☀ IST PVSolar Simulator V8.1.1 — Help & User Guide
IEC 61724-1:2021 | IEC 61853-1:2011 | IEC 61215:2021 | IS 16169:2014 | IS 16221 | CEA 2010 (Amdt 2023) | MNRE 2025 | BIS | PMSGMY 2024🎯 Quick Tour Guide — Complete Step-by-Step Walkthrough
Use the 🎯 Tour button in the title bar to launch an interactive guided overlay inside the simulator. This written guide covers every step in detail with standards references and best-practice recommendations.
1Welcome & Overview
IST PVSolar Simulator V8.1.1 is a professional, browser-based PV simulation platform aligned with IEC 61724-1:2021, IEC 61853, BIS IS 16169, CEA Technical Standards 2010 (Amended 2023), and MNRE 2025 guidelines. The simulation engine uses POA transposition, cell temperature (Uc+Uv model), monthly energy, PR, P50/P90 exceedance probability, and LCOE/NPV/IRR financial analysis.
IST PVSolar Simulator V8.1.1 is a professional, browser-based PV simulation platform aligned with IEC 61724-1:2021, IEC 61853, BIS IS 16169, CEA Technical Standards 2010 (Amended 2023), and MNRE 2025 guidelines. The simulation engine uses POA transposition, cell temperature (Uc+Uv model), monthly energy, PR, P50/P90 exceedance probability, and LCOE/NPV/IRR financial analysis.
2Tab 1 — Project & Site Information
Enter Project Name, Client, Engineer name and location. Enter site Latitude/Longitude (decimal degrees). Click "Fetch NASA SSE Data" to auto-load 20-year monthly GHI, DNI, DHI, Temperature, and Wind Speed from NASA POWER API.
Set temperature parameters for string voltage design:
Enter Project Name, Client, Engineer name and location. Enter site Latitude/Longitude (decimal degrees). Click "Fetch NASA SSE Data" to auto-load 20-year monthly GHI, DNI, DHI, Temperature, and Wind Speed from NASA POWER API.
Set temperature parameters for string voltage design:
- Min Winter Temp (°C) — absolute minimum for Voc limit check per IEC 62548:2016 / IS 16221
- Winter Vmpp Temp (°C) — operating winter temperature for MPPT max voltage design
- Summer Vmpp Temp (°C) — peak cell temperature for MPPT min voltage and power loss
- CO₂ Factor (kg/kWh) — default 0.82 kg/kWh per CEA Grid Emission Factor 2023–24
- Altitude (m) — site altitude affects air mass and irradiance correction
Standards: IEC 61724-1:2021 §5 (measurement quality), NASA POWER community/RE API (MERRA-2 data), CEA Grid Emission Factor Report 2023–24
3Tab 2 — Orientation & POA Irradiance
Set Tilt (°) and Azimuth (°) (0° = South for Northern Hemisphere; 180° for Southern Hemisphere). Click "Calculate POA" — the simulator computes monthly Plane-of-Array irradiance (H_POA) using solar declination, zenith angle, and isotropic sky transposition model per IEC 61853-3.
"⚡ Auto-Optimize Tilt" sweeps 0°–60° in 1° steps and selects the tilt yielding maximum annual POA. The Orientation Loss display shows % deviation from optimum.
📐 Row Spacing Calculator (new): Click the orange button to open the shadow-free row spacing tool. Enter module height, front edge clearance and shading window. The calculator uses winter-solstice worst-case solar altitude to size the minimum pitch. Three synchronized views (Side, 3D, Front) animate the sun movement and live shadow. Click "Apply to Tab 2" to write the calculated pitch directly to the Row Spacing field.
Set Tilt (°) and Azimuth (°) (0° = South for Northern Hemisphere; 180° for Southern Hemisphere). Click "Calculate POA" — the simulator computes monthly Plane-of-Array irradiance (H_POA) using solar declination, zenith angle, and isotropic sky transposition model per IEC 61853-3.
"⚡ Auto-Optimize Tilt" sweeps 0°–60° in 1° steps and selects the tilt yielding maximum annual POA. The Orientation Loss display shows % deviation from optimum.
📐 Row Spacing Calculator (new): Click the orange button to open the shadow-free row spacing tool. Enter module height, front edge clearance and shading window. The calculator uses winter-solstice worst-case solar altitude to size the minimum pitch. Three synchronized views (Side, 3D, Front) animate the sun movement and live shadow. Click "Apply to Tab 2" to write the calculated pitch directly to the Row Spacing field.
Standards: IEC 61853-3:2018 (POA transposition, isotropic diffuse model), IEC 61724-1:2021 §6 (irradiance measurement), MNRE 2025 rooftop design guidelines (row spacing ≥ 2× module height rule of thumb)
4Tab 3 — System Parameters (Module & Inverter Selection)
Select a PV Module from the database (filter by manufacturer). Module STC parameters auto-populate: Pmax, Voc, Isc, Vmp, Imp, TC_Pmax, TC_Voc, NOCT, Fill Factor, Rs, Rsh, Bifacial Factor.
Select an Inverter. Inverter specs populate: rated AC power, max DC voltage, MPPT voltage range (min/max), max DC current, efficiency.
The String Voltage Calculator computes at your site temperatures:
Select a PV Module from the database (filter by manufacturer). Module STC parameters auto-populate: Pmax, Voc, Isc, Vmp, Imp, TC_Pmax, TC_Voc, NOCT, Fill Factor, Rs, Rsh, Bifacial Factor.
Select an Inverter. Inverter specs populate: rated AC power, max DC voltage, MPPT voltage range (min/max), max DC current, efficiency.
The String Voltage Calculator computes at your site temperatures:
- Voc_max @ T_min — must be ≤ Max DC Voltage of inverter
- Vmp_max @ T_winter — must be ≤ MPPT Max Voltage
- Vmp_min @ T_summer — must be ≥ MPPT Min Voltage
Standards: IEC 61215-1:2021 (module performance), IEC 62548:2016 / IS 16221:2015 (string voltage design safety factor 1.15×), IEC 62109-1:2010 (inverter safety), IS 16221 Part 1 (DC overvoltage protection)
5Tab 4 — Loss Calculation & Sankey Diagram
Review and adjust the 15-component loss table (default values from MNRE loss study data):
Review and adjust the 15-component loss table (default values from MNRE loss study data):
- LID — Light-Induced Degradation: 1.5–2% (mono-PERC/TOPCon: 0.5–1.5%)
- Mismatch — 1–2% for standard strings, 0.5% with optimizers
- DC Ohmic — target 1–1.5% per IS 16169 / MNRE wiring standards
- Soiling — 1–5% depending on location; MNRE recommends bi-weekly cleaning for Indian conditions
- IAM — Incidence Angle Modifier: 1–3% annual average
- Thermal — 4–8% depending on Uc, cell temperature and NOCT
- Bifacial Gain — enter as negative (−3 to −12%) for gain
- Clipping — auto-computed from ILR setting
Standards: IEC 61724-1:2021 Annex A (loss categories), IEC 61853-2:2016 (temperature-irradiance performance matrix), MNRE Quality Control Order 2022 (soiling norms), IS 16169:2014 §7 (DC wiring losses)
6Tab 5 — Sub-array Design & Live Electrical Safety Check
The selected module and inverter spec cards appear at the top for quick reference.
Enter configuration: Modules/String, Strings/MPPT, MPPT used/Inverter, No. of Inverters.
The Live Electrical Check performs 5 safety checks instantaneously:
The selected module and inverter spec cards appear at the top for quick reference.
Enter configuration: Modules/String, Strings/MPPT, MPPT used/Inverter, No. of Inverters.
The Live Electrical Check performs 5 safety checks instantaneously:
- Voc @ T_min ≤ Max DC Voltage of inverter IEC 62548 / IS 16221
- Vmp @ T_winter_op ≤ MPPT Max Voltage
- Vmp @ T_summer ≥ MPPT Min Voltage
- Array Current per MPPT ≤ MPPT Input Max Current
- Total DC Current per Inverter ≤ Inverter Max DC Current
Standards: IEC 62548:2016 §6 (string fusing, blocking diodes), IS 16221 Part 1 & 2 (DC system design), CEA Technical Standards 2010 §15 (protection), IEC 60364-7-712:2017 (PV supply systems)
7Tab 6 — Economic Evaluation
Fill the CAPEX table (line items, qty, unit rate, GST%). Enter financing: Own Fund, PM Surya Ghar Muft Bijli Yojana (PMSGMY) subsidy, State subsidy, Loan amount/rate/tenure. EMI auto-calculates. Enter OPEX (annual O&M), tariff (₹/kWh), escalation rate (%), discount rate, project life (years), degradation rate (%/yr).
Click "💰 Calculate Economics" for: LCOE (₹/kWh), NPV (₹), IRR (%), Simple Payback (years), ROI (%), 25-year cash-flow projection table with highlighted payback year.
Use the "✅ Include in Report" toggle to include or exclude economic pages from the PDF report.
Fill the CAPEX table (line items, qty, unit rate, GST%). Enter financing: Own Fund, PM Surya Ghar Muft Bijli Yojana (PMSGMY) subsidy, State subsidy, Loan amount/rate/tenure. EMI auto-calculates. Enter OPEX (annual O&M), tariff (₹/kWh), escalation rate (%), discount rate, project life (years), degradation rate (%/yr).
Click "💰 Calculate Economics" for: LCOE (₹/kWh), NPV (₹), IRR (%), Simple Payback (years), ROI (%), 25-year cash-flow projection table with highlighted payback year.
Use the "✅ Include in Report" toggle to include or exclude economic pages from the PDF report.
Standards/Schemes: MNRE PMSGMY 2024 (PM Surya Ghar Muft Bijli Yojana — ₹30,000–78,000 subsidy for 1–3 kW residential), MNRE Benchmark Cost 2024–25, IEC 62257-9-8 (rural electrification economics), SEBI ESG guidelines (for commercial projects)
8Tab 7 — Run Simulation & Results
Click "▶ RUN SIMULATION". The engine computes month-by-month: POA irradiance → cell temperature → E_array (with bifacial, thermal, DC losses) → clipping → E_AC (with inverter η, AC losses).
Results display:
Click "▶ RUN SIMULATION". The engine computes month-by-month: POA irradiance → cell temperature → E_array (with bifacial, thermal, DC losses) → clipping → E_AC (with inverter η, AC losses).
