referred to as the current–voltage (IV) curve, this measurement is a cornerstone of solar performance diagnostics across the PV system lifecycle.

The characteristic shape of a PV module IV curve arises from physical processes inside the solar cell. When sunlight is absorbed by the semiconductor material, electron–hole pairs are generated and separated by the internal electric field, creating current flow. At low voltages, current is primarily limited by internal resistive effects. As voltage increases, charge carrier recombination processes increasingly limit the available current, causing output current to decrease until it reaches zero at the open‑circuit voltage.

It plots:

Current (I) on the vertical axis
Voltage (V) on the horizontal axis

PV Module IV Curve

The curve is generated by sweeping the electrical load from open‑circuit to short-circuit conditions, or vice versa, and recording all possible operating points.

Under standard test conditions (STC) — 1000 W/m² irradiance, 25 °C cell temperature, AM 1.5 spectrum — the IV curve defines the module’s rated electrical characteristics. In the field, IV curves shift continuously as irradiance, temperature, and operating conditions change.

Because of this sensitivity, IV curves are widely used not only in module manufacturing and certification, but also during commissioning and targeted operational diagnostics.

Key parameters of a PV module IV curve

Understanding a PV module IV curve begins with four defining points:

Open‑circuit voltage (Voc) – The maximum voltage when no current flows.
Voc is highly temperature‑dependent and provides insight into cell behavior, long-term degradation, and electrical integrity.

Short‑circuit current (Isc) – The maximum current is produced when voltage is zero.
Isc is directly proportional to irradiance and is often used to assess how much usable sunlight reaches the module.
Maximum power point (MPP) – The point where the product of voltage and current is highest: Pmax = Vmp × Imp. This is the operating target for inverters and maximum power point tracking (MPPT) algorithms.
Fill factor (FF) – A dimensionless quality metric: FF = Pmax / (Voc × Isc) . Typical values: High‑quality crystalline silicon modules: 70–85%. A reduced fill factor often signals resistive losses, mismatch, or early degradation. Two internal electrical characteristics strongly influence fill factor: series resistance and shunt resistance. Series resistance arises from contacts, interconnects, and semiconductor material, and should be as low as possible to minimize power losses. Shunt resistance results from unintended current paths caused by material defects and should be as high as possible. Increases in series resistance or decreases in shunt resistance reduce fill factor and overall module efficiency.

IV-Curve-Fill-Factor

How environmental conditions shape the PV module IV curve

A PV module IV curve is not static. Its shape and position shift continuously with environmental conditions.

Irradiance effects

Primarily affect Isc
Lower irradiance compresses the curve vertically
Shape remains similar if measurement is accurate

Iv IV Curve - Irradiance

Temperature effects

Primarily affect Voc

Higher temperatures reduce voltage and power output

Soiling and shading

Introduce distortions in curve shape

Activate bypass diodes

Reduce fill factor and power output

Because IV curves are so sensitive, accurate irradiance and temperature measurement is essential for correct interpretation. Without reliable environmental data, it becomes difficult to distinguish between true performance issues and normal operating variation.

Degradation

Primarily affects Pmax and fill factor

Caused by environmental factors and electrical loading, etc.

IV Curve - Degradation

What a PV module IV curve reveals about system performance

Beyond basic definitions, PV module IV curve analysis enables deeper diagnostics that are not always visible in aggregated KPIs such as energy yield or performance ratio alone.

IV curve analysis supports:

Identification of soiling losses not evident in production data

Detection of partial shading and mismatch

Early warning of degradation trends

Validation of commissioning quality

Differentiation between environmental effects and true faults

In fleet‑scale systems, population‑level IV analysis helps isolate underperforming modules before yield losses escalate.

Common PV module IV curve defects and what they indicate

Common PV Module IV Curve Signatures	Likely Cause	Performance Impact
Low Isc	Soiling, shading, reduced irradiance	Reduced power output
Low Voc	High temperature, cell damage	Voltage clipping
Rounded knee (low FF)	Series resistance, degradation	Lower Pmax
Stepped curve	Bypass diode activation	Intermittent losses
Compressed voltage leg	Cell mismatch, microcracks	Long‑term degradation

These patterns are widely documented across field diagnostics literature.Under non‑uniform soiling or partial shading, losses in maximum power (Pmax) are not necessarily proportional to reductions in short‑circuit current (Isc). In these cases, relying on Isc‑based indicators alone can underestimate true power losses, making full IV curve analysis essential for accurate assessment.

Watch: PV module IV curve behaviour in real‑world conditions

The following field demonstration shows how IV curves behave under real operating conditions and why environmental correction is critical for interpretation.

Best practices for accurate PV module IV curve measurement

Reliable IV curve analysis requires:

Stable irradiance conditions, typically above 600 W/m²

Simultaneous measurement of irradiance and temperature

Normalisation to reference conditions for meaningful comparison

Traceable sensor calibration to minimise uncertainty

Without accurate environmental data, IV curves risk being misinterpreted — leading to false diagnostics or masking real performance issues.

Why measurement quality determines IV curve confidence

A PV module IV curve is only as trustworthy as the measurements behind it.

Sensor drift, angular mismatch, or poor temperature correction can distort the curve — making normal behaviour appear as underperformance or concealing genuine system issues. For this reason, measurement traceability, calibration discipline, and uncertainty awareness are foundational to credible IV curve analysis.

