SECI tender awards are decided by tariff, and tariff is decided by the cost of energy delivery. The engineering inputs (yield assumptions, cable sizing, inverter loading ratio, plant auxiliary consumption, degradation model) collectively determine whether your bid is viable at ₹2.60/kWh or whether you are leaving money on the table at ₹2.75/kWh.
Most developers bid on intuition backed by a vendor’s yield estimate. The ones who consistently win bid on engineering-grade inputs that others do not have the process to produce.
Quick answer. Winning a SECI solar auction on engineering inputs means producing a bankable PVsyst P50 simulation with site-matched meteo data, optimizing the inverter loading ratio to raise energy per MW of AC capacity, sizing DC cables to minimize ₹ lost to I²R losses over 25 years, and running a sensitivity analysis on degradation assumptions that most IE firms will challenge at financing stage. The engineering advantage is typically worth 4-8 paise/kWh in the tariff calculation, enough to win or lose a competitive auction.
This playbook is for Indian utility-scale developers preparing a 50-500 MW SECI submission and needs to know which engineering decisions directly affect bid tariff, which inputs are most commonly misjudged by competitors, and how to structure the engineering deliverables to survive IE review at the financing stage.
TL;DR
- Recent SECI solar tariffs have cleared in a narrow band in the mid-₹2/kWh range, narrow enough that engineering precision, not intuition, decides who wins the auction.
- Five decisions make up the Engineering Margin Framework: meteo data source, inverter loading ratio, bifacial gain modeling, soiling calibration and degradation curve selection. Together they can move a bid by several paise/kWh.
- A bankable PVsyst report must meet the IE-accepted standard across eight parameters, from meteo source to horizon shading, or it risks rejection at financing stage.
- Correct DC string sizing and cable cross-section under IS 732 reduce ohmic loss and are worth 0.2-0.3 paise in tariff sensitivity on a 100 MW plant.
- ALMM module selection drives the PAN file, bifacial factor and temperature coefficient, all of which must come from manufacturer data, not generic PVsyst database entries.
- Bid-stage and financial-close deliverables must use the same meteo source and module specification; switching between them creates a discrepancy that lenders and IEs will flag.
Understanding the SECI Auction Engineering Stack
For the tenders open right now, see our SECI tender 2026 calendar.
SECI (Solar Energy Corporation of India) auctions for utility-scale ground-mount projects require two categories of engineering inputs: bid-stage inputs that determine your tariff proposal, and financial-close inputs that lenders and independent engineers review before releasing debt. Mercom India’s auction results tracker shows recent solar-only winning tariffs clustered in a narrow band, where each paise of engineering precision translates directly to auction outcome.
The bid-stage inputs include:
- Annual energy yield (P50) in MWh/year per MW installed
- Plant auxiliary consumption as a percentage of AC output
- Cable loss budget (DC side and AC side separately)
- Degradation rate assumption (first year and subsequent years)
- Inverter loading ratio (ILR or DC:AC ratio)
- Land area and ground coverage ratio (GCR)
The financial-close inputs add:
- P90 yield (for debt sizing and DSCR calculation)
- Independent engineer-reviewed PVsyst project file
- Bankability certification for module and inverter specifications
- ALMM compliance confirmation for module selection
- Compliance with the CEA connectivity regulations for grid interconnection
The gap between bid-stage assumptions and financial-close inputs is where most developers lose margin. A P50 yield assumption that does not survive IE review squeezes equity returns, because the tariff is fixed once the PPA is signed.
Definition. A bankable PVsyst report in the context of SECI auctions is a simulation report that an accredited independent engineer (IE) has reviewed and accepted as representing the site's energy yield potential. The lender will not disburse debt without IE acceptance of the yield simulation.
The Engineering Margin Framework for SECI Bids
The framework that separates engineering-led bidders from assumption-led bidders is a set of five engineering decisions that collectively move a SECI tariff bid by several paise/kWh.
Each decision is worth roughly 0.3-1.5 paise in isolation; together they determine whether a developer can competitively bid below the market-clearing tariff or must bid above it. For the underlying tariff math behind each decision, see our breakdown of how engineering inputs move SECI bids by 4 paise/kWh.
Meteo data source selection (0.5-1.2 paise/kWh)
Using different meteo sources (Meteonorm 8.x versus Solargis, for example) for the same Rajasthan or Gujarat site produces P50 estimates that differ by 1.5-3%. For a 100 MW project at ₹2.65/kWh, a 2% yield difference is worth approximately ₹1.1 Cr/year in revenue, enough to move the tariff by 1.2 paise. Use site-validated satellite time-series data wherever available.