Results display:
- KPI cards: Annual E_AC (MWh), PR (%), Specific Yield (kWh/kWp), CO₂ avoided (t)
- Monthly simulation table (12 months + annual)
- 6 charts: Monthly Energy, P50/P75/P90/P95 CDF, Grid Injection, 25-yr Life, Monthly PR, Cumulative CO₂
- Probability table: P50/P75/P90/P95 with exceedance interpretation
- "💡 How to Improve PR" suggestions panel — rated Poor/Average/Good with numbered actionable recommendations per your configuration
Standards: IEC 61724-1:2021 (PR definition, Yf, Ya, CF), IEC 61724-3:2016 (data quality), MNRE SPV Rooftop Guidelines 2023 (minimum PR 75% for commissioning), IS 16169:2014 §9 (performance monitoring)
9Generate Report (A4 PDF)
Click "📄 Generate Report" in Tab 7 or the menu bar. An 8-page (or 6-page if economics excluded) A4 HTML report opens in a modal. Click "🖨 Print / PDF" — a dedicated clean print window opens. Use browser Print dialog → Save as PDF with paper A4, margins None/Minimum.
Click "📄 Generate Report" in Tab 7 or the menu bar. An 8-page (or 6-page if economics excluded) A4 HTML report opens in a modal. Click "🖨 Print / PDF" — a dedicated clean print window opens. Use browser Print dialog → Save as PDF with paper A4, margins None/Minimum.
- Page 1: Cover — project info, system summary, client & engineer details, signatures
- Page 2: Project Summary — weather, KPIs, POA chart, orientation loss
- Page 3: System Info — unit config, loss table, Sankey diagram, clipping analysis
- Page 4: Main Results — monthly simulation table, E_AC chart
- Page 5: Probability Analysis — P50/P75/P90/P95, CDF, grid injection chart
- Pages 6–7: Economic Analysis (if included) — CAPEX, OPEX, LCOE/NPV/IRR, 25-yr projection
- Page 8 (or 6): Declaration & Signatures — standards compliance, sign-off
10Databases — Modules & Inverters
Open the Databases tab to manage PV modules and inverters. Import
Open the Databases tab to manage PV modules and inverters. Import
panel.json / inverter.json for bulk loading. Add, edit, delete individual records. Data is stored in localStorage for offline use. Export updated databases as JSON for sharing.11Save, Load & Settings
💾 Save exports a
💾 Save exports a
.pro JSON file containing all project data (site, weather, units, simulation results, economics). 📂 Load restores any saved project. Tab 1 weather can be saved as a .SIT file. Settings panel configures CO₂ factor, start year, and report options.Introduction & Features — IST PVSolar Simulator V8.1.1
IST PVSolar Simulator V8.1.1 is a professional-grade, browser-based solar PV energy simulation software for for designing, modeling, and analyzing grid-connected solar photovoltaic systems. It is fully aligned with international IEC standards and Indian national codes applicable as of April 2026. The simulation engine is using identical formulas for POA transposition, cell temperature, energy calculation, PR, and financial analysis.
Standards Complied (as of April 2026): IEC 61724-1:2021 · IEC 61853-1/2/3/4 · IEC 61215:2021 · IEC 62548:2016 · IEC 62109-1:2010 · IEC 60364-7-712:2017 · BIS IS 16169:2014 · IS 16221:2015 · IS 16527 · CEA Technical Standards 2010 (Amdt 2023) · MNRE SPV Rooftop Guidelines 2023 · MNRE PMSGMY 2024 · CEA Grid Emission Factor 2023–24 · BIS Quality Control Order 2022 · ISTS Waiver CERC
Key Features
- NASA POWER SSE MERRA-2 data is a straightforward process to source solar and meteorological data.
- Plane-of-Array (POA) transposition (isotropic sky model, albedo, incidence angle)
- Cell temperature: NOCT model and Uc+Uv (Ross coefficient) model selectable
- Live Electrical Design Check (Voc, Vmp×3, current — 5 checks before Add Sub-aaray (Unit))
- 15-component loss table with live energy-flow diagram
- Evaluating Inverter Loading Ratio (ILR) clipping analysis as per IEC 61853 energy-rating methodology
- P50/P75/P90/P95 probability analysis with interannual variability (IAV), is a critical component of the total uncertainty used to calculate these values, representing the natural year-to-year fluctuation of solar resources
- Full LCOE, NPV, IRR, payback financial analysis with 25-year projection
- PMSGMY 2024 subsidy integration in financing model
- PR improvement suggestions panel (post-simulation)
- 📐 Row Spacing Calculator — 3D animated shadow-free pitch design (new V8.1.1)
- ± Stepper buttons on all numeric inputs (new V8.1.1)
- Professional 10-page A4 printable report with economics toggle
- Module & inverter database management (JSON import/export)
- Interactive 🎯 Quick Tour overlay
- Save/Load project as .pro file; weather as .SIT file
Design Workflow — Step-by-Step
Follow this sequence for a complete, code-compliant PV system simulation:
1Tab 1 — Project & Site: Enter project details, site Lat/Lon, fetch NASA MERRA-2 weather data (GHI, DNI, DHI, Temperature, Wind). Set temperature parameters for string voltage design. Set CO₂ factor (CEA 2023–24 default: 0.82 kg/kWh).
2Tab 2 — Orientation & POA: Set tilt and azimuth. Calculate POA (isotropic transposition). Use Auto-Optimize Tilt for maximum annual yield. Use Row Spacing Calculator (📐) for shadow-free minimum pitch — apply winter worst-case result.
3Tab 3 — System Parameters: Select PV module (IEC 61215/BIS certified) and grid-tied inverter (IEC 62109 / CEA approved). Verify string voltage checks (Voc_max, Vmp max/min). Adjust Modules/String until all checks pass.
4Tab 4 — Loss Calculation: Review 15-component loss table against MNRE/IEC benchmarks. Adjust soiling for local conditions (dust, monsoon). Review Sankey diagram. Set ILR for clipping analysis. Bifacial gain: enter as negative loss.
5Tab 5 — Sub-array Design: Review module/inverter spec cards. Configure string layout per Tab 3 guidance. Verify all 5 live electrical safety checks pass (GREEN). Add Sub-array or units to system. Review Total System Summary (total kWp, ILR, strings).
6Tab 6 — Economics: Enter CAPEX (civil, modules, inverter, BOS, installation, GST). Enter PMSGMY / state subsidy, loan terms. Enter OPEX (O&M 0.5–1%/yr of CAPEX per MNRE). Set tariff and escalation. Calculate LCOE/NPV/IRR. Toggle report inclusion.
7Tab 7 — Simulation: Run simulation. Review KPI cards, monthly table, 6 charts. Review P50/P90 probability. Read PR improvement suggestions. Generate 8-page A4 report (Print → Save as PDF).
Quick Check — Before Running Simulation: ✅ Module selected · ✅ Inverter selected · ✅ At least one unit added in Tab 5 · ✅ POA calculated · ✅ Losses reviewed · ✅ Economics entered (or excluded from report)
Standards & Codes Reference — Updated April 2026
IST PVSolar Simulator V8.1.1 is designed and validated against the following standards and codes, current as of April 2026:
IEC International Standards
| Standard | Title | Relevance in Simulator |
|---|---|---|
| IEC 61724-1:2021 | PV System Performance Monitoring — Measurement, data exchange and analysis | PR definition, Yf, Ya, capacity factor, loss categories, data quality classes A/B/C |
| IEC 61724-3:2016 | PV System Energy Evaluation — Accuracy of energy production assessment | Uncertainty budgeting, P50/P90 exceedance probability methodology, IAV |
| IEC 61853-1:2011 | PV Module Performance Testing — Irradiance and temperature performance measurements | Module STC parameters (Pmax, Voc, Isc, Vmp, Imp), temperature coefficients |
| IEC 61853-2:2016 | PV Module Performance — Spectral responsivity, incidence angle and module operating temperature | IAM correction, NOCT/T_cell calculation, temperature-irradiance performance matrix |
| IEC 61853-3:2018 | PV Module Performance — Energy rating of PV modules | POA transposition using isotropic diffuse sky model, energy rating formulas |
| IEC 61215-1:2021 | Terrestrial PV Modules — Design qualification and type approval | Module database qualification, damp-heat, thermal cycling, UV tests |
| IEC 61215-2:2021 | Test procedures for crystalline silicon PV modules | Module parameter verification, flash test at STC |
| IEC 62548:2016 | PV Arrays — Design requirements (string fusing, wiring, overvoltage protection) | String voltage design: Voc safety factor, blocking diode selection, DC overvoltage |
| IEC 62109-1:2010 | Safety for Power Converters — General requirements (inverters, converters) | Inverter max DC voltage safety limit, grid connection protection |
| IEC 62109-2:2011 | Safety for Power Converters — Inverters for grid connection | Anti-islanding protection, grid voltage/frequency limits, reconnection delay |
| IEC 60364-7-712:2017 | Low-voltage electrical installations — Solar photovoltaic (PV) supply systems | DC wiring, earthing, protection coordination, AC connection |
| IEC 62257-9-8 | Renewable energy — Rural electrification systems (economics) | LCOE, NPV, IRR methodology used in Tab 6 financial analysis |
| IEC 60891:2021 | Procedures for temperature and irradiance corrections to measured I-V characteristics | STC correction formulas for temperature coefficient application |
Indian National Standards — BIS
| Standard | Title | Relevance |
|---|---|---|
| IS 16169:2014 | Grid Interactive SPV Power Generating Systems — Specification and performance | PR ≥ 75% commissioning benchmark, DC wiring loss ≤ 1.5%, system performance criteria |