Reference‑grade irradiance measurement and well‑maintained sensors help ensure that IV curves support confident, data‑driven decisions rather than assumptions.

Applying IV Curve Analysis at Scale

As PV portfolios grow in size and complexity, the value of IV curve analysis extends beyond individual modules or one‑off diagnostics. Applied at scale, IV curves enable consistent performance assessment across strings, arrays, and entire fleets—supporting earlier detection of systemic issues, clearer differentiation between environmental effects and true faults, and more confident long‑term performance tracking. By combining IV curve data with accurate, traceable environmental measurements, teams can move from isolated troubleshooting toward repeatable, fleet‑level insight that supports operational decisions throughout the PV system lifecycle. In this context, IV curves serve not only as diagnostic tools, but also as a foundation for more detailed electrical performance modeling over time.

Population‑level analysis – Comparing IV curves across large module populations helps identify systematic issues that may not be visible at string or inverter level.

Bifacial module considerations – Rear‑side irradiance influences Isc and curve shape, requiring careful measurement of both front and rear plane‑of‑array conditions.

IV curves and performance ratio (PR) – IV curves complement PR analysis by explaining why performance changes occur, rather than only how much output changes.

Put IV Curve Insight into Practice

Understanding a PV module IV curve is the first step. Applying it consistently—across modules, strings, and entire portfolios—requires accurate measurement, reliable interpretation, and confidence in the data behind every curve.

Explore practical guidance and tools that help teams move from IV curve understanding to repeatable, data‑driven performance assessment.

Soiling Measurement for Capacity Testing in Utility‑Scale Solar

divyamaria.sunil@otthydromet.com (Divya Maria Sunil) — Tue, 14 Apr 2026 10:45:12 GMT

Why Measurement Strategy Matters More Than Ever

Executive Summary

Soiling is a well‑established cause of energy loss in photovoltaic (PV) systems. Less widely recognized is its impact during capacity and performance testing, where even small losses can have contractual and financial consequences.

Field research presented at the IEEE Photovoltaic Specialists Conference shows that soiling losses of just 1–2% can influence capacity testing outcomes in utility‑scale solar plants. The research also highlights a recurring issue: soiling is often measured too late to be useful during commissioning.

This page explains why early, accurate soiling measurement is essential for reducing performance risk, supporting defensible capacity testing, and enabling confident decision‑making across the solar project lifecycle.

What Is Soiling in Solar PV Systems?

Soiling refers to the accumulation of dust, dirt, pollen, agricultural residue, and other airborne particles on the surface of PV modules. These particles reduce light transmission through the module glass, resulting in measurable power losses.

The magnitude of soiling losses varies depending on:

Local climate and precipitation patterns

Land use and nearby activities such as farming or construction

Wind direction and seasonal effects

Cleaning frequency and site accessibility

While soiling is commonly addressed during operation, its effect during commissioning and capacity testing is often underestimated.

Why Soiling Measurement for Capacity Testing Requires a Different Strategy

Utility‑scale PV projects must demonstrate performance compliance before reaching milestones such as substantial completion. Capacity testing is commonly used to validate system output, often following standards such as ASTM E2848 or evolving international methods.

Capacity tests allow only limited total losses. Under these conditions, even modest unexplained losses can cause a test to fail.

Field data shows that soiling losses of 1–2%, when combined with normal measurement uncertainty, can push a technically sound system outside acceptable performance limits, leading to:

Delays in project completion

Disputes between developers, EPCs, and asset owners

Unplanned cleaning or retesting costs

Increased uncertainty for financiers and investors

When capacity tests fail due to unexplained losses, the consequences extend beyond technical troubleshooting. Delays at this stage can trigger contractual disputes between developers, EPCs, asset owners, and third‑party engineers—particularly around responsibility for cleaning, loss compensation, and test acceptance criteria.

In many projects, the treatment of soiling during capacity testing is not fully defined in contracts prior to construction. This can lead to last‑minute negotiations, unplanned cleaning activities, or repeat testing campaigns, all of which increase cost and schedule risk. By contrast, projects that incorporate defensible soiling measurement strategies early in the construction timeline are better positioned to manage these risks transparently and efficiently.

Accurate soiling data does not eliminate commercial discussions—but it provides a shared, objective basis for them.

Soiling in the Context of Capacity Testing Standards

Capacity testing in utility‑scale solar is typically performed within tightly defined frameworks, such as ASTM E2848 in the United States and evolving international methods including IEC 61724‑1. These methodologies are designed to validate system performance against modeled expectations within narrow uncertainty bands.

Under these standards, total allowable losses are limited. When soiling losses are not explicitly measured—or cannot be defensibly quantified—they are effectively treated as unexplained performance degradation. Even small unaccounted losses in the range of 1–2% can therefore cause a capacity test to fall outside acceptable limits, despite the system being fundamentally sound.

This is why soiling measurement for capacity testing must be approached differently than long‑term operational monitoring. Measurement strategies that are sufficient for O&M reporting may not provide data of adequate timing, resolution, or representativeness for commissioning and performance validation. Early, standards‑aligned measurement planning is essential to ensure that environmental losses can be confidently distinguished from system‑related issues during formal testing.

