NABCEP - Certified North American Board of Certified Energy Practitioners Specialist Solar Site and Shading Analysis Questions and Answers — Questions and Answers
Question 1: A solar site assessor in the Northern Hemisphere uses a compass to determine the optimal azimuth for a fixed-tilt PV array. The compass indicates south at 180 degrees. However, the local magnetic declination is 12 degrees East. To what azimuth should the array be oriented to face True South?
- 168 degrees
- 180 degrees
- 192 degrees (Correct answer)
- It is not possible to determine with the information given.
Correct answer: 192 degrees
True South is the geographic South Pole, which provides consistent solar optimization. A compass points to the magnetic South Pole. Magnetic declination is the angle difference between magnetic north and true north. An East declination means the magnetic north is east of true north. Therefore, to find True South when the declination is 12 degrees East, you must add 12 degrees to the magnetic south reading of 180 degrees, resulting in an azimuth of 192 degrees.
Question 2: A site analysis reveals significant shading on a proposed rooftop array area only during early morning and late afternoon hours in the summer. Which of the following technologies would be most effective at mitigating the energy production losses from this type of shading?
- A string inverter with a single MPPT
- Bifacial modules on a low-albedo roof
- Module-Level Power Electronics (MLPE) like microinverters or DC optimizers (Correct answer)
- A larger gauge DC conductor to reduce voltage drop
Correct answer: Module-Level Power Electronics (MLPE) like microinverters or DC optimizers
Module-Level Power Electronics (MLPE), such as microinverters or DC power optimizers, operate at the individual module level. When some panels are shaded, MLPE allows the unshaded panels to continue producing at their maximum power, without being dragged down by the underperforming shaded modules. A single-MPPT string inverter would limit the output of the entire string to the level of the lowest-performing (shaded) module.
Question 3: Which of the following metrics provides the most comprehensive assessment of a potential solar site's energy production potential by accounting for both shading and the array's tilt and orientation?
- Solar Access Value (SAV)
- Tilt and Orientation Factor (TOF)
- Insolation Value
- Total Solar Resource Fraction (TSRF) (Correct answer)
Correct answer: Total Solar Resource Fraction (TSRF)
The Total Solar Resource Fraction (TSRF) is the most comprehensive metric as it combines the effects of both shading and the specific design orientation. TSRF is calculated by multiplying the Solar Access Value (which accounts for shading) by the Tilt and Orientation Factor (which accounts for the array's specific tilt and azimuth relative to optimal).
Question 4: When using a Solar Pathfinder to conduct a manual shading analysis, what is the primary purpose of the reflective dome?
- To measure the ambient temperature and its effect on irradiance
- To provide a panoramic reflection of all shading obstacles on the horizon (Correct answer)
- To digitally capture a fisheye photograph of the sky
- To calculate the magnetic declination automatically
Correct answer: To provide a panoramic reflection of all shading obstacles on the horizon
The Solar Pathfinder uses a highly polished, transparent dome to reflect a panoramic view of the site. This reflection includes all potential shade-casting objects like trees and buildings. The user then traces this reflected skyline onto a sun path chart placed under the dome to analyze when shadows will fall on the proposed array location throughout the year.
Question 5: A client is deciding between a rooftop and a ground-mounted solar array for their property, which has ample unshaded land. From a purely shading and production standpoint, what is a primary advantage of the ground-mounted system?
- It provides beneficial shading to the building, reducing cooling costs.
- It is less susceptible to shading from nearby trees and buildings.
- It allows for precise optimization of tilt and azimuth for maximum solar exposure. (Correct answer)
- It requires less land area than a rooftop installation of the same capacity.
Correct answer: It allows for precise optimization of tilt and azimuth for maximum solar exposure.
Unlike a rooftop array, which is constrained by the existing roof's slope and orientation, a ground-mounted system can be precisely oriented to the optimal tilt and azimuth (True South in the Northern Hemisphere) to maximize year-round energy production. This flexibility is a key advantage when unshaded land is available.
Question 6: In a large, multi-row ground-mounted PV array, what is the term for the shading caused by one row of modules casting a shadow onto the row behind it, especially when the sun is at a low angle?
- Horizon shading
- Albedo shading
- Inter-row shading (Correct answer)
- Soft shading
Correct answer: Inter-row shading
Inter-row shading, also known as mutual shading or self-shading, occurs in large arrays when one row of solar panels casts a shadow on the subsequent row. This effect is most pronounced during the winter months or early/late in the day when the sun is lower in the sky. Proper row spacing is critical to minimize these losses.
