Chapter 4. Diesel Generators

Introduction

Diesel generators have powered industrial and critical infrastructure since the early 20th century. While the core technology has matured, recent innovations focus on enhancing fuel efficiency, reducing emissions, and integrating aftertreatment systems like Selective Catalytic Reduction (SCR) and Diesel Particulate Filters (DPF). Diesel gensets have a low capital cost, but high fuel cost. As a result, they remain a cost-effective solution for backup power but are generally unsuitable for continuous base load applications.

Diesel generators operate by transforming the chemical energy in diesel fuel into mechanical energy, which is then converted into electrical energy. The process begins with air intake into the engine, where it is compressed to raise its pressure and temperature. When the air reaches a high enough temperature, diesel fuel is injected directly into the combustion chamber. The heat from the compressed air causes the fuel to ignite spontaneously, initiating combustion that drives the engine’s pistons. These pistons turn the crankshaft, producing mechanical energy that powers the generator’s alternator. Inside the alternator, a rotating rotor spins within a magnetic field, inducing an electrical current in the stator windings through electromagnetic induction—thus generating electricity.

Diesel generators are prized for their high torque, durability, and rapid response times, often starting within 10 to 20 seconds from a cold state. Their thermal efficiency typically ranges from 30% to 40%, with newer and larger models achieving the higher end of this spectrum. Their ability to operate independently of the grid makes diesel generators essential in remote areas and during power outages. In 2024, over 74% of backup generators deployed in data centers were diesel-powered [1], underscoring their critical role in mission-essential applications.[2]

1 Deployment Schedule

Deploying diesel gensets for large systems includes several unique steps including the development, preconstruction, construction, commissioning and turnover to operations. Of this, permitting, and especially air permits, are the most challenging for diesel generators.  Smaller diesel genset systems that run purely for back-up power and restrict operation to less than a hundred hours per year can move along quickly.  Large diesel generator plants that will run more continuously with potential grid-connect functions can takes 3 to 6 years to come on-line from concept to operation.

Permitting and Regulatory Approvals

In the preconstruction phase of deploying diesel generators for large power systems, permitting is a critical step. This includes securing environmental permits, interconnection agreements (if the system will be grid-connected), and construction permits.

Because of liquid storage and handling of large quantities of fuel and oils, water and air permits require special attention for diesel generators. A Stormwater Pollution Prevention Plan takes 1-3 weeks to organize depending on site complexity.  A Notice of Intent (NOI) with the EPA and state is required at least 14 days before earth disturbing activities. [3] Some jurisdictions such as states with impaired waters or tidal issues, will require additional review. After completing the earthwork a Notice of Termination (NoT) must be submitted and can take up to 4 weeks to complete. Total time for water permits can take 2-4 months.[4][5]

Prevention of Significant Deterioration (PSD) and New Source Review (NSR) permits are federal air permitting programs required under the Clean Air Act for large or new sources of air pollution. PSD permits apply in areas that meet NAAQS (attainment areas) and require facilities to install Best Available Control Technology (BACT), conduct detailed air quality modeling, and complete a public review process. [6] NSR permits apply in nonattainment areas and typically mandate the most stringent emissions controls, known as Lowest Achievable Emission Rate (LAER), along with securing emissions offsets to prevent any net increase in pollution. [7] Large-scale diesel generator projects that exceed regulated emissions thresholds may trigger one or both of these permitting pathways depending on the project’s location and expected emissions. Acquiring a PSD or NSR permit generally takes 12 to 18 months, with the process often extending beyond a year if public concerns arise or additional environmental analysis is required. [8] These lengthy timelines must be factored into project development schedules to avoid delays in construction or operation.

There are also permits at the state level, for example, Texas implements additional air quality regulations through the Texas Commission on Environmental Quality (TCEQ). The TCEQ oversees diesel generator permitting through three primary pathways: Permit by Rule (PBR), Standard Permit, and New Source Review (NSR). Under 30 TAC §106.511, PBRs are available for portable, standby, and emergency-use generators that meet emission and usage limits. [9][10] For stationary, continuous-use generators, §106.512 allows permitting via rule provided the system complies with pollutant thresholds, uses ultra-low sulfur diesel (ULSD), and maintains detailed operational records.[11] Systems that exceed these thresholds must obtain a Standard Permit, which involves emissions calculations and registration with TCEQ.[11] If the generator still cannot meet the Standard Permit conditions, a full New Source Review (NSR) permit is required, entailing a detailed emissions and technology evaluation. [12]

