Everything About the SMP12 Class A Pyranometer

Solar demand is rising. Modern PV plants require solutions that are accurate, fast responding, simple to install and integrate, and long-lasting. Sustaining the site for the long haul with premium, long-lasting components is possible.

The new SMP12 is a Class A Pyranometer that offers integrated heating with no moving parts (solid-state technology) and the finest surge protection. It complies with ISO and IEC standards.

Users can empower their performance with complete confidence, decrease the total cost of ownership and improve production with the SMP12. It also offers all-weather dependability and outcomes.

Everything About the SMP12 Pyranometer

Image Credit: OTT HydroMet - Solar Energy

Everything About the SMP12 Pyranometer

Image Credit: OTT HydroMet - Solar Energy

Everything About the SMP12 Pyranometer

Image Credit: OTT HydroMet - Solar Energy

Key Benefits SMP12—Tailor-Made for Solar

Integrated Dome Heating for Untouchable Precision

No morning dew and frost will influence the accuracy of the measurements because the outer dome holds a slightly higher temperature than the surrounding air. Consequently, the user can fully comply with IEC-61724:2021.

Safeguard Production with Enhanced Surge Protection

Concentrate on plant performance rather than nitpicky power sources and inadequate grounding. Learn about cutting-edge surge protection that minimizes failure risks, prevents costly on-site replacements, and preserves performance.

Focus on Performance, Not Maintenance

The SMP12 offers industry-first built-in dome heating that has no moving parts, as well as remote internal humidity monitoring. It requires very little maintenance because of solid-state technology and an internal drying cartridge that can last for up to 10 years.

The Right Tilt Angle for Reliable Results

Understanding that the installation angle remains stable will help increase the data’s long-term reliability. It is possible to remotely monitor tilt angle installation with the SMP12 down to ±0.5°.

Easily Integrate with All Systems

The SMP12 is simple to integrate with all of the user’s data loggers and SCADA systems thanks to industry-standard RS-485 connectivity and the Modbus® protocol.

Everything About the SMP12 Pyranometer

Image Credit: OTT HydroMet - Solar Energy

For All the Monitoring Needs

Simplified and Integrated Experience

Everything About the SMP12 Pyranometer

Image Credit: OTT HydroMet - Solar Energy

For meteorological equipment, handling multiple vendors, interfaces, and communication maps can be difficult. Using an entire environmental monitoring system from OTT HydroMet, users can save an enormous amount of time and finish projects more quickly.

One output cable from a Smart Hub can be used to attach the SMP12 and other pyranometers, soiling monitoring systems, and weather sensors. The instruments can also be connected directly to the data logger or SCADA system.

SMP12 — Frequently Asked Questions

SMP12 Key Features

What distinguishes the SMP12 from the other SMP models?

The SMP12 has the following extra features in addition to improved data dependability:

  • Internal relative humidity measurement to remotely verify the efficiency of the internal desiccant
  • Integrated dome heating without moving parts to prevent dew and frost
  • Tilt measurement to remotely check the proper installation angle of the instrument and any changes over time
  • Enhanced electrical protection against power surges


What is the purpose of the heated SMP12 dome?

The glass dome and instrument body of the SMP12 are heated in accordance with IEC61724 recommendations to prevent dew or frost buildup in the early morning hours. This enables the user to more precisely measure the solar irradiation when the PV modules might still be covered in dew or frost and produce less energy than expected.

How is the SMP12 heater operated?

The internal heater is always on from 10 to 30 VDC. Depending on the atmospheric conditions, the heater will raise the instrument’s temperature by 5 to 15 ⁰C above ambient.

How much power does the SMP12 require?

A maximum of 3.5 W DC is required by the SMP12.

How long does it take for the SMP12’s heating function to stabilize?

It takes 3 hours approximately. The measurement of solar radiation is impacted by temperature. The heat will be transmitted through the body to the detector once SMP12 is turned on. The readings will have more uncertainty during the transfer phase due to the ongoing temperature changes.

What distinguishes the internal heater from a ventilation system?

Dew and frost are prevented by heating the dome. Sand and dust are less likely to adhere to the dome because it is dry. The same result can be achieved by using a ventilation unit with the fan running and the heating on. The airflow also reduces soiling.

In CMP and SMP pyranometers, for instance, the Kipp & Zonen CVF4 minimizes thermal zero offsets by a factor of 2. However, in comparison to other models, SMP12’s offsets are already very small. IEC 61724-1:2021 requires weekly dome cleaning unless monitored or automated, dew & frost mitigation, and no external ventilation.

Does the heater have a switch or command to turn it off?

The heater cannot be turned off using any particular switch or command. It never turns off.

When power is limited, can the heater be cycled on and off?

The heating function can technically be turned off by lowering the supply voltage to 6 VDC. The thermal zero offset correction, however, is predicated on the heating being on, and the user will experience an offset of 2–3 W/m2.