The Hidden Risk: Soiling Is Often Measured Too Late

Most utility‑scale solar plants include soiling sensors as part of the meteorological station. These sensors are designed primarily for long‑term operational monitoring, not commissioning.

As a result, they are often installed after PV modules have already been exposed to environmental conditions for weeks or months.

This creates a mismatch:

Modules have accumulated soiling

Sensors begin from a clean state

Because the sensors do not share the same exposure history as the modules, their data cannot reliably quantify soiling losses during capacity testing.

Common Workarounds and Their Limitations

When representative soiling data is unavailable, project teams often rely on:

Visual inspection or photographs

Pre‑ and post‑cleaning electrical measurements

Negotiated assumptions about acceptable losses

These approaches introduce subjectivity, cost, and delay. Research indicates that many of these challenges can be avoided through earlier measurement planning.

Measure Soiling from Day One: A Proactive Strategy

Field research consistently points to a simple recommendation:

Soiling sensors should be deployed concurrently with PV module installation.

Installing sensors at the same time as modules ensures identical environmental exposure throughout construction and commissioning. This enables:

Reliable compensation of soiling losses during capacity testing

Early identification of excessive soiling

Data‑driven cleaning decisions

Reduced contractual ambiguity

Importantly, this approach does not require early SCADA integration. Sensors can be installed and left unpowered during construction because it does not require any calibration, allowing natural soiling accumulation.

A Common Misconception: SCADA Integration Is Not Required Early

A frequent barrier to early soiling sensor deployment is the assumption that sensors must be powered, logged, and integrated into SCADA systems from the moment they are installed. Field research shows this is not the case.

For capacity testing, the most critical requirement is that soiling sensors share the same exposure history as PV modules. Sensors can be installed concurrently with module deployment and left unpowered during construction. During this time, they naturally accumulate dust and are cleaned by rainfall in the same way as the modules.

Once commissioning approaches, the sensors can be activated and immediately provide representative soiling loss data—without requiring months of prior logging. This simple shift in deployment strategy removes a major practical obstacle to early soiling measurement and enables more reliable compensation of soiling losses during testing.

What Makes a Soiling Sensor Suitable for Capacity Testing?

Research identifies four requirements for sensors used during construction and commissioning:

Calibration‑free operation – Allows immediate installation without delaying project schedules.

High sensitivity at low loss levels – Capacity testing requires resolution below 1%, with sensitivity to changes under 0.5%.

Ease of deployment – Sensors must be compact, robust, and suitable for construction environments.

Cost‑effective scalability – Soiling varies across large sites; distributed measurement improves confidence.

These principles align with Kipp & Zonen’s long‑standing focus on measurement accuracy, robustness, and traceability.

With Atonometrics now part of the Kipp & Zonen portfolio, optical soiling measurement is integrated into a broader, bankable solar measurement framework.

Field Evidence: Soiling Is Spatially Variable

Field data from a ~100 MW utility‑scale PV plant shows that soiling is rarely uniform across a site. Measurements revealed:

Rapid accumulation during nearby agricultural activity

Losses reaching several percent within weeks

Clear spatial variation depending on location and wind exposure

These results demonstrate that assuming uniform soiling across a utility‑scale site can materially misrepresent actual performance during capacity testing, reinforcing the need for distributed soiling measurement, rather than relying on a single sensor to represent an entire plant.

Linking Soiling Data to Capacity Test Outcomes

Across multiple capacity testing campaigns, field measurements showed a clear relationship between:

Reductions in soiling losses (from rainfall or cleaning)

Improvements in measured capacity test ratios

This demonstrates the value of soiling data in distinguishing environmental effects from system‑related issues during performance validation.

Understanding the Limits of Soiling Measurement

While optical soiling sensors accurately measure transmission losses, they do not capture all electrical loss mechanisms. Non‑uniform soiling patterns can lead to additional power losses that require complementary diagnostics.

Soiling measurement should therefore be part of a comprehensive performance assessment strategy, not a standalone metric.

From Reactive Testing to Proactive Performance Assurance

Soiling has traditionally been treated as an operational issue. Research now shows it should also be considered a commissioning and project‑delivery risk.

Early soiling measurement strategies complement broader solar resource and irradiance measurement practices, helping ensure consistency between commissioning data, long‑term performance monitoring, and bankability assessments across the project lifecycle.

At Kipp & Zonen, accurate measurement is not just about data — it is about enabling confident, defensible decisions across the full lifecycle of a solar asset.

Contact us to learn how early, accurate soiling measurement can reduce performance risk and support confident capacity testing in your utility‑scale solar projects.

Webinar: How to Process and Interpret Soiling Data - Kipp & Zonen Blog

Kipp & Zonen Blog Team — Mon, 13 Apr 2026 12:38:29 GMT

PV modules perform best when they are clean. When contamination collects on the surface of modules, sunlight is blocked from reaching the PV cell, thus reducing the amount of electricity generated. This performance loss is described by the transmission loss and the soiling ratio.

The Kipp & Zonen DustIQ is a unique optical instrument for accurately measuring the soiling ratio of PV modules, providing information required to keep PV installations operating effectively.

In our recent webinar, Sajad Badalkhani, Service Manager Europe at OTT HydroMet, introduces the phenomenon of soiling and the measurement principles of the DustIQ. He also explains how to process and interpret the readings. Watch the recording below.