Title V Operating Permits, established under the Clean Air Act and administered by the U.S. Environmental Protection Agency (EPA) or delegated state and local agencies, consolidate all applicable federal and state air quality requirements into a single, legally enforceable document for major emission sources. These permits are required for facilities with potential emissions of 100 tons per year or more of any criteria pollutant, or 100,000 tons per year of CO₂-equivalent greenhouse gases; if the location is in an air-quality non-attainment area the numbers are lower as shown in Table 4.1. A county receives an EPA non-attainment designation when its ambient air quality monitoring data show that the concentrations of one or more criteria pollutants exceed the federally mandated National Ambient Air Quality Standards (NAAQS). The permitting process typically takes 9 to 14 months from the time of application and includes public notice, comment periods, and EPA review. For large diesel generator projects, a Title V permit ensures compliance through mandatory monitoring, recordkeeping, and annual certification by a responsible official. [13]

In Texas you must notify TCEQ at least 30 days before constructing or modifying fuel tanks regardless of above ground or below ground.[14] Nationwide, permitting and approvals will take between 2-6 weeks depending on jurisdiction, site sensitivity, and engineering requirements.

If fuel storage or delivery could affect environmentally sensitive areas—like streams, wetlands, or aquifer recharge zones—site assessments may be required. For instance, TCEQ mandates compliance with aquifer protection rules when operating above ground storage tanks near the Edwards Aquifer, including secondary containment and reporting under the state’s jurisdiction.[14] These studies, along with agency coordination, typically take 4–12 weeks for standard sites, but timelines can extend to several months depending on ecological complexities. [15]

Negotiating a fuel supply contract (covering delivery frequency, pricing structures, liability, and logistics) generally takes 2–4 weeks once stakeholders align. When multiple suppliers or storage facilities are involved contract resolution can stretch longer, particularly under custom service terms or high security requirements.

Building out fueling infrastructure, such as installing tanks, piping, pumps, containment systems, and completing pressure and acceptance testing generally takes 4–8 weeks, based on construction standards. Linking fuel delivery controls to the generator management system, verifying operational logic, and passing final acceptance testing can add another 2–4 weeks, depending on vendor schedules and utility coordination. If tied to electrical interconnection, an interconnection agreement and final testing can extend this phase by 6–12 weeks, particularly for large-scale, grid-tied systems. [16]

Diesel storage and generator installations require Fire Marshal approval in most jurisdictions. Applicants must submit detailed plans, covering fire access lanes, hydrants (often within 200 ft of units), and secondary containment, prior to issuance. Reviews for these can take up to 30 days though large or complex sites might take longer.

Transporting oversized generators or mobile gensets may require Oversize/Overweight (OS/OW) permits if loads exceed legal dimensions or weights. Approval often takes 1 to 2 weeks, plus coordination with local transport authorities. Existing infrastructure along the route must be evaluated to ensure it can accommodate large or wide loads, and any necessary upgrades to roads or bridges can significantly increase project lead times and costs.

Procurement

The global diesel generator market is dominated by a few key manufacturers that offer a wide range of products designed to meet the varying needs of different industries. As of 2025, some of the leading companies in this space in the USA include:[17]

• Cummins Inc. – Columbus, IN
• Caterpillar Inc. – Irving, TX
• Kohler Co. – Kohler, WI
• Generac Holdings Inc. – Waukesha, WI
• Mitsubishi Heavy Industries – Chiyoda City, Tokyo, Japan

These companies are not only manufacturing diesel generators but also provide maintenance services and other operational solutions, ensuring their customers have reliable systems in place. The global market for diesel generators is expanding, driven by growing energy demands, particularly in regions where the power grid is unreliable or unavailable.[2]

Diesel generators are produced by several major manufacturers globally, which operate large production facilities primarily in the U.S. and Europe. These facilities are responsible for meeting both domestic and international demand. The manufacturing lead time for large diesel generators typically ranges from 8 to 28 weeks, depending on the size and customization of the unit. More specialized or high-demand models, such as those required for infrastructure projects or during surges in demand (e.g., due to climate events), may have lead times that extend up to 36 weeks.[18] These lead times fluctuate based on market conditions, supply chain bottlenecks, raw material availability, and production capacity constraints.

