C&G 2922-34 Solar PV flashcards

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

PV DC live when illuminated

PV modules produce dangerous DC voltage whenever light falls on them; the DC side remains live even when the AC isolator is open.

G98 notification threshold

G98 applies to grid-connected generation up to 16 A per phase, equivalent to 3.68 kW single-phase; install and notify the DNO within 28 days.

G99 application process

G99 applies to generation above 16 A per phase; a connection application must be made to the DNO and approval received before commissioning.

DC isolator rating

A DC isolator must be rated for the system maximum Voc and Isc and be DC-rated; AC isolators must not be used on PV DC circuits.

Part P scope

In England and Wales, electrical work in dwellings is notifiable under Part P; PV installations must comply with BS 7671 and be certified by a competent person.

Working at height hierarchy

Avoid work at height where possible; prevent falls using edge protection or scaffolds; mitigate residual risk with harnesses and fall-arrest systems.

String maximum voltage

Calculate string Voc at the lowest expected cell temperature using the Voc temperature coefficient; it must not exceed inverter or module maximum system voltage.

MPPT minimum string voltage

The string Vmp at the highest expected cell temperature must stay above the inverter MPPT minimum or the inverter will not track maximum power.

Ideal UK roof pitch

A south-facing roof at 30–40° tilt gives near-optimal annual yield in the UK; east/west or flatter arrays reduce output and alter the yield profile.

Roof structural load

PV arrays typically add 10–20 kg/m²; the roof structure and fixings must be checked for dead, wind and snow loads before installation.

DC voltage drop target

Keep DC cable voltage drop typically below 1% to minimise energy loss and avoid inverter input voltage issues; AC drop is usually below 3–5%.

Inverter DC:AC ratio

The array peak DC power divided by inverter AC rating; typical ratios are 1.1–1.3 in the UK, balancing clipping losses against yield.

Shading survey tool

Use a solar pathfinder, Solmetric SunEye or similar to quantify shade across the year; avoid shading or use optimisers or module-level electronics.

Module clamp zones

Mounting clamps must be positioned within the manufacturer's specified clamp zones, commonly 1/4 and 3/4 along the module frame, and torqued correctly.

Rafter fixing requirement

Roof hooks and brackets should be fixed into structural rafters or trusses, not just tile battens, using stainless steel fixings sized for wind uplift.

DC cable rating

PV DC cable should be double-insulated, UV-resistant and rated at least 1000 V DC, often 1500 V DC, with correct current rating for Isc.

MC4 connector rule

Only mate connectors from the same manufacturer and type; use the correct crimp tool and test pull-out; mixed-brand MC4 connectors can overheat.

Series vs parallel

Connecting modules in series adds voltages while current stays constant; parallel connection adds currents while voltage stays constant.

Roof penetration sealing

Every roof fixing must be sealed with a flashing or sealant compatible with the roof covering to prevent water ingress and long-term decay.

Inverter AC isolator

A lockable AC isolator must be installed adjacent to the inverter so the unit can be safely isolated for maintenance and clearly labelled.

RCD type for inverters

Some inverters require Type A or Type B RCDs depending on DC residual current characteristics; follow the inverter manufacturer's instructions and BS 7671.

Anti-islanding requirement

The inverter must disconnect from the grid when supply is lost, preventing islanding that could endanger utility workers and damage equipment.

Consumer unit dedicated way

The PV inverter should be connected via a dedicated MCB or RCBO in the consumer unit, sized to the inverter maximum AC output current.

Export limitation CT

A current transformer clamp on the incoming supply measures export; the inverter or export limiter reduces output to stay within the DNO-approved limit.

Dual supply label

A warning label at the consumer unit and meter position must state that the installation has a dual supply, including the PV system.

DC insulation resistance

Measure insulation resistance of DC strings to earth before connection; a value below 1 MΩ indicates a fault and requires investigation.

Voc string test

Measure open-circuit voltage of each string and compare with expected Voc corrected for cell temperature and irradiance; a missing string shows zero or low voltage.

I-V curve tracing

An I-V curve tracer compares actual array performance with the expected curve, revealing shading, soiling, mismatch or failed bypass diodes.

Thermal imaging use

Thermal cameras detect hot spots, faulty bypass diodes, loose connections and cell damage during commissioning and maintenance inspections.

RCD trip test

Test the RCD protecting the inverter AC circuit with a suitable tester; verify trip time and current meet BS 7671 requirements.

Annual maintenance checks

Annual checks include visual inspection, connector torque, DC insulation resistance, inverter error logs, cleaning and verification of labels and documentation.

Ground fault diagnosis

An earth fault on a PV array is located by isolating strings and testing insulation resistance to earth; the faulty string shows low resistance.