Questions & Answers: Launching the New SMP12 Class A Pyranometer

SMP12 Pyranometer

Solar demand is surging. Modern PV plants need fast responding precise solutions that are easy to install and integrate, ones that will last. Our new pyranometer, the Kipp & Zonen SMP12 can help you achieve this. On this page, we present our webinar with Clive Lee – Technical Sales and Service Consultant, Dr. Joop Mes – Senior Scientist, and Brandon Sims – Global Product Manager, who present the latest addition to the trusted family of Kipp & Zonen solar radiation instruments.

In this post, we gathered questions from people attending the webinar and gave it to a team of experts to answer them. In case you missed webinar when it aired live, fret not. Watch the recorded session below. Before, if you don’t know the SMP12 yet, you can download the product guide here.

Watch the webinar on our new SMP12 Class A pyranometer

Questions and answers

The uncertainty of tilt measurement is ± 0.5°.

The inclination sensor does not indicate the direction, there is one angle value that is the tilt away from horizontal.

A silicon photodiode sensor or cell in the POA is suitable for monitoring the efficiency of PV modules. These are ISO 9060:2018 Class C pyranometers. Note that the cell type should match the technology of the PV modules. These inherently have relatively low accuracy/high uncertainty.

They should not be used for GHI measurements to compare with meteorology, satellite, or model data; which is all for the complete spectrum of solar radiation/energy. Only spectrally flat pyranometers should be used for GHI measurements and are also best for POA PV plant Performance Ratio irradiance monitoring because they measure all the available radiation under all sky conditions.

ISO 9060:2018 Class A models have high accuracy. IEC 61724-1:2021 specifies that if a reference cell is used for Class A monitoring, it must have calibration uncertainty ≤ 2 % at 1000 W/m2, range up to 1500 W/m2, resolution ≤ 1 W/m2. These are very expensive and cost more than a Spectrally Flat Class A pyranometer.

Heating of the dome prevents dew and frost forming. Because the dome is dry, sand and dust is less likely to stick to it. Using CVF4 with the ventilation fan running and the heating on has the same effect. It is also likely to reduce soiling in general due to the air flow. CVF4 reduces thermal zero offsets in CMP and SMP pyranometers by a factor of 2. But, these offsets are already very low in SMP12 compared to the other models. IEC 61724-1:2021 does not require external ventilation – it requires dew & frost mitigation AND weekly dome cleaning unless monitoring or automated.

The spectral response of the SMP12 is determined by the optical characteristics of the glass dome, the quartz diffuser and the small black thermopile detector. The overall response is very consistent across instruments, but it does not meet the spectral selectivity and spectral error requirements of a ISO 9060:2018 Spectrally Flat Class A pyranometer. The custom-designed optical filter has the inverse (mirror) response and corrects the errors and it is the same for all SMP12 units. There is no individual adjustment needed.

To allow for a heated dome and upper housing, the well-known large black thermopile had to be changed to minimize their thermal influences. There is a much smaller thermopile detector that is also thermally isolated from the sensor body. Because the detector is small, the white quartz diffuser is necessary to collect radiation from all angles and direct it towards the detector with good directional (cosine) response. In an ‘insulation’ sense, the diffuser acts like the inner dome of a conventional pyranometer. The result is that thermal zero offsets types a) and b) are very low.

Technically the heating function can be stopped by reducing the supply voltage to 6 VDC. However, the thermal zero offset correction is based on the heating being on and you will have an offset in the range of 2-3 W/m2. We do not recommend turning the heater on and off by changing the supply voltage. There is increased measurement uncertainty while the instrument stabilizes (approx. 3 hours). It cannot prevent dew or frost formation while the heating is off, or in the process of warming up. The dome needs to be at least 2°C above the dew-point. The recommendation is to add power and collect better irradiance measurements, which is much easier and more affordable in 2022 than ever before.

There is no isolation because the galvanic isolated RS-485 interface is too large to fit into the sensor and requires a larger power draw.

Calibration of all Kipp & Zonen pyranometers is recommended every two years. This is the same interval as specified in IEC 61724-1:2021 for Class A irradiance monitoring sensors and in ISO 9060:2018 for classified pyranometers.

The SMP12 is currently available for order. Please contact your local representative for a quote and availability details.

In case your question is not answered here, don’t hesitate to contact our experts and ask them. They’re happy to help and answer any open questions as well as exchange thoughts on the new Kipp & Zonen SMP12 Class A pyranometer.

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