It is not advisable to change the supply voltage to turn on and off the heater. While the instrument stabilizes, measurement uncertainty increases (approximately 3 hours). While the heating is off or warming up, the formation of dew or frost cannot be prevented. The dome needs to be at least 2 °C above the dew-point. It is advised to increase power and take better measurements of irradiance.

Why do measurements taken at night produce a negative output?

Zero offset Type A is responsible for this error. This zero offset typically exists when the dome’s temperature differs from the sensor’s cold junctions (the instrument housing). When the sky is clear, this is almost always the case. The Earth’s surface radiates upward about 100 W/m2 of long-wave infrared energy due to the low effective sky temperature (0 °C).

This emission is also present in the outer glass dome of a pyranometer, which is cooling to a temperature several degrees below that of the surrounding air (the emissivity of glass in this wavelength range is almost 1).

The body’s heat emission is drawn away from it by wind, infrared radiation, and conduction in the domes. The heat flow is opposite to the heat flow when absorbing solar radiation and causes the well known zero depression at night. On a clear day, this negative zero offset set is also present, but it is concealed by the solar radiation signal.

Diffuser Technology

Why does the SMP12 look different?

The conventional large black thermopile had to be swapped out for a white diffuser, optical filter, and smaller thermopile underneath to make room for a heated dome.

What is the diffuser’s mechanism?

The diffuser takes the place of the inner dome to enable the heating of the instrument. For optimal cosine response and thermal insulation, the outer dome and diffuser behave like a double dome. The diffuser is an optical component that directs incoming energy into the thermopile while diffusing and transmitting light from all directions.

Since the introduction of the SUV product line in the 1990s, Kipp & Zonen has employed diffuser technology. It has also been utilized with the RaZON+ PR1 in conjunction with a thermopile detector.

How are offsets impacted by the diffuser and filter?

Thermal isolation separates the smaller thermopile detector from the sensor body. The white quartz diffuser is required because of how small the detector is in order to collect radiation from all directions and direct it there with a good directional (cosine) response. The diffuser functions, in terms of “insulation,” like the inner dome of a typical pyranometer. Thermal zero offsets a and b are consequently very small.

Internal Tilt Measurement

What can the tilt sensor be used for?

For accurate readings, proper horizontal leveling with a bubble level or a precise tilt angle for a plane of array (POA) is essential. The SMP12 enables remote monitoring of this tilt over a broad temperature range with a long accuracy of 0.5° to ensure that the installation angle has not changed over time.

Is the tilt mounting kit required to utilize the tilt sensor data?

The tilt sensor determines the accuracy of the installation angle and any alterations over time. Both GHI and POA installations are compatible with it. This sensor can provide an accurate tilt angle reading without the tilt mounting kit.

Is cardinal direction indicated by the tilt sensor?

There is only one angle value, which is the tilt from horizontal, provided by the inclination sensor; it does not provide a direction. It quantifies the tilt of the smart sensor with respect to the gravitational field of the earth using a three-axis accelerometer (the tilt angle from horizontal).

Internal Relative Humidity Measurement

What is the purpose of internal relative humidity measurement?

The internal relative humidity (RH%) must be kept below the condensation point of 100% for proper operation. Under normal conditions, the SMP12’s internal desiccant and build quality guarantee a 10-year lifespan without the need to replace it. The desiccant will typically change during calibration in an OTT HydroMet-approved facility.

Why is checking the interior humidity critical?

The Modbus® register for internal relative humidity can be used to test the effectiveness of the instrument seal and desiccant in the interim between recalibrations. Confirming that the internal desiccant is properly functioning ensures continued confidence in the solar irradiation data.

Recording the initial value following installation and comparing the internal relative humidity over longer time periods is advised (months–years). When possible, this should be performed at roughly the same reported body temperature during the cooler part of the day, above the freezing point (at midnight).

What is the main point of entry for humidity?

All SMP instruments are built with a waterproof, but not gastight, seal. Due to temperature and pressure changes, water vapor can slowly enter because there are two seals. The SMPs with internal desiccant have an important sealing that allows the internal desiccant to last for up to 10 years. When measured during a cool, non-freezing night, an entirely new SMP12 will start with an internal humidity of roughly 0–15%.

Surge Protection

What does “improved electrical surge protection” mean?

Power line or lightning-induced surges are what surge protection is all about, and the size of the surge protection Device (SPD) directly impacts the ability to protect the instrument. The more energy the SPD can absorb during the surge, the better the SPD is at protecting the electrical equipment. For its size, the SMP12 offers the best protection available.

Why does the SMP12 surge protection device not have isolation?

Since the galvanic isolated RS-485 interface cannot fit inside the sensor and would require a higher power draw, there is no isolation.

Modbus® Registers

Why is the SMP12 given a scale factor of “1”?

The resolution for the SMP12 is set at 0.1 W/m2. The scale factor of 1 is used to define the number of decimal places shown (1 decimal place) in the irradiance reading to provide this resolution.

Video Credit: OTT HydroMet - Solar Energy

This information has been sourced, reviewed and adapted from materials provided by OTT HydroMet - Solar Energy.

For more information on this source, please visit OTT HydroMet - Solar Energy.


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