Before a renewable project reaches financial close, lenders rely on an independent engineer to interrogate the yield, technology, electrical design, contracts, permits and financial-model assumptions. This methodology walks through the full technical due-diligence (TDD) scope, the role of the lender’s and owner’s engineer, and how TDD de-risks a project-financed deal.
Why technical due diligence exists
Renewable energy projects are usually financed through a special-purpose vehicle on a non-recourse or limited-recourse basis: the lenders’ debt is repaid from the project’s own cash flow, not the sponsor’s balance sheet. Because that cash flow depends entirely on the plant performing as promised, technical risk is scrutinised in detail before any debt is drawn down.
Three streams of due diligence
Financing typically runs three parallel due-diligence streams before close: legal (permits, land rights and the EPC/O&M/PPA contracts), insurance (adequacy and gaps), and technical. Equity-stage diligence may work from preliminary information; debt-stage diligence works from detailed designs. The independent engineer owns the technical stream — and its conclusions feed directly into the lender’s decision.
The technical scope, item by item
A thorough TDD works through: plant sizing and layout (does the design fit the available land, respect shading buffers, and match the grid-connection capacity?); the layout of modules, mounting, trackers and inverters (inter-row shading and access); electrical design (DC and AC losses, earthing and protection, and compliance with safety standards); a technology review of the major components (environmental suitability, supplier and model track record, certifications, warranties, design life and degradation assumptions); an energy-yield review (resource source, shading, uncertainty method and a theoretical-PR sanity check); a contract review across the EPC, O&M, grid and PPA interfaces; and a review of the financial-model assumptions.
Independent Engineer versus Owner’s Engineer
The two roles are related but distinct. The owner’s engineer performs design review on the sponsor’s behalf and witnesses key construction stages and tests. The lender’s (independent) engineer certifies progress: it signs the percentage-complete certificates that release milestone drawdowns during construction, giving lenders assurance that money is released only against real progress.
How TDD flows into the financial model
The technical findings are not academic — they set the numbers in the model. The P50 and P90 yields, the availability assumption and the degradation rate drive the debt-service-cover ratio (DSCR); a minimum DSCR below 1 in any year means the project cannot service its debt that year. Lenders therefore require sensitivity analysis that flexes capex, opex, yield and interest rates to prove the project survives a bad year, typically within a structure of roughly 15–20% equity and 80–85% debt.
What good looks like — and engaging early
Bankability is a package: an independent, bank-grade yield; an EPC contract with retention held to first revenue and a performance-ratio guarantee; an O&M availability guarantee backed by liquidated damages; robust, assignable warranties from solvent manufacturers; a realistic model with visible contingencies; and permits and land rights secured before construction. Environmental and social performance is part of that package too, with the IFC Performance Standards the private-sector benchmark. The projects that clear diligence cleanly are usually the ones that engaged the independent engineer early — so lender and IE input shapes equipment selection, rather than blocking the deal late.