City & Guilds 2922 — Small Solar Photovoltaic (PV) Systems (UK)

In a solar cell, what physical process converts sunlight directly into electrical energy?

• AThe photoelectric heating of water
• BThe photovoltaic effect
• CElectromagnetic induction
• DThermionic emission

Solar irradiance at a site is normally expressed in which units?

• AWatts per square metre (W/m2)
• BKilowatt-hours (kWh)
• CAmperes (A)
• DLumens (lm)

PV modules are rated at Standard Test Conditions (STC). Which set of values defines STC?

• A800 W/m2, 20 C cell temperature, AM1.0
• B1000 W/m2, 25 C cell temperature, AM1.5
• C1000 W/m2, 45 C cell temperature, AM1.0
• D1200 W/m2, 25 C cell temperature, AM2.0

On a module I-V curve, which point represents the condition where the module delivers its greatest power output?

• AThe open-circuit voltage (Voc)
• BThe short-circuit current (Isc)
• CThe maximum power point (MPP)
• DThe point where current equals zero

What happens to a crystalline silicon module's open-circuit voltage (Voc) as the cell temperature falls below 25 C?

• AVoc decreases
• BVoc increases
• CVoc stays exactly the same
• DVoc drops to zero

Three identical 12 V, 8 A PV modules are connected in series. What is the approximate output voltage and current of the string?

• A12 V at 24 A
• B36 V at 8 A
• C36 V at 24 A
• D12 V at 8 A

Two PV strings, each producing 30 V at 9 A, are connected in parallel. What is the combined output?

• A60 V at 9 A
• B30 V at 18 A
• C60 V at 18 A
• D30 V at 9 A

A roof has space for 10 PV modules each rated at 410 Wp. What is the nominal peak power (array rating) of the installation?

• A41 kWp
• B4.1 kWp
• C410 kWp
• D0.41 kWp

What does the term 'peak power' or Wp of a PV module describe?

• AIts output at any time of day
• BIts rated DC power output at Standard Test Conditions
• CThe maximum AC power its inverter can deliver
• DIts output on the shortest day of the year

Why is the current produced by a PV array described as direct current (DC) rather than alternating current (AC)?

• ABecause it reverses direction 50 times per second
• BBecause it flows in one direction only
• CBecause it is always above 230 V
• DBecause it cannot be measured with a meter

Which factor will most directly reduce the instantaneous power output of a PV array on a given day?

• AA fall in solar irradiance due to cloud cover
• BAn increase in the property's electricity tariff
• CA change in the colour of the roof tiles
• DThe age of the consumer unit

What is the typical cause of reduced module efficiency on a very hot, sunny summer day compared with a cool, bright day?

• AHigher cell temperature lowers the operating voltage
• BThe irradiance is too low to generate power
• CThe modules switch automatically to AC output
• DThe inverter increases the DC voltage to compensate

In a PV module, several individual solar cells are connected in series primarily to:

• AReduce the module's physical size
• BBuild up a useful working voltage
• CEliminate the need for an inverter
• DConvert the output to alternating current

Annual energy yield from a PV system is normally expressed in:

• AWatts per square metre
• BKilowatt-hours per year (kWh/year)
• CAmperes per module
• DVolts at open circuit

A 4 kWp system is installed where the estimated specific yield is 950 kWh per kWp per year. Roughly how much energy should it generate annually?

• AAbout 950 kWh
• BAbout 3800 kWh
• CAbout 380 kWh
• DAbout 38000 kWh

What is the main function of an inverter in a grid-connected PV system?

• ATo store surplus energy in a battery
• BTo convert the array's DC into grid-compatible AC
• CTo increase the irradiance reaching the modules
• DTo earth the metal module frames

In a microinverter system, the inverters are:

• AMounted in the consumer unit only
• BFitted at each individual module to produce AC at the module
• CLocated inside the electricity meter
• DBuilt into the DC isolator

A string inverter differs from microinverters in that it:

• AConverts the DC from a whole string of series-connected modules at one central unit
• BIs fitted to each module individually
• CProduces DC output for storage only
• DCannot perform maximum power point tracking

What is the purpose of a power optimiser fitted to each module in some PV systems?

• ATo store DC energy for night use
• BTo perform per-module MPPT while keeping a central string inverter
• CTo convert DC directly to 230 V AC at the module
• DTo replace the need for DC cabling

Which connector type is most commonly used to join PV module leads and DC string cables?

• ABS 1363 13 A plug
• BMC4-type PV connector
• CRJ45 connector
• DIEC C13 connector

DC string cabling for a PV array should be:

• AStandard indoor flat twin-and-earth cable
• BSingle-core, double-insulated cable suitable for PV/DC use and UV exposure
• CBell wire rated at 12 V
• DFlexible cord rated only for indoor appliances

What is the function of the generation meter in a domestic PV installation?

• ATo switch the inverter off at night
• BTo measure the total electrical energy generated by the PV system
• CTo convert DC to AC
• DTo isolate the DC array for maintenance

Mounting and racking systems for roof-mounted PV are primarily designed to:

• AIncrease the irradiance on the modules
• BSecurely fix the modules and transfer wind and snow loads to the roof structure
• CConvert the DC output to AC
• DProvide earthing for the consumer unit

In an AC-coupled battery storage system added to an existing PV installation, the battery:

• AIs connected directly to the PV DC strings before the inverter
• BHas its own inverter/charger and connects on the AC side of the installation
• CStores energy as direct current at 230 V
• DReplaces the PV generation meter

Which of the following best describes the array of a PV system?

