FAQ

• General

  • What does DustIQ measure?

    • The DustIQ measures the amount of light relected by the dust back into the sensor. This is converted into Transmission Loss and Soiling Ratio. The DustIQ reports 2 independent transmission losses and soiling ratios of its 2 sensors.  (Transmission loss = 100% - soiling ratio)

  • How does soiling loss translate into power/energy loss?

    • How does soiling loss translate into power/energy loss? Transmission loss, according to several publications and reports, directly translates into energy loss because the relationship is almost linear for soiling losses up to 20%.

  • What is the accuracy of dust measurement by the DustIQ?

    • Transmission loss measurement accuracy: ± 10% of reading after local dust calibration (not including zero offset). Zero offset: < ± 1% when clean.

  • What can I do with the zero offset ?

    • The zero offset can be subtracted from the measurements to reach zero again. E.g. a transmission loss of 0.3% for a completely clean DustIQ is within specification and can be compensated by TLcorrected = TL - 0.3 or Soiling Ratiocorrected = Soiling Ratio + 0.3

  • How closely do dust levels on sensor and PV plant panels match?

    • When installed next to or in between the actual PV modules the relationship is between 80 and 100%.

  • Is the Dust IQ soiling loss accurate when compared with a 2-panel system?

    • A 2-panel system with PV modules identical to the ones used in the PV plant and cleaned every day is the most accurate but also most expensive solution. It is also very unlikely that a 2-panel system can be installed right in between the real PV modules and thus the soiling will be different. The DustIQ is the optimum balance between accuracy and being maintenance-free with a low TCO.

  • What is the maximum soiling measurement range of DustIQ?

    • The DustIQ can measure up to 50% soiling loss.

  • How can the soiling be the same as on the panels?

    • The DustIQ is installed next to or in between the actual PV modules and will get the same dust, wind, rain and cleaning. The surface is also very similar to a many PV modules.

  • What is the significance of the solar cell on the DustIQ?

    • The silicon cell is only used once for the local dust calibration to correlate the step change in energy with the optical sensor measurement.

  • What is the impact of the panel temperature on the Dust IQ?

    • The DustIQ uses its own Optical Soiling Measurement. The DustIQ performance is not affected by external factors in the temperature range given in the specifications: from -20 to +60° C

  • What is the purpose of the temperature option when selecting the correct model of DustIQ?

    • The PV module temperature sensor (standard since 2019) can be connected to the second port on the DustIQ to measure the rear temperature of a nearby PV module. The IEC advises to take many temperature measurements to be able to take the PV module temperature into account in the Performance Ratio calculations.

  • How many DustIQs are needed relative to the installed PV plant power? (Number of sensors per 1 MW)

    • "The standard IEC61724-01 on monitoring gives recommendations. Due to copyright we cannot share the document. Table 1 in the document advises as follows:
      
      5MW 1 instrument
      40MW 2 instruments
      100MW 3 instruments
      200MW 4 instruments
      300MW 5 instruments
      500MW 6 instruments
      
      Please see below for a preview and ways to buy the document. https://webstore.ansi.org/Standards/IEC/IEC61724Eden2017

  • Technically speaking, how does the DustIQ measure soiling according to IEC 61724?

    • "IEC 61724 specifies two methods to measure soiling that were available at that time:
      
      Method 1: max power and temperature of the soiled device
      
      Method 2: short-circuit current and temperature measurement
      
      The optical measurement that has been introduced with the release of the DustIQis equivalent to the short-circuit current method. Obviously it does not measure short-circuit current but the reflected light, that then is translated into transmission loss. The local dust calibration is done based on the step change of the short-circuit current of the built-in silicon panel."

  • Is the DustIQ useful for Polycrystalline or Thin-film modules?

    • Yes, it is. Although the Thin-film might react a little bit different, the relationship between sunlight lost due to soiling and energy loss remains the same.

  • What is the expected soiling loss percentage with respect to dry cleaning and wet cleaning?

    • This question is best answered by the people supplying the dry cleaning robots. However, we have seen dry cleaning robots to reach 0.5% soiling loss compared to 8% loss before the cleaning. Wet cleaning sometimes is better but only when done very carefully, with very clean water and in absence of wind that brings new dust directly sticking to the wet PV modules.

