By AGILE Consulting Engineers, Solar PV and Battery Energy Storage Systems (BESS) specialists.
Owners sometimes ask why they need to pay for an Owner’s Engineer when they are already paying an EPC contractor to deliver a fully engineered plant. It is a fair question, and the answer is not that the EPC contractor cannot be trusted. It is that the EPC contractor and the Owner’s Engineer are answering different questions, for different people, under different incentives, and a project genuinely needs both answered.
Table of Contents
- Two Different Jobs, Not One Job Twice
- Who Each Party Represents
- The Incentives Behind the Advice
- Where Their Scopes Actually Differ
- Why Having Both Is Not Redundant
- Where Friction Shows Up, and Why That Is Useful
- The Australian Delivery Context
- What to Do Next
- FAQ
Two Different Jobs, Not One Job Twice
An Engineering, Procurement and Construction (EPC) contractor is engaged to design, procure, and build a solar PV or Battery Energy Storage System (BESS) plant to a defined scope, price, and schedule. It is a delivery role, and a good EPC contractor is judged on whether the plant gets built on time, on budget, and to specification. An Owner’s Engineer (OE), by contrast, is engaged to independently review, verify, and advise on that same work on behalf of the party paying for it. It is an oversight role, and a good OE is judged on whether problems get caught before they become expensive.
Put simply, the EPC contractor does the engineering and construction. The OE checks it. Treating these as the same function, or assuming one makes the other unnecessary, is where a lot of avoidable project risk quietly accumulates.
Who Each Party Represents
The EPC contractor represents itself, within the bounds of its contract with the owner. That is not a criticism, it is simply what a fixed-price delivery contract is structured to do: the EPC agrees to deliver a defined outcome, and its commercial performance depends on managing cost, schedule, and risk within that agreement. The OE represents the owner directly, with no construction, supply, or delivery obligations of its own, and no commercial outcome tied to how the EPC contract plays out.
This is also where the OE differs from a Lender’s Technical Advisor (LTA), a related independent role engaged by a financing bank rather than the owner, typically to support due diligence at financial close and construction monitoring tied to loan drawdowns. An LTA protects the lender’s position specifically. The OE protects the owner’s position across a broader scope and, usually, a longer timeframe.
The Incentives Behind the Advice
An EPC contractor’s incentives are shaped by its contract. Fixed-price arrangements create pressure to manage variations carefully, to resolve design ambiguities in ways that protect margin, and to move through construction efficiently once work is underway. None of this is inherently adversarial to the owner’s interests, and reputable EPC contractors build long-term business on delivering well. But it does mean that when a design decision has more than one technically defensible answer, the EPC contractor’s preferred answer will not always be the same one an independent reviewer, weighing only the owner’s long-term interest, would land on.
An OE has no equivalent pressure. It is not proposing to build the alternative it recommends, is not compensated based on which equipment supplier is selected, and has no schedule of its own to protect by waving through a shortcut. That absence of a competing incentive is the entire value proposition of the role, and it is why credible OE practice keeps a firm from acting as OE on a project where it or a related entity also holds or is bidding for the EPC contract.
Where Their Scopes Actually Differ
The EPC contractor’s scope is typically comprehensive and prescriptive: detailed design, procurement, construction, testing, and commissioning to a specification agreed at contract signing. The OE’s scope is narrower in one sense and broader in another. It is narrower because the OE does not perform detailed design or construction itself, and broader because OE involvement can start well before an EPC contract is even signed, informing site selection, technology choice, and contract structuring during feasibility, and can continue after practical completion into early operations if the owner wants ongoing independent technical support.
In day-to-day terms, this means the OE spends its time reviewing drawings and calculations against the design basis and relevant Australian Standards, attending site to verify progress against program, scrutinising Factory Acceptance Testing (FAT) and Site Acceptance Testing (SAT) documentation, and translating technical findings into terms the owner can act on commercially. The EPC contractor is producing that underlying work; the OE is testing it.