What is PV Soiling?

PV soiling is the accumulation of solid material on the surface of a PV module.

When dirt and particulate matter collect on a PV device, it both absorbs and scatters incident light. This has a major effect on energy yield. Alongside high temperatures, soiling is one of the primary causes of PV output degradation and is known to account for losses of three to four percent of global PV production.

PV soiling can result from many sources, including mineral dust, bird droppings, organic growth (such as lichen, fungi and mosses), pollen, engine exhaust and agricultural emissions. The rate at which these materials accumulate depends on many factors, including properties of the dust and PV module surfaces, as well as climate-related factors such as wind, rain, temperature, irradiance and humidity. PV module orientation can also have a significant effect. Interpreting and understanding regional soiling losses depends on careful consideration of all these factors.

The impact of soiling is generally described in two quantities:

Soiling Ratio (SR): The ratio of the actual power output of a soiled PV array to the power output that would be expected if the array were clean.
Transmission Loss (TL) or Soiling Level (SL): Fractional power loss due to soiling given by 1-SR.

For example, if a PV array were soiled to the point that it produced 5% less power than its clean state, the soiling ratio would be 95%, while the transmission loss would be 5%.1

There are two common methods for measuring the soiling ratio of a PV array.

One method is to set up two reference PV devices and allow one to soil naturally (at the same rate as the rest of the array) while keeping one clean. Despite being common, this method produces an instantaneous value of the soiling ratio, with uncertainties of the measurement, in particular, due to misalignment between the two reference devices and also due to the angle-dependence of scattering by soiling. This method also requires that one of the reference devices is perpetually cleaned.

The other method is to use an optical measurement device such as DustIQ. Optical systems work by producing an infrared light pulse from inside the module – i.e., from underneath the soiled surface – and measuring the portion that reflects and scatters back. Using a calibration constant, this measurement can then be converted into a soiling ratio measurement which is completely independent of the angle of incidence.

Ensuring Reliable Data Collection

There are several factors that have an influence on the reliability of soiling measurements.

Location and Number of Sensors

IC61724 sets out recommendations for the number of soiling sensors to be used for a given AC system size in megawatts1 However, this is something of a rule of thumb. It is possible to have significant variations in soiling profiles between sensors when following these recommendations, especially where there are variations in ground textures or wind speed and direction.

The best practice is always to observe the site and check if it can be divided into different “dust regions” – each of these regions should be monitored, ideally by a centrally located sensor.

Installation, Commissioning and Maintenance

DustIQ can be placed anywhere on an array – at the top, side or bottom of a PV module. However, we advise installing it vertically: soiling typically varies most in the vertical direction, so horizontal installation can be less effective at getting the full picture.

We also recommend investigating electrical protection. DustIQ is equipped with features to ensure it remains electrically protected in the field – however it is always a good idea to provide external protection as well.

Make sure to check and validate the Modbus input register values, to ensure a reliable commissioning process.

To best utilize your soiling data, it is essential to consider the following factors:

Sampling frequency: Soiling is a slow phenomenon, so even sampling just once per day can provide useful results. However, we recommend sampling every 15 minutes for better insight.
Environmental parameters: Local environments dictate soiling conditions, so having data on environmental parameters – such as weather – can provide a much better understanding of soiling.
Local calibration: DustIQ is calibrated in the lab using a standard dust sample. The properties of dust and particulate matter can vary greatly – thus, DustIQ must also be locally calibrated at least once.
Taring: “Taring” is the process of compensating for the zero offset of data. This should be carried out regularly to prevent drift over time – we recommend doing so each time your modules are cleaned.

Processing Data to Maximize Findings

Proper data handling is essential in order to optimize the utility of your DustIQ data. Follow these steps for easy-to-interpret data:

1. Reject outliers.

This means removing any data points which are unrealistic.

2. Linearly interpolate missing data.

3. Select solar noon values.

Working with solar noon values minimizes the effects of “daily transients” due to frost and dew and also minimizes the effects of angle-of-incidence variation throughout the day. We recommend selecting data gathered from 12-2 pm.

4. Average over solar noon data.

5. Apply zero-offset compensation/taring.

If your DustIQ is not routinely tared, it is essential to compensate for zero offset during data processing. Though it is best to tare data when cleaning is carried out, it is possible to address this even if you are not cleaning your PV modules by considering “environmental cleaning conditions.” Incorporating weather data enables you to tare soiling measurement data according to specific environmental factors.

6. Smooth data with a moving-average filter.

Following these simple steps ensures you can convert any unclear noisy measurements into usable and simple-to-interpret soiling data, revealing trends and enabling efficient maintenance.

In 2022, we released a new DustIQ firmware update that simplifies local calibration and taring and improves the sensitivity of measurements.

To learn more about processing data from DustIQ, watch the webinar above or get in touch with our experts with any questions.

Class A Pyranometers: Choosing the Right Type for Your PV Plant - Kipp & Zonen Blog

martin.maly@otthydromet.com (Martin Maly) — Mon, 13 Apr 2026 12:37:19 GMT

To ensure top performance of solar PV installations, leading irradiance measurement instrumentation is required for both site assessment and resource monitoring. The quality of pyranometers and pyrheliometers is defined by the international standard ISO 9060. Within its highest Class A, OTT HydroMet manufactures three different smart pyranometers under their Kipp & Zonen brand.