Construction to Start-Up

For large -scale deployments, such as those exceeding 100 MW, the construction phase involves substantial site preparation, including grading, foundation pouring for multiple generator units, and the installation of large-scale electrical infrastructure (e.g., switchgear, transformers, and distribution panels). It also includes placement of extensive fuel storage systems, often requiring dedicated spill containment and fire protection. Generators are installed, mechanically and electrically integrated, and tested to meet performance and emissions standards. For projects of this scale, construction typically spans 12 to 24 weeks, depending on site complexity, permitting delays, and coordination with utility interconnection. In noise-sensitive areas, additional mitigation steps such as acoustic barriers or enclosures may be required.

The commissioning and start-up phase is a critical final step before system turnover and involves a series of mechanical and electrical inspections, calibration, and performance testing. According to industry guidance, this process typically includes no-load testing, partial-load and full-load load bank testing, safety trip verifications, control logic validation, and synchronization checks with utility or backup systems. For large-scale diesel generator systems, completion of this phase usually takes 2 to 6 weeks, depending on system complexity, the number of gensets, and the extent of regulatory, utility, or emissions testing. Documentation such as commissioning plans, system readiness reports, and operator training must be finalized during this period. [19]

2 Operational Capabilities

Diesel generators rated for high power outputs (e.g., 10’s of MW and above) can be used in settings such as manufacturing plants or data centers, where a stable and substantial power supply is critical. These generators can be networked to provide Gigawatt size power across large areas or facilities, ensuring that even if one unit fails, others can take over the load. Many diesel generators can be configured in parallel with individual units typically ranging from 1 MW to 3 MW. This setup allows operators to scale total capacity up to 100 MW or more by adding units as needed—without requiring a full redesign of the power system. This approach is especially effective for large facilities that require flexible, high-capacity backup or primary power solutions. [20]

Dispatchability and Flexibility

Diesel generators are highly dispatchable. Many different options in the market can accept a full load in under 60 seconds making them ideal in backup roles or to help with black start operations. [21]. Their reliability and speed of response make them valuable assets in microgrids, islanded systems, and critical infrastructure, where maintaining grid stability or backup capability is essential. Additionally, diesel gensets can be controlled remotely, automated through load-sensing systems, and integrated with supervisory control systems for efficient dispatch within larger energy systems. Historically diesel generators have been used for energy peaking roles on the grid; however, they are now considered last choice efforts due to the cost of fuel and their high air emissions. Petroleum-fueled plants account for 3% of US electric generating capacity and produce less than 1% of US electricity generation. [22]

Diesel generators are well known for their operational flexibility. Manufacturers offer a wide range of unit sizes capable of reliably handling loads from 30% to 100% of rated capacity, though optimal performance is typically achieved between 70% and 100% of the generator’s continuous rating. [23] Operating below this range for extended periods can lead to issues such as wet stacking or carbon buildup. [24]

Ramp Rates

Diesel generators can typically start within 10–20 seconds from a cold start, making them highly suitable for emergency and backup power applications. They can ramp power output up or down quickly to match changing demand and perform reliably in varied environmental conditions due to their compression ignition system.

NFPA 110 standards, which are commonly required for hospitals, data centers, and life-safety systems in the U.S., specify that emergency backup units must start within 10 seconds and reach full load within 60 seconds: equivalent to a ramp rate of 1.67% of full load per second. [21] Another standard, ISO 8528-5 Class G3, which is often used for generators in international or industrial applications, requires that generators are capable of accepting large load step changes and stabilize within 3 seconds: indicating a potential ramp rate of over 30% per second under critical conditions. [25]

Grid Stability and Power Quality

The inertia of diesel generators provide stability to power systems by resisting sudden speed changes during disturbances. This inertial capability is measured by the inertia constant (H), the ratio of stored kinetic energy to generator MVA rating. For typical high-speed industrial diesel gensets, H ranges from 0.5 to 0.6 seconds. [26] However, in larger grid-connected reciprocating engines, H can range from 1.1 to 2.1 seconds, depending on rotor mass and design. [27]

Diesel generator systems can both contribute to and help mitigate power quality issues, depending on their configuration and the nature of the connected loads. On the downside, diesel gensets may struggle with voltage and frequency stability, especially under rapidly changing or non-linear loads, leading to fluctuations that affect sensitive equipment. However, with proper control systems and integration of automatic voltage regulators (AVRs) and power factor correction equipment, diesel gensets can actively support grid stability and improve power quality. Some advanced gensets are also equipped with harmonic filtering systems or can be paired with external filters to reduce waveform distortion. A properly designed diesel generator system can contribute to improved power quality management.

