NABCEP PVTS flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Solar window shading fraction

The share of annual sun-path hours blocked by obstructions, read from a Solar Pathfinder or SunEye. Above roughly 20% annual shade, arrays are usually uneconomic without module-level electronics.

Peak sun hours (PSH)

The daily solar energy received expressed as hours at 1000 W/m² irradiance. Annual kWh equals array kW times PSH times 365 times the system derate factor.

Azimuth convention

Compass direction the array faces, measured in degrees from true north. South is 180°, east 90°, west 270°. Roofs within 30° of south are generally strong production orientations.

Roof pitch conversion

Pitch in degrees equals arctangent of rise divided by run. A 4:12 pitch is about 18.4° and 6:12 is about 26.6°, which affects row spacing and self-shading.

Usable array area

Total roof area minus required setbacks for fire access, ridges, edges, vents, chimneys, and skylights. It sets the maximum module count and system size.

System derate factor

A multiplier, typically 0.75 to 0.85, applied to nameplate output to account for soiling, temperature, mismatch, wiring, inverter, and availability losses in production estimates.

120% busbar rule

NEC 705.12(B) permits the sum of the main breaker and the backfed PV breaker to reach 120% of the panel busbar rating when the PV breaker sits opposite the utility feed.

Maximum string voltage

Module open-circuit voltage at STC times the number of modules times the cold-temperature correction factor. It must not exceed the inverter maximum DC input voltage.

Minimum string length

The fewest modules whose Vmp at the highest expected cell temperature stays above the inverter MPPT minimum operating voltage and start voltage.

Voc temperature coefficient

The percentage change in open-circuit voltage per degree Celsius, typically about minus 0.25 to 0.35 percent. It drives cold-weather maximum voltage calculations for string sizing.

Pmax temperature coefficient

The percentage change in maximum power per degree Celsius above 25 °C, typically minus 0.30 to 0.45 percent. Hotter modules produce less power at the same irradiance.

Rapid shutdown requirement

NEC 690.12 limits conductors within the array boundary to 80 volts within 30 seconds of shutdown. Module-level electronics or listed shutdown devices satisfy the requirement.

DC conductor ampacity rule

PV source and output conductors must be sized at 125% of short-circuit current for continuous duty. Voltage drop should stay near 2% on the DC home run.

UL 2703 listing

The standard for racking and mounting systems that provides listed bonding and grounding paths between modules and rails, simplifying equipment grounding conductor installation.

Microinverter vs string inverter

Microinverters provide per-module MPPT and monitoring with no high-voltage DC on the roof. String inverters cost less per watt but are sensitive to shading and string mismatch.

Simple payback

Net installed cost after incentives divided by first-year utility savings. It ignores rate escalation, degradation, and inverter replacement, so it should accompany a 25-year cash flow.

Levelized cost of energy

Present value of all lifecycle costs divided by present value of lifetime kWh produced. Comparing LCOE to the customer's blended utility rate shows economic value.

Residential clean energy credit

A 30% federal credit on qualified residential solar installed cost, claimed on IRS Form 5695. Battery storage also qualifies when installed with the system.

Commercial ITC basis

The investment tax credit applies to eligible installed cost but excludes portions funded by non-taxable grants or rebates. The depreciable basis is reduced by half the credit.

MACRS depreciation

A five-year accelerated depreciation schedule for commercial solar, often paired with bonus depreciation. It lowers taxable income and improves commercial project returns.

Net metering vs net billing

Net metering credits exports at the retail rate. Net billing credits exports at a lower avoided-cost or export rate, reducing the value of overproduction.

Incentive stacking order

Apply grants and rebates first to reduce cost basis, then the federal tax credit, then state credits or SREC income. Confirm each program's rules against double-dipping.

P50 versus P90 estimate

P50 is the median expected annual production. P90 is the value exceeded with 90% confidence, used for conservative financial projections and production guarantees.

Permit package contents

Typically a site plan, single-line diagram, structural letter, module and inverter datasheets, and UL listings. Incomplete submittals are the most common cause of delay.

Interconnection application

A separate utility filing from the building permit that requests permission to parallel with the grid. Approval and any upgrade costs must be disclosed before contract signing.

Contract essentials

Scope, price and payment schedule, change-order process, timeline, warranty terms, cancellation rights, and clear assignment of who claims which incentive.

Warranty stack

Module product and power warranties, inverter warranty, rack warranty, workmanship warranty, and any production guarantee. Each has a different term and claimant process.

Supply-side connection

A PV interconnection made ahead of the main breaker on the service conductors. It avoids the busbar 120% limit but requires utility approval and a service disconnect.

Arc-fault protection

NEC 690.11 requires DC arc-fault circuit protection on PV circuits operating at 80 volts or more, detecting and interrupting series arcs on the array wiring.

PV system labeling

Placards at the DC disconnect, point of interconnection, rapid shutdown equipment, and service stating system voltage and current, required for inspector and firefighter safety.

Performance ratio (PR)

Actual energy yield divided by the theoretical yield at nameplate rating for the received irradiance. Well-designed systems typically run 0.75 to 0.85.

IV curve tracing

A field test that sweeps module or string voltage and current to reveal ground faults, failed bypass diodes, mismatch, and connector degradation without dismounting modules.