Mixed Deck — All NABCEP Topics Flashcards

Which financial metric is most commonly used to evaluate the economic viability of a PV system?

Answer: Payback period

During a site assessment, performing a shading analysis is critical to identify any potential obstacles, such as trees, chimneys, or adjacent buildings, that could cast shadows on the PV array. Even partial shading can significantly diminish the energy production of an entire string of modules. Identifying these obstacles allows for optimal panel placement and accurate energy yield predictions.

What is the primary purpose of an inverter in a PV system?

Answer: To convert DC electricity generated by the PV panels to AC electricity used by home appliances

Solar panels generate direct current (DC) electricity, but most home appliances and the electrical grid operate on alternating current (AC). The primary purpose of an inverter in a photovoltaic (PV) system is to convert this DC electricity into usable AC electricity. This conversion is essential for powering household devices and feeding excess energy back into the grid.

Which factor is most important when determining the tilt angle for PV modules in a fixed-tilt system?

Answer: Latitude of the installation site

A shading analysis is an essential step during the design phase of a PV system to identify any potential obstructions, such as trees, chimneys, or adjacent buildings, that might cast shadows on the PV array. Even partial shading can significantly reduce the output of an entire string of modules. By identifying and mitigating shading, designers can optimize module placement and predict accurate energy production.

What does 'interconnection agreement' refer to in a small wind turbine installation?

Answer: A formal agreement with the utility authorizing the turbine to connect to and export power onto the electric grid

A utility interconnection agreement is a legal contract governing the technical, safety, and metering requirements for connecting a distributed generation system to the utility's distribution grid.

What is the significance of the 'cut-in wind speed' of a wind turbine?

Answer: The minimum wind speed at which the turbine begins generating electricity

Cut-in wind speed is the minimum wind speed at which the rotor generates enough torque for the generator to produce useful electricity; below this speed the turbine is idle.

What must an inspector verify regarding the PV system's interconnection with the utility service panel to ensure NEC 705 compliance?

Answer: The sum of breaker ampere ratings on a busbar does not exceed 120% of the busbar's ampere rating (120% rule) when the solar breaker is at the opposite end from the main breaker

NEC 705.12(B) allows the supply-side connection via the 120% rule: the sum of the main breaker and solar breaker must not exceed 120% of the busbar rating, and the solar breaker must be at the opposite end.

In a DC-coupled battery storage system, where is the battery typically connected?

Answer: Between the PV array and the inverter on the DC bus

In DC-coupled systems, the battery is connected to the DC bus between the PV array and the inverter, allowing direct DC charging without an extra AC-DC conversion step.

What is the typical depth of discharge (DoD) limit recommended to maximize cycle life in lithium-ion battery storage systems?

Answer: 80–90% DoD as the operational maximum

Operating lithium-ion batteries within 80–90% DoD rather than full discharge extends cycle life significantly because deep cycling degrades the electrochemical structure faster.

Why does wind power output increase with height above ground?

Answer: Surface friction slows wind near the ground; wind speed increases with height due to the wind shear profile

Ground surface friction creates a boundary layer that slows wind; wind speed increases with height following the wind shear power law, which is why taller towers capture significantly more energy.

What is the purpose of a wind turbine's furling mechanism in small horizontal-axis turbines?

Answer: To passively turn the rotor out of the wind in high-speed conditions to prevent overspeed and damage

Furling uses a hinged tail mechanism to turn the rotor sideways out of high winds, passively protecting the turbine from overspeed without electronic controls.

Which IEC standard governs the design requirements and safety of wind turbines used in small wind energy system applications?

Answer: IEC 61400-2 (Design requirements for small wind turbines)

IEC 61400-2 specifies structural, aerodynamic, and electrical safety design requirements specifically for small wind turbines with rotor swept areas up to 200 m², the category relevant to distributed wind installations.

What is the purpose of a check valve in an active solar thermal system's piping loop?

Answer: To prevent reverse thermosiphoning at night that would lose heat from the storage tank to the cold collectors

At night, cooled fluid in collectors can sink and pull warm fluid from the storage tank upward through the collectors, losing stored heat; a check valve prevents this reverse flow.

When sizing a battery storage system for self-consumption optimization, what load data is most critical?

Answer: Historical hourly load profile of the facility

Hourly load profile data reveals when energy demand peaks and troughs throughout the day, enabling accurate sizing of battery capacity to maximize self-consumption.

An inspector observes PV modules installed on a roof without any visible rapid shutdown equipment. The system is on a building in a jurisdiction that has adopted NEC 2017 or later. Is this a code violation?

Answer: Yes, NEC 690.12 requires rapid shutdown for PV systems on buildings under NEC 2017 and later

NEC 690.12 (2017 and later) requires rapid shutdown for all PV systems installed on buildings, regardless of occupancy type, to protect emergency responders.

Which instrument is the primary tool used to measure wind speed during a small wind site assessment?

Answer: Anemometer

An anemometer measures wind speed and is the standard instrument used in wind resource assessments to collect site data.

What protection device is required on a grid-tied small wind system to prevent the turbine from energizing utility lines during a grid outage?

Answer: Anti-islanding protection

Anti-islanding protection automatically disconnects the wind system from the grid during utility outages, protecting utility line workers from unexpected energization.

An inspector finds that MC4 connectors from two different manufacturers have been mismated (cross-mated) in a PV system. What is the concern?

Answer: Cross-mating connectors from different manufacturers can cause arc faults, increased resistance, and connector failure as they are not tested together

MC4-style connectors from different manufacturers may not mate reliably, creating hot spots, arc faults, and potential fire hazards; NEC 690.33(C) requires compatible connectors from the same manufacturer.

Which document should a commissioning technician provide to the system owner at project closeout?

Answer: As-built drawings, system manual, and commissioning report

As-built drawings, the system manual, and a commissioning report give the owner accurate documentation for operation, maintenance, and future service.

n PV system design, what is the significance of the system's "derate factor"?

Answer: It estimates the loss in system performance due to inefficiencies

Considering local building codes and regulations is paramount when designing a PV system to ensure the installation is safe, compliant, and avoids legal penalties. These codes dictate structural requirements, electrical standards, and permitting processes, all of which are essential for the system's integrity and long-term operation. Adherence guarantees the system meets minimum safety and quality standards.

Which installation orientation and tilt maximizes annual solar thermal energy collection in the continental US?

Answer: True south at a tilt angle approximately equal to the local latitude

Facing collectors true south and tilting them at the local latitude angle maximizes annual solar irradiance interception across all seasons in the Northern Hemisphere.