  • Can we trigger automatic movement of robotic cleaners for cleaning of modules through RS-485?

    • The short answer is no. The data produced needs "clever" robot control software to filter out rain and dew events, to be able to start a cleaning cycle. Humans can see immediately from a graph and the weather report what happened. Computers need machine learning and AI. Thus, in the future this can be possible.

  • Can the soiling data be transmitted to SCADA via Wi-Fi?

    • The DustIQ doesn't have Wi-Fi as customers told us they don't trust the connection to be 100% available all the time. Therefore, we use Modbus RTU over RS-485 wired connection that also supplies the 12-24V power. However, the solution can be made wireless by using an integrator or customer supplied RS-485 to Wi-Fi converter and Modbus over TCP/IP.

  • Can we link in to SCADA system to measure the Performance Ratio (PR)?

    • Absolutely. The DustIQ produces Modbus registers to be read out. Please see the manual.

  • Can the DustIQ resist harsh conditions, for example in locations near the sea?

    • Yes. The DustIQ is made with glass and aluminium with PV standard quality. Thus the same procedures for using and cleaning the PV modules can be used.

  • Is there a way to identify the soiling rate on the glass dome of a pyranometer using the DustIQ?

    • There is no direct relationship between the soiling of the flat DustIQ and the round glass dome of a pyranometer. Also the influence of soiling on a round dome on solar radiation measurement changes from plus to minus over the day and with the angle of the sun. Currently, there is no better solution than regular cleaning of the dome.

  • What is the advantage by using blue LED light?

    • Only blue LEDs are available with manufacturer documents to show long time stability in UV rich environments.

  • Why can the reported soiling ratio differ between the two sensors of the DustIQ?

    • Analyses show that the bottom of PV modules often gets soiled more than the top part and so will the bottom DustIQ sensor. Resulting in higher reported transmission loss.

  • Following IEC 61724-01, would you recommend measuring soiling in heavy rainy areas, e.g. Quebec in Canada?

    • According to IEC 61724-01, soiling monitoring is necessary when energy losses can exceed more than 2%. In areas with a lot of rainfall, this probability is very small and measuring soiling would not be needed.

  • How fast can the DustIQ report data?

    • The DustIQ takes a measurement once per minute. It operates throughout the whole day. The measurements are reliable as long as the device is dry. Storing 24x7 measurements of every minute does not really make sense as soiling grows very slowly. A few measurement points per day are enough.

  • The DustIQ is obviously smaller than a solar panel. By saying "it has PV panel dimensions", what does that mean?

    • Its length (996 mm) is the most common width of PV modules as is its height (35mm). The aluminium frame and glass are PV module equivalent, too.

  • What if the soiling buildup does not look the same on the DustIQ collection area compared to other modules?

    • Theoretically, the DustIQ measurement could be different then. According to the experience our customers made, the results are still close enough.

  • Many PV plants are installed near the ocean or industrial areas. What do you recommend to handle bird droppings and organic material or soot?

    • Bird droppings are very local and only a 2-panel system can work accurately. However, preventing bird colonies even when building the PV plant is paramount. Cleaning is very difficult or expensive and once colonized, the birds are difficult to deter.

  • What is the main difference between normal soiling station of other makes and DustIQ?

    • Normal 2-panel systems require daily cleaning of the clean reference cell or panel, they do not fit in between the real PV modules and they only work well on sunny, cloudless days around solar noon. The DustIQ works 24/7 as long as the DustIQ is free from rain or dew. It even works up-side-down for bifacial PV plants.

  • How does the DustIQ compare to the Atonometrics MARS sensor?

    • They both use optical soiling measurement. The MARS uses a camera and only works around sunset and with a clear sky. Thus, one measurement window per day. The DustIQ measures accurately 24x7 as long as the DustIQ itself is dry. Supposedly, the MARS does not need dust calibration, but no prove has been published.

  • Does DustIQ work independently or for all PV technologies, i.e. Bifacial PV?

    • It works for all silicon- based PV modules and also upside down for bifacial.

  • What if there are different types of dust throughout the year?

    • The DustIQ has not been designed for that.

  • Is there a plan to offer a traceable temperature sensor for the DustIQ?

    • This is under investigation.