Inverter loading ratio optimization (0.4-0.8 paise/kWh)
An ILR of 1.25-1.30 versus a conservative 1.15 raises energy delivered per MW of AC capacity by several percent on high-irradiance sites, at the cost of some clipping loss. Producing a clipping loss analysis in PVsyst to justify the higher ILR, and having the IE accept it, is a direct tariff input worth 0.4-0.8 paise.
Bifacial gain modeling (0.5-1.5 paise/kWh)
Bifacial gain on single-axis trackers is typically around 5-10% over monofacial, depending on albedo, ground clearance and row spacing. A PVsyst bifacial simulation with site-matched albedo data (0.22 for sandy Rajasthan terrain versus PVsyst's default 0.20) captures this gain correctly. Developers who use monofacial module specs for bifacial modules leave 0.5-1.5 paise on the table. See our [bifacial module design guide](/blog/solar-bifacial-module-design-2026/) for the inputs.
Soiling loss calibration (0.3-0.6 paise/kWh)
A flat 2% soiling loss is a common industry assumption. Site-specific soiling data from nearby operating plants or a soiling study may justify a lower assumption of 1.5% in clean-air highland terrain or require a higher assumption of 3-4% in Thar Desert locations. A 1% soiling difference on a 100 MW plant is worth roughly ₹60-70 lakh/year in P50 revenue.
Degradation curve selection (0.5-1.0 paise/kWh)
A generic 0.7%/year degradation assumption versus a TOPCon module's warranted 0.4%/year leaves a year-25 output gap of about 7 percentage points (about 3.5 points averaged over the life). On a 100 MW plant that is worth 0.5-1.0 paise in tariff sensitivity.
PVsyst Configuration for SECI-Bankable Yield Reports
The PVsyst simulation for a SECI bid must meet the standards that accredited independent engineers apply at the financing stage. The IE will check the following parameters in the PVsyst project file. Developers evaluating which simulation and design platform to standardize on across their bid pipeline can cross-check PVsyst against alternatives in SurgePV’s comparison of the top solar design software.
| PVsyst Parameter | Common Bid Assumption | IE-Accepted Standard | Impact |
|---|---|---|---|
| Meteo source | Meteonorm (default) | Validated satellite time series (e.g. Solargis) | ±1.5-3% yield |
| Module PAN file | Generic from PVsyst database | Manufacturer-certified PAN file | ±0.5-1% yield |
| Bifacial parameters | Disabled | Enabled with site-matched albedo | +5-10% yield |
| Soiling loss | Flat 2% | Site-calibrated 1.5-4% | ±1% yield |
| Mismatch loss | 1% (default) | String-sizing-matched | ±0.3% yield |
| IAM model | Generic default | Manufacturer-measured IAM where available | ±0.5% yield |
| Horizon shading | Manual estimate | LiDAR or drone-survey horizon | ±0.5-2% yield |
| Degradation | PAN file default | Manufacturer warranty curve | ±3-8% lifetime |
An IE who accepts the report at bid stage will check all eight of these parameters at financing stage. Any change from bid to financing that reduces P50 yield by more than 1% creates a lender conversation that delays disbursement.
Watch out. Producing a PVsyst report at bid stage with one meteo source and then switching at financing stage, because the new number is 2% lower, creates an IE report that contradicts the bid. Lenders treat this as a material discrepancy. Use your final meteo source from the bid stage onwards.
Check the specific RfS on SECI’s tender page for the documents and timelines it requires. Whatever the tender asks for, keep the bid-stage and financing-stage yield reports methodologically consistent: same meteo source, same module specification, same loss table.
String Sizing for SECI Projects: How It Affects Tariff
String sizing for a 50+ MW SECI project is not a desk exercise. The DC cable sizing, the inter-row spacing, and the combiner box configuration collectively determine the DC ohmic loss, which is a line item in the PVsyst simulation that directly affects the P50 yield. For the calculation basics behind Vmp, string length, and voltage windows, see Qbits Energy’s string sizing glossary.
| String Length (modules) | DC String Voltage (Vmp at STC) | DC Cable Cross-section | Ohmic Loss |
|---|---|---|---|
| 24 modules | 960V | 4 mm² | 0.8% |
| 26 modules | 1,040V | 4 mm² | 0.7% |
| 28 modules | 1,120V | 6 mm² | 0.6% |
These values are illustrative. The maximum string length is set by the module’s cold-temperature Voc, which must stay below the 1,500 V system limit; check it for every module you shortlist.
