Data centers are under mounting pressure to balance resilience with decarbonization and compliance. Diesel remains the default, but alternatives—liquefied petroleum gas (LPG/propane), liquefied natural gas (LNG), and compressed natural gas (CNG)—offer varying tradeoffs. This brief compares their suitability for backup power systems, incorporating current codes, emissions realities, and market trends.
LPG (propane): Best for <10 MW loads needing fast deployment utilizing industry proven technology, standard ASME tanks, and easier permitting under NFPA 58. Strong logistics support across North America. Plan for vaporization capacity and minor engine derates. Renewable propane is emerging but limited.
LNG: Ideal for 10–50+ MW multi-day runtime where on-site cryogenic storage under NFPA 59A is acceptable. Requires specialist O&M, boil-off gas handling, and higher CapEx. Regional availability varies.
CNG: Flexible and non-cryogenic but logistics-heavy. High-pressure trailer swaps and Joule-Thomson heating must be managed. Effective for shorter-duration outages but challenging above ~10 MW.
Emissions & ESG: Gas fuels reduce NOₓ and PM compared to diesel, but methane slip (1–5% unburned methane) is a key risk. Lifecycle CO₂ benefits can be eroded without RNG offsets. Diesel with renewable diesel (HVO) remains a strong competitor on lifecycle CO₂ without methane concerns.
Compliance: Design to NFPA 110 (2022) for EPSS, apply NFPA 58 (LPG) and NFPA 59A (LNG) for storage, and reference ANSI/TIA-942-C (2024) for data center infrastructure. For air permitting, align with EPA NSPS JJJJ (spark-ignited engines) and the 2025 EPA guidance on limited non-emergency operations.
| Criteria | LPG (Propane) | LNG | CNG |
|---|---|---|---|
| On-site storage | ASME tanks (NFPA 58); simple permitting | Cryogenic tanks (NFPA 59A); complex | High-pressure trailers; swap logistics |
| Energy density | High | High | Low |
| Runtime scalability | 10-50 MW practical | 10–50+ MW feasible | 1–10 MW practical |
| Refueling cadence | Multiday runtime possible | Multi-day runtime possible | Frequent trailer swaps at scale |
| Emissions profile | Lower PM, NOₓ vs diesel; CO₂ ~15% less | Same; but BOG & methane slip matter | Same; methane slip matters |
| RNG/renewable option | Renewable propane (limited) | RNG via injection/certificates | RNG via injection/certificates |
| CapEx/O&M complexity | Low | High | Medium |
| Regulatory framework | NFPA 58, NFPA 110 | NFPA 59A, NFPA 110 | NFPA 110, DOT/PHMSA |
LPG: Vaporization and pressure regulation are critical design points. Engines may see modest derates compared to NG nameplate. Robust distribution network across North America.
LNG: Requires cryogenic handling, vaporization, impoundment design, and BOG management. Specialist O&M essential.
CNG: Pressure let-down heating required to avoid freezing. Trailer swap cadence increases traffic and safety considerations for multi-MW operations.
EPA NSPS JJJJ governs NOₓ, CO, and VOC emissions from stationary spark-ignited engines.
EPA guidance (2025): Allows limited non-emergency hours (50–100 per year) for demand response and testing.
Methane slip: Lean-burn SI engines may emit 1–5% unburned methane. Mitigation via oxidation catalysts and calibration is possible.
RNG/rLPG: Supply is growing but limited; typically allocated to transport markets first.
Diesel backup dominates, but HVO/renewable diesel adoption is growing as a drop-in decarbonization strategy.
Natural gas interest is accelerating for on-site generation and backup, driven by AI workloads and interconnection delays.
Regulatory scrutiny is increasing: permitting authorities question large diesel banks and push for lower-carbon alternatives.
Corporate clean energy procurement is at record highs, affecting backup fuel choices as part of broader Scope 2/3 strategies.
Methane accounting is gaining importance; investors expect mitigation of methane slip and upstream leaks.
Determine required power requirements, taking into account any potential expansion or growth.
Clarify whether the generation system will be primary, backup, or a bridge solution.
Decide if the system will be operated internally or contracted out.
Determine generator type—reciprocating engine or turbine.
Select fuel type, supplier, and logistics facilitator.
Choose engineering group and contractor(s) for the project.
Define operational autonomy targets to determine volume of storage.
Review site for required setbacks and spacing as per applicable code.
Verify operational requirements of the generator—fuel flow, pressure, and temperature.
Complete code analysis and permitting requirements.
Establish start-up, commissioning, testing, and maintenance program.
LPG, LNG, and CNG each offer unique advantages and limitations. The right choice depends on scale, runtime requirements, site permitting conditions, and corporate ESG priorities:
Choose LPG for small-to-medium data centers prioritizing fast deployment and simple permitting.
Choose LNG for large-scale, multi-day resiliency with tolerance for cryogenic infrastructure.
Choose CNG for flexible, mid-scale deployments where logistics can be actively managed.
Consider diesel with HVO if lifecycle CO₂ reduction is the priority and methane slip is a concern.
By aligning with current codes (NFPA 110, 58, 59A, TIA-942-C), EPA guidance, and market realities, operators can make defensible, forward-looking fuel strategy decisions.
Backup fuel decisions directly impact data center resilience, compliance, and long-term sustainability. To explore how these strategies apply in practice and see our full range of expertise, visit our Data Center Solutions page.