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Courses/Solar PV & Renewables/System Design & Sizing

lesson · 10min · Lesson 9 of 29

Yield estimation: kWh/kWp calculations

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 · 10min
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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

Yield estimation: kWh/kWp calculations

Solar Pv · Lesson 9 · Intermediate

IntermediateReview: professional review pending

Purpose

Estimate annual PV yield with explicit resource, orientation, shading and system-loss assumptions and an uncertainty range.

Before you beginElectrical fundamentals · DC voltage and current

Learning objectives

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

kWp is rated power; kWh is energy over time. Annual yield cannot be derived from nameplate power alone.

ARRAY STRING AND YIELD DESIGNARRAY STRING AND YIELD DESIGNMODULEMPPTcold Voc · hot Vmpirradiance · temperature · shading · exact product limits

Core theory

A simple estimate multiplies installed kWp by a site-specific annual specific yield in kWh/kWp. The yield model should state weather dataset, orientation/pitch, horizon and near shading.

Loss assumptions include cell temperature, irradiance response, mismatch, soiling/snow, DC wiring, inverter conversion/clipping, availability, degradation and export/curtailment behavior.

Report central, low and high cases rather than false precision. Compare measured performance only after normalizing for weather, downtime, curtailment and configuration.

Terms, symbols, and units
TermMeaningSymbolUnit
Installed capacitySum of module STC powerNot applicablekWp
Specific yieldAnnual energy per installed peak powerNot applicablekWh/kWp/year
Performance ratioNormalized delivered-to-reference yield ratioPRNot applicable
Eannual ≈ Pinstalled × Yspecific

Yspecific must already embody the stated site/model losses.

kWh/year
Worked exampleA 5.2 kWp array has supplied model cases 820, 900 and 970 kWh/kWp/year.

Assumptions: Cases share the same capacity basis.

  1. Low: 5.2×820=4264 kWh/year.
  2. Central: 5.2×900=4680 kWh/year.
  3. High: 5.2×970=5044 kWh/year.

Illustrative range is 4264–5044 kWh/year, central 4680 kWh/year.

Reasonableness check: Energy is capacity multiplied by hours-equivalent specific yield.

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 a range preferable to a single exact annual yield?

Weather, shading, losses and availability are uncertain. Documented scenarios communicate that uncertainty.

Answer: Weather, shading, losses and availability are uncertain. Documented scenarios communicate that uncertainty.

Practical exercise

Build low/central/high yield cases from a supplied site model and loss register.

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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