Synchronization and Control

Synchronization and control systems are essential for safely connecting diesel generators to the grid or other generators. Before connecting a generator to the grid, the generator goes through the synchronization process where the generator’s voltage, frequency, and phase angle must match those of the grid to prevent large inrush currents or system instability. This is typically managed by an automatic synchronization controller, which adjusts engine speed and excitation to align frequency and voltage. Once synchronized, governors and automatic voltage regulators (AVRs) maintain stable operation by responding to load changes and keeping frequency and voltage within tight tolerances.

Typically, a master controller has a lead generator assigned to fix the frequency (isochronous operation) and the other units follow, or match, that frequency.  An algorithm in the master control dispatches power sharing between the gensets to match the load demand on the slow time scale (minutes), and for sub-second fast dynamic response units are in a droop control mode that ramps up their power output if the frequency slows down due to a sudden increase in load, or ramps down their power output if the frequency speeds up due to a decrease in load demand.  These control systems are critical for ensuring reliable power delivery, load sharing, and maintaining overall power quality in multi-generator or grid-parallel setups.

In multi-unit generator systems, a master controller is essential for coordinating power output and ensuring stable operation. This is typically achieved by designating one unit as the lead generator to operate in isochronous mode, meaning it actively adjusts its power output to precisely fix the system frequency. All other units then follow and synchronize with this established frequency. The master controller employs an algorithm that sends setpoints, or dispatches, for power setting to all of the generators that share in supplying the overall load demand.  The set points are refreshed every few seconds or minutes. For fast dynamic response (sub-second), the generator units rely on droop control. This mode allows each generator to independently adjust its power output automatically to ramp up or down power output based on sudden changes in the load.

Parasitic Loads and Degradation

Parasitic losses are minimal, typically ranging from 2% to 4% of rated output, allowing most of the generated power to be delivered to the load.[28] Diesel generator degradation is gradual and largely dependent on maintenance quality, operating conditions, and load usage. A well-maintained generator running efficiently, particularly one that avoids issues like wet stacking, can reach up to 40,000 operating hours before requiring a major overhaul, which translates to roughly four years of continuous use. However, this figure is highly influenced by the quality of fluids used, adherence to preventive maintenance schedules, and the surrounding environment. Standby or emergency-use generators, which operate only intermittently, may go over a decade before requiring a rebuild, provided they are routinely exercised and properly cared for.[29]

3 Service Reliability

Availability and Failures

The long history of diesel generators makes them reliable. Diesel generators with regular maintenance have an mean time between failure (MTBF) ranging from 800 to 2,400 hours, indicating reliable operation for extended periods.[30] Diesel generators operating in continuous service typically require about one week (168 hours) of annual maintenance, resulting in a per-unit availability of approximately 98.08%. Standby units, needing only around 72 hours of maintenance per year, have a higher availability of about 99.18%. However, even small amounts of downtime can compromise system reliability when scaled across many units. Thus, redundancy strategies, such as N+1 or N+2, are therefore critical. By adding extra generators, the system can maintain full load coverage during maintenance or equipment failure. This boosts overall system availability to effectively 100%, ensuring uninterrupted power delivery in critical applications.

Well-maintained diesel generators have a failure-to-start rate (FTS) of around 1%. Poorly maintained systems can have an FTS of over 5%, which emphasizes the need for regular maintenance and testing.[29] Diesel generators require a strict maintenance schedule to ensure peak performance. Weekly, the generator should be run under no load to verify control functions. Monthly checks include inspecting battery voltage and electrical connections, while an annual load bank test is crucial to confirm the generator’s ability to handle its rated capacity.[31]

For diesel gensets operating in a continuous power supply configuration—such as a 100 MW data center powered by 50 × 2 MW units—the Mean Time Between Failures (MTBF) typically ranges from 6,000 to 15,000 hours per unit, depending on manufacturer quality, environmental conditions, and maintenance practices. Premium Tier 4-compliant gensets from manufacturers like Caterpillar, Cummins, or MTU can reach MTBF values exceeding 15,000 to 20,000 hours under optimal conditions. In a fleet of 50 units, an average MTBF of 10,000 hours would imply a statistical expectation of one genset failure every 200 operating hours. Over the course of a year, this results in approximately 43 individual genset failures, though redundancy and N+1 or N+2 configurations typically prevent these events from causing full system outages. Continuous operation places greater wear on gensets compared to standby use, so ensuring proper load balancing, routine servicing, and environmental controls is critical to maximizing system reliability.

