By AGILE Consulting Engineers, Solar PV and Battery Energy Storage Systems (BESS) specialists.
An EPC (Engineering, Procurement and Construction) contract sets the terms. It does not, on its own, tell an owner whether those terms are actually being met on any given week of construction. That gap between what the contract promises and what is verifiably happening on site is where Owner’s Engineer (OE) oversight of contractor performance earns its place in a solar or Battery Energy Storage System (BESS) project, and it is a more structured, ongoing function than a single design review at the start of the job.
Table of Contents
- Why EPC Performance Needs Independent Tracking
- Reviewing Performance Against Contract
- Reviewing Performance Against Design
- Reviewing Performance Against Schedule
- Milestone Sign-Off Process
- Payment Certification
- What to Do Next
- FAQ
Why EPC Performance Needs Independent Tracking
Most EPC contracts for solar and BESS projects are structured around defined milestones, tied to progress payments, with technical requirements, standards and performance guarantees set out in schedules attached to the head contract. The contractor is naturally best placed to report on its own progress, since it holds the day-to-day site data, but relying solely on the contractor’s self-reported status creates the same structural issue that runs through independent engineering more broadly: the party being assessed is also the party doing the assessing. An OE’s ongoing performance review function exists to give the owner a verified, independent view of progress, quality and schedule status rather than an unverified one.
This is not typically an adversarial relationship in practice. A well-functioning OE performance review process works alongside the EPC’s own project controls and quality teams, cross-checking rather than duplicating their reporting, and most experienced EPC contractors operating in the Australian market treat this oversight as a normal part of delivering a bankable, well-documented project rather than as an obstacle.
Reviewing Performance Against Contract
Reviewing performance against contract means checking that the work being delivered, and the way it is being delivered, actually matches what the EPC agreement specifies, not just in terms of headline scope but in the specific technical schedules, equipment specifications, and quality and testing standards attached to the contract. This becomes particularly important where variations have been raised during construction, since a variation that changes scope, equipment or methodology needs to be tracked against the contract’s variation procedures to make sure the owner’s position is protected and that any resulting cost or schedule impact is properly documented rather than absorbed silently into the build.
An OE reviewing contractual performance will typically also monitor whether the EPC is meeting its own documentation and reporting obligations under the contract, since gaps here, missing test certificates, incomplete as-built drawings, absent inspection records, tend to surface as much larger problems later during commissioning, handover or any future dispute, when the underlying paperwork should already exist and does not.
Reviewing Performance Against Design
Reviewing performance against design is the ongoing companion to the design review work done earlier in the project. As construction proceeds, an OE typically checks that installed work matches the approved for-construction drawings and specifications, and that any design changes made on site during construction, which are common and often reasonable responses to real site conditions, are captured, reviewed and formally approved rather than implemented informally and left undocumented. Left unchecked, an accumulation of small, undocumented site-level design deviations can add up to a plant that no longer matches its approved design basis, which creates real problems at commissioning when performance testing is meant to verify the plant against that original design intent.
This review typically draws on a combination of site attendance, review of inspection and test records, and spot checks against drawings, focused on higher-risk and higher-consequence elements of the plant such as electrical protection settings, structural connections and battery system installation, rather than attempting to verify every element of the build in exhaustive detail.
Reviewing Performance Against Schedule
Reviewing performance against schedule involves comparing the EPC’s reported progress against the contracted program, using objective evidence such as site records, procurement status and completed inspection and test records rather than relying solely on the contractor’s own progress percentage claims. A contractor under schedule pressure has a natural incentive to report progress optimistically, not necessarily out of bad faith but because admitting slippage early can trigger difficult conversations the contractor would rather defer. Independent schedule review is intended to surface genuine delay risk while there is still time to manage it, whether through resequencing, additional resourcing or early engagement with the owner on realistic revised dates, rather than after a milestone has already been missed.