| IS 16221 Part 1:2015 | Safety requirements for grid-connected PV inverters | DC voltage limits, anti-islanding, protection relays (OVP, OFP, UVP, UFP) |
| IS 16221 Part 2:2016 | Grid-connected PV systems — Design requirements for arrays | String design, blocking diodes, surge protection, earthing of PV arrays |
| IS 16527:2016 | Thin-film PV modules — Design qualification and type approval | For thin-film/CdTe/CIGS module entries in database |
| IS 14286:1995 (Amdt) | Crystalline Si modules — Thermal cycling and humidity freeze tests | Module qualification; equivalent to IEC 61215 for Indian type approval |
| IS 16653:2017 | Concentrated PV systems design and commissioning | Not directly used; reference for DNI-heavy sites |
CEA — Central Electricity Authority
| Regulation/Order | Key Requirement | Relevance in Simulator |
|---|---|---|
| CEA Technical Standards (Connectivity) 2010 — Amended 2023 | Grid connection of solar PV systems; anti-islanding, protection settings, metering | Inverter grid protection settings; net metering architecture |
| CEA Grid Emission Factor 2023–24 | 0.82 kgCO₂/kWh (national grid baseline CO₂ intensity) | Default CO₂ factor in Tab 1 Settings; environmental impact calculation in Tab 7 |
| CEA Metering Regulations 2006 (Amdt 2019) | Net metering, gross metering, bi-directional meters for solar prosumers | Export tariff logic in Tab 6 economic model |
| CEA RE Integration Standards 2022 | Frequency response, ramp rates, reactive power for utility-scale solar | Reference for large-scale projects; not enforced for residential in simulator |
MNRE — Ministry of New and Renewable Energy
| Guideline/Scheme | Key Provisions | Relevance |
|---|---|---|
| MNRE Rooftop SPV Guidelines 2023 | Phase-II rooftop targets, approved vendor list, quality standards, net metering mandate, commissioning requirements (PR ≥ 75%, 5-year warranty) | PR benchmark for Tab 7 suggestions; warranty period in economics |
| PM Surya Ghar Muft Bijli Yojana (PMSGMY) 2024 | Central Financial Assistance: 1 kW=₹30,000, 2 kW=₹60,000, 3 kW=₹78,000; only for residential ≤10 kW on BIS-certified modules/inverters | PMSGMY subsidy field in Tab 6 financing; subsidy eligibility note in report |
| MNRE Benchmark Cost 2024–25 | ≤3 kW: ₹45,000/kWp; 3–10 kW: ₹42,000/kWp; >10 kW: ₹36,000/kWp (capex ceiling for subsidy) | CAPEX validation reference in Tab 6 |
| MNRE Quality Control Order (QCO) 2022 | Mandatory BIS certification for PV modules (IS 14286/IS 16527) and inverters (IS 16221) sold in India; import restrictions on non-BIS product | Module and inverter database should contain only QCO-compliant products |
| MNRE Soiling Guidelines 2020 | Recommended cleaning frequency: bi-weekly in dusty regions (Rajasthan, MP, UP), monthly in coastal/monsoon regions | Default soiling loss recommendation in Tab 4 |
| MNRE ALMM (Approved List of Models & Manufacturers) | Only ALMM-listed modules eligible for government/PSU projects (updated quarterly) | Module database tag: flag if ALMM-listed (informational) |
Key Design Parameters from Codes
| Parameter | Code Requirement | Simulator Default |
|---|---|---|
| Max DC string voltage | IEC 62548 / IS 16221: apply 1.0×Voc at T_min (no separate factor; inverter rating is limit) | Checked live in Tab 5 |
| DC wiring loss | IS 16169: ≤ 1.5%; MNRE: ≤ 1–2% | Default 1.5% in Tab 4 |
| Soiling loss (India) | MNRE: 2–5% depending on location/season | Default 2% (adjustable) |
| Performance Ratio | IS 16169 / MNRE: ≥ 75% at commissioning | PR shown in Tab 7; ≥75% = Good in suggestions |
| CO₂ grid factor | CEA 2023–24: 0.82 kgCO₂/kWh | Default 0.82 in Tab 1 |
| Anti-islanding delay | CEA/IEC 62109-2: reconnect ≥ 3 min after grid restoration | Informational note in Tab 3 inverter specs |
| Minimum module warranty | MNRE QCO 2022: 10-yr product + 25-yr linear power (80% at year 25) | Degradation rate default 0.55%/yr in Tab 3 module |
| Project life | MNRE / IEC: standard 25-year project horizon | Default 25 years in Tab 6 |
Tab 1 — Project & Site Information
Project Information Fields
| Field | Description | Best Practice / Code Reference |
|---|---|---|
| Project Name | Name of the PV system/project | Use official name for report compliance |
| Client Name | Customer/owner name | Required on MNRE commissioning certificate |
| Engineer Name | Designer/EPC engineer | Accredited by MNRE/BEE/SECI recommended |
| System Type | Grid-tied, hybrid, off-grid | Affects CEA connectivity standards applicable |
Site & Weather Parameters
| Field | Typical Range | Notes |
|---|---|---|
| Latitude | 8°–37°N (India) | Decimal degrees; determines optimum tilt ≈ latitude ± 5° |
| Longitude | 68°–97°E (India) | Used for solar time, sun position calculations |
| Altitude (m) | 0–3000+ m | Affects air mass; high altitude = slightly higher irradiance |
| Min Winter Temp (°C) | –5 to 15°C | Worst-case for Voc_max check per IEC 62548 / IS 16221. Use P1 or absolute minimum from met data, not average. |
| Winter Vmpp Temp (°C) | 5–20°C | Operating winter cell temperature for MPPT upper voltage check. Typ. ambient + 10–15°C. |
| Summer Vmpp Temp (°C) | 55–75°C | Peak cell temperature: ambient_max + (NOCT–20)/800×1000. Used for MPPT lower voltage and thermal loss. |
| CO₂ Factor (kg/kWh) | 0.82 (India 2023–24) | CEA Grid Emission Factor Report 2023–24. Varies by grid zone. Use 0.82 for national average. |
| NASA Start/End Year | 2005–2024 | MNRE recommends ≥10 years of data. NASA POWER provides MERRA-2 data from 1984–2024. |
For Indian projects: use minimum 15–20 years of NASA MERRA-2 data (2005–2024). Set T_min to absolute minimum from nearest IMD station — not the NASA monthly average. Set summer Vmpp temp to 70–75°C for rooftop systems without active cooling (MNRE experience data).
Codes: NASA POWER Community/RE API (MERRA-2), IMD climatological normals, CEA Grid Emission Factor 2023–24, IEC 61724-1:2021 §5 (meteorological measurements)
Tab 2 — Orientation & POA Irradiance
Tilt & Azimuth
| Parameter | Recommended Value | Code/Practice Reference |
|---|---|---|
| Tilt Angle (°) | Latitude ± 5° for fixed-tilt systems; 10–15° for rooftop (soiling/monsoon) | IEC 61853-3:2018 energy rating; MNRE rooftop guidelines (min 5° for self-cleaning); IS 16169 §6 |
| Azimuth (°) | 0° (True South) for Northern Hemisphere; 180° for Southern Hemisphere | IEC 61724-1:2021. Deviation ≤ 15° = energy loss <2%. ≤ 30° = loss <5%. |
| Ground Albedo | 0.2 (concrete/soil), 0.3 (light concrete), 0.5–0.7 (snow/white membrane) | IEC 61853-3, MNRE rooftop: 0.25 for painted concrete roof. |
| Row Spacing (m) | Shadow-free pitch from winter solstice worst-case solar altitude — use Row Spacing Calc | MNRE 2023 rooftop design: minimum row spacing = 2× module height as rule of thumb; use shadow calculator for exact value |
POA Calculation Method
The simulator uses the isotropic sky diffuse model (Liu & Jordan 1963, widely adopted in IEC 61853-3:2018):
H_POA = H_beam_tilted + H_diffuse_iso + H_ground_reflected
H_beam_tilted = GHI × R_b [beam transposition factor]
H_diffuse_iso = DHI × (1 + cos β)/2 [isotropic diffuse]
H_ground = GHI × ρ × (1 − cos β)/2 [reflected from ground, ρ = albedo]
H_beam_tilted = GHI × R_b [beam transposition factor]
H_diffuse_iso = DHI × (1 + cos β)/2 [isotropic diffuse]
H_ground = GHI × ρ × (1 − cos β)/2 [reflected from ground, ρ = albedo]
Standards: IEC 61853-3:2018 §5 (POA transposition), IEC 61724-1:2021 §6 (irradiance on inclined surface), MNRE SPV Design Manual 2023
POA Irradiance is the actual sunlight hitting a solar panel at its specific tilt and orientation. TMY (Typical Meteorological Year) is a synthetic dataset of hourly weather values meant to represent an "average" year over a long historical period
To get the most accurate performance estimate for a PV plant, system designers take the raw horizontal GHI data from a TMY file and mathematically transpose it into POA Irradiance using the planned panel angles.
| Feature | POA Irradiance | Typical Meteorological Year (TMY) |
|---|---|---|
| What it is | The exact sunlight (Direct + Diffuse + Reflected) reaching the physical panel surface. | A 12-month data file stitched together from different historical years to represent long-term "typical" conditions. |
| Variables | Incoming sunlight. | Global Horizontal Irradiance (GHI), air temperature, wind speed, humidity, etc. |
| Specificity | Geometrically dependent on panel tilt and azimuth (direction). | Generally site-specific, but applies to a standard horizontal plane before any panel geometry is factored in. |
| Use Case | Calculating exact performance ratio, efficiency, and real-time losses of a specific system. | Long-term energy yield modeling, financial forecasting, and building design. |
📐 Row Spacing Calculator — Shadow-Free Pitch Design
Click the orange "📐 Row Spacing Calc" button in Tab 2 to open the Row Spacing Calculator popup. This tool calculates the minimum row-to-row pitch (centre-to-centre distance between front edges of successive panel rows) to ensure zero inter-row shadow during the design shading window.
