By AGILE Consulting Engineers, Solar PV and Battery Energy Storage Systems (BESS) specialists.
A solar project’s financial model is only as reliable as the technical assumptions sitting underneath it. Yield forecasts, degradation rates, equipment ratings, and site conditions all get typed into a spreadsheet as numbers, but each one started life as a technical judgement that can be wrong. Technical due diligence is the process of testing those judgements before capital is committed, and it is one of the core reasons an Owner’s Engineer gets engaged early rather than after financial close.
Table of Contents
- What Technical Due Diligence Actually Covers
- Design Review
- Resource and Yield Assessment Review
- Site Assessment
- Equipment Selection Scrutiny
- Contracts, Permits, and Grid Connection Status
- How This Feeds Into the Investment Decision
- What to Do Next
- FAQ
What Technical Due Diligence Actually Covers
Technical due diligence, in an Owner’s Engineer (OE) context, is an independent review of whether a solar project is likely to perform, physically and commercially, the way it is being represented. It sits alongside financial, legal, and environmental due diligence as one leg of the assessment an investor, developer, or lender runs before committing to a transaction, whether that is an acquisition, a financial close, or a corporate Power Purchase Agreement (PPA). The OE’s job in this process is narrow and specific: test the engineering and technical assumptions, and flag where they do not hold up.
The scope of a technical due diligence review generally covers energy production estimates, equipment and technology selection, electrical and civil design, contracting and permitting status, and forward-looking operating and maintenance cost assumptions. Depending on project stage, it can also include site visits, review of manufacturer documentation, and assessment of construction progress against program for projects already underway.
Design Review
Design review checks whether the plant’s engineering, as documented, is coherent, compliant, and appropriately conservative for the site it sits on. This includes electrical single line diagrams, protection philosophy, cabling and inverter or Power Conversion System (PCS) layout, structural design of racking and foundations, and civil works such as access roads and drainage, assessed against the conceptual expectations of relevant Australian Standards and the project’s own design basis document. The reviewer is not redesigning the plant, but checking that what has been designed is internally consistent and defensible, and that any departures from typical practice are justified rather than simply cheaper.
Design review at due diligence stage often surfaces gaps between what a developer’s marketing materials imply and what the design documentation actually supports, which is precisely the kind of discrepancy an investor needs surfaced before signing rather than after.
Resource and Yield Assessment Review
Every solar project’s financial case rests on an energy yield assessment, typically expressed as a probabilistic range rather than a single number, most commonly a P50 estimate representing the production level expected to be exceeded roughly half the time, alongside more conservative estimates such as P90, representing production a plant is expected to exceed with higher confidence. Lenders and conservative investors generally size debt and returns closer to the P90 end of that range rather than the more optimistic P50 figure, precisely because it better reflects downside risk.
An OE reviewing a yield assessment is checking the inputs behind that probabilistic range: the solar resource dataset used, the loss factors applied across the full chain from irradiance to delivered energy, the degradation assumptions used for the panels and inverters over the project life, and whether the uncertainty analysis behind the P50 to P90 spread is methodologically sound rather than simply asserted. A yield assessment that looks reasonable on its headline number can still rest on optimistic assumptions buried several layers down, and this review is where those get tested.
Site Assessment
Site assessment covers the physical characteristics of the land the plant sits on or will sit on, including topography, geotechnical conditions relevant to foundation design, flood and bushfire risk, shading from terrain or vegetation, and access constraints that affect both construction and long-term operations and maintenance. For projects already under construction or operating, this extends to a physical inspection comparing built condition against design documentation and identifying any visible defects or non-conformances.
Site conditions that look minor in a desktop review, such as a marginal geotechnical profile or a access track that floods seasonally, can translate into real cost and schedule risk once construction starts, which is why a genuine site assessment component, not just a desktop document review, matters for due diligence on projects of any meaningful scale.
Equipment Selection Scrutiny
Equipment scrutiny looks at the specific modules, inverters or PCS units, transformers, and, for hybrid or storage-inclusive projects, battery technology proposed for the plant, assessed against factors including manufacturer track record, warranty terms, bankability standing, and technical suitability for the site’s climate and grid connection requirements. This is not a brand preference exercise. It is a check on whether the equipment specified genuinely supports the performance and durability the financial model assumes, and whether warranty and performance guarantee terms are structured in a way that is actually enforceable if equipment underperforms.
Where a project proposes newer or less established equipment, this scrutiny becomes more important rather than less, since the historical performance data an experienced reviewer would normally lean on is thinner, and the technology risk needs to be weighed explicitly rather than assumed away by a lower purchase price.
Contracts, Permits, and Grid Connection Status
Technical due diligence also looks at the status of grid connection approvals, planning permits, and the key technical schedules within EPC and offtake contracts, since a technically excellent design attached to an unresolved grid connection or an unfavourable performance guarantee structure still carries significant project risk. In the Australian context, this includes understanding where a project sits in the National Electricity Market (NEM) connection process administered by the Australian Energy Market Operator (AEMO), including the status of Generator Performance Standards negotiations, since connection timing and conditions can materially affect both project schedule and long-term revenue.
How This Feeds Into the Investment Decision
The output of a technical due diligence process is typically a structured report setting out findings, flagged risks, and recommended conditions or mitigations, which feeds directly into the investment committee or lending decision alongside the financial and legal workstreams. A clean report supports proceeding with confidence. A report with material findings does not necessarily kill a transaction, but it usually changes its terms, whether through price adjustment, additional conditions precedent, contingency reserves, or requirements for specific remediation before or after close.
The value of this process is proportional to how early and how honestly it is done. A due diligence review commissioned to validate a decision that has effectively already been made delivers far less protection than one genuinely used to inform the decision.
What to Do Next
If you are assessing a solar acquisition, or preparing your own project for a due diligence process a counterparty will run, an independent technical review early in that process can surface issues while they are still cheap to address, rather than after terms are locked in. We’ve helped project teams work through exactly this kind of review before committing to contracts, and would be glad to talk through what a due diligence scope should look like for your transaction.
FAQ
What is the difference between technical due diligence and a general project review?
Technical due diligence is specifically structured to support an investment, financing, or acquisition decision, with findings that feed directly into commercial terms or conditions. A general project review may be broader or narrower depending on its purpose and does not necessarily connect to a specific transaction milestone.
How long does a typical technical due diligence review take?
Timeframes vary considerably with project size and how complete the available documentation is, ranging from a few weeks for a straightforward, well-documented project to significantly longer where site visits, additional data requests, or unresolved permitting issues are involved. Building adequate time into the transaction schedule for this step is generally worthwhile.
Does a P50 yield estimate mean the project is guaranteed to produce that much energy?
No, P50 represents a roughly even chance of production being higher or lower than the estimate, not a guarantee. This is exactly why conservative investors and lenders typically reference more conservative estimates such as P90 when sizing debt or setting return expectations.
Can technical due diligence findings actually change the price of a transaction?
Yes, material findings commonly lead to price adjustments, additional conditions precedent, or contingency arrangements rather than simply being noted and ignored. This is one of the main reasons the review needs to happen before commercial terms are finalised, not after.
Is equipment scrutiny only relevant for unfamiliar or new technology?
No, even well-established equipment brands warrant scrutiny of the specific model, warranty terms, and suitability for the particular site and climate involved. Track record reduces but does not eliminate the need for this review on any project.
Does technical due diligence cover the grid connection process?
Yes, understanding a project’s status within the National Electricity Market connection process, including Generator Performance Standards negotiations with AEMO, is typically part of the review, since connection risk directly affects project schedule and revenue certainty.