Where equipment lead times or grid connection approval timeframes sit outside the EPC’s direct control, an OE’s schedule review also typically tracks these external dependencies against the program, since delays originating outside the contractor’s own workforce, for example connection compliance testing timeframes with AEMO (Australian Energy Market Operator) and the network service provider, still need to be factored into a realistic view of the overall project schedule.
Milestone Sign-Off Process
Milestone sign-off is the point where contract, design and schedule review come together into a formal decision: has the EPC actually achieved the defined milestone, and is the supporting evidence sufficient to confirm that. In a typical solar or BESS EPC contract, milestones might include mechanical completion of defined plant sections, completion of Factory Acceptance Testing (FAT) for major equipment, completion of Site Acceptance Testing (SAT), and practical completion once performance testing has demonstrated the plant meets its contracted output. An OE’s role in this process is usually to independently verify that the evidence submitted by the EPC genuinely supports the milestone claim, checking test results, inspection records and, where relevant, direct site observation, before recommending the owner accept the milestone as achieved.
This independent verification step matters because milestone achievement is rarely just an administrative formality, it usually triggers a contractual consequence, most commonly a progress payment, and sometimes a shift in risk or responsibility from the contractor to the owner. Getting that verification wrong in either direction, accepting a milestone that was not genuinely met, or unreasonably withholding sign-off on one that was, has real commercial consequences for both parties.
Payment Certification
Payment certification is the process of confirming that a progress claim submitted by the EPC is supported by the work actually completed and verified, before the owner releases payment. In practice this typically means the OE cross-references the EPC’s payment claim against the independently verified milestone and progress status discussed above, flags any discrepancy between claimed and demonstrated progress, and provides the owner with a recommendation on the certified payment amount. This is one of the more concrete, recurring touchpoints in an OE’s ongoing engagement, since it happens on a regular cycle throughout construction rather than as a one-off event.
Because payment certification sits directly at the intersection of technical verification and commercial outcome, it is also one of the clearest illustrations of why independence matters in this role. An adviser whose own fee or future work depended on keeping the EPC satisfied would face an obvious conflict of interest at exactly the point where an accurate, sometimes unwelcome, assessment is most needed.
What to Do Next
Ongoing, independent tracking of EPC performance against contract, design and schedule is not a substitute for a well-drafted EPC agreement, but it is what makes that agreement enforceable in practice rather than aspirational on paper. This is the point where an independent technical review early in a project can save months of rework later. We’ve helped project teams work through exactly this before committing to contracts.
FAQ
How often does an Owner’s Engineer typically review EPC contractor performance during construction?
This varies by project size and risk profile, but ongoing review typically follows a regular cycle aligned with the EPC’s own progress reporting and payment claim cycle, supplemented by site attendance at key construction and testing milestones.
What happens if an Owner’s Engineer disagrees with an EPC’s milestone claim?
The OE typically documents the specific gap between the claim and the verified evidence and provides this to the owner as a recommendation, leaving the commercial decision on how to proceed, whether further evidence is requested or the claim is disputed under the contract, with the owner.
Does payment certification by an Owner’s Engineer replace the need for a quantity surveyor or cost consultant?
No, these roles are typically complementary rather than overlapping. A quantity surveyor or cost consultant generally focuses on commercial valuation of work, while the OE’s technical certification focuses on whether the underlying work and testing evidence genuinely support the progress being claimed.
Can EPC contractor performance review help avoid disputes later in a project?
Yes, one of the practical benefits of ongoing independent review is a well-documented, contemporaneous record of progress, quality and schedule status, which tends to reduce the scope for disagreement about what happened and when if a dispute does arise later.
Is EPC performance review only relevant for large, complex projects?
The core principles apply at any project scale, though the intensity and frequency of review, such as how often site attendance occurs, is typically scaled to match the size, complexity and risk profile of the specific project.
Who has final authority to accept or reject a milestone claim?
The owner retains that authority under the EPC contract. The Owner’s Engineer’s role is to provide an independent, evidence-based recommendation that informs the owner’s decision, not to exercise contractual authority in the owner’s place.