Input Parameters
| Field | Description | Typical Value |
|---|---|---|
| Latitude (°) | Auto-filled from Tab 1. Governs solar altitude at solstice. | 8°–37°N for India |
| Longitude (°) | Auto-filled from Tab 1. Used for solar time (Equation of Time). | 68°–97°E |
| Panel Azimuth (°) | Auto-filled from Tab 2 azimuth. 0 = South (NH). Azimuth offset from south affects shadow gap. | 0° (true south) |
| Tilt Angle (°) | Auto-filled from Tab 2. Higher tilt → taller panel → longer shadow. | 10°–25° for India rooftop |
| Module Height H (m) | Panel slant length along slope (not horizontal). 60-cell ≈ 1.65m; 72-cell ≈ 2.0m; 144-half-cell ≈ 2.1m | 2.0–2.2 m |
| Front Edge Min Ht (m) | Minimum clearance of panel lower (front) edge above ground. Affects rear row irradiance; 0.3m minimum for cleaning. | 0.3–0.5 m |
| Morning/Evening Limit (hr) | Shading window: only ensure shadow-free during this period. Narrowing the window (e.g. 10am–2pm) reduces required pitch. | 9:00–15:00 (default) |
Calculation Method
V = H × sin(θ) [vertical rise of panel face, metres]
F = H × cos(θ) [horizontal footprint of panel, metres]
Gap = V × cos(az_offset) / tan(solar_altitude)
Pitch = Gap + F [full row-to-row distance]
For each season (Winter Dec 21, Equinox Mar 20, Summer Jun 21), the calculator sweeps the shading window in 15-minute steps and finds the worst-case (minimum) solar altitude. The pitch is sized to eliminate inter-row shadow at that moment. Winter always gives the largest required pitch and is used as the design standard.
Three Synchronized Views
| View | What it Shows |
|---|---|
| Side View (full width, top) | Elevation looking East. Panel profiles at correct tilt, mount posts, V/F/Pitch/Gap dimension arrows. Sun disc sweeps sky with dashed ray to panel top-edge → shadow ray to ground. Orange Gap dimension shown separately. |
| 3D Perspective View (bottom left) | Isometric perspective from SE looking NW. Both panel rows on flat ground plane with metric grid. Animated shadow polygon sweeps the ground in real time — turns red with ⚠ if it hits Row 2. Gap and Pitch dimension arrows on ground. Sun in 3D sky. |
| Front View (bottom right) | Looking South face-on. Full panel face with cell grid, mount posts. Sun arc sweeps East→West overhead with sunlight rays hitting panel face. E/W compass, altitude annotation. |
Industry Best Practice — Row Spacing
MNRE rooftop design rule-of-thumb: Row pitch ≥ 2 × module height. For exact shadow-free design, use the winter solstice solar altitude at 09:00–15:00 window. For high-latitude sites (>25°N), winter sun altitude may be <10° — consider narrowing the acceptance window to 10:00–14:00 to achieve a practical pitch.
Shading Flag: If minimum solar altitude in the window is below ~10°, a ⚠ warning appears — this means the required pitch would be impractically large. Narrow the shading window (e.g., 10am–2pm) to reduce pitch at the cost of some morning/evening yield. For most Indian locations (latitude 8°–30°N), the 9am–3pm winter window gives practical pitches of 2.5–4 m for a 2.1 m module at 15–25° tilt.
References: MNRE Rooftop SPV Design Guidelines 2023, IS 16169:2014 §6.3 (row spacing), IEC 62548:2016 §4.2 (shading assessment), Solar Resource Assessment — IMD/NIWE methodology
Tab 3 — System Parameters
Befor start your project design simulation, choose Module and Inverter manufactures, select available model and Add specification datasheet , Save and download datasheet in your folder to use in your simulation. If you are using default database models, inverters carefully compare the software's loaded values against the downloaded manufacturer datasheet. To ensure an accurate simulation, you must always align your software's component database with the manufacturer's exact specifications.
Module Selection
Filter by manufacturer and select from the database. Key parameters to verify for code compliance:
| Parameter | Typical Range | Standard/Requirement |
|---|---|---|
| Pmax (Wp) | 300–700 Wp (residential/commercial) | IEC 61215:2021 type approval; MNRE ALMM listing required for govt projects |
| Voc (V STC) | 35–50 V per module | IEC 61215-1:2021 §10; used in string voltage design |
| TC_Pmax (%/°C) | –0.30 to –0.45 %/°C | IEC 61853-1. TOPCon: –0.30%; mono-PERC: –0.35–0.40% |
| TC_Voc (%/°C) | –0.24 to –0.32 %/°C | Critical for Voc_max (cold) and Vmp_min (hot) calculations per IS 16221 |
| NOCT (°C) | 41–47°C | IEC 61215-2:2021 §11.13 test at 800W/m², 20°C ambient, 1m/s wind |
| Bifacial Factor ɸ | 0 (mono), 0.65–0.75 (bifacial PERC/TOPCon) | IEC 60904-1-2:2019 bifacial measurement standard |
| Degradation (%/yr) | 0.45–0.7 %/yr | MNRE QCO 2022: ≤ 0.7%/yr (80% at 25 yr minimum warranty) |
Inverter Selection
| Parameter | Typical Range | Standard |
|---|---|---|
| Max DC Voltage | 600–1500 V | IEC 62109-1; IS 16221 Part 1; 1000V for residential, 1500V for utility-scale |
| MPPT Voltage Range | 100–950 V | Design string so Vmp_winter ≤ MPPT_max and Vmp_summer ≥ MPPT_min |
| Efficiency η | 96–98.5% | IEC 61683:1999 European/CEC weighted efficiency standard |
| ILR (DC/AC Ratio) | 1.1–1.25 recommended | IEC 61853 energy rating: ILR 1.1–1.3 optimises LCOE for Indian irradiance profiles (MNRE 2023 study) |
String Voltage Calculator
Voc_max = Voc_STC × [1 + TC_Voc/100 × (T_min − 25)] × N_mod → must be ≤ Inverter Max DC Voltage
Vmp_max = Vmp_STC × [1 + TC_Voc/100 × (T_winter − 25)] × N_mod → must be ≤ MPPT Max Voltage
Vmp_min = Vmp_STC × [1 + TC_Pmax/100 × (T_summer − 25)] × N_mod → must be ≥ MPPT Min Voltage
Standards: IEC 62548:2016 §6 (string design), IS 16221 Part 1 & 2, IEC 62109-1:2010 (inverter safety), CEA Technical Standards 2010 §15
Tab 4 — Loss Calculation & Loss Diagram
15-Component Loss Table
| Loss Component | Default (%) | Typical Range | Code/Reference |
|---|---|---|---|
| LID — Light-Induced Degradation | 1.5 | 0.5–2.0 (TOPCon: 0.5%) | IEC 61215-1 §10.19; mono-PERC stabilises by year 1 |
| Module Quality / Mismatch | 1.5 | 0.5–2.0 (with optimisers: 0.3%) | IEC 61724-1 Annex A; MNRE QCO 2022 ±3% power tolerance |
| DC Wiring / Ohmic | 1.5 | 1.0–2.0 | IS 16169:2014 §7: ≤ 1.5%; IEC 60364-7-712 (cable sizing) |
| Soiling / Dust | 2.0 | 1.0–8.0 | MNRE Soiling Guidelines 2020: bi-weekly cleaning for north India dust belts (Rajasthan 5–8%, Chennai 1–2%) |
| IAM — Incidence Angle Modifier | 2.5 | 1.5–4.0 | IEC 61853-2:2016; glass encapsulant BSRN correction |
| Thermal Loss | 5.0 | 3.0–8.0 | IEC 61853-2, NOCT model; Uc+Uv model. Uo Represents the constant heat loss to the surroundings (5.0W/m2/K). U1 Represents the additional cooling effect of the wind. The range 3.0 to 8.0 W/m2K/(m/s). |
| Shading (far/near) | 1.0 | 0.0–10.0 | IEC 62548:2016 §4 (shading avoidance); use Row Spacing Calc for inter-row shading |
| AC Wiring Loss | 0.5 | 0.3–1.0 | IS 732 (wiring); IEC 60364-7-712 §712.524 (AC cable sizing) |
| Inverter Loss (extra) | 0.0 | 0.0–1.0 | IEC 61683 weighted efficiency; inverter η already from specs |
| Transformer Loss (if any) | 0.0 | 0.0–1.0 | IS 2026 / IEC 60076 (power transformer losses) |
| Bifacial Gain (enter negative) | 0.0 | –3 to –12 | IEC 60904-1-2:2019; bifacial factor × albedo × rear irradiance fraction |
| Clipping Loss | Auto (ILR) | 0.5–5.0 | IEC 61853 energy rating; ILR = DC kWp / AC kW |
| Availability / Downtime | 0.5 | 0.0–2.0 | MNRE O&M guidelines: ≥ 98% availability for grid-tied residential; SCADA monitoring recommended |
| Degradation (yr 1) | 0.55 | 0.45–0.70 | MNRE QCO 2022: 0.7%/yr maximum (25-yr linear warranty) |
| Other / Margin | 0.5 | 0.0–2.0 | Project-specific contingency; P90 uncertainty allocation |
MNRE audit data (2022–2024): Most underperforming Indian rooftop systems suffer from: (1) soiling >4% due to lack of cleaning contract, (2) DC wiring losses >2.5% due to undersized cables, (3) thermal losses >7% in rooftop buildings without ventilation gap under modules.
ILR & Clipping Analysis
Set ILR (DC/AC ratio) in the Tab 4 ILR slider. The CDF chart shows the percentage of time during which the inverter is operating at clipping — i.e., the DC input power exceeds AC rated output. Cumulative Distribution Function (CDF) clipping of <5% is acceptable for MNRE-compliant designs.
It is recommended to use inverters with a wide Maximum Power Point Tracking (MPPT) voltage range.
Standards: IEC 61724-1:2021 Annex A (loss categories), IEC 61853-2:2016, MNRE Soiling Study 2020, IS 16169:2014 §7, IEC 60364-7-712:2017
Tab 5 — Sub-array Design & Live Electrical Safety Check
Tab 5 is the electrical design and safety verification step. The selected module and inverter spec cards from Tab 3 are displayed at the top for quick reference.
