NABCEP Solar Site and Shading Analysis 3

Question 1

A designer uses the 'worst-month' method for a standalone PV system in Colorado. What is the purpose of identifying the worst month?

Accepted Answer

To size the battery bank and array for the month with the least solar resource relative to load

Answer

The worst month is when the ratio of available solar energy to the system load is smallest, ensuring the system is sized to meet demand even under the most challenging solar conditions.

Question 2

True south in the continental US differs from magnetic south because of magnetic declination. In Seattle, WA, where declination is approximately 15°E, a compass-south-facing array is actually oriented:

Accepted Answer

15° east of true south

Answer

An easterly declination of 15° means magnetic north is 15° east of true north, so a compass-south reading points 15° east of true south.

Question 3

During a shading analysis consultation, a client insists on keeping a large oak tree that shades the array from 8–9 AM year-round. The designer should explain that morning shading primarily reduces:

Accepted Answer

Early morning energy production but has minimal impact on total daily kWh in most US locations

Answer

Early morning irradiance is relatively low compared to midday, so shading during the first hour after sunrise reduces total daily energy production by a proportionally small amount in most temperate US locations.

Question 4

What is the 'sky diffuse' component of solar radiation, and why is it important in shading analysis?

Accepted Answer

Radiation scattered by the atmosphere arriving from all parts of the sky dome, which is reduced by nearby obstructions blocking portions of the sky

Answer

Sky diffuse radiation comes from the entire sky dome; obstructions that block portions of the sky reduce diffuse irradiance in addition to blocking direct beam radiation, making full 3D shading analysis important.

Question 5

A roof-mounted array has a 2% annual shading loss according to a simulation. If the system produces 18,000 kWh/year without shading, what is the estimated annual production WITH shading?

Accepted Answer

17,640 kWh

Answer

A 2% shading loss means production = 18,000 × (1 − 0.02) = 18,000 × 0.98 = 17,640 kWh per year.

(NABCEP) Certified North American Board of Certified Energy Practitioners Specialist Practice Test

(NABCEP) Certified North American Board of Certified Energy Practitioners Specialist Practice Test

NABCEP Solar Site and Shading Analysis 3