Solar Site and Shading Analysis Flashcards

A site assessment reveals that a proposed rooftop array will have a solar access value of 82% annually. According to NABCEP guidelines, how should this value be used in client communications?

Answer: Use it to calculate a derated energy production estimate, clearly communicating that shading will reduce output by 18% compared to an unshaded system

Solar access of 82% means 18% of potential solar energy is blocked by shading; this factor should be applied to the unshaded energy estimate to give the client an accurate production projection.

Which of the following site conditions would most benefit from using microinverters or DC power optimizers compared to a standard string inverter configuration?

Answer: A complex roofline with modules on multiple orientations and partial shading from a chimney

Microinverters and DC optimizers provide module-level MPPT, which is most beneficial when modules experience unequal shading or different orientations that would otherwise cause severe mismatch losses in a string.

When using the Solmetric SunEye for shading analysis, the device is placed at the array plane and photographs the sky. The resulting 'TOF' (Table of Obstructions) reports shading by:

Answer: Monthly and annual solar access percentages accounting for both beam and diffuse shading

The SunEye TOF report provides monthly and annual solar access percentages that factor in both direct beam shading from obstructions and the reduction in diffuse sky radiation from blocked sky dome portions.

A NABCEP-certified designer finds that the proposed array location has only 68% annual solar access due to mature trees. According to best practices, what should the designer do FIRST before recommending system downsizing?

Answer: Evaluate whether tree trimming, removal, or alternative mounting locations could improve solar access above an acceptable threshold

Before accepting poor solar access, the designer should explore mitigation options such as selective tree trimming, removal, or relocating the array to an area with better solar access.

In solar resource data analysis, the term 'P90' production estimate means:

Answer: There is a 90% probability that actual annual production will meet or exceed this energy estimate

P90 is a financial risk metric meaning there is a 90% probability (high confidence) that the system will produce at least this much energy annually, accounting for weather variability and uncertainty in the resource data.

A shading analysis shows that an obstruction causes 'hard shading' on one module during peak hours from November through January. To minimize the annual energy impact, which module layout strategy is MOST effective?

Answer: Isolate the shade-affected module on its own dedicated string or optimizer circuit

Isolating the shade-affected module on its own string or DC optimizer allows it to operate at its own MPPT, preventing its reduced output from dragging down all other modules sharing the same string.

Which standardized dataset is MOST commonly used in the US for hourly solar resource data in PV system performance simulations?

Answer: NREL's National Solar Radiation Database (NSRDB) TMY or PSM data

NREL's NSRDB provides Typical Meteorological Year (TMY) and Physical Solar Model (PSM) data widely used in US PV simulation tools such as PVWatts, SAM, and PVsyst for bankable energy production estimates.