Configuration Inputs
| Input | Description | Design Guidance |
|---|---|---|
| Modules per String | Series-connected modules per string. Determines string voltage. | Start from Vmp_min / Vmp_module (summer) for min modules; Vmp_max / Vmp_module (winter) for max modules. Both limits must pass. |
| Strings per MPPT | Parallel strings per MPPT input. Determines MPPT current. | Array current per MPPT = Strings × Imp_STC. Must be ≤ MPPT_Imax. CEA recommends fusing if > 2 strings per MPPT input. |
| MPPT used per Inverter | Number of MPPT channels active (≤ inverter's MPPT count) | Each MPPT can connect different orientations/tilts independently — allows mixed-tilt design per IEC 62548. |
| No. of Inverters | Number of identical inverters in parallel | Total system kWp = Modules/Str × Strings/MPPT × MPPT × N_inv × Pmod/1000 |
5 Live Electrical Safety Checks
| # | Check | Formula | Standard |
|---|---|---|---|
| 1 | Voc_max ≤ Inverter Max DC Voltage | Voc_STC × [1 + TC_Voc/100 × (T_min−25)] × N_mod | IEC 62548:2016 §6.1; IS 16221 Part 1 |
| 2 | Vmp_max ≤ MPPT Max Voltage | Vmp_STC × [1 + TC_Voc/100 × (T_winter−25)] × N_mod | IEC 62548:2016 §6.2; IS 16221 Part 2 |
| 3 | Vmp_min ≥ MPPT Min Voltage | Vmp_STC × [1 + TC_Pmax/100 × (T_summer−25)] × N_mod | IEC 62548:2016; inverter MPPT range |
| 4 | Array Current/MPPT ≤ MPPT Imax | Imp_STC × Strings_per_MPPT | IEC 62548:2016 §6.3; fuse >2 strings |
| 5 | Total DC Current/Inverter ≤ Inv Max DC Current | Imp × Str/MPPT × MPPT_used | IEC 62109-1:2010 §12; IS 16221 Part 1 |
System Design Default value
| Sl | Description | Value | Unit | Default |
|---|---|---|---|---|
| # | Site & Orientation | |||
| 1 | CO₂ Factor | 0.82 | kg/kWh | |
| 2 | Ground Albedo (the baseline fraction (20%) of incident solar radiation) | 0.2 | ||
| 3 | Module Height (clearance height) is commonly used in PV design | 0.5 | m | |
| 4 | Row Spacing (Calculate it) | 3 | m | |
| # | System Parameters | |||
| 1 | Approx. Plant Size(Change it) | 10 | KWp | |
| 1 | Modules per String (Change it to make check OK) | 10 | Nos | |
| # | PV System Loss | |||
| 1 | Thermal Loss Coeff Uc for Free-Standing / Open-Rack | 29 | W/m²K | |
| 2 | Thermal Loss Coeff Uc for Semi-Integrated / Roof-Integrated | 22 | W/m²K | |
| 3 | Thermal Loss Coeff Uc for Close Roof-Mounted (Flush) | 15 | W/m²K | |
| 4 | Wind Factor Uv 0 means module's thermal loss is not affected by wind | 0 | W/m²K/ms | |
| 5 | Wind Factor Uv (when wind speed is available) | 1.2 | W/m²K/ms | |
| 6 | Interannual Variability σ (estimate year-to-year fluctuations in solar irradiance) | 5 | % | |
| 7 | Array Thermal Loss (Uc+Uv) default for array thermal losses (not universally recommended) | 5 | % | |
| 8 | DC Ohmic Loss (Wiring), Annual Average energy yield loss is usually around 0.9% to 1.3% | 1.5 | % | |
| 9 | AC Ohmic Loss (Cabling) for Small/Residential Systems | 0.5 to 1 | % | |
| 10 | AC Ohmic Loss (Cabling) for Utility/Commercial Systems | 0.3 to 1.5 | % | |
| 11 | Module LID Loss (1st year) (traditional PERC) (Negligible for TOPCon or HJT) | 2 | % | |
| 12 | Module Mismatch Loss | 1 | % | |
| 13 | Module Mismatch Loss if very long string lengths, or the installation spans multiple orientations | 2 | % | |
| 14 | Module Mismatch Loss if heavy, uneven soiling (dust/grime) or partial shading affects | 3 | % | |
| 15 | Soiling Loss (heavy rainfall ) | <2 | % | |
| 16 | Soiling Loss (dry climates ) | 10 to 20 | % | |
| 17 | Soiling Loss (lower tilt angles ) | 5 | % | |
| 18 | IAM Loss (Incidence Angle) range from 2% to 5% | 2.5 | % | |
| 19 | Module Aging/Degradation (PERC, TOPCon, HJT) | 0.3 to 0.8 | % | |
| 20 | Module Aging/Degradation (High-end modules) | 0.2 to 0.3 | % |
Safety Rule (IEC 62548 / IS 16221): Voc_max must NEVER exceed the inverter's rated Max DC voltage — this can cause arc faults, insulation failure, and fire. Use the absolute coldest temperature recorded at the site for T_min, not the NASA monthly average (which is always warmer).
NMOT (Nominal Module Operating Temperature) replaced NOCT in IEC 61215:2016 and is formally defined in IEC 61853-2:2016. NMOT measures back-of-module temperature, not cell temperature directly.
Standards: IEC 62548:2016 (PV array design), IS 16221 Part 1 & 2:2015/16, IEC 62109-1:2010 (inverter safety), IEC 60364-7-712:2017 (PV installations), CEA Technical Standards 2010 §15 (protection), MNRE wiring guidelines
Tab 6 — Economic Evaluation
CAPEX — Capital Expenditure
Enter line items (modules, inverter, mounting, cabling, installation, civil, metering, GST). MNRE Benchmark Cost 2024–25 for reference:
| System Size | Benchmark CAPEX (₹/kWp) | PMSGMY Subsidy |
|---|---|---|
| ≤ 1 kWp | ₹45,000/kWp | ₹30,000 (Central) |
| 1–2 kWp | ₹45,000/kWp | ₹30,000 + ₹15,000 per additional kW |
| 2–3 kWp | ₹45,000/kWp | ₹60,000 + ₹12,000 per additional kW (max ₹78,000) |
| 3–10 kWp | ₹42,000/kWp | No additional central subsidy beyond 3 kW; state subsidy may apply |
| > 10 kWp (Commercial) | ₹36,000/kWp | No PMSGMY subsidy; check SECI/NTPC tender pricing |
Financing Model
| Field | Description | Best Practice |
|---|---|---|
| Own Fund | Customer's upfront equity contribution | Typical 20–30% of CAPEX after subsidies |
| PMSGMY Subsidy | Central govt subsidy (MNRE 2024) — for residential ≤10 kWp, BIS-certified modules/inverters only | Apply before loan calculation. Subsidy disbursed post-commissioning. |
| State Subsidy | State-specific additional subsidy (MP, Rajasthan, Gujarat, Kerala vary) | Check state nodal agency (MPUVNL, RUVNL, GEDA, ANERT) for current rates |
| Loan ROI (%/yr) | Interest rate on balance loan | NABARD solar loans: 7.5–9%; Commercial bank: 9–12%; PM SVANidhi: 7% for small systems |
| OPEX (₹/yr) | Annual O&M cost | MNRE norm: 0.5–1% of CAPEX/yr. Include cleaning contract, AMC, insurance. |
| Tariff (₹/kWh) | Electricity buy-back / avoided import tariff | Use current DISCOM retail tariff for your consumer category. Net metering: credited at APPC (average purchase cost) in most states. |
| Tariff Escalation (%/yr) | Annual increase in electricity price | India historical average: 4–7%/yr. MNRE economic model uses 5%/yr. |
| Discount Rate (%/yr) | WACC or opportunity cost of capital | Typical 10–12% for Indian solar projects; MNRE uses 10% for benchmark LCOE |
| Degradation Rate (%/yr) | Annual power output decline | 0.55%/yr (TOPCon/HJT), 0.65%/yr (mono-PERC), 0.7%/yr (multicrystalline — MNRE QCO limit) |
Schemes/References: MNRE PMSGMY 2024 (notification dated Jan 29, 2024), MNRE Benchmark Cost Order 2024–25, NABARD Rural Infra Dev Fund solar loans, CEA Metering Regulations 2019, SERC net metering orders (state-specific)
Tab 7 — Simulation Results & Analysis
Simulation Engine
The simulator runs a 12-month energy model (monthly resolution approach):
- POA irradiance (H_POA from Tab 2 transposition)
- Effective irradiance: apply IAM correction, soiling factor
- Cell temperature: NOCT model or Uc+Uv model (per Uc, Uv, wind speed)
- E_array: Pnom × H_POA_eff × temperature correction × DC loss chain × bifacial gain
- Clipping: apply ILR-based clipping loss
- E_AC: E_array × η_inverter × (1 − AC_wiring_loss)
- P50/P75/P90/P95: apply Gaussian IAV uncertainty (z-values from normal distribution)
Key Performance Indicators (KPIs)
| KPI | Formula | Code Reference / Benchmark |
|---|---|---|
| Annual E_AC (kWh/yr) | Σ monthly E_AC | IEC 61724-1:2021 §7.2 |
| Performance Ratio PR (%) | E_AC / (H_POA × P_nom) × 100 | IEC 61724-1 §7.3. MNRE benchmark: ≥75% at commissioning; good system: 80–85% |
| Specific Yield Yf (kWh/kWp/yr) | E_AC / P_nom | IEC 61724-1 §7.4. India typical: 1200–1800 kWh/kWp/yr by location |
| Array Yield Ya (kWh/kWp/yr) | E_array / P_nom | IEC 61724-1 §7.4 |
| Capacity Factor CF (%) | E_AC / (P_nom × 8760) × 100 | India grid-tied typical: 15–22% |
| CO₂ Avoided (t/yr) | E_AC_P90 × CO₂_factor / 1000 | CEA Grid EF 2023–24: 0.82 kg/kWh (use P90 for conservative claim per IEC 61724-3) |
Probability Analysis
| Level | z-value | Formula | Use Case |
|---|---|---|---|
| P50 | 0 | E_annual (base case) | Median expected production; use for energy forecasting |
| P75 | 0.674 | P50 × (1 − 0.674 × σ) | Conservative estimate for operational planning |
| P90 | 1.282 | P50 × (1 − 1.282 × σ) | Bank / lender standard — exceeded 90% of years; used for debt service coverage ratio (DSCR) per MNRE/IREDA lending norms |
| P95 | 1.645 | P50 × (1 − 1.645 × σ) | Ultra-conservative; used for insurance and guarantee pricing |
σ = IAV (Interannual Variability) / 100. Default IAV = 5%. India solar resource IAV typically 4–7% from NASA POWER 20-year data. MNRE recommends reporting both P50 and P90 in project feasibility reports.
PR Improvement Suggestions
After simulation, the "💡 How to Improve PR" panel rates your system (Poor/Average/Good) and gives numbered recommendations based on your specific configuration — covering soiling schedule, tilt optimisation, bifacial upgrade, inverter ILR, cable sizing, thermal management.
