Design Principles Flashcards

In the US, which standard is most commonly used to calculate wind loads on PV mounting structures?

Answer: ASCE 7

ASCE 7, Minimum Design Loads for Buildings and Other Structures, sets the wind, snow, and seismic loads used for racking design.

Two strings face different azimuths (east and west). What is the best way to connect them to a string inverter?

Answer: Connect each orientation to a separate MPPT input

Separate MPPT inputs let each orientation run at its own optimal operating point and avoid mismatch losses.

A home needs 10 kWh of usable storage, and the battery's recommended depth of discharge is 80%. What is the minimum nominal capacity?

Answer: 12.5 kWh

Nominal capacity equals usable energy divided by DoD: 10 ÷ 0.8 = 12.5 kWh.

A site receives 5.5 kWh/m²/day of plane-of-array irradiation. How many peak sun hours is that?

Answer: 5.5 hours

One peak sun hour is 1 kWh/m² (1000 W/m² for one hour), so 5.5 kWh/m²/day equals 5.5 peak sun hours.

Under the NEC 705.12 120% rule, a 200 A busbar with a 200 A main breaker allows what maximum PV backfed breaker at the opposite end?

Answer: 40 A

120% × 200 A = 240 A, minus the 200 A main, leaves 40 A for the PV breaker.

Which design choice most effectively reduces soiling losses in a dusty, low-rainfall area?

Answer: Increasing tilt and planning a scheduled cleaning program

Steeper tilt helps dust shed and rain wash it off, and scheduled cleaning recovers losses where rain is scarce.

A 6 kW DC array at a site with 5 peak sun hours and an 80% derate factor produces about how much energy per day?

Answer: 24 kWh

6 kW × 5 h × 0.80 = 24 kWh per day.