NABCEP Solar Site and Shading Analysis 2 — Questions and Answers
Question 1: A Solar Pathfinder instrument is used at a proposed installation site. What does it primarily measure?
- Magnetic declination at the site
- Percentage of annual solar access blocked by obstructions (Correct answer)
- Roof pitch and azimuth simultaneously
- Ground reflectance (albedo) coefficient
Correct answer: Percentage of annual solar access blocked by obstructions
The Solar Pathfinder captures a panoramic reflection of surrounding obstructions and overlays a sun path diagram to quantify the percentage of annual solar energy available at that location.
Question 2: Which shading loss factor specifically accounts for the electrical mismatch caused when one module in a string is partially shaded while others remain unshaded?
- Soiling loss factor
- String mismatch loss (Correct answer)
- Wiring resistance loss
- Spectral correction factor
Correct answer: String mismatch loss
String mismatch loss occurs because a shaded module forces its series-connected string partners to operate below their maximum power points, reducing total string output disproportionately.
Question 3: When performing a shading analysis using simulation software, a designer enters a 'horizon elevation angle' of 12° at azimuth 180°. What does this mean?
- The roof tilt faces 12° off true south
- An obstruction 12° above the horizon blocks sun at due south (Correct answer)
- The site latitude is 12° north of the equator
- The array is tilted 12° from horizontal toward south
Correct answer: An obstruction 12° above the horizon blocks sun at due south
A horizon elevation angle of 12° at azimuth 180° means that an obstruction (such as a hill or building) rises 12° above the horizontal plane when looking due south from the site.
Question 4: A site in Phoenix, AZ (latitude ~33°N) has a tree located 10 feet north of the array. At what time of year is this tree LEAST likely to cause shading on the array?
- Winter solstice at solar noon
- Spring equinox at 9 AM
- Summer solstice at solar noon (Correct answer)
- Fall equinox at 3 PM
Correct answer: Summer solstice at solar noon
At summer solstice, the sun reaches its highest elevation angle of the year (approximately 80° in Phoenix), so a tree directly north casts minimal shadow southward onto the array.
Question 5: The 'irradiance threshold' parameter in PVsyst's shading loss calculation refers to:
- The minimum GHI required to start the inverter
- The plane-of-array irradiance level below which shading losses are ignored in the model (Correct answer)
- The rated capacity of the irradiance sensor used on site
- Maximum irradiance before modules enter thermal derating
Correct answer: The plane-of-array irradiance level below which shading losses are ignored in the model
PVsyst's irradiance threshold sets the POA irradiance level below which detailed shading calculations are skipped, as low-light periods have negligible energy contribution.
Question 6: Which instrument uses a fish-eye lens to photograph the sky dome and then analyzes the image to calculate solar access and shading fractions?
- Pyranometer
- Pyrheliometer
- HemisView or SunEye device (Correct answer)
- Inclinometer
Correct answer: HemisView or SunEye device
The HemisView and Solmetric SunEye are hemispherical (fish-eye) camera tools that capture the full sky dome and overlay sun path diagrams to compute shading-adjusted solar access values.
Question 7: A commercial rooftop in Chicago has HVAC units that will shade the southern portion of the proposed array. The BEST design strategy to minimize electrical mismatch losses is to:
- Use a central inverter and series-connect all modules uniformly
- Orient shaded modules in separate sub-arrays on distinct MPPT inputs (Correct answer)
- Increase system voltage by adding more modules in series
- Apply anti-reflective coating to shaded modules only
Correct answer: Orient shaded modules in separate sub-arrays on distinct MPPT inputs
Placing shaded modules on a dedicated MPPT input allows the inverter to optimize that sub-array independently, preventing shaded modules from dragging down unshaded strings.
NABCEP Solar Site and Shading Analysis 2
A Solar Pathfinder instrument is used at a proposed installation site.
What does it primarily measure?