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Size on-site generator fuel storage from the selected generator models’ fuel-consumption curves, the loads they must serve, and the runtime the project must sustain. Add only the reserve the project has defined, then verify that the tank, pumps, transfer equipment, layout, and refueling plan can deliver that fuel under the required operating scenarios. There is no universal data-center runtime or reserve percentage: confirm both the resilience target and the rules adopted by the project’s authority having jurisdiction (AHJ).
How to calculate generator fuel requirements
Calculate consumption for the generators expected to operate at the same time, using each unit’s hourly fuel rate at the relevant load. Do not size a final system from a generic gallons-per-kilowatt figure: the selected model’s fuel curve and the project’s actual operating scenarios are the design inputs.
1. Define the load and operating scenarios
Identify the critical load the backup system must support, how that load is divided among generator sets, and which units run concurrently in each scenario. Include the project’s expected operating load for each unit rather than assuming every generator always runs at rated output.
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Request the manufacturer’s fuel-consumption curve for each selected generator and record the rate at every relevant operating load. A Cummins application manual from 2015 gives an approximate screening benchmark of 0.07 U.S. gallons per hour per rated kilowatt at full load (about 0.26 liters per hour per rated kilowatt). Its illustration for a 1,000 kW unit is approximately 70 gallons per hour. These are rough full-load examples, not a substitute for the selected unit’s curve or a final design value.
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3. Calculate gross fuel consumed
For each operating scenario, multiply each concurrently running unit’s load-specific hourly rate by its planned runtime, then add the units’ consumption:
Gross fuel consumed = Σ (unit’s fuel rate at its operating load × planned runtime)
For a simple illustration using the 2015 Cummins benchmark, one 1,000 kW generator running at full load for 24 hours would consume approximately 1,680 U.S. gallons before any reserve or unusable tank volume is considered. This arithmetic example is not a sizing recommendation; the actual generator’s curve may produce a different result.
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4. Convert consumption into tank capacity
Set the project’s required reserve and establish how much of the tank’s nominal capacity is usable before relying on a design capacity. Account for pickup or suction limits, level controls, operating constraints, and any inventory that must remain unavailable to the engine. The cited guidance does not establish a universal reserve percentage or unusable-volume allowance.
The practical check is that the system’s usable fuel volume covers calculated consumption for the chosen runtime plus the reserve defined by the project. Use the tank manufacturer’s usable-capacity information and have the fuel-system designer verify the calculation.
How many hours of fuel should a data center store?
Set autonomy as a project requirement, not by applying a single industry-wide number. The owner’s resilience target, the backup-load assumptions, local code and amendments, and the AHJ’s interpretation all affect the required on-site supply.
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A cited New York City Building Code Chapter 27 provision calls for an on-premises supply sufficient for at least six hours of full-demand operation for systems that rely on fuel. That is a local code example, not a general rule for data centers elsewhere. Confirm the governing edition and local requirements for the actual site.
Separately document the planned runtime used in the fuel calculation and the assumptions for replenishment. The sources cited here do not establish a universal refill interval or guarantee that fuel deliveries will be available during an emergency; those assumptions belong in the site’s resilience and emergency-planning process.
Which fuel-tank arrangement fits the site?
A generator may use a tank integrated below its base, a remote bulk tank, or a remote arrangement that feeds an intermediate day tank. Choose by usable capacity and the ability to deliver fuel reliably to the engine—not by tank type alone. Cummins’ 2015 application guidance notes that a sub-base arrangement can reduce site work, while capacity needs, code constraints, and refill access may limit it.
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| Arrangement | What to evaluate |
|---|---|
| Sub-base tank | Usable capacity for the required runtime; access for refueling and maintenance; site-work implications; and applicable code and siting constraints. |
| Remote bulk tank | Required usable inventory; distance and route to the generator; transfer equipment and flow capability; refueling access; maintenance; and installation constraints. |
| Remote bulk tank with an intermediate day tank | Whether an intermediate tank is needed for reliable engine supply; transfer and control arrangements; capacity at each stage; and how the system operates during expected scenarios. |
A remote bulk tank may require a day tank, but that is not automatic. Have the genset manufacturer and fuel-system designer review the selected configuration, equipment, and delivery rates together.
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Confirm the jurisdiction and adopted editions
Determine which building, fire, electrical, and environmental provisions apply at the site, including local amendments and the editions actually adopted. Code examples from one jurisdiction should not be treated as nationwide requirements.
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Review liquid-storage requirements for the actual installation
The 2024 International Fire Code Chapter 57 addresses flammable and combustible liquid storage. Applicable controls depend on the fuel classification, tank construction and location, stored quantity, and locally adopted rules. Have the code and fire-protection team evaluate the proposed arrangement before fixing tank locations or assuming clearances and protection measures.
Screen for federal SPCC applicability
EPA describes multiple conditions for Spill Prevention, Control, and Countermeasure (SPCC) applicability: the facility must store, transfer, use, or consume oil; exceed an applicable storage-capacity threshold; and have a reasonable expectation of discharging oil to navigable waters or adjoining shorelines. The EPA page identifies thresholds of more than 1,320 U.S. gallons in aggregate for qualifying aboveground containers (counting containers of at least 55 gallons), or more than 42,000 gallons in completely buried containers. A threshold alone does not determine applicability. The owner or operator should evaluate the full rule, exceptions, and site-specific facts.
What to validate before finalizing the design
- Generator models, fuel type, load-specific consumption curves, and the units expected to run concurrently.
- Critical-load and runtime scenarios, the owner’s resilience target, and the project-defined reserve.
- Tank nominal and usable capacity, pickup or suction limitations, level controls, and operating constraints.
- Fuel delivery rates and transfer capability, including whether a remote tank needs an intermediate day tank.
- Tank location, installation and maintenance access, fire and building requirements, and any applicable spill-prevention obligations.
- Refueling access and the assumptions behind replenishment during an outage or emergency.
Have the genset supplier, fuel-system engineer, fire-protection and code team, and AHJ validate the final basis. The right storage capacity is the result of those project-specific inputs, not a generic runtime or tank-size rule.
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