Standards: IEC 61724-1:2021 (PR, yields, capacity factor), IEC 61724-3:2016 (uncertainty, P50/P90), MNRE rooftop commissioning checklist 2023, IS 16169:2014 §9 (performance monitoring), IREDA project finance norms (P90 for DSCR)
Databases — PV Modules & Inverters
PV Module Database
Manage the module database in the Databases tab. Import panel.json for bulk loading. Each module record contains: Manufacturer, Model, Pmax, Efficiency, Voc, Isc, Vmp, Imp, TC_Pmax, TC_Voc, TC_Isc, NOCT, Length/Width/Weight, Area, Fill Factor, Rs, Rsh, Degradation, Bifacial Factor.
For MNRE/govt projects: only include modules from MNRE ALMM (Approved List of Models & Manufacturers) in the database. ALMM is updated quarterly — check mnre.gov.in/ALMM. BIS certification (IS 14286 / IS 16527) is mandatory per QCO 2022 for all modules sold in India.
Inverter Database
Each inverter record: Manufacturer, Model, Rated AC Power, Max DC Voltage, MPPT Voltage Range (min/max), Max DC Current, No. of MPPT, Efficiency.
For India: Inverters must carry BIS certification (IS 16221 Part 1 & 2) per MNRE QCO 2022. CEA-approved inverters with anti-islanding protection (tested per IEC 62116) are mandatory for grid-tied systems under CEA Technical Standards 2010 (Amended 2023).
POA Irradiance Formulas
Solar Declination
δ = −23.45 × cos(360/365 × (DOY + 10)) degrees
DOY mid-month: Jan=15, Feb=46, Mar=75, Apr=105, May=135, Jun=162, Jul=198, Aug=228, Sep=258, Oct=288, Nov=318, Dec=344
Solar Zenith Angle (daily mean)
cos(θz) = sin(φ) × sin(δ) + cos(φ) × cos(δ) [φ = site latitude, δ = declination, both radians]
Incidence Angle on Tilted Plane
cos_inc = cos(tilt) × cos(θz) + sin(tilt) × sin(θz) × cos(γ_azimuth)
γ_azimuth = surface_azimuth − solar_azimuth [azimuth offset]
POA Transposition (Isotropic Sky Model)
H_POA_beam = H_beam × cos_inc / cos(θz) [beam component on tilted surface]
H_POA_diffuse = DHI × (1 + cos β) / 2 [isotropic diffuse; β = tilt angle]
H_POA_albedo = GHI × ρ × (1 − cos β) / 2 [ground-reflected; ρ = albedo]
H_POA = (H_POA_beam + H_POA_diffuse + H_POA_albedo) × Days_in_month
References: IEC 61853-3:2018 §5, Liu & Jordan (1963), Duffie & Beckman "Solar Engineering of Thermal Processes" 4th ed., IEC 61724-1:2021 §6
POA Irradiance is the actual sunlight hitting a solar panel at its specific tilt and orientation. TMY (Typical Meteorological Year) is a synthetic dataset of hourly weather values meant to represent an "average" year over a long historical period
To get the most accurate performance estimate for a PV plant, system designers take the raw horizontal GHI data from a TMY file and mathematically transpose it into POA Irradiance using the planned panel angles.
| Feature | POA Irradiance | Typical Meteorological Year (TMY) |
|---|---|---|
| What it is | The exact sunlight (Direct + Diffuse + Reflected) reaching the physical panel surface. | A 12-month data file stitched together from different historical years to represent long-term "typical" conditions. |
| Variables | Incoming sunlight. | Global Horizontal Irradiance (GHI), air temperature, wind speed, humidity, etc. |
| Specificity | Geometrically dependent on panel tilt and azimuth (direction). | Generally site-specific, but applies to a standard horizontal plane before any panel geometry is factored in. |
| Use Case | Calculating exact performance ratio, efficiency, and real-time losses of a specific system. | Long-term energy yield modeling, financial forecasting, and building design. |
Cell Temperature Formulas
Method 1 — NOCT Model (IEC 61215-2)
T_cell = T_ambient + (NOCT − 20) / 800 × G_eff [G_eff in W/m², NOCT in °C]
Method 2 — Uc + Uv Model (IEC 61853-2)
T_cell = T_ambient + G_eff / (Uc + Uv × Wind_speed) [if Uc > 0]
Uc = constant thermal loss coefficient (W/m²K); default 29 W/m²K (open-rack roof)
Uv = wind-speed dependent coefficient (W/m²K/(m/s)); default 0
| Mounting Type | Uc (W/m²K) | Uv (W/m²K·(m/s)) | Reference |
|---|---|---|---|
| Free-standing (open rack) | 25–29 | 1.2–2.0 | IEC 61853-2 |
| Rooftop (vented 10 cm gap) | 20–26 | 0.5–1.0 | MNRE rooftop thermal study 2020 |
| Rooftop (flush, no gap) | 15–22 | 0 | High thermal penalty; MNRE discourages flush mounting |
| BIPV (integrated) | 10–15 | 0 | IEC 62925; special BIPV Uc values |
MNRE rooftop guidelines recommend a minimum 10–15 cm ventilation gap under modules. Flush-mounted rooftop systems can have T_cell 10–15°C higher, increasing thermal loss by 3–5% annually.
Energy Calculation Formulas
DC Array Energy (monthly)
E_array(kWh) = P_nom(kWp) × H_POA_eff(kWh/m²) × T_corr × DC_loss_chain × Bifacial_gain
T_corr = 1 + γ_Pmax/100 × (T_cell − 25) [temperature correction; γ_Pmax negative]
DC_loss_chain = ∏(1 − loss_i/100) for all DC loss components i (LID, mismatch, ohmic, soiling, IAM, shading, thermal)
H_POA_eff = H_POA × (1 − IAM_loss/100) × (1 − soiling/100) [effective POA after angular and soiling losses]
Bifacial Gain
Bif_gain = 1 + (mod_bifacial_factor × albedo_rear × rear_irradiance_fraction)
Simplified in simulator: Bif_gain = 1 + 0.1 × ɸ [enter bifacial loss as negative in Tab 4]
Clipping Loss (ILR-based)
Clipping(%) = min(10%, (ILR − 1) × 2.5 × 100) [empirical approximation for Indian irradiance profiles; ILR > 1.0]
E_array_clipped = E_array × (1 − Clipping/100)
AC Energy Output
E_AC(kWh) = E_array_clipped × η_inverter × (1 − AC_wiring_loss/100)
References: IEC 61853-3:2018 (energy rating), IEC 61724-1:2021 §7 (energy calculation) energy model
Performance Ratio & Yield Formulas
PR (%) = [E_AC_annual (kWh) / (H_POA_annual (kWh/m²) × P_nom (kWp))] × 100
Yf (kWh/kWp/yr) = E_AC_annual / P_nom [Final Yield]
Ya (kWh/kWp/yr) = E_array_annual / P_nom [Array Yield]
CF (%) = E_AC_annual / (P_nom × 8760) × 100 [Capacity Factor]
Lc = Ya − Yf [Inverter + AC losses, kWh/kWp/yr]
La = H_POA_annual / G_ref − Ya [Array capture losses, kWh/kWp/yr; G_ref = 1000 W/m²]
| PR Range | Rating | MNRE Benchmark |
|---|---|---|
| < 70% | Poor — investigate losses | Below acceptable for grid subsidy claim |
| 70–75% | Marginal | Minimum acceptable per IS 16169 / MNRE commissioning |
| 75–80% | Good | Industry average for well-designed Indian rooftop |
| 80–85% | Very Good | Achieved with low soiling, low thermal loss, low DC ohmic loss |
| > 85% | Excellent | Best-in-class; requires active cleaning, optimal mounting, premium modules |
Standards: IEC 61724-1:2021 §7.3–7.5 (PR, Yf, Ya, CF, Lc, La definitions), IS 16169:2014 §9.2, MNRE Rooftop Monitoring Protocol 2023
Probability Analysis — P50/P75/P90/P95
Probabilistic energy yield accounts for interannual variability in the solar resource. The simulator applies a Gaussian uncertainty model per IEC 61724-3:2016:
σ = IAV / 100 [IAV = Interannual Variability in %, default 5%]
P50 = E_annual [median expected production — 50% chance of exceedance]
P75 = P50 × (1 − 0.674 × σ) [exceeded 75% of years]
P90 = P50 × (1 − 1.282 × σ) [exceeded 90% of years — lender/bank standard]
P95 = P50 × (1 − 1.645 × σ) [exceeded 95% of years — insurance/guarantee pricing]
| IAV Setting | Recommended For | P90 = P50 × factor |
|---|---|---|
| 3% (optimistic) | Long data series > 20 yr, low-variability equatorial sites | P50 × 0.962 |
| 5% (default) | India standard — MNRE feasibility reports, 20-yr NASA MERRA-2 data | P50 × 0.936 |
| 7% | Short data series (<10 yr), high monsoon variability sites | P50 × 0.910 |
| 8% | Himalayan foothills, cloud-prone NE India — very high year-to-year variability | P50 × 0.897 |
Financial Use: IREDA (Indian Renewable Energy Dev Agency) and most Indian banks require P90 energy yield for computing Debt Service Coverage Ratio (DSCR ≥ 1.2 for project finance). P50 is used for equity returns and LCOE calculation per MNRE benchmark methodology.
