Before Detailed Due Diligence: An Assumption-Readiness Gate for LDES Projects

Long-duration energy-storage projects rarely begin with a shortage of ideas. They begin with a shortage of aligned assumptions.

A project team may have a credible use case, an attractive technology pathway, and an initial cost model. But the duration rationale may not match the revenue case. The CAPEX range may mix unlike scopes. The proposed grid date may sit far outside observed interconnection timelines. A project-specific commercial advantage may be real, but supported only by an informal statement rather than evidence a committee can test.

These are not detailed-engineering failures. They are earlier and more basic: the decision file is asking later-stage questions before its foundational assumptions are ready.

This article proposes a distinct gate between concept development and detailed diligence: an assumption-readiness review. Its purpose is not to approve a project. It is to identify which assumptions are sufficiently framed for the next diligence step, which remain unsupported, and which departures from public benchmarks need project-specific evidence.

The question is not “Is this project good?” The earlier and more useful question is: “Is the current assumption set strong enough to justify the next round of diligence?”

LDES projects are assumption systems before they become assets

The U.S. Department of Energy defines long-duration energy storage as storage capable of delivering electricity for ten or more hours.^[1] That threshold contains a wide range of mechanical, electrochemical, thermal, and chemical pathways, each with different cost structures, operational characteristics, and commercial maturity. DOE’s commercialization framework separates technology readiness from adoption readiness and includes project development, capital, infrastructure, supply chains, siting, and permitting—not only equipment performance.^[2]

“40 hours of storage” becomes meaningful only when connected to questions such as:

• What system need requires that duration?
• Is the technology class credible for the intended duty cycle?
• Which costs are included in the CAPEX range, and in what currency year?
• What grid, procurement, and commissioning assumptions support the target date?
• Which claims are public-baseline assumptions, and which depend on project-specific commercial evidence?

Different levels of capital and project commitment require different levels of evidence. The earliest decision should not imitate a full lender or independent-engineer review. It should determine whether the file is ready to enter one.

Why public benchmarks are necessary—and insufficient

An internal project model needs an external reference point. Otherwise, a number can become “reasonable” simply because it has circulated through enough versions of the same spreadsheet.

These sources define observable external conditions, but none knows the full circumstances of a specific project. A contract may change procurement economics. A site may have favorable geology. A utility may have completed studies that improve the grid schedule. Conversely, a CAPEX figure may exclude scope included in the reference.

An assumption-readiness gate

The gate is a bounded, pre-CAPEX review after a project has enough structure to be described, but before the team commits to deeper and more expensive work. It should perform five jobs.

1. Establish an explicit input contract

Distinguish a stated assumption from a rationale, customer-provided evidence, independently verified evidence, and a fact that is not yet established. “Unknown” is a valid early-stage answer. Silent absence is not: the former identifies a task; the latter can disappear inside a model.

Minimum identification can reduce unnecessary disclosure. A project alias and regional site descriptor may be sufficient for an early baseline; exact coordinates, vendor identities, and unredacted documents need not be required when they do not affect the comparison. This is not a zero-data service—the submitted assumptions still have to be processed.

2. Compare like with like

A CAPEX comparison should check technology class, power, duration, estimate scope, source year, currency year, and whether the declared range is complete enough to interpret. Timeline metrics need the same discipline: request-to-agreement is not request-to-commercial-operation, and procurement lead time is not commissioning lead time.

When no comparable reference exists, the correct output is not evaluable, with a named reason—not an interpolated number presented as fact.

3. Create an Assumption Exception Register

Project-specific departures should be structured rather than buried in narrative.

The review is no longer telling an experienced team that its negotiated economics or site conditions are impossible. It is helping the team make the exception challenge-ready.

4. Keep readiness separate from confidence

Readiness asks whether assumptions are complete, internally coherent, and sufficiently supported for the next diligence step. Confidence describes the strength and coverage of the evidence behind that evaluation. Neither forecasts project outcome. A high-readiness file can still fail later diligence; a low-readiness result means the current file needs work, not that the underlying project is necessarily unattractive.

5. Produce a path forward, not only a diagnosis

Replace “Improve the CAPEX assumption” with “Reconcile EPC, owner’s costs, grid connection, and contingency scope, then provide a dated basis for the low/base/high range.” Replace “Validate the schedule” with a request for the current interconnection milestone and distinct agreement and commercial-operation dates.

A worked example: a deviation that may be justified

Consider a fictional 40-hour storage project with declared CAPEX below the nearest public reference. A simplistic tool would label it unrealistic. A useful review asks whether the reference is comparable, whether both values include the same scope, what explains the lower position, where that explanation came from, and what artifact would make it decision-grade.

How this complements detailed due diligence

An assumption-readiness review should make later advisers more effective, not pretend to replace them.

A project that passes the early gate is not “approved.” It is better organized for the next specialist question. A useful brief reconciles its outcome to the underlying findings, shows confidence separately, identifies benchmark limits, distinguishes declarations from verified evidence, and connects scenarios, next evidence, and provenance in one traceable record.

Where DurationX fits

DurationX calls this a vendor-independent, pre-CAPEX assumption readiness audit for long-duration energy-storage decisions. It compares structured project assumptions with versioned public reference data, records relevant project exceptions, separates readiness from confidence, and produces a human-reviewed decision brief with a Path to Ready: a prioritized roadmap of the evidence gaps the next audit would assess first.

It is intentionally narrower than detailed technical, financial, legal, environmental, or bankability due diligence. It does not recommend vendors, rank suppliers, approve investments, or guarantee project outcomes. Its role is to help a team enter the next diligence step with a more explicit, traceable, and challenge-ready assumption set.