On a 100 MW plant, a 0.3% reduction in DC ohmic loss from correct string sizing is worth roughly ₹20 lakh/year in P50 revenue. Over a 25-year PPA, discounted at 9% WACC, that is about ₹2 Cr in present value, or a fraction of a paise in tariff sensitivity.
For the full cable sizing methodology under IS 732 (Indian Standard for electrical wiring installations), see our guide on how to calculate solar cable size.
Single-Axis Tracker Design Inputs for SECI Projects
Single-axis trackers are now standard in SECI ground-mount projects above 10 MW. The tracker design inputs that affect the PVsyst simulation are:
- GCR (Ground Coverage Ratio): The ratio of module width to inter-row pitch. SECI projects typically target 0.35-0.42 GCR. Lower GCR gives more yield but requires more land; higher GCR gives more capacity per hectare but increases shading loss.
- Backtracking algorithm: The tracker backtracking algorithm that prevents inter-row shading at low sun angles. All modern trackers include this, but PVsyst must be configured to account for backtracking in the shading calculation.
- Max rotation angle: Typically ±55° for standard single-axis trackers. The PVsyst simulation must match the hardware specification.
- N-S slope correction: For sites with significant north-south slope, PVsyst’s tracker model must be adjusted for the terrain. Sites with more than 1% N-S slope require a slope-corrected simulation.
ALMM Compliance and Module Selection for SECI Bids
ALMM (Approved List of Models and Manufacturers) List-I applies to modules in government and government-assisted projects, which covers SECI tenders. The order took effect in April 2021, was held in abeyance for FY 2023-24, and applies again from April 2024; ALMM List-II for cells applies to projects with later cut-off dates. Check the tender’s cut-off date and the ALMM list and its BOQ impact. Modules also need BIS registration under IS 14286.
The engineering inputs affected by module selection:
- PAN file availability: ALMM-listed modules must have manufacturer-certified PAN files for the specific module variant. Generic database entries in PVsyst are not acceptable to most IEs.
- Bifacial factor: The bifacial factor (typically 0.65-0.75) must be from the manufacturer’s data sheet, not estimated.
- Temperature coefficient: The Pmax temperature coefficient (typically -0.35% to -0.28%/°C for TOPCon) must match the actual module specification. Using a generic -0.45%/°C coefficient for a TOPCon module understates yield by 0.8-1.2% in hot desert conditions.
For how these inputs fit the wider workflow, see our coverage of solar engineering for Indian EPCs.
The SECI Bid Engineering Deliverable Stack
A complete SECI bid requires three tiers of engineering deliverables, each with a defined purpose:
Tier 1: bid stage (submitted with the techno-commercial bid):
- Indicative yield report (PVsyst P50, signed by competent engineer)
- Single-line diagram showing plant configuration
- Land utilization plan with module layout and access roads
- Equipment schedule (module, inverter, transformer specifications)
- BOQ (bill of quantities) for solar and civil BOS
Tier 2: LOA stage (submitted on the timeline the tender sets after the Letter of Award):
- Detailed project layout with GPS coordinates
- Revised yield report incorporating site survey data
- Electrical system design with protection relay coordination study
- Structural design basis document
Tier 3: financial close (required for lender disbursement):
- IE-reviewed PVsyst report (P50 and P90)
- Bankability confirmation for module and inverter from lender’s accepted list
- CEIG drawing package for state interconnection
- Complete IFC drawing set (GA, SLD, civil, structural, electrical)
Most developers produce Tier 1 on their own. Tier 2 and Tier 3 usually need engineering firm support with IE experience.
Field tip. Submit your Tier 1 yield report using the same meteo source and module PAN file you will use for Tier 3. Changing these inputs between bid and financing stage creates an IE audit trail that lenders treat as a discrepancy. The engineering cost of consistency at bid stage is zero; the cost of inconsistency at financing stage is significant.
ENGINEERING ADVANTAGES
- Site-validated Solargis meteo data
- Manufacturer-supplied PAN files for bifacial TOPCon
- ILR optimized at 1.25-1.30 with clipping analysis
- Site-matched soiling and albedo parameters
- IE-accepted PVsyst project file from bid stage
COMMON SHORTFALLS
- One meteo source at bid, a different one at financing
- Generic PVsyst module PAN file for ALMM module
- Conservative ILR of 1.15 without optimization analysis
- Default soiling of 2% regardless of site conditions
- No IE pre-review before bid submission
Lenders such as IREDA typically make an IE-reviewed yield report a condition precedent for first disbursement. Delays here push out financial close, and the PPA’s financial-closure deadline still applies.