Why Having Both Is Not Redundant
It can look, on paper, like paying two parties to think about the same design is duplication. In practice it is closer to how a well-run construction project already treats other functions, such as an independent structural certifier reviewing a builder’s engineering rather than the builder self-certifying. The EPC contractor is the party best placed to actually design and build the plant efficiently, given its scale, supply chain relationships, and construction experience. The OE is the party best placed to tell the owner, without any stake in the outcome, whether that design and build are genuinely serving the owner’s interests.
Removing either role weakens the project. Without an EPC contractor with real delivery capability, the owner has no one competent to actually build the plant. Without an OE, the owner has no independent way to know whether the plant being built matches what was promised, beyond taking the EPC contractor’s own assurances at face value.
Where Friction Shows Up, and Why That Is Useful
Some friction between an EPC contractor and an OE is normal and, within reason, a sign the arrangement is working. An OE that never raises a query or challenges a design assumption over the life of a project is either reviewing very little or working on a very simple plant. Well-managed friction stays technical and document-based: a design query raised, a calculation requested, a test procedure clarified, resolved through the project’s normal communication channels rather than escalating into a standing dispute.
Where this works well, the EPC contractor treats OE queries as a normal part of a professionally delivered project rather than an obstruction, and the OE calibrates its scrutiny to genuine risk rather than pursuing every minor stylistic preference. Getting that balance right depends heavily on the OE having real design and construction experience of its own, since credibility with an EPC contractor’s engineering team is earned through competent, specific technical challenge, not through position alone.
The Australian Delivery Context
In the Australian market, EPC contracts for utility-scale solar and battery projects sit within a National Electricity Market (NEM) connection framework administered by the Australian Energy Market Operator (AEMO), which adds its own layer of technical complexity around Generator Performance Standards and connection studies. An OE with genuine familiarity with that framework, and with the conceptual expectations of relevant Australian Standards for electrical and structural design, can meaningfully shorten the distance between an EPC contractor’s technical submissions and an owner’s understanding of what those submissions actually commit the project to. This is one area where local delivery experience matters more than generic international project experience.
What to Do Next
If your project is being delivered under an EPC contract and you are relying solely on the EPC contractor’s own quality assurance to know whether the plant is being designed and built to standard, that gap is worth closing before it becomes expensive to close. This is the point where an independent technical review, run in parallel with the EPC contract rather than instead of it, can save months of rework later. We’ve helped project teams work through exactly this kind of arrangement before committing to contracts, and are glad to talk through what independent oversight would look like on your project.
FAQ
Does engaging an Owner’s Engineer mean the owner does not trust the EPC contractor?
No, it reflects standard project governance rather than distrust of a specific contractor. Even highly reputable EPC contractors operate under fixed-price incentives that make independent review a sensible check, in the same way audited accounts do not imply a company is assumed to be dishonest.
Can the same engineering firm act as both EPC contractor and Owner’s Engineer on one project?
Credible practice avoids this, since it removes the independence the OE role depends on. A firm holding or bidding for the EPC contract has a direct commercial stake in the outcomes the OE is meant to be reviewing objectively.
Who has final decision-making authority when the EPC contractor and Owner’s Engineer disagree?
The owner does, since both parties are ultimately advising or delivering on the owner’s behalf. The OE’s role is to give the owner the independent technical information needed to make that call, not to override the EPC contract directly.
Does an Owner’s Engineer add significant cost to a project?
OE fees are typically a modest proportion of total project cost relative to the design and construction risk they help manage. The bigger cost risk usually sits with the rework, delay, or underperformance that independent review is intended to catch early.
Is an Owner’s Engineer involved in negotiating the EPC contract itself?
Often, yes, particularly around the technical schedules, performance guarantees, and testing requirements within the contract. Commercial and legal terms remain the owner’s and its legal advisors’ responsibility, but the OE’s technical input helps ensure those terms are grounded in a realistic design and delivery basis.
