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Repair Windows errors before they cause bigger problemsFix Now →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Clear out junk files and repair common Windows errorsFree Scan →There is no universally best backup fuel for a data center. Natural-gas generators can start quickly but depend on pipeline service unless fuel is stored onsite; hydrogen fuel cells avoid onsite CO₂ and NOx but require a viable low-carbon hydrogen supply and substantial storage and integration planning; renewable diesel can keep compatible diesel-generator equipment in service while reducing lifecycle emissions, subject to fuel availability and OEM approval. The right choice turns on outage duration, fuel autonomy, emissions goals, local permitting, site constraints, and cost.
What is being compared?
Natural gas and renewable diesel are fuels for combustion engines or turbines. Hydrogen is a different pathway in this comparison: the Cheyenne data-center demonstration used hydrogen in a fuel cell, which produces electricity electrochemically rather than by burning fuel in a generator engine. These options therefore differ not only in fuel but also in equipment, integration, and emissions profile.
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For a data center, backup power is a system decision. The fuel source must work with the required load, startup and step-load behavior, redundancy design, controls, runtime target, and the site’s existing or planned equipment. A fuel that is attractive on paper may not provide the necessary autonomy or be available in the required quantity during a regional emergency.
How the three options compare
| Option | Fuel resilience and runtime | Onsite and lifecycle emissions | Equipment and site implications | Main uncertainties |
|---|---|---|---|---|
| Natural-gas generator | Can draw on pipeline supply, avoiding routine onsite liquid-fuel storage; that also creates dependence on pipeline service during emergencies. A site can assess a dedicated or otherwise more resilient supply arrangement, but its adequacy must be established for the actual location. | Combustion produces onsite Scope 1 CO₂ and may be associated with methane emissions upstream. Reductions relative to diesel are described as moderate, not zero, in the October 2025 Sustainable Data Centers Roadmap. | Mature combustion pathway. The 2025 roadmap describes natural-gas generator startup as fast and capable of approaching or matching diesel. Confirm the specific equipment’s start, ramp, and load acceptance characteristics. | Pipeline outage exposure, applicable emissions limits and permits, fuel contract and infrastructure terms, and lifecycle emissions accounting. |
| Hydrogen fuel cell | Stored onsite hydrogen can provide fuel autonomy, but runtime depends on the load, system design, and amount of usable hydrogen stored and replenished. Delivery and storage arrangements are central to resilience. | Fuel-cell operation produces no onsite CO₂ or NOx. Lifecycle emissions depend on how hydrogen is made and delivered; hydrogen from fossil feedstocks can still carry substantial upstream emissions. | Requires fuel-cell equipment, hydrogen storage and delivery infrastructure, and integration with batteries and controls as needed. Space and power density are material design factors. | Low-carbon hydrogen supply, cost, logistics, storage footprint, first cost, and commercial availability for the specific project. |
| Renewable diesel / HVO | Liquid fuel can be stored onsite, decoupling backup runtime from a gas pipeline. Practical autonomy depends on tank capacity, replenishment logistics, and fuel availability in the region. | Can reduce lifecycle CO₂ compared with fossil diesel, but the reduction depends on the fuel pathway and actual supply; it is not zero-emission. Combustion still produces onsite emissions. | Can be a drop-in replacement in compatible diesel equipment, potentially retaining installed generator systems. Verify the specific fuel specification, storage practices, and generator OEM approval. | Regional supply and delivery reliability, OEM compatibility, fuel quality, and lifecycle accounting assumptions. |
No consistent current cost comparison establishes a universal cost ranking across these pathways. Capital, fuel, storage, delivery, integration, permitting, and maintenance costs need to be developed for the site and the required runtime.
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Can hydrogen power a data center for 48 hours?
A hydrogen fuel-cell system has been demonstrated at a live data center in a simulated 48-hour backup event, but that result is a site-specific demonstration, not proof that any data center can obtain 48 hours of hydrogen backup economically or commercially at scale.
At Microsoft’s Cheyenne, Wyoming data center, a Caterpillar microgrid controller integrated two PGS 1260 battery energy-storage systems with a 1.5 MW Ballard hydrogen fuel cell. Caterpillar reported that the test simulated a 48-hour backup event and took place at 6,086 feet (1,855 meters) and below-freezing conditions. During the DOE H2IQ Hour webinar held February 23, 2024, Caterpillar’s Paul Wang described gaseous hydrogen delivered at the pressure and temperature needed by the system. These are reported facts about that project, not a general runtime guarantee.
To determine whether 48 hours is feasible at another site, engineers must size the fuel supply against the actual critical load and system efficiency, then confirm storage capacity, usable fuel, delivery arrangements, equipment footprint, and integration with batteries and controls. The webinar identifies hydrogen cost and availability, first cost, power density, and space as barriers. It does not establish a universal design threshold or a general price for 48-hour service.
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Which backup generator fuel is most reliable?
Reliability depends on which part of the fuel chain is most exposed at a particular site. Onsite liquid fuel can reduce dependence on an operating gas pipeline during an outage, while a pipeline-fed gas plant depends on pipeline service. Hydrogen can also be stored onsite, but its resilience depends on the storage design and the ability to procure and replenish suitable hydrogen. No fuel is inherently most reliable without the site’s outage scenario, fuel autonomy target, and supply-chain details.
