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Courses/Solar PV & Renewables/Inverters

lesson · 8min · Lesson 14 of 29

Inverter selection criteria

Course syllabusCourse overview
01PV Physics & Panel Technology
  1. ReadPhotovoltaic effect: how a cell works
  2. ReadMonocrystalline vs polycrystalline vs thin-film
  3. ReadPanel specifications: Voc, Vmp, Isc, Imp
  4. ReadTemperature and irradiance effects
  5. quizPV physics quiz
02System Design & Sizing
  1. ReadSite survey: roof orientation, shading, pitch
  2. ReadString sizing: voltage and current matching
  3. ReadSeries vs parallel string configurations
  4. ReadYield estimation: kWh/kWp calculations
  5. exerciseSystem sizing design exercise
03Inverters
  1. ReadString inverters: topology and MPPT
  2. ReadMicroinverters and power optimisers
  3. ReadHybrid inverters for battery systems
  4. ReadInverter selection criteria
  5. quizInverter quiz
04Battery Storage
  1. ReadBattery chemistries: LFP vs NMC
  2. ReadBattery sizing for self-consumption
  3. ReadAC vs DC coupled systems
  4. ReadBattery safety and installation requirements
  5. exerciseBattery sizing exercise
05Grid Connection
  1. ReadG98: systems up to 3.68kW per phase
  2. ReadG99: larger systems, DNO approval
  3. ReadExport limitation and smart export tariffs
  4. ReadGeneration and export metering
  5. quizGrid connection quiz
06Installation & Commissioning
  1. ReadRoof mounting systems: rail and clamp
  2. ReadDC cable sizing and routing
  3. ReadCommissioning and functional testing
  4. quizFinal assessment
Lesson · 8min
PV STRING → INVERTER → GRIDarray (DC)INVERTERDC→ACGRID230V 50HzBATTERYoptional compatible storage portstring V within inverter MPPT window at coldest temp
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PurposeCore theoryWorked exampleKnowledge checkSources

In this lesson

PurposeCore theoryWorked exampleKnowledge checkSources
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ElectraCore lesson handout

Inverter selection criteria

Solar Pv · Lesson 14 · Advanced

AdvancedReview: professional review pending

Purpose

Select an inverter from compatible DC, AC, environmental, control and network limits rather than a single kW ratio.

Before you beginPV strings and I-V curves · AC/DC protection fundamentals

Learning objectives

  • Explain the architecture
  • Match electrical limits
  • Identify safety/protection boundaries
  • Use exact product evidence

An inverter must accept every credible array condition, deliver the intended AC function, coordinate protection and have the correct current network-compliance status.

INVERTER PORTS AND MPPT PATHSINVERTER PORTS AND MPPT PATHSMODULEMPPTcold Voc · hot Vmpirradiance · temperature · shading · exact product limits

Core theory

Check cold maximum Voc, hot MPPT/start voltage, per-input and total Isc/current, strings per tracker, polarity, DC power, clipping objective and module/connector compatibility.

Check AC voltage/phases/current, fault contribution, protective devices/RCD guidance, earthing, isolation, harmonics, reactive/grid-support functions and G98/G99/G100 status for exact hardware/software.

Check IP/environment, altitude, temperature derating, ventilation, noise, fire location, communications/cyber support, monitoring, warranty and service access. Type-test status is indicative; DNOs retain site authority.

Terms, symbols, and units
TermMeaningSymbolUnit
DC/AC ratioInstalled array STC power divided by inverter AC ratingNot applicableNot applicable
DeratingReduction of output under environmental or thermal limitsNot applicableNot applicable
Type-testedCompliance evidence for a declared exact product/configurationNot applicableNot applicable
DC/AC ratio = Parray,STC / Pinverter,AC

A screening metric, not a selection rule by itself.

dimensionless
Worked exampleA 6.0 kWp array is proposed with a 5.0 kW inverter.

Assumptions: All numerical data are supplied fictional design inputs.

  1. Ratio: DC/AC=6.0/5.0=1.20.
  2. Interpret: This suggests possible clipping but no annual amount without time-series/site data.
  3. Verify: All voltage/current, thermal, network, protection and manufacturer limits remain.

Screening DC/AC ratio is 1.20; suitability remains unproved.

Reasonableness check: The result is checked against the stated architecture and limits, not treated as universal product approval.

Common mistakes
  • Selecting from power rating alone
  • Assuming grid loss makes ordinary outputs backed up
  • Mixing nominal, usable and delivered battery energy

Where this appears in practice

PV and storage design coordinates conversion equipment, protection, controls, network requirements, fire safety and user operating modes.

SafetyPV DC and batteries remain energized independently of the public supply. Follow exact shutdown, isolation, verification and emergency procedures; never unplug loaded DC connectors.
Local code checkConfirm current BS 7671 Chapter 57/Section 712, PAS 63100 where applicable, DNO G98/G99/G100 process, exact ENA/Connect Direct status, fire risk assessment, manufacturer-approved battery/inverter combination and all protection/isolation/earthing requirements. Stored energy and illuminated PV remain hazardous after grid isolation.

Knowledge check

Can DC/AC ratio alone select an inverter?

No. Port limits, environment, protection and network compliance remain.

Answer: No. Port limits, environment, protection and network compliance remain.

Practical exercise

Complete a pass/fail inverter matrix from supplied array, site, DNO and product data.

Summary

  • Architecture changes fault and energy paths
  • Every port has independent limits
  • Backup behavior must be deliberately designed

Sources and review

  • IEC 62109-3:2020: Safety of PV power converters: IEC; 2020; International
  • IEC 62619:2022: Safety requirements for secondary lithium cells and batteries: IEC; 2022; International
  • Amendment 4:2026 impact on BS 7671: IET; 2026; United Kingdom
  • ENA generator type-test register: Energy Networks Association; Current status must be checked in Connect Direct; Great Britain / Northern Ireland

Editorial review date: 2026-08-22. Professional electrical review is pending.

Educational material for learning and preliminary checks. Verify current local requirements and exact equipment instructions. This lesson does not replace competent professional work.

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