Standards: IEC 61724-3:2016, MNRE Feasibility Report Format 2023, IREDA Project Finance Guidelines 2024, SolarPACES Task 1 uncertainty methodology
Financial Formulas
EMI (Equated Monthly Instalment)
EMI = P × r × (1+r)^n / [(1+r)^n − 1]
P = loan principal (₹); r = monthly rate = annual_rate/12/100; n = tenure × 12
LCOE — Levelized Cost of Energy
LCOE (₹/kWh) = [CAPEX + Σ_{t=1}^{N} OPEX_t / (1+d)^t] / Σ_{t=1}^{N} E_t / (1+d)^t
d = discount rate; N = project life (yr); E_t = annual energy in year t (degraded P50)
NPV — Net Present Value
NPV = −CAPEX_net + Σ_{t=1}^{N} (Revenue_t − OPEX_t) / (1+d)^t
CAPEX_net = CAPEX − subsidies; Revenue_t = E_t × tariff_t; tariff_t = tariff_0 × (1+esc)^(t−1)
IRR — Internal Rate of Return
IRR: solve NPV(d=IRR) = 0 via Newton-Raphson iteration (100 iterations)
Decision: IRR > discount rate → invest; IRR > WACC → positive EVA
Simple Payback & ROI
Payback (yr) = CAPEX_net / (Annual Revenue − Annual OPEX) [simple; no discounting]
ROI (%) = (Total_Net_Savings − CAPEX_net) / CAPEX_net × 100 [over project life]
References: MNRE LCOE Benchmark Methodology 2024, IREDA Project Finance Guidelines 2024, IEC 62257-9-8 (rural electrification economics), IS 16653 Annex B (financial evaluation), BEE/MNRE DPR format for solar projects
CO₂ & Environmental Impact
CO₂_annual (kg) = E_AC_P90 (kWh/yr) × CO₂_factor (kgCO₂/kWh)
CO₂_factor India (CEA 2023–24) = 0.82 kg/kWh [national average; use regional if available]
CO₂_25yr (t) = CO₂_annual × 25 × (1 − degradation/2) [approximate; accounts for declining output]
Trees_equivalent = CO₂_annual / 21.77 [kg CO₂ absorbed per mature tree per year — IPCC value]
Cars_off_road = CO₂_annual / 4600 [kg CO₂ per car per year — Indian passenger car average]
| Grid Zone | CO₂ Factor (kgCO₂/kWh) — CEA 2023–24 |
|---|---|
| National Grid Average | 0.82 |
| Northern Region | 0.89 (coal-heavy) |
| Southern Region | 0.79 |
| Western Region | 0.80 |
| Eastern Region | 0.98 (highest coal dependency) |
| Northeastern Region | 0.71 |
Use P90 energy generation (not P50) for conservative CO₂ offset claims — recommended by IEC 61724-3 and UNFCCC CDM methodology (AMS-I.D for grid-connected solar). Using P90 prevents over-claiming of emission reductions.
References: CEA Grid Emission Factor Report 2023–24, UNFCCC CDM AMS-I.D (grid-connected solar), GHG Protocol Scope 2 (purchased electricity), IPCC AR6 carbon sequestration (21.77 kg CO₂/tree/yr for tropical broadleaf)
Electrical Design Formulas (Tab 5)
String Voltage at Temperature
Voc(T) = Voc_STC × [1 + TC_Voc/100 × (T − 25)] × N_modules
Vmp(T) = Vmp_STC × [1 + TC_Voc/100 × (T − 25)] × N_modules [using Voc TC as conservative approx]
OR (more accurate): Vmp(T) using TC_Pmax proxy if TC_Vmp not given separately
Safety Limits — Complete Table
| Calculation | Must Satisfy | Temperature | Standard |
|---|---|---|---|
| Voc_max | ≤ Inverter Max DC Voltage | T_min (absolute coldest) | IEC 62548:2016 §6.1; IS 16221 Part 1 |
| Vmp_max | ≤ MPPT Max Voltage | T_winter_op (operating winter) | IEC 62548:2016 §6.2 |
| Vmp_min | ≥ MPPT Min Voltage | T_summer (peak cell temp) | IEC 62548:2016; inverter MPPT window |
| Isc × 1.25 | ≤ String fuse rating (if used) | STC (irradiance correction) | IEC 62548:2016 §7 (fusing); NEC 690.9 reference |
| Array I per MPPT | ≤ MPPT input max current | STC Imp | IEC 62548:2016; inverter datasheet |
| Total DC I per Inverter | ≤ Inverter max DC current | STC Imp | IEC 62109-1:2010 §12; IS 16221 Part 1 |
Cable Sizing Reference (IS 16169 / IEC 60364-7-712)
DC cable: size for Isc × 1.25 × 1.25 (double safety factor per IEC 62548)
Voltage drop: ≤ 1% per run; total DC system ≤ 1.5% (IS 16169)
Use solar-rated DC cables (TÜV 2PfG1169, UL4703, IS 694) — 90°C insulation rating minimum
Row Spacing Geometry Formulas
The Row Spacing Calculator uses exact solar geometry and shadow projection to determine the shadow-free minimum pitch between two panel rows.
Panel Geometry
H = module height along slope (metres)
θ = tilt angle (degrees from horizontal)
V = H × sin(θ) [vertical height of panel face, metres]
F = H × cos(θ) [horizontal footprint of panel, metres]
Shadow Gap Calculation
solar_altitude = elevation angle of sun above horizon (degrees, at worst-case time)
az_offset = |sun_azimuth − panel_azimuth| [if > 180°, use 360° − az_offset]
Gap = V × cos(az_offset) / tan(solar_altitude) [minimum shadow-free gap between row back-foot and next row front-foot]
Pitch = Gap + F [total row-to-row distance, front edge to front edge]
GCR = F / Pitch [Ground Coverage Ratio = 1 − Gap/Pitch]
Solar Position Algorithm
Declination: δ = −23.45 × cos(360/365 × (DOY + 10))°
Equation of Time: EoT = 9.87×sin(2B) − 7.53×cos(B) − 1.5×sin(B) minutes; B = 360/365×(DOY−81)°
Local Solar Time: LST = UTC_hour + longitude/15 + EoT/60
Hour Angle: HRA = (LST − 12) × 15°
Solar Altitude: alt = arcsin[sin(lat)×sin(δ) + cos(lat)×cos(δ)×cos(HRA)]
Solar Azimuth: az = arccos[(sin(δ) − sin(lat)×sin(alt)) / (cos(lat)×cos(alt))] [from North, CW]
Design Seasons
| Season | Date (DOY) | Solar Declination | Solar Altitude at Noon (lat=19°N) | Design Use |
|---|---|---|---|---|
| Winter Solstice | Dec 21 (355) | −23.45° | 90 − 19 − 23.45 = 47.55° | Design standard — worst-case shadow; gives maximum pitch requirement |
| Equinox | Mar 20 (79) | 0° | 90 − 19 = 71° | Intermediate — for seasonal comparison |
| Summer Solstice | Jun 21 (172) | +23.45° | 90 − 19 + 23.45 = 94.45° (sun overhead) | Minimum shadow — very short shadow, not binding |
References: MNRE Rooftop SPV Design Guidelines 2023 §4.3 (row spacing), IEC 62548:2016 §4.2 (shading assessment), IS 16169:2014 §6.3, NREL "Photovoltaics: Design and Installation Manual", Duffie & Beckman Ch.1 (solar geometry)
NASA POWER API Guide
API Parameters Used
| NASA Parameter | Full Name | Used As |
|---|---|---|
| ALLSKY_SFC_SW_DWN | All-sky surface shortwave downward irradiance | Global Horizontal Irradiance — GHI (kWh/m²/day) |
| ALLSKY_SFC_SW_DNI | All-sky surface direct normal irradiance | Direct Normal Irradiance — DNI (kWh/m²/day) |
| ALLSKY_SFC_SW_DIFF | All-sky surface diffuse shortwave irradiance | Diffuse Horizontal Irradiance — DHI (kWh/m²/day) |
| T2M | Temperature at 2 metres above surface | Ambient temperature (°C monthly average) |
| WS10M | Wind speed at 10 metres | Wind speed (m/s monthly average) |
Endpoint and Parameters
Primary URL: https://power.larc.nasa.gov/api/temporal/monthly/point?
Parameters: parameters=ALLSKY_SFC_SW_DWN,ALLSKY_SFC_SW_DNI,ALLSKY_SFC_SW_DIFF,T2M,WS10M
&community=RE&longitude={lon}&latitude={lat}&start={year}&end={year}&format=JSON
Fallback: community=RE with start=2005&end=2020 (climatology endpoint)
HTTP 422 Fix: Always use
community=RE (Renewable Energy), NOT SB or AG. Lat/Lon must be formatted to 4 decimal places. If primary endpoint returns 422, the app automatically falls back to the monthly climatology endpoint (start=2005&end=2020). Check internet/firewall if all attempts fail.NASA POWER data uses MERRA-2 reanalysis — 0.5° × 0.625° spatial resolution. For detailed site assessment, validate against nearest IMD station data or ground-measured pyranometer readings (IEC 61724-1 Class A). NASA data is generally within ±5% of ground measurements for Indian locations.
Report Generation
Click 📄 Generate Report in Tab 7 or the menu bar for a professional A4 simulation report.
Economics include/exclude toggle — unchecking "Include in Report" in Tab 6 header omits pages 6 & 7. Page count changes from 8 to 6, page numbers auto-adjust.
Dedicated clean print window — "🖨 Print / PDF" opens a clean print-only window with no app chrome. Use browser Print → Save as PDF, paper A4, margins None/Minimum for perfect output.
Report Structure
| Page | Content | Standards Referenced |
|---|---|---|
| 1 | Cover — project info, system summary, client & engineer, signatures | MNRE commissioning certificate format |
| 2 | Project Summary — weather data table, KPI cards, POA chart, orientation loss | IEC 61724-1:2021 §7; IS 16169 §9 |
| 3 | System Information — Sub-array (unit) configuration, loss table, Sankey diagram, ILR/clipping CDF | IEC 61724-1 Annex A; IEC 61853-2 |
| 4 | Main Results — 12-month simulation table, E_AC vs E_array chart | IEC 61724-1:2021 §7.2–7.5 |
| 5 | Probability Analysis — P50/P75/P90/P95 table, CDF chart, grid injection chart | IEC 61724-3:2016; IREDA P90 requirement |
| 6* | Economic Analysis — CAPEX table, OPEX, 25-year projection, payback highlighted | MNRE DPR format; IREDA finance norms |
| 7* | Financial Results — LCOE/NPV/IRR, energy/revenue chart, PR chart, CO₂ impact | MNRE LCOE methodology 2024; CEA GEF 2023–24 |
| 8 (or 6) | Declaration & Signatures — standards compliance, client & engineer sign-off | MNRE commissioning; CEA Technical Standards |
* Pages 6 & 7 only when "Include in Report" is checked in Tab 6.
Industry Best Practices — Indian Solar PV (2025–2026)
System Design
- Module technology: TOPCon (n-type) and mono-PERC are the industry standard for 2024–2026 new installations. HJT (heterojunction) offers highest temperature coefficient advantage for hot Indian climates. Avoid multicrystalline (p-type BSF) for new designs — MNRE ALMM is predominantly TOPCon/PERC.