Redundant & Resilient Architecture

Diesel generators require a reliable fuel management system to operate efficiently, especially during prolonged outages. Fuel autonomy expectations vary depending on facility type and mission criticality. For example, the National Institutes of Health recommends 24 to 48 hours of on-site fuel capacity for medical and research facilities.[32] In contrast, NEC 708 mandates a minimum of 72 hours for Critical Operations Power Systems (COPS), such as emergency response and public safety infrastructure. While commercial data centers like those operated by Microsoft or OpenAI are not bound by NEC 708, they often design for 72 hours or more of backup power to meet uptime certifications and service-level commitments.[33] For a diesel generator, fuel consumption typically ranges from 65 to 80 gallons (250 to 300 liters) per MWh, depending on generator efficiency, load factor, and system design.

External Risks

Diesel generator systems face several operational risks that extend beyond emissions. Severe weather events such as hurricanes, floods, and wildfires can physically damage equipment, block access to fuel supplies, or disrupt local distribution networks. Cold snaps may cause diesel fuel to gel, preventing startup, while extreme heat can overburden cooling systems. These generators also rely heavily on supporting infrastructure, including passable roads for fuel delivery, operational telecommunications, and functional grid interconnection points for synchronization. Any of these systems can fail during an emergency.

Fuel market volatility poses another major risk. During crises, diesel prices can spike, or supply may be disrupted entirely, limiting generator runtime. In some cases, regional supply chain failures or emergency regulations can delay refueling, even if the generator itself remains operational. These risks highlight the importance of on-site fuel storage, robust logistical planning, and diversified sourcing strategies to ensure reliable performance during critical periods.

4 Environmental Sustainability

While diesel generators are valued for their reliability and quick response, they raise concerns regarding environmental impact. Diesel combustion emits greenhouse gases (GHGs) such as CO₂, as well as pollutants like nitrogen oxides (NOₓ), particulate matter (PM), and volatile organic compounds (VOCs). Advances in engine technology and emissions controls, such as Tier 4 Final standards and diesel particulate filters (DPFs), have significantly reduced these impacts in newer models.

Emissions & Air Quality Impacts

Compared to other technologies, Diesel generators emit higher air pollutants including NO_x, Particulate Matter (PM), CO, and CO₂, which contribute to smog, respiratory illness, and climate change.

Diesel generators must comply with various emissions standards set by the Environmental Protection Agency (EPA) to minimize their environmental impact. These regulations are particularly important for non-road diesel engines used in stationary power generation. The EPA Tier System classifies diesel engines based on their emissions performance, with progressively stricter limits, particularly for nitrogen oxides (NOx) and particulate matter (PM). Below is a summary of the emission limits for diesel engines rated 75 kW and above, as well as guidelines on when each tier applies, based on the type of operation (continuous vs. emergency/backup). In the United States, only Tier 4 Final engines are compliant for new installations operating in continuous or prime power roles, as they meet the most current EPA emissions standards. Older Tier 2 and Tier 3 engines may still operate under grandfathered or emergency-use conditions but are not permitted for new continuous-duty applications.

• Tier 2 requires engines to emit no more than 6.6 g/kWh of NOx, 0.30 g/kWh of PM, and 5.0 g/kWh of CO, with a maximum smoke level of 15%. These engines were previously used for continuous operation and prime power applications but are now typically found in legacy systems operating under grandfathered permits. [34]
• Tier 3 engines have a reduced NOx emission limit of 4.0 g/kWh, while maintaining the same PM and CO levels as Tier 2. Though once used for continuous and industrial applications, Tier 3 engines are now primarily limited to emergency or backup-only use due to updated federal and state emissions regulations. [34]
• Tier 4 engines further reduce PM emissions to 0.02 g/kWh, with NOx remaining at 4.0 g/kWh. These engines are required in areas where stringent emissions limits are enforced and are typically mandated for any generator operating more than 1,000 hours per year. [34]
• Tier 4 Final represents the most stringent emissions standard currently in force, with NOx reduced to 0.19 g/kWh, PM emissions at 0.02 g/kWh, and CO at 3.5 g/kWh. These generators are required for new continuous-use installations and are commonly deployed in urban environments, data centers, and industrial sites where environmental compliance is critical. [34]

While sulfur oxides (SOₓ) are not directly capped under the EPA Tier 1–4 emissions standards for diesel generators, they are effectively controlled through federal fuel regulations requiring the use of Ultra-Low Sulfur Diesel (ULSD) with sulfur content limited to 15 ppm. This fuel requirement, enforced under 40 CFR §80.510, is critical for both emission compliance and the functionality of advanced Tier 4 emission control systems. As a result, SO₂ emissions from Tier 4 diesel gensets are typically limited to approximately 0.2 to 0.25 kg per megawatt-hour (kg/MWh), depending on generator efficiency and fuel quality. [35]