Below we provide an overview on the international standard ISO 9060 and our Class A certified Kipp & Zonen pyranometers. But let’s start with the standard itself.

Introduction: What is ISO 9060

ISO, an acronym for the International Organization for Standardization, brings together global experts to develop and publish standards for varying industries. In 1990, ISO released ISO 9060 for the classification and specification if instruments measuring hemispherical and direct solar radiation. The 2018 update also included new classifications (Class A, B, and C) and changed the spectral response parameter from spectral selectivity to spectral error.

If you’d like to learn more about the changes to the original ISO 9060 with the release of the 2018 version, check the article Spectral Selectivity vs. Spectral Error: Shedding Light on ISO 9060:2018.

Kipp & Zonen Pyranometers

Following the international standard ISO 9060, only the most accurate instruments pyranometers are rated certified as Class A. Still, there are is a variety of pyranometers to choose from. OTT HydroMet’s comprehensive portfolio of premium environmental monitoring equipment includes three pyranometer models that fulfill the high requirements of Class A: the Kipp & Zonen SMP10, the SMP12, and the SMP22.

Similarities Across the SMP Series

Let’s start with the similarities: The Kipp & Zonen SMP range of smart pyranometers is based on the proven technology of the analogue CMP series, but has a micro-processor, memory, and firmware that makes them digital and faster. All SMP pyranometers are ‘Spectrally Flat’ according to ISO 9060, which means they provide a steady response across the solar spectrum. In technical terms, spectrally flat pyranometers have a spectral selectivity of less than 3% (guard bands 2%) in the wavelength range from 350 nm to 1500 nm (0.35 µm to 1.5 µm).

All SMP pyranometers communicate via Modbus RTU, which makes it a very convenient choice for easy SCADA integration.

Standard 5 Year Warranty

Engineers and technicians around the world appreciate the long lifetime of Kipp & Zonen pyranometers, which usually exceeds 10 years significantly. That’s why we trust in our products and grant a five year warranty – that is more than double the standard warranty of other goods – for all CMP and SMP pyranometers.

OTT HydroMet offers three different Class A smart pyranometers under the product brand Kipp & Zonen:

SMP10

SMP12

SMP22

SMP10: Our Proven Best-seller

On PV plants around the world, whenever you spot a yellow cable, chances are high to find a Kipp & Zonen SMP10. With over 65,000 manufactured devices, the SMP10 is the most sold instrument from OTT HydroMet’s product brand Kipp & Zonen. It is used for reliable and accurate measurement of the incoming sunlight including specific components such as GHI, PoA, DHI, albedo, or others. The SMP10 is a spectrally flat Class A pyranometer and has an internal desiccant that will last for at least 10 years if the housing is not opened. This minimizes maintenance significantly. The SMP10 is available in two versions; both communicate via RS485 Modbus RTU and one analogue output, as version V (0 to 1 V) or A (4 to 20 mA).

SMP12: Kipp & Zonen’s Most Innovative Pyranometer Yet

The new SMP12 is a fast response spectrally flat Class A pyranometer combining solid-state dome heating, no moving parts, and best-in-class surge protection to maximize accuracy and minimize maintenance. Thanks to its smaller detector and tailored firmware, the SMP12 reacts quicker than any other SMP model. Additionally, it features integrated sensors to monitor the tilt angle in pitch and roll as well as and internal humidity, which enables maximum control on remote operation.

SMP22: The World’s Most Accurate Smart Pyranometer

Users who expect the highest possible accuracy choose the SMP22. Meteorologists and climate researchers rely on the SMP22 and its analogue brother, the CMP22. Both are used around the globe as part of the Baseline Surface Radiation Network (BSRN). The SMP22 shares all class-leading characteristics of the CMP22, in addition to the advantages of a smart pyranometer, including temperature compensation over a large range. A 10 K thermistor internal temperature sensor is standard, a Pt-100 sensor is optional. The SMP22 is available in two versions; both communicate via RS485 Modbus RTU and one analogue output, as version V (0 to 1 V) or A (4 to 20 mA). In recent years, there is a growing demand for the SMP22 on large utility-scale PV plants, too.

Overview

This table gives an overview which pyranometer is the appropriate one for your purpose.

	SMP10	SMP12	SMP22
Spectrally Flat Class A (ISO 9060:2018)	✅	✅	✅
Integrated heater	-	✅	-
Fast Response Time (ISO 9060:2018)	-	✅	-
Response time (63%)	< 0.7 s	< 0.15 s	< 0.7 s
Communication via RS485 Modbus RTU	✅	✅	✅
Analogue output available (A- and V- versions)	✅	-	✅
Tilt angle monitoring	-	✅	-
Internal humidity monitoring	-	✅	-
Zero offset A // thermal radiation (at 200 W/m²)	< 7 W/m²	< 1 W/m²	< 3 W/m²
Zero offset B // temperature change (5 K/h)	< 2 W/m²	< 1.5 W/m²	< 1 W/m²
Directional response (up to 80° with 1000W/m² beam)	< 10 W/m²	< 10 W/m²	< 5 W/m²
Temperature response (-40 °C to +70 °C)	< 2%	< 2%	< 0.3%

Are you interested in learning more? You can find the technical specifications and more details of the three models above and other Kipp & Zonen pyranometers in the Pyranometer brochure. Download the brochure by clicking on the button below. Further questions? Our team of researchers and technical experts is happy to help.