- Bifacial modules: Use for ground-mount and elevated rooftop with light-coloured or concrete surface (albedo 0.25–0.35). Rear-side gain 5–15% for ground-mounted. Verify with IEC 60904-1-2:2019 compliant datasheet.
- ILR (DC/AC Ratio): 1.15–1.25 is industry sweet-spot for Indian irradiance profiles (high GHI, clear-sky conditions). ILR above 1.3 leads to excessive clipping loss — accepted only with storage integration.
- String sizing: Always verify with site-specific T_min from IMD records, not default values. Over-voltage tripping is a leading cause of downtime in Indian rooftop installations (MNRE audit 2022–2024).
- Surge Protection: Mandatory per IS 16221 and CEA standards — install Type II DC SPD at array combiner box; Type II AC SPD at inverter AC output. Lightning arrestor for elevated ground-mount structures.
- Earthing: IEC 62548 §11 / IS 3043 — all metallic frames connected to earth; maximum earth resistance ≤ 5Ω per CEA Standards.
Performance Monitoring
- IEC 61724-1:2021 Class A monitoring: reference cell (pyranometer) in POA, module temperature sensor, DC/AC energy meters (Class 1 or better per IS 1248)
- MNRE mandates monitoring data upload to SRMS (Solar Rooftop Monitoring System) portal for subsidy-claimed systems
- PR calculation frequency: minimum monthly per IS 16169; quarterly PR report for MNRE compliance
- Thermographic inspection (IEC TS 60904-13): annually for commercial systems; detect hot spots, delamination, bypass diode failures
- EL (electroluminescence) imaging: biennial for warranty claim support
Cleaning & O&M
- Dust belt (Rajasthan, MP, UP, Delhi): bi-weekly cleaning — MNRE Soiling Study 2020 shows 4–8% soiling loss if cleaned only monthly
- Coastal/monsoon (Kerala, Tamil Nadu, Goa): monthly cleaning, inspect for salt deposition and corrosion annually
- Use deionised or soft water (TDS < 100 ppm) for cleaning; avoid abrasive cloths
- Anti-soiling coating (optional): reduces soiling loss by 30–50%, but re-coating required every 2–3 years (cost vs benefit analysis recommended)
Financial & Regulatory
- Net metering: available for systems up to 10 kW in most Indian states (some states allow up to 1 MW). Excess generation credited at APPC (Average Power Purchase Cost) — typically ₹3.5–5.5/kWh.
- GST: 12% on solar PV systems (modules, inverters, mounting structures, cables) as per GST Council 2023 revision (earlier 5% was rescinded for non-residential). Residential systems ≤ 500W: 5% GST.
- Accelerated Depreciation (AD): 40% AD benefit under Income Tax Act for commercial solar installations — significant for corporate buyers (Section 32, IT Act)
- ALMM compliance: Only ALMM-listed modules eligible for MNRE subsidy programs and government/PSU tenders. Verify current ALMM list at mnre.gov.in before specifying modules.
- ISTS waiver: Interstate Transmission System charges and losses waived for solar projects commissioned before December 2026 (CERC order). Benefit ₹0.50–0.80/kWh for large projects.
Row Spacing & Site Layout
- Use winter solstice 9am–3pm as design window for shadow-free operation — industry consensus per MNRE/NIWE guidelines
- For high-latitude sites (> 25°N, e.g., Punjab, HP, J&K): winter solar altitude at 9am can be <10° — use 10am–2pm window for practical pitch; accept small morning/evening losses
- GCR (Ground Coverage Ratio): rooftop 30–40% typical; ground-mount utility-scale 35–45%
- Elevated mount (minimum 300 mm gap under module): reduces thermal loss by 3–5°C cell temperature; preferred per MNRE rooftop guidelines 2023
- East-West (EW) mounting: reduces row spacing by 60–70% vs South-facing. Suitable for flat rooftops with low tilt (5–15°). Reduces yield by 5–10% but increases GCR and total installed capacity per roof area. Growing adoption in large commercial rooftops.
Troubleshooting
| Issue | Cause | Solution |
|---|---|---|
| NASA data fetch fails (HTTP 422) | Wrong community or data format | App auto-falls back to monthly endpoint with community=RE. Check internet. Try sample Mumbai data as backup. |
| Simulation gives 0 energy | Module and/or inverter not selected; no sub-array added | Select module in Tab 3 → Select inverter → Go to Tab 5 → Pass all electrical checks → Add Sub-array → Tab 7 → Run. |
| Live check shows RED warnings in Tab 5 | String voltage out of inverter limits | Reduce Modules/String (lower Voc_max) if check 1 fails. Increase if check 3 fails (Vmp_min too low). Adjust T_min if temperature inputs are wrong. |
| PR is very low (<70%) | High losses, wrong configuration, low irradiance | Review Tab 4 loss table — reduce soiling, thermal, ohmic losses. Check ILR — if >1.4, clipping loss is high. Check POA — was it calculated? |
| Report print cuts off at edges | Browser margin settings | Use "🖨 Print / PDF" button (not browser Ctrl+P). Set paper A4, margins None/Minimum in browser print dialog. Landscape for charts only if needed. |
| Module not visible in Tab 5 | Module not selected in Tab 3 | Go to Tab 3 → Select module → spec card appears in Tab 5 after selectModule() fires. |
| Economics not in report | "Include in Report" toggle unchecked in Tab 6 | In Tab 6 header, check the "✅ Include in Report" checkbox. Run simulation again then generate report. |
| Row Spacing Calc gives very large pitch | High latitude + wide shading window (9am–3pm winter) | Narrow the shading window to 10am–2pm. Accept small morning/evening losses. Common for sites north of 25°N latitude. |
| Stepper ± buttons not appearing on inputs | stepper.js not loaded | Check that stepper.js is included after main.js in index.html script tags. Clear browser cache and reload. |
| Save .pro file fails | Browser download blocked | Allow file downloads from the app in browser settings. Check download folder permissions. |
Glossary
| Term | Full Form / Definition |
|---|---|
| GHI | Global Horizontal Irradiance — total solar radiation on a horizontal surface (kWh/m²/day or W/m²) |
| DNI | Direct Normal Irradiance — solar radiation perpendicular to sun's rays (beam component) |
| DHI | Diffuse Horizontal Irradiance — scattered sky radiation on horizontal surface |
| POA | Plane of Array — irradiance incident on the tilted panel surface (kWh/m²) |
| H_POA | Monthly or annual in-plane irradiance sum on tilted surface (kWh/m²) |
| PR | Performance Ratio — ratio of actual AC energy to theoretical DC energy at STC irradiance (%); IEC 61724-1 |
| Yf | Final Yield — specific AC energy output per installed kWp (kWh/kWp/yr); IEC 61724-1 |
| Ya | Array Yield — specific DC array energy per kWp (kWh/kWp/yr); IEC 61724-1 |
| ILR / DCR | Inverter Load Ratio / DC ratio = installed DC kWp / AC inverter kW rating |
| MPPT | Maximum Power Point Tracker — inverter sub-circuit that tracks module's peak power voltage |
| NOCT | Nominal Operating Cell Temperature — module temp at 800 W/m², 20°C ambient, 1 m/s wind (IEC 61215-2) |
| LID | Light-Induced Degradation — initial power loss on first light exposure (mono-Si: 0.5–2%) |
| IAM | Incidence Angle Modifier — correction for reflection losses as sunlight hits module at non-normal angle (IEC 61853-2) |
| IAV | Interannual Variability — year-to-year variability in solar resource (%; used in P50/P90 calculation) |
| LCOE | Levelized Cost of Energy — lifetime cost per unit energy generated (₹/kWh); MNRE benchmark metric |
| NPV | Net Present Value — present value of all future net cash flows (₹); positive NPV = viable project |
| IRR | Internal Rate of Return — discount rate at which NPV = 0 (%); compare with WACC for investment decision |
| DSCR | Debt Service Coverage Ratio — EBITDA / Debt Service; banks require DSCR ≥ 1.2 for solar project loans (IREDA norms) |
| CAPEX | Capital Expenditure — total initial investment including modules, inverter, BOS, installation, civil, GST |
| OPEX | Operating Expenditure — annual O&M costs; MNRE norm 0.5–1% of CAPEX/yr |
| EMI | Equated Monthly Instalment — fixed monthly loan repayment |
| PMSGMY | PM Surya Ghar Muft Bijli Yojana — India's national residential rooftop solar subsidy scheme (2024) |
| ALMM | Approved List of Models & Manufacturers — MNRE list of certified PV modules and inverters eligible for govt schemes |
| QCO | Quality Control Order — MNRE 2022 mandatory BIS certification for PV modules and inverters in India |
| GCR | Ground Coverage Ratio — panel footprint area / total ground area = F/Pitch; inversely related to inter-row spacing |
| Pitch | Row-to-row distance — from front edge of one panel row to front edge of next row (metres) |
| TOPCon | Tunnel Oxide Passivated Contact — n-type silicon cell with low temperature coefficient; market-leading technology 2024–2026 |
| HJT | Heterojunction Technology — amorphous/crystalline silicon hybrid; highest efficiency + lowest TC_Pmax |
| MERRA-2 | Modern-Era Retrospective analysis for Research and Applications v2 — NASA reanalysis climate dataset used by NASA POWER API |
| STC | Standard Test Conditions — 1000 W/m², 25°C cell temperature, AM1.5 spectrum (IEC 61215) |
| APPC | Average Power Purchase Cost — rate at which DISCOMs credit net metered solar generation in India |
| ISTS Waiver | Inter-State Transmission System charges & losses waiver — CERC benefit for solar projects commissioned before Dec 2026 |
| P50/P90 | Energy exceedance probabilities — P90 exceeded in 90 out of 100 years (conservative, used by lenders) |
| CF | Capacity Factor — ratio of actual annual energy output to theoretical maximum at nameplate capacity (%) |
| BOS | Balance of System — all components other than modules and inverter (cables, mounting, SPD, combiner, metering, earthing) |
| SPD | Surge Protection Device — protects DC and AC circuits from lightning-induced voltage surges (IS 16221 / IEC 61643) |