In addition to the EPA’s Tier standards, diesel generators must also comply with other national regulators as well as local and regional emissions regulations. National Emission Standards for Hazardous Air Pollutants (NESHAP) require the use of Ultra-Low Sulfur Diesel (ULSD) and regular maintenance to ensure compliance, particularly for hazardous pollutants like formaldehyde and particulate matter. [7][36] And at the state level specific fuel requirements apply, for example, under the Texas Low Emission Diesel (TxLED) program, which limits aromatic hydrocarbons in diesel fuel to no more than 10% by volume and sets a minimum cetane number of 48. These regulations are designed to reduce emissions in high-density urban areas, particularly for non-emergency and continuous-use diesel engines.[37]

Diesel engines used in continuous operation must meet the most stringent standards, particularly Tier 4, due to their extended operational hours and base-load power generation. For emergency and backup operations, less stringent standards (Tier 2 or Tier 3) may apply, as these systems are typically used for less than 100 hours per year. However, local regulations may require even backup generators to meet Tier 4 standards, especially in areas with stricter air quality rules. For instance, the California Air Resources Board (CARB) mandates that new non-emergency diesel engines, including generators, meet Tier 4 Final emission standards, and certain air districts may impose additional requirements even for emergency units. [38] Similarly, in Texas, regions designated as ozone nonattainment areas, such as Bexar County, have implemented rules that limit NOₓ emissions from major sources, potentially affecting the operation of backup generators.[39] In Virginia, the Department of Environmental Quality (DEQ) has proposed regulations that would allow Tier II and Tier IV generators to operate during specific grid emergencies, indicating a move towards stricter controls on generator emissions. [40]

To meet emissions requirements, diesel generators must adopt technologies like Selective Catalytic Reduction (SCR) and Diesel Particulate Filters (DPF). These emissions control technologies enable compliance with U.S. EPA Tier 4 Final standards by reducing nitrogen oxides (NOₓ) and particulate matter (PM) emissions by approximately 80–90% compared to older, uncontrolled diesel engines. These reductions allow modern systems to operate continuously in applications with strict air quality requirements while maintaining high performance and reliability. [41]

Through the use of Biodiesel (B100) or Hydrotreated Vegetable Oil (HVO) CO₂ and PM emissions from diesel generators can be greatly reduced by as much as 50% compared to standard petroleum diesel depending on blend ratios and feedstock choices.[42][43] However, using these fuels introduces cost variability tied to agricultural commodity markets and feedstock supply fluctuations.

Water Use and Thermal Discharge

While diesel generators are not as water-intensive as traditional thermoelectric plants, they still require water for cooling, particularly in liquid-cooled systems. Though modest in comparison to large-scale generation technologies, this water use must be carefully managed in regions facing scarcity.

End-of-Life and Recyclability

At the end of a diesel generator’s operational life, it enters the decommissioning phase, which includes safe shutdown, removal of fuel and hazardous materials, and dismantling. Many diesel generators can be remanufactured or refurbished, extending their service life and reducing the need for new material inputs. Components such as engines, alternators, and control systems are commonly rebuilt and resold in the secondary market. Generators are primarily composed of recyclable metals like steel, copper, and aluminum, as well as plastics and electronics. According to industry estimates, up to 85–90% of a generator’s mass can be recycled or reused, depending on condition and design. Proper end-of-life handling ensures environmental compliance while supporting circular economy goals through material recovery and equipment repurposing. [44]

Hazardous Materials and Waste Management

Diesel generators involve several hazardous materials that require careful handling, storage, and disposal to ensure environmental and personnel safety. Key materials include diesel fuel, lubricating oils, coolants (often glycol-based), and lead-acid or lithium-ion batteries all of which can pose significant risks if leaked or improperly managed. During operation and maintenance, diesel systems also generate regulated waste, such as used oil, oil and fuel filters, oily rags, and fuel residues. These byproducts are classified as hazardous or special waste under the Resource Conservation and Recovery Act (RCRA) and applicable state regulations.

Proper waste management practices include secondary containment systems for fuel and oil storage, spill prevention and countermeasure (SPCC) plans, and clearly labeled, sealed containers for collecting and segregating waste streams. Batteries must be stored and recycled according to Universal Waste Rules, and coolant disposal must meet local wastewater or hazardous waste standards. Facilities operating diesel generators must maintain waste manifests, comply with generator status requirements (e.g., large vs. small quantity generator), and often conduct employee training on hazardous materials handling. Robust waste management programs not only ensure regulatory compliance but also reduce the risk of environmental contamination, liability, and cleanup costs.