Podcast: Analog or Smart Sensor? Choosing the Right Instrument - Kipp & Zonen Blog

martin.maly@otthydromet.com (Martin Maly) — Mon, 13 Apr 2026 12:35:23 GMT

Food for geeks! Most measurement instruments are either analog or smart. This applies to our Kipp & Zonen portfolio for solar irradiance monitoring, too. But which one to choose for which application?

In this episode of OTT CAST, we welcome Sajad Badalkhani, an experienced technical expert for solar monitoring instruments. We discuss the technical differences between analog and smart sensors and who they are designed for. Sajad explains the concept of the Modbus protocol and introduces the SMP12, an ISO 9060:2018 Class A pyranometer with integrated heating and built-in sensors for remote monitoring of humidity and tilt angle.

Tune in and learn about:

Pros and cons of analog and smart sensors, as the CMP and SMP series
Introducing the Modbus protocol
Next level monitoring with the new Kipp & Zonen SMP12

In case the embedded player does not appear, listen to the episode on Buzzsprout via this link.

How to Choose the Right Sun Tracker? - Kipp & Zonen Blog

martin.maly@otthydromet.com (Martin Maly) — Mon, 13 Apr 2026 12:33:50 GMT

A complete measurement of solar irradiance includes global (GHI), direct (DNI), and diffuse (DHI or DIF) radiation. To accomplish this, a high-quality solar monitoring station typically comprises an automatic sun tracker fitted with instruments to measure these components individually. Depending on the application, long-wave radiation and reflected short-wave radiation may be added to provide the total radiation balance. This is especially relevant for meteorological and climatological observations. Furthermore, ultraviolet radiation and other measurements may also be taken.

For most applications it is not only the momentary value of the parameter being measured that is important. Variations in the amount of energy received over a period of time, and the effects to be expected as a result, are extremely important. It is usual to measure and record meteorological parameters during the diurnal cycle (daily course) in order to make predictions about the future weather conditions.

RaZON+

SOLYS2

SOLYS Gear Drive

Three models, choose the right sun tracker for your application

To keep all instruments aligned with the solar orbit, automatic sun trackers follow the path of the sun. OTT HydroMet offers three different models under the product brand Kipp & Zonen:

RaZON+

ALL-IN-ONE Solar Monitoring System that provides global (GHI), direct (DNI) and diffuse (DHI) irradiance and can be expanded to a full weather station with third party sensors. GPS and data logging are integrated. Customer friendly interface and anti-soiling design to reduce maintenance.

Applications: It is a perfect fit for small meteorological stations, used in temperate climates. Ideal for solar energy resource mapping, Concentrated Solar Power (CSP), Concentrated Photovoltaics (CPV) and tracking PV site prospecting. Continuous power plant monitoring.

SOLYS2

Versatile sun tracking solution, a wide range of radiometers can be mounted. The integrated GPS automatically configures location and time. Solar position and status monitoring information are available via the communication ports.

Applications: For use in harsher climates and to carry multiple instruments. Meteorology, climatology and BSRN stations. Solar energy site prospecting and plant monitoring.

SOLYS Gear Drive

High-end sun tracker for all weather conditions and locations. It builds on the features of the SOLYS2 and has enhanced capabilities that make it suitable for use with heavy loads and in the harshest climates, such as polar conditions.

Applications: Designed for use in extreme climates; very hot, very cold and high wind speeds. Can carry a large number of instruments and heavy loads. Ideal for many scientific research purposes.

Overview

This table gives an overview which sun tracker is the appropriate one for your purpose.

	RaZON+	SOLYS2	SOLYS Gear Drive
Best price/performance ratio	✅	✅	✅
Easy transportable, low weight	✅	-	-
Low power	✅	-	-
Integrated measurement / calculation of GHI, DNI, DIF	✅	-	-
Anti-soiling radiometer design	✅	-	-
Allows fitting of non Kipp & Zonen radiometers	-	✅	✅
Other instruments can be loaded	-	✅ up to 20 kg	✅ up to 80 kg
Operates under extreme cold conditions (< -20 °C)	-	✅ (AC power only)	✅ (AC power only)
Sun sensor for active tracking	-	✅ optional	✅
Daily uncertainty GHI	2%	1 to 2%	1 to 2%
Daily uncertainty DNI	2%	1%	1%
Baseline Surface Radiation Network (BSRN) compatible	-	✅	✅

Are you interested in learning more? You can find the technical specifications and more details on the Sun Tracker Comparison. Further questions? Our team of researchers and technical experts is happy to help.

Podcast: RWIS Lite - Increasing Safety with Streamlined Road Weather Information Systems - OTT Blog

martin.maly@otthydromet.com (Martin Maly) — Mon, 13 Apr 2026 12:30:09 GMT

Keeping roads and highways safe is critically important. In addition to autumn’s and winter’s perils, the increase of weather fluctuations and extreme weather events throughout the year pose further challenges to road decision-makers.

Ideally, a dense network of road weather monitoring stations reliably provides accurate, hyper-local data. Wherever that is not feasible, be it due to local characteristics or tight budgets, mobile sensing, and streamlined Road Weather Information Systems (RWIS) based on proven, versatile instrumentation by Lufft can fill the gaps and ensure availability of essential weather and road surface information.

