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Courses/Solar PV & Renewables/PV Physics & Panel Technology

lesson · 8min · Lesson 4 of 29

Temperature and irradiance effects

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
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In this lesson

PurposeCore theoryWorked exampleKnowledge checkSources

In this lesson

PurposeCore theoryWorked exampleKnowledge checkSources
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ElectraCore lesson handout

Temperature and irradiance effects

Solar Pv · Lesson 4 · Intermediate

IntermediateReview: professional review pending

Purpose

Correct module voltage, current and power for declared temperature and irradiance effects without mixing ambient and cell temperature.

Before you beginElectrical fundamentals · DC voltage and current

Learning objectives

  • Interpret the governing data
  • Calculate on a declared basis
  • Identify design limits
  • State uncertainty

Irradiance mainly drives available photocurrent, while rising cell temperature usually reduces crystalline-silicon voltage and power. Exact coefficients are module-specific.

PV I-V CURVE AND OPERATING POINTSPV I-V CURVE AND OPERATING POINTSMODULEMPPTcold Voc · hot Vmpirradiance · temperature · shading · exact product limits

Core theory

Use the manufacturer coefficient sign and units, whether %/°C or absolute units, and apply it relative to the coefficient reference temperature. Include stated product tolerance where it worsens the design case.

Cold cells increase Voc and can exceed inverter or module-system voltage. Hot cells reduce Vmp and can fall below the MPPT/start window. These are separate string-length boundaries.

Isc generally rises with irradiance and often slightly with temperature. Cloud-edge, bifacial gain and required standard factors may govern current; do not scale only from annual average irradiance.

Terms, symbols, and units
TermMeaningSymbolUnit
Temperature coefficientChange per degree from referenceβ or α%/°C
Cell temperatureTemperature of active PV cellsNot applicable°C
IrradianceIncident solar power per areaGW/m²
X(T)=Xref×[1+(γ/100)(T−Tref)]

Use only for the stated coefficient/range; preserve γ sign.

same unit as X
Worked exampleVoc=50.0 V at 25 °C and coefficient −0.28%/°C. Estimate Voc at −10 °C.

Assumptions: Linear coefficient is permitted over this range; No tolerance added.

  1. Change: ΔT=−10−25=−35 °C.
  2. Factor: 1+(−0.28/100)(−35)=1.098.
  3. Voltage: 50.0×1.098=54.9 V.

Estimated cold Voc is 54.9 V per module.

Reasonableness check: Negative coefficient and falling temperature increase Voc.

Common mistakes
  • Treating STC as guaranteed field output
  • Using nominal values instead of exact datasheets
  • Ignoring temperature, tolerance or mismatch

Where this appears in practice

Traceable PV design uses exact product data, site evidence and compatible worst-case assumptions.

SafetyPV arrays can sustain hazardous DC voltage and arcs whenever illuminated. Use competent PV-specific isolation, connectors, PPE and access controls.
Local code checkUse the exact module, inverter, mounting and protection manufacturer data; current IEC/BS EN/BS 7671 requirements; MCS standards where applicable; site-specific climate, structure, fire, wind, shading and DNO constraints. PV conductors remain live in daylight. Classroom calculations do not authorise roof access, DC connection, isolation or energisation.

Knowledge check

Why is ambient temperature not automatically the coefficient input?

The coefficient applies to cell temperature. Operating cells can be much hotter than ambient.

Answer: The coefficient applies to cell temperature. Operating cells can be much hotter than ambient.

Practical exercise

Compute cold Voc and hot Vmp from a supplied datasheet, including adverse tolerance.

Summary

  • Conditions define the value
  • Worst cases must be compatible
  • Record sources and assumptions

Sources and review

  • IEC 61215-2:2021: Terrestrial photovoltaic modules: test procedures: IEC; 2021; International
  • HEM-TP-18 PV generation and self-consumption: UK Government; Current published methodology; United Kingdom
  • PV research data and modelling tools: National Renewable Energy Laboratory; Current online resources; International research

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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