How to ensure optimal data quality

How to ensure optimal data quality


It is important to be aware that there is an “optimal data collection window”. This time window will vary from region to region and can be affected by several meteorological factors. You should always monitor the weather conditions and look to collect data during peak conditions. 

What are optimal data collection conditions?

To comply with IEC standards and maximise the quality and efficiency of reporting, we collect data only when certain environmental conditions are met. 
Table 1: Data collection environmental requirements from IEC TS 62446-3

Table 2: variables affecting data quality

When are the optimal data collection conditions?

Table 3: Inspection conditions regional lookup table
*NR – Not recommended

Days in the “Peak” seasons have the most hours of good data collection conditions, whilst “Low” season days have the fewest. 

Within each of these regions, there will be extreme weather events that cannot be simply accounted for in the table (tornado season in USA Midwest for example).

Factors affecting data quality

Tracker inclination (where applicable)


During peak data collection conditions, the tracker array is positioned within this optimum range for the longest duration, and its transit from facing East-West is slowest. 

"Peak” data collection window: 
  1. Trackers inclined between +/-45° for at least 280 minutes per day, with corresponding >600W/m2 irradiance conditions.
  2. Minimal thermal reflections. 

Predominant impacts of sub optimal condition:  
  1. Foreshortening: PV modules appear narrower in image when angle of incidence is not perpendicular to camera. 
  2. Row-to-Row reflections: Heat from the adjacent row is reflected onto target module row, manifesting as a “Hot Stripe”. (link to image)
  3. Some anomalies may be missed or report false temperatures if present in an affected area.

Moisture 

"Peak” data collection: 
  1. No precipitation.
  2. Ambient temperature exceeding 5°C.
  3. More than a day after a significant weather event – e.g. heavy rain/snowfall. 
Predominant impacts of sub optimal condition:  
  1. Higher incidence of visual artefacts in imagery. Anomalies are less obvious, or more ambiguous.
  2. Inaccurate/misrepresented temperature reporting. 

Extreme ambient temperatures

“Peak” data collection:
  1. Ambient temperature between 5°C – 30°C.
  2. Thermal sensor at operating temperature before inspection (defined by sensor manufacturer).

Predominant impacts of sub optimal condition:  
  1. Shorter flight times in cold weather (<5°) due to voltage drop in batteries.
  2. Shorter flight times in hot weather (30°+) due to battery overheating. 
  3. Thermal sensor can overheat in hot weather and takes time to warm to operating temperature in cold conditions – reducing the time available for inspections. 
  4. Images are less aesthetically consistent

Glare (sun-path)



"Peak” data collection window: 
  1. No glare hotspot. Glare hotspot occupying 1/4 of image frame can be accepted.
  2. Cannot be avoided when the sun remains low in the sky throughout the day.
  3. Can be avoided when the sun arc is highest, which corresponds with periods of ideal irradiance.  

Predominant impacts of sub optimal conditions:  
  1. Some anomalies may be missed or report false temperatures if present in an affected area.
  2. Root causes may be indeterminable due to lower contrast RGB images. 

Row-to-row shading (sun-path)



"Peak” data collection period:
  1. Minimal to no row-to-row shading is present in data.
  2. Shading is minimal when the sun arc is highest, which corresponds with periods of ideal irradiance. 

Predominant impacts of sub optimal conditions:  
  1. Temperature inaccuracies in affected areas.
  2. Some anomalies may be missed or report false temperatures if present in an affected area.
  3. Images are less aesthetically consistent 

Low Irradiance (<400W/m2, <600W/m2 for IEC)

"Peak” data collection window:
  1. Irradiance above 600W/m2 at time of flight.
  2. Consistent light source (not cloudy).

Predominant impacts of sub optimal conditions:
  1. Data captured at lower irradiance has higher noise and can be prone to smearing. 
  2. Increased analysis time.
  3. Data collected below IEC irradiance levels (600+) may be ineligible evidence for a warranty claim. 


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