5 Site Feasibility

Proximity to Energy Resources & Infrastructure

Diesel generators can be located anywhere a large load would be located, and diesel fuel is distributed to just about anywhere in the US. This is another strong advantage for diesel generator systems.

Land Use & Power Density

Based on industry guidance, the following factors should be considered when estimating land use for large diesel generator systems:

• Generator Footprint and Clearance: Each large diesel generator, typically rated between 1 MW and 3 MW, takes up a footprint of roughly 250 to 300 square feet. For example, a 1 MW unit may measure around 21.5 feet by 11.5 feet and weigh over 40,000 pounds when fueled. To allow for maintenance access and proper weight support, the concrete pad should be sized at approximately 1.5 times the generator’s footprint, with at least 3 feet of clearance on all sides. [45]
• Fuel Storage: Large-scale diesel installations require multiple above-ground tanks, typically 25,000 to 50,000 gallons each, to support a 100 MW system’s high fuel demand. These tanks are typically placed on concrete pads with spill containment and spaced for truck access, safety, and maintenance. A single 50,000-gallon tank with containment and setbacks can require up to 1,200–1,500 square feet. For multiple tanks, a fuel storage area may occupy 0.5 to 1 acre, depending on layout, regulatory clearances, and local fire codes.
• Substation: A 100 MW diesel generator system requires dedicated space for medium-voltage switchgear, transformers, and protective controls. Based on Eaton’s design specifications and NFPA 70/NEC clearance requirements, a consolidated electrical building housing multiple switchgear lineups, busbars, and safety clearances would typically require between 3000 and 5000 ft² of space. This includes room for equipment aisles (minimum 3 to 5 ft clearances), dual egress for systems over 1,200 amps, and access for cable routing and ventilation. Final layout will depend on system redundancy and voltage class (e.g., 15–38 kV). [46] [47]

Taking all components into account—generator footprints and pads, fuel storage tanks with containment, electrical infrastructure, and necessary clearances for vehicle access, maintenance, and fire code compliance—each 100 MW of diesel generator installation would typically require 6 to 10 acres.  This translates to a power land density of 10 to 17 MW per acre. The exact land requirement will vary based on site layout, equipment spacing, regulatory setbacks, and whether structures are enclosed or open-air. This estimate includes allowances for refueling trucks, service access lanes, and emergency egress.

Aesthetics & Acoustic Considerations

While less intrusive than other generator technologies, large diesel generators and their enclosures can still be visually intrusive, particularly in residential or scenic areas. Strategic design choices, such as landscaping, low-profile siting, color matching, or placing units behind existing structure, can help mitigate visual impact and reduce community complaints.

Noise pollution is a significant community impact of diesel generators. Depending on the size and design, diesel generators can produce noise levels between 70 dB (similar to city traffic) and 120dB (comparable to a jet engine).[48] This can be disruptive, particularly in residential or urban areas, where noise restrictions are stricter. To mitigate this, soundproof enclosures or acoustic barriers are often used, but even then, noise remains a concern, especially for large-scale generators running for extended periods. [49]

Public Perception & Perceived Harm

Communities may be concerned that diesel exhaust contains fine particulate matter, nitrogen oxides, and known carcinogens. The International Agency for Research on Cancer classifies diesel exhaust as carcinogenic, linking long term exposure to lung cancer as well as respiratory and cardiovascular diseases. [50]

6 Evolving Policy

Policy Volatility

Emissions regulations for diesel generators in the United States have seen significant fluctuation in recent years, reflecting broader shifts in environmental policy. While the EPA introduced stricter standards in 2024 aimed at reducing smog and particulate emissions diesel engines, and the Diesel Emissions Reduction Act of 2025 was introduced in Congress to reauthorize funding for emissions-reducing technologies and programs through 2029 [51], a major deregulation initiative in early 2025 signaled a reversal of some of these efforts. This included reconsideration of greenhouse gas rules and a broader push to reduce regulatory burdens on diesel-powered equipment. These conflicting actions—tightening standards on one hand and rolling back enforcement on the other—have created uncertainty for manufacturers and operators of diesel generators, complicating compliance and long-term planning

Incentives

Diesel Generators don’t generally qualify for clean-energy incentives; however, alternative fuel mandates, such as the Diesel Emissions Reduction Act, can supply grants or funding for update emission control systems or lower emission units.