• AA single solar cell
• BA group of modules connected together to form the complete generator
• CThe AC distribution board
• DThe inverter cooling fan

What is the purpose of a DC isolator switch in a PV system?

• ATo convert DC to AC
• BTo allow the DC circuit between the array and inverter to be safely disconnected
• CTo measure the generated energy
• DTo boost the array voltage in winter

Why must a switch used as a PV DC isolator be specifically rated for DC duty rather than only AC?

• ADC arcs do not self-extinguish at a zero crossing as AC does, so DC switching is more dem…
• BDC current is always smaller than AC current
• CAC-rated switches cannot carry any current
• DDC circuits never produce an arc

In a typical grid-connected PV system, where are isolation means generally required?

• AOnly at the inverter input
• BOn both the DC side (between array and inverter) and the AC side (between inverter and su…
• COnly at the consumer unit
• DOnly on the AC side

An important safety characteristic of a PV array that an installer must always remember is that:

• AIt is only live when the inverter is switched on
• BIt produces a voltage whenever it is exposed to light and cannot simply be switched off
• CIt is completely safe to touch at any time
• DIt only produces voltage at night

Which section of BS 7671 sets out the special requirements for solar photovoltaic (PV) power supply systems?

• ASection 701
• BSection 712
• CSection 711
• DSection 559

When calculating the maximum DC voltage a PV string can reach for cable and isolator selection, which condition should be used?

• AThe module Voc at the lowest expected cell temperature
• BThe module Vmp at 25 C
• CThe module Voc at 70 C
• DThe nominal grid voltage of 230 V

Which roof orientation generally gives the highest annual PV yield in the UK?

• ADue north
• BDue south
• CDue east
• DDue west

Roughly what roof pitch (tilt from horizontal) is generally considered close to optimum for a fixed PV array in the UK?

• AAbout 0 degrees (flat)
• BAbout 30 to 40 degrees
• CAbout 70 to 80 degrees
• DExactly 90 degrees (vertical)

Why is shading analysis an important part of PV system design?

• AShade has no effect on output
• BEven partial shading of modules can disproportionately reduce string output
• CShade increases the array voltage
• DShading only affects the AC side

When part of a module is shaded, what device built into the module helps current bypass the shaded cells and limits hot-spot heating?

• AA bypass diode
• BA blocking capacitor
• CA surge arrester
• DA residual current device

Before installing a rooftop array, why must the roof structure be assessed?

• ATo check it can carry the additional dead load and wind/snow loading of the array
• BTo decide the colour of the modules
• CTo set the electricity tariff
• DTo choose the inverter brand

Which publication gives detailed industry best-practice guidance for the design and installation of grid-connected PV, supplementing BS 7671?

• AThe IET Code of Practice for Grid-Connected Solar Photovoltaic Systems
• BThe Building Regulations Approved Document B
• CBS EN 60898
• DThe Gas Safe Register handbook

Working on a domestic roof to install PV is classed as working at height. Which is the most appropriate primary control measure?

• ARely on a colleague to catch you if you slip
• BUse suitable access equipment such as scaffolding with edge protection and a safe working…
• CWork only in wet weather to reduce dust
• DRemove all guard rails to improve access

Which regulations primarily govern the planning and carrying out of work on a domestic PV roof installation to prevent falls?

• AThe Work at Height Regulations 2005
• BThe Gas Safety (Installation and Use) Regulations
• CThe Pressure Systems Safety Regulations
• DThe Control of Asbestos Regulations only

Exposed conductive parts such as PV module frames and metal mounting rails are connected to the earthing system primarily to:

• AIncrease the array output voltage
• BProvide protection against electric shock under fault conditions
• CReduce the weight of the array
• DImprove the appearance of the installation

A surge protection device (SPD) may be specified in a PV installation to:

• AConvert DC to AC
• BProtect equipment against transient overvoltages, for example from lightning activity
• CIncrease the system's annual yield
• DReplace the DC isolator

Warning labels and notices required on a PV installation are intended mainly to:

• AAdvertise the installer's company
• BAlert anyone working on the installation to the presence of a second, PV-generated source…
• CIndicate the module manufacturer's warranty
• DShow the energy tariff in use

Which of the following is a recognised reason to keep DC cable runs as short and as well-managed as practicable in a PV installation?

• ATo reduce the risk of DC arc faults and minimise the area of any potential loop that coul…
• BTo increase the inverter's switching frequency
• CTo raise the module open-circuit voltage
• DTo avoid the need for any isolation

When sizing the AC cable from the inverter to the consumer unit, the installer must mainly ensure it is:

• AThe thinnest cable available to save cost
• BRated for the inverter's maximum AC output current with acceptable voltage drop and corre…
• CIdentical to the DC string cable in every case
• DOnly rated for 12 V

The maximum number of modules that may be connected in a single series string is limited mainly by:

• AThe colour of the modules
• BThe maximum DC input voltage of the inverter (compared with the cold Voc of the string)
• CThe length of the AC cable
• DThe price of the inverter

A module has an open-circuit voltage of 40 V at the lowest expected temperature. The inverter has a maximum DC input voltage of 600 V. What is the greatest number of these modules that can be safely placed in one series string?

• A10 modules
• B15 modules
• C20 modules
• D25 modules

Why should the inverter generally be located in a cool, well-ventilated position rather than in direct sun in a hot loft?

• ATo make it easier to paint
• BBecause high ambient temperature can cause the inverter to derate and reduce its output
• CTo increase the array Voc
• DBecause inverters must always be outdoors