Podcast: Get the most out of your sensors and infrastructure

In this episode, our road weather monitoring experts Brandon Ankney (USA) and Steven Marks (Germany) discuss various ways to monitor road surface conditions and atmospheric properties cost-effectively. Tune in and learn about:

Essential atmospheric parameters for road weather monitoring
Slim two-sensors Road Weather Information Systems (RWIS Lite)
Retrofitting stations with new technology by utilizing existing infrastructure

Lufft is one of OTT HydroMet’s strong brands for professional environmental monitoring. Do you want to learn more about OTT HydroMet’s product portfolio and how it can help you to make roads safer? Our team is happy to help you.

Weather and Runway Observation for Airports | OTT HydroMet

Kipp & Zonen Blog Team — Tue, 31 Mar 2026 18:22:35 GMT

Some Airports Where Lufft Sensors are in Use

References for photos in carousel below.

Airport Frankfurt/Hahn
Airport Düsseldorf, Germany
Airport Paderborn, Germany
Airport Turin, Italy
Many Airports in Belgium including Belgocontrol

Podcast: Meet the Dutch Couple Who Drove to Cape Town and Back - OTT Blog

martin.maly@otthydromet.com (Martin Maly) — Tue, 17 Mar 2026 19:49:59 GMT

Special Holidays Episode! This Dutch couple has seen quite a big part of the world. Maarten van Pel and Renske Cox always have been passionate travelers. But one day, they decided to stop flying. This decision gave birth to a spectacular idea and their biggest adventure yet: Driving from the Netherlands to Cape Town and back – powered mainly by solar energy.

In this episode of OTT CAST, we welcome two dedicated ambassadors for sustainable traveling. Maarten and Renske talk about their 13-months trip with more than 38.000 kilometers driven in a Skoda Enyaq, a battery electric vehicle (BEV). Thanks to PV panels on the rooftop and in the trunk of their car, they were able to generate more than half of the needed energy form the sun.

38.238 km in 13 months, that's the impressive summary of Maarten's and Renske's trip to South Africa and back.

The couple chose an all-electric Skoda Enyaq iv80 with a rooftop tent and PV panels to charge while driving. The Kipp & Zonen CMP3 pyranometer provided continuous solar irradiance measurements.

Tune in and learn about:

Impressions from Africa, a beautiful continent full of contrasts
How and where to charge a BEV with solar panels
Effective use of Kipp & Zonen CMP3 pyranometer to optimize charging performance

In case the embedded player does not appear, listen to the episode on Buzzsprout via this link.

5 Reasons Why You Should Visit Ott HydroMet at Meteorological Technology World Expo 2022 - Ott Blog

martin.maly@otthydromet.com (Martin Maly) — Mon, 16 Mar 2026 19:42:42 GMT

Bonjour Paris! After three long years, the world’s meteorological community finally reunites at Meteorological Technology World Expo. As a leading developer and manufacturer of environmental monitoring solutions, Ott HydroMet is excited to join the show at booth 8020. Here are five reasons why you should consider stopping by.

1. Discover Ott HydroMet’s Broad and Synced Portfolio of Proven Instruments for Meteorology and Climate Measurements

Meteorologists and climate researchers around the world trust in OTT HydroMet’s sophisticated suite of instruments, anchored by proven brands such as Lufft, Kipp & Zonen, OTT, ADCON, Sutron, and others. Even in remote and extreme locations, for example in Greenland or high in the Swiss Alps, our sensors reliably do their service with minimal maintenance required. Many of them are in operation for far over a decade, supported by a mean time between failures of more than 10 years. Gain insight at point blank into OTT HydroMet’s broad portfolio including Lufft ceilometers, ultrasonic anemometers and compact weather sensors, Kipp & Zonen radiometers, OTT precipitation gauges, and many more.

2. Precipitation is too Important to Rely on Guessing

Measuring precipitation is essential for meteorological and climatological purposes, but also for hydrological applications and local communities. Depending on the application and the place of operation, there are different kinds of instruments to detect rain, snow, and hail. Ott HydroMet offers various types of instruments to equip every monitoring station with a fitting technology, compliant with WMO No. 8 or CIMO guidelines.

The Ott Pluvio² weighing rain gauge has become the standard for accurate and reliable monitoring of liquid and solid precipitation with more than 15,000 units deployed worldwide. Thanks to its robust design, maintenance is limited to one visit per year to empty its bucket. The Pluvio² is available in two sizes; S and L – choose the one that fits your purpose.

Discover the Ott Parsivel² disdrometer, a laser-optical instrument for capturing particle size and velocity of hydrometeors, that is any kind of liquid or solid precipitation.

For compact and cost-efficient precipitation monitoring, the Lufft WS Smart Weather Sensors provide reliable data based on radar measurements. The Lufft WS100, for example, adds precipitation measurement with a small footprint to every weather monitoring station. The versatile Lufft WS600 includes additional sensors for wind speed and direction, air temperature and pressure, and relative humidity – all in one housing.

3. Precisely Measuring Snow Depth with the Experts’ Sensor of Choice

Precise determination of snow depth is a central indicator for many global weather application decisions. OTT HydroMet snow sensors have become the standard for meteorological snow measurements in climate research, flood and avalanche risk detection, and winter sport/traffic safety assessments.