- For pipeline gas: assess local gas-system resilience under the same severe-weather or regional-disruption scenarios used for electric service, along with the actual service arrangement.
- For hydrogen: confirm source, delivery mode, storage quantity, pressure and handling requirements, supplier capacity, and replenishment time.
- For renewable diesel: verify local availability and delivery commitments, tank capacity, fuel specification, and storage procedures.
Reliability also includes whether the power system can start, accept the site’s load steps, coordinate with UPS and batteries, and sustain the critical load through the required event. Those are equipment and integration questions, not fuel labels alone.
Separate onsite air emissions from lifecycle climate impact
Onsite emissions and lifecycle greenhouse-gas emissions answer different questions. Onsite emissions concern what the equipment releases at the facility during operation. Lifecycle accounting also considers fuel production and delivery. A fuel with no onsite CO₂ can still have significant upstream emissions; a fuel with lower lifecycle emissions can still have onsite combustion emissions.
- Natural gas: combustion produces onsite CO₂. The October 2025 Sustainable Data Centers Roadmap also notes potentially associated methane emissions. The roadmap characterizes reductions versus diesel as moderate rather than zero.
- Hydrogen fuel cells: fuel-cell operation produces no onsite CO₂ or NOx, but the climate benefit depends on hydrogen production and delivery. The DOE/Caterpillar scenario analysis found onsite-wind hydrogen had the lowest modeled carbon intensity among the cases it considered; grid-powered electrolysis varied with the regional electricity mix. These are scenario results, not a universal ranking of hydrogen supplies.
- Renewable diesel / HVO: can reduce lifecycle CO₂, with the scale depending on the production pathway and delivered fuel. The roadmap gives no single reduction percentage that applies to all supplies.
For context, a DOE-hosted presentation for the 2024 demonstration used conversion-efficiency assumptions of 34% for diesel generators, 45% for natural-gas generators, and 55% for fuel cells, based on fuel lower heating value (LHV). It also assumed 61% electrolyzer efficiency and 72% liquefaction efficiency. These are inputs to that presentation’s scenario analysis, not a standardized head-to-head test or guaranteed efficiency for equipment at a given site. Its 90% carbon-capture assumption for steam-methane-reforming scenarios and its 1,065-mile Ontario, California-to-Cheyenne, Wyoming hydrogen transport case are likewise scenario parameters, not general system values.
What else has been demonstrated?
A separate Caterpillar announcement dated June 24, 2025 describes a 2.0 MW combined heat and power (CHP) demonstration that ran on 100% hydrogen and 100% natural gas for up to 200 hours on each fuel. Caterpillar also says it has generator sets from 400 kW to 4.5 MW configured for natural-gas blends containing up to 25% hydrogen by volume, using factory-installed hardware or retrofit kits. Those are manufacturer-reported specifications and refer to a separate demonstration and product configurations—not the Cheyenne data-center backup test. Confirm current, model-specific availability and operating limits with the manufacturer before using them in a project design.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Renewable diesel is not the same as biodiesel
Renewable diesel, often called hydrotreated vegetable oil (HVO), and biodiesel made through fatty-acid methyl ester (FAME) chemistry are distinct fuel types. Do not assume that a statement about HVO compatibility applies to biodiesel, or vice versa. For a proposed HVO supply, check the precise fuel specification, the generator manufacturer’s approval for the equipment and duty, storage and handling requirements, and whether the regional supplier can support the required volume and replenishment schedule. The U.S. Department of Energy Alternative Fuels Data Center’s Fuel Properties Comparison distinguishes these fuel chemistries.
Permitting and operating limits in the United States
U.S. stationary combustion turbines and engines used for data-center power may be subject to applicable Clean Air Act requirements, including New Source Performance Standards (NSPS) and National Emission Standards for Hazardous Air Pollutants (NESHAP). EPA’s Clean Air Act Resources for Data Centers points to separate requirements for turbine, compression-ignition engine, spark-ignition engine, and reciprocating-engine categories. EPA says state and local air agencies issue most air permits. Applicability depends on the equipment, operating classification, jurisdiction, and permit conditions, so a generic fuel comparison cannot determine a project’s requirements.
EPA’s potential-to-emit guidance says 500 hours is an appropriate default assumption for estimating how many hours an emergency generator might operate under worst-case conditions. EPA allows alternative estimates case by case when justified. This is not a universal operating allowance or permission to use an emergency generator for maintenance, testing, or non-emergency operation beyond applicable requirements. Verify current federal, state, and local rules during project design.
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A project-specific recommendation requires these facility and supply facts:
Quick Recap
- Site jurisdiction: identify the state and local air agencies, applicable permitting pathway, equipment classification, and operating conditions.
- Critical load and redundancy: establish which loads must remain online, the design load, redundancy architecture, startup and step-load needs, and how generators, fuel cells, batteries, UPS, and controls will coordinate.
- Required fuel autonomy: define the outage duration the system must cover and whether fuel must be available without deliveries during the event.
- Fuel-system resilience: evaluate pipeline service for natural gas; source, delivery and storage for hydrogen; or local HVO availability, storage, and replenishment.
- Equipment compatibility and space: confirm OEM approval and retrofit needs, then account for tanks or hydrogen storage, setbacks, access, and supporting infrastructure.
- Cost and carbon boundary: compare site-specific capital, fuel, delivery, integration, and operating costs, and state whether emissions accounting includes upstream fuel production and transport.
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