DustIQ: Soiling Monitoring of PV

Kipp & Zonen DustIQ, the industry-leading soiling monitoring system, is getting even better. OTT HydroMet is now providing a new firmware for the DustIQ that facilitates easy handling and calibration. The new firmware is also available to active users.

DustIQ: Soiling Monitoring of PV

Image Credit: OTT Hydromet B.V- Kipp & Zonen & Solar

Better Response to Soiling with Increased Sensitivity

DustIQ previously overlooked the degree of transmission loss with its prior factory calibration dust slopes, according to measurements taken outdoors in various desert regions around the world.

According to those sites, the outdoor dust slope was reported at a factor reaching 1.8 and 2.6 higher than the factory calibration. An average factor 2 is discovered based on these reports. Independent studies also prove that the DustIQ’s factory calibration dust slope underestimates transmission loss.

The factory calibration dust slope is now corrected by this factor 2 with the firmware update to version 22000. For instance, a sensor that previously read 98.5% soiling ratio before the update (1.5% transmission loss) will now read 97.0% soiling ratio after the update (3.0% transmission loss).

Easier and Faster Field Calibration Procedure

Field experiments have proved that it is possible to perform a simpler shorter field calibration while maintaining the quality of measurements. At present, condensing the calibration process to an easier and briefer procedure requires pressing the button twice and cleaning the complete DustIQ in a single step rather than the multiple steps that were previously required.

The briefer the method, the simpler it is to execute, threats of possible errors are reduced and there are huge time savings. Moreover, the required soiling ratio threshold of 5% has been reduced to 3%. Tests have displayed that this has a minimal influence on the precision of the field calibration.

Tests have shown that the new Firmware update enables an easier field calibration and a faster response.

Tests have shown that the new Firmware update enables an easier field calibration and a faster response. Image Credit: OTT Hydromet B.V- Kipp & Zonen & Solar

Plain Communication Thanks to Numerical Error Code Display

To alert users of potential errors, the DustIQ tended to use binary bits (0000 0000 0000 0000) for its reports. However, errors are now depicted with numerical codes to make readings easier. The DustIQ now also communicates using signed integers in registers 26 and 27 with the new firmware.

Register 26 indicates whether the DustIQ is ready for field calibration, if there is insufficient soiling, if something is missing or if there is too little sunlight.

After the field calibration has begun, register 27 is used to provide feedback. These are simple numerical codes like 1, which indicates successful calibration, or 1000, which indicates that there is insufficient sunlight for field calibration.

New Tare Function: Offsetting a Negative Transmission Loss

When the clean baseline signal changes owing to variation in site conditions, negative transmission loss values can occur. The new tare procedure removes the offset by adjusting the baseline.

The steps are outlined in the instruction sheet. It also reduces the DustIQ’s minor temperature sensitivity when used at temperatures other than the factory calibration (25°C).

When to Calibrate, When to Tare?

To improve the quantitative accuracy of the DustIQ, a site-specific calibration is used to match the soiling that subsides on the modules at the site. When both sensors read higher than 3% soiling, the sky is clear and the irradiance is greater than 500 Wm-2, calibration can be done.

Negative transmission loss values that arise owing to variation in factory and field environments are corrected using the tare procedure. When the DustIQ is completely clean and the sky is clear, the tare procedure can be performed.

Example 1

The DustIQ reads greater than 3.0% transmission loss (soiling ratio <97.0), with clear skies and irradiance higher than 500 Wm-2. The “Local Calibration” can be carried out, followed by the tare procedure.

Example 2

The DustIQ displays that there is a 2.2% transmission loss (soiling ratio <97.8), clear skies and irradiance higher than 500 Wm-2. The tare procedure and the “Local Calibration” cannot be performed without cleaning.

The time needed for soiling to reach 3.0% transmission loss will be reset if cleaning is done to conduct the tare procedure. If no rain is expected, then users are advised to wait until the calibration is able to be carried out before commencing with the tare procedure.

Example 3

The DustIQ shows a 0.4 % transmission loss (< 99.6 soiling ratio), there are clear skies and irradiance is more than 500 W m-2. In this case, ‘Local Calibration’ cannot be carried out, and the tare procedure cannot be performed without cleaning.

In this example, cleaning may not erase a significant amount of soiling time, and users are advised to clean the DustIQ and perform the tare procedure.

Calibration Button Changes

One of the three actions can now be triggered by the calibration button: The following is a list of how to activate them:

  1. Restore to factory configuration: Hold the button for 20 seconds. There will be no change in the communication settings
  2. Start field calibration: Hold the button for 4 seconds
  3. Start tare function: Press the button three times

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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