With thousands of installed instruments on every continent, both the Lufft SHM 31 and its predecessor model, the SMH 30, have established themselves as the standard for precisely measuring the depth of snow. Its powerful laser sensor measures the density of snow from above, without the need for contact; it is designed to be safe for the eyes (class-2 laser) and, thanks to its built-in heating module, it requires no maintenance.

4. Lufft Ceilometers CHM 15k & 8k: Scientific All-rounders

Originally built for measuring cloud height and aerosols, a ceilometer can do way more. From air quality to wildfire observation to ground blizzards – scientists from various disciplines are discovering its strengths and benefits. OTT HydroMet offers the proven Lufft CHM series, that is enjoying growing popularity within the scientific community. Before visiting our booth, check out this selection of projects showing that with a bit of creativity, ceilometers are extremely versatile and cost-efficient research instruments.

5. Pyranometer Innovation: The New Kipp & Zonen SMP12

The first manufacturer of pyranometers, Kipp & Zonen, a product brand of Ott HydroMet, introduces another innovation to solar radiation monitoring. The new ISO- and IEC-compliant SMP12 is the industry’s first Class A pyranometer that delivers integrated heating with zero moving parts (solid-state technology) and best-in-class surge protection.

Ott HydroMet’s scientists and engineers focused on making the new instrument fully compliant with the highest class of ISO 9060:2018 and created a “spectrally flat, fast response pyranometer of Class A”.

Get your free ticket for Meteorological Technology World Expo 2022 and check out Ott HydroMet’s broad portfolio of proven instruments and monitoring solutions at our booth 8020!

Are you monitoring solar irradiance? If so, we recommend joining our upcoming webinar on “the Impact of Dew, Frost, and Soiling on Solar Radiation Monitoring – and Ways to Mitigate it”. Join our solar monitoring experts Victor Cassella and Clive Lee on September 29 at 10:00 ET/15:00 BST.

Blog - K&Z

PV Module IV Curve: A Definitive Guide to Understanding Solar Performance

What is a PV module IV curve?

Key parameters of a PV module IV curve

How environmental conditions shape the PV module IV curve

Irradiance effects

Temperature effects

Soiling and shading

Degradation

What a PV module IV curve reveals about system performance

Common PV module IV curve defects and what they indicate

Watch: PV module IV curve behaviour in real‑world conditions

Best practices for accurate PV module IV curve measurement

Why measurement quality determines IV curve confidence

Applying IV Curve Analysis at Scale

Put IV Curve Insight into Practice

Soiling Measurement for Capacity Testing in Utility‑Scale Solar

Why Measurement Strategy Matters More Than Ever

Executive Summary

What Is Soiling in Solar PV Systems?

Why Soiling Measurement for Capacity Testing Requires a Different Strategy

Soiling in the Context of Capacity Testing Standards

The Hidden Risk: Soiling Is Often Measured Too Late

Common Workarounds and Their Limitations

Measure Soiling from Day One: A Proactive Strategy

A Common Misconception: SCADA Integration Is Not Required Early

What Makes a Soiling Sensor Suitable for Capacity Testing?

Field Evidence: Soiling Is Spatially Variable

Linking Soiling Data to Capacity Test Outcomes

Understanding the Limits of Soiling Measurement

From Reactive Testing to Proactive Performance Assurance

Webinar: How to Process and Interpret Soiling Data - Kipp & Zonen Blog

What is PV Soiling?

Ensuring Reliable Data Collection

Location and Number of Sensors

Installation, Commissioning and Maintenance

Processing Data to Maximize Findings

Class A Pyranometers: Choosing the Right Type for Your PV Plant - Kipp & Zonen Blog

Introduction: What is ISO 9060

Kipp & Zonen Pyranometers

Similarities Across the SMP Series

Standard 5 Year Warranty

SMP12: Kipp & Zonen’s Most Innovative Pyranometer Yet

SMP22: The World’s Most Accurate Smart Pyranometer

Overview

Further reading & listening

Podcast: Analog or Smart Sensor? Choosing the Right Instrument - Kipp & Zonen Blog

Further reading

How to Choose the Right Sun Tracker? - Kipp & Zonen Blog

Three models, choose the right sun tracker for your application

RaZON+

SOLYS2

SOLYS Gear Drive

Overview

Podcast: RWIS Lite - Increasing Safety with Streamlined Road Weather Information Systems - OTT Blog

Podcast: Get the most out of your sensors and infrastructure

Further reading

Weather and Runway Observation for Airports | OTT HydroMet

Some Airports Where Lufft Sensors are in Use

Podcast: Meet the Dutch Couple Who Drove to Cape Town and Back - OTT Blog

Further reading

5 Reasons Why You Should Visit Ott HydroMet at Meteorological Technology World Expo 2022 - Ott Blog

1. Discover Ott HydroMet’s Broad and Synced Portfolio of Proven Instruments for Meteorology and Climate Measurements

2. Precipitation is too Important to Rely on Guessing

3. Precisely Measuring Snow Depth with the Experts’ Sensor of Choice

4. Lufft Ceilometers CHM 15k & 8k: Scientific All-rounders

5. Pyranometer Innovation: The New Kipp & Zonen SMP12