1 · The load and the reliability the site requires
Screening a mine-site project like a commercial rooftop, as annual energy times a tariff less the cost of the system, produces a misleading number. A commercial building can often assess electricity primarily as an operating cost. At a remote mine, power reliability is also a production constraint, so the cost of interruption has to be included in the energy decision. When the plant stops, the loss is measured in lost production per hour, not cents per kWh. That single difference reorders the whole problem.
A common early-stage error is to design for the maximum renewable share while assuming away the operating role diesel still performs. A screen that respects operational continuity looks different from the first line.
Mines and heavy industrial sites often run peak loads several times their average, driven by intermittent high-draw equipment. Sizing a solar and battery system to meet those rare peaks raises capital cost while utilisation falls, and the economics fail before a contract is drafted. The better approach is to size for the sustained, predictable load: average demand, night load and baseload consumption. Diesel keeps the peaks. The BESS is asked to displace a meaningful, contractable share of diesel energy, and to do it every day.
The screen therefore turns on one question:
What diesel is doing today
Diesel generation at a remote mine performs several jobs at once. A model that treats diesel only as an energy source will underestimate the capacity and reliability the replacement system needs:
- Energy supply — the baseload kilowatt-hours the site runs on.
- Capacity reserve — firm capacity available on demand, regardless of weather.
- Backup — cover for solar variability and equipment outages.
- Peak support — the buffer for mill start-ups, hoist cycles and compressor surges.
- Contingency supply — power during rare or extended shortfalls.
Only the first of those is straightforward to displace with PV and storage. The others are why the site keeps diesel on even when it is expensive. A design that assumes diesel can simply be removed misreads what the customer is buying. The practical question is which part of the load can be served reliably and economically by solar and storage, while diesel stays available for peaks and contingencies.
The operating architecture that follows coordinates energy, fast response and firm capacity around the production load, with a defined control boundary:
Reliability is a binding constraint. The controller must make the portfolio behave as one power station.
The Paces off-grid analysis reports that high renewable shares can remain competitive when firming generation is retained, while the final move towards 100% renewable supply becomes disproportionately expensive. The system must then overbuild generation and storage to cover rare low-resource periods.
For a mine or industrial site, the practical architecture is therefore not “battery instead of engines”. It is:
- a renewable block carrying a large share of annual energy;
- BESS providing shifting, ramp control, peak support and short-duration firming;
- diesel or gas generation retained for deep lulls, contingencies and reliability;
- a future grid connection, longer-duration asset or additional renewable block treated as an option rather than a prerequisite.
The final increment towards 100% renewable supply can require disproportionate generation, storage and backup capacity. The preferred share is therefore a reliability and capital decision, not only an energy-cost decision.
2 · Supply options and connection risk
Two questions decide the supply route: how quickly power is needed, and what a grid connection would actually deliver.
Time to power
Paces’ starting point is a sobering development statistic: only a minority of projects taken into a utility-scale pipeline ultimately reach construction. Many projects that look viable on a spreadsheet fail later on grid cost, permitting, land or community constraints — after substantial time and money have already been committed.
The useful lesson is sequencing. Traditional development often spends deeply before the most dangerous assumptions have been tested. A better process scores completion risk early and advances only sites with a credible pathway through interconnection, approvals and procurement.
For fast-growing loads such as data centres, a grid offer several years away may have little practical value. The opportunity cost of delay can exceed the premium for building dedicated generation beside the load. That pushes projects behind the meter and changes the comparison from which option has the lowest standalone cost of energy to which option can deliver reliable power within the required time.
Remote mines have always faced a version of the same decision. They build power because extending or strengthening the grid is slow, expensive or impossible. What is changing is that the same logic is now being validated by large, capital-rich energy users.
Connection risk
- Queue position is not usable capacity. A project can wait behind speculative applications and still receive an uneconomic connection outcome.
- Upgrade cost arrives late. A transformer, substation or protection requirement can destroy the economics after the site has already absorbed development spend.
- Grid conditions change while the project waits. Available capacity can be consumed by other projects, and assumptions made at origination may not survive the study process.
- Planning risk can move in the opposite direction. Areas with attractive grid capacity may attract concentrated development and trigger local opposition or new restrictions.
Development schedules can be lost in procurement as easily as in permitting. Long-lead transformers, switchgear, PCS, battery containers and generation equipment may decide when a project can energise. A credible time-to-power plan therefore needs supplier engagement, lead-time evidence, deposit assumptions and interface ownership early in development.
3 · Mine life and contract term
Remaining mine life sets the tenor over which any energy asset and its contract can be recovered. A hybrid system with a fifteen-year design life at a mine with six years of reserves is either a short-term contract with a residual-value problem, a redeployable asset, or a project that cannot recover its cost within the available mine or contract life. Mine life and the expiry of the existing power contract are public for most operations; fleet age and load data are not. The screen therefore checks mine life and contract term first, and asks the owner for the rest.
4 · The commercial boundary, and when to commission a feasibility study
The reliability requirement directly affects equipment size, redundancy, capital cost and the amount of debt the project can support. Which loads are critical, and how long they must keep operating during an outage, determine:
- BESS duration and how much autonomy is really required
- PCS sizing and whether grid-forming capability is needed
- Redundancy (N+1) and spinning-reserve assumptions
- O&M intensity and availability guarantees
- CAPEX — and therefore the debt the cash flow has to carry
The required reliability standard affects both design cost and financeability. A system can meet the reliability requirement and still fail the financing test, because the added capital cost exceeds what the contracted diesel saving can support. Size the system to what the commercial structure can support, rather than to the maximum renewable share that is technically achievable.
The part of site demand that can be served reliably and under contract defines the scope used in the commercial model. The diesel saving inside that boundary has to become a contracted cash flow before it is project revenue; how that conversion works is set out in From customer savings to financeable project cash flow.
When to proceed to a feasibility study
- An early screen pays for itself. It identifies approval, site, grid, boundary and financing gaps before formal development spending begins.
- Off-grid hybrid is an economic pathway in its own right. For remote and constrained sites it can provide a faster, self-controlled route to power while preserving reliability.
- Schedule and equipment belong in the first client conversation. A technically attractive design without a credible procurement and energisation pathway is not development-ready.
A project moves from screen to feasibility study when the served-load boundary is defined, the connection or islanded route is chosen on time-to-power grounds, mine life and contract term support the tenor, and the owner has supplied load, diesel and reliability data. Until then, a feasibility study would be proving a design that may be answering the wrong question. The screen itself is set out in A Pre-DD screen is not a feasibility study and the F1–F4 methodology.