Design Principles Flashcards

When calculating the maximum system voltage of a PV string, which temperature should be used?

Answer: Lowest expected ambient temperature

Module Voc rises as temperature falls, so the coldest expected ambient temperature produces the highest string voltage.

Under the NEC, what is the maximum PV system DC voltage permitted for one- and two-family dwellings?

Answer: 600 V

NEC 690.7 limits PV DC circuits on one- and two-family dwellings to 600 V.

Fixed-tilt ground-mount row spacing in the continental US is typically designed to avoid inter-row shading during which period?

Answer: 9 a.m. to 3 p.m. solar time on the winter solstice

The winter solstice has the lowest sun angles, so a design free of shade from 9 to 3 then stays clear for the rest of the year.

For maximum annual energy from a fixed-tilt array, the tilt angle is usually set close to what value?

Answer: The site latitude

A tilt near the site latitude roughly maximizes annual irradiance on the array plane, often adjusted slightly lower for summer-peaking climates.

Ground coverage ratio (GCR) is defined as which of the following?

Answer: Collector slope length divided by row pitch

GCR is the collector length in the direction of the slope divided by the center-to-center row spacing (pitch).

A designer chooses a DC-to-AC (inverter loading) ratio of 1.3. What is the main tradeoff?

Answer: Some clipping losses at peak irradiance in exchange for more energy during low-light hours

Oversizing the DC array raises shoulder-hour and cloudy-day production but clips power when DC output exceeds the inverter's AC rating.

What is the main purpose of bypass diodes in a crystalline silicon PV module?

Answer: Let current flow around shaded cell groups and prevent hot spots

Bypass diodes conduct when a cell substring is shaded, limiting reverse bias and hot-spot heating.