MNRE’s current solar policy framework and the SECI standard PPA terms define the documentation timeline that developers must meet. Many of the deliverables above are tender, PPA or lender conditions, so plan them from day one.
How Heaven Designs Helps
Heaven Designs produces engineering deliverables for SECI auction participants, from bid-stage yield studies to IFC drawing sets.
- Solar Ground Mount Design: Complete IFC drawing set for utility-scale projects: GA, SLD, civil, structural, HV interconnection.
- MW-Scale Project Management Consultancy: Owner’s engineer and PMC for SECI projects from bid stage through commissioning.
- Bankable PVsyst Reports: P50/P90 simulations calibrated for IE acceptance, with site-matched meteo data, manufacturer PAN files, and bifacial modeling.
- STAAD Pro Report Calculations: Structural analysis for tracker foundations, mounting structures, and ground-mount civil design.
- Download a sample SECI deliverable package: includes a 2 MWp utility ground-mount package with civil, structural and cable layout, plus full PVsyst reports with P50/P90.
Contact us for a SECI bid engineering review. We will assess your current inputs against the five decisions above and identify where your bid has recoverable yield assumptions.
Disclosure. Heaven Designs and SurgePV are part of the same group. Any pricing mentioned is indicative and changes without notice, so confirm it with the vendor. Product names and trademarks belong to their respective owners and are used for identification only. Spotted an error? Tell us.
FAQ
What meteo data source does IREDA accept for bankable yield reports?
Lenders generally rely on the IE’s judgment rather than a fixed list. Solargis and Meteonorm are both widely used, provided the source is documented and the IE accepts it. Many IEs prefer satellite time-series data such as Solargis for Rajasthan and Gujarat sites. For background, see our guide to GHI, DNI and DHI data in India.
How does the ILR optimization affect SECI plant performance over 25 years?
A higher ILR (1.25-1.30 versus 1.15) increases annual energy per MW of AC capacity on high-irradiance sites, because the extra DC capacity fills the inverter for more hours of the day.
As modules degrade over 25 years, the effective ILR decreases, so the clipping loss shrinks over time. An ILR of 1.30 at Year 1 becomes approximately ILR 1.12 at Year 25 (assuming 0.6% degradation), still within acceptable operating range.
What is the difference between P50 and P90 yield in a SECI context?
P50 is the median annual yield: the number that has a 50% probability of being achieved or exceeded in any given year. P90 is the yield that has a 90% probability of being achieved or exceeded. SECI PPA revenue calculations typically use P50 for tariff justification.
Lenders use P90 (or P75) for debt sizing because they need a conservative yield assumption that covers the DSCR under adverse conditions. A project that is marginally viable at P50 may not service debt at P90 without adequate reserves.
Can I use a PVsyst simulation produced by the module vendor for the SECI bid?
It is risky. Most IEs treat vendor-produced simulations as marketing material. Have the PVsyst simulation produced by an engineering firm that is independent of the module and inverter suppliers. Submitting a vendor-produced simulation and having the IE reject it at the financing stage is a common delay scenario.
What CEIG drawing requirements apply to SECI projects?
SECI ground-mount projects connect to the state grid at 33 kV or higher voltage, requiring CEIG (Chief Electrical Inspector to Government) approval in most states. CEIG drawings must include the complete HV electrical system: transformer sizing, protection relay schedule, earthing system design, and LT panel layout.
The CEIG approval process often takes several weeks and is a pre-condition for energization. Our state-by-state CEIG drawing approval walkthrough covers the documentation each state electrical inspectorate expects.
How far in advance should engineering inputs be finalized before a SECI bid submission?
Engineering inputs should be finalized at least 3-4 weeks before the bid submission deadline. This allows time for: PVsyst simulation run and internal review (1 week), peer review by a senior engineer (3-5 days), sensitivity analysis and cross-check against competing yield assumptions (3-5 days), and any revisions needed before the final bid is signed.
Finalizing inputs in the 48 hours before submission is the most common cause of errors in SECI bid-stage yield reports.
What is the ALMM requirement for SECI auctions in 2026?
MNRE’s ALMM List-I requires modules in government and government-assisted projects, including SECI tenders, to come from listed models and manufacturers. ALMM List-II for cells applies to projects with later cut-off dates, so check the tender. The lists are updated regularly on the MNRE website. Verify that your selected module model and wattage are on the current ALMM list before finalizing your BOQ and PVsyst simulation.