Other Policy Risks

Several agencies can halt or delay diesel generator projects including: EPA and State Air Agencies – emission limits, reporting changes, State Environmental Bodies (such as TCEQ) – Fuel usage restrictions or permitting changes, and Local Utility or Public Utility Commissions – certificate of need, interconnection reviews, or other policy shifts

There are other factors posing risks to diesel generator projects. Tariffs can change quickly causing some market stability as manufacturers will outsource parts to 3^rd party companies, often overseas. Local Jurisdictions could change diesel content; for example, in Minnesota all diesel fuel sold in the state has some amount of biodiesel content. In the summer it can be as high as 20% and in the winter, levels drop down to 5%, which can complicate fuel supply contracts and make pricing volatile. [52] Emerging climate regulations may impose stricter emissions regulations specifically on NO_x and PM emissions. International policy effects diesel supply and production, which can drive diesel fuel prices in either direction based.

7 Cost of Capacity & Energy

While diesel generators offer flexibility and rapid deployment, their operational costs can be significantly higher than grid power or alternative generation sources due to the cost of fuel.

Capital and Operating Expenditures

The major components of capital expenditure (CAPEX) for diesel gensets include the generator equipment, diesel fuel storage, and the electrical network. The size of fuel storage (often expressed in hours of operation at full power) is one variable designed to target a reliability target. Exhaust clean-up is another design variable that depends on the use case and local environmental regulation.

Based on industry benchmarks, installing a turn key diesel generator system at large scale costs between $650,000/MW (low case) and $1,035,000/MW (high case) in 2025 dollars, not including the fuel storage.[53] The installed cost of above ground diesel storage tank ranges $2 to $3 per stored gallon.[54] If the system includes a storage capacity for 72 hours of on-site fuel, compliant with NEC 708 requirements, there will be about 6000 gallons (22,700 liters) of fuel storage per MW of generator power, which adds $15,000/MW to the capital cost.

Operations and maintenance (O&M) expenditures include a combination of fixed and variable components. Fixed OPEX is around $13,000 per megawatt per year, while variable OPEX ranged from $13.12 to $19.68 per megawatt-hour not including fuel.[55] Scheduled maintenance requires 168 hours of downtime per generator annually, with no impact on system output due to the inclusion of N+2 redundancy in the plant design. For example, a 100 MW rated system would include a 105 MW capacity running 76% capacity factor, or 700,800 MWh of annual output, and result in total annual O&M costs ranging from approximately $10.6 million to $15.2 million.

Variable costs include fuel and diesel exhaust fluid (DEF), lubricating oils, filters, and associated labor maintenance. Consumption rates of fuel based on manufacturer specifications at full load are about 70.0 gallon/MWh of diesel and 3.56 L/MWh liters of diesel exhaust fluid (DEF) per hour.[56] For calculating the base LCOE in this report, delivered diesel was priced at $2.61 per gallon, accounting for both the rack rate and a $0.06/gallon delivery premium.[57][60] DEF was modeled at $4.00 per gallon, inclusive of delivery costs.[58] Aggregated across the fleet, annual fuel and DEF expenditures were estimated at approximately $127 million and $10.2 million, respectively. Diesel prices have historically trended upward and remain influenced by global factors as shown in Figure 4.2.[59] Regional differences also play a role, with higher prices commonly seen along the Pacific Coast, particularly in California and Washington, and lower prices typically found along the Gulf Coast, such as in Texas and Louisiana.[60]

Levelized Cost of Capacity and Levelized Cost of Energy

Based on the above information for capital and fixed operating expenditures, Levelized Cost of Capacity (LCOC) for a diesel generator power systems in the hundreds of MW size ranged from $79,200 per MW per year to $151,600 per MW per year. Diesel generators offer the lowest LCOC, making them an ideal choice for standby and backup power applications.

The Levelized Cost of Energy (LCOE) based on the above costs ranged from $143 to $409 per megawatt-hour, representing the full lifecycle cost of diesel generation under continuous operation. Due to the relatively low CAPEX, the LCOE does not depend so much on utilization, only changing LCOE by 20% between a Capacity Factor of 20% and 80%. Fuel cost is the biggest driver of LCOE, which changes in fuel cost with a doubling of the fuel cost resulting in a 75% increase in LCOE as shown in Figure 4.3 and Figure 4.4 with data from Table 4.1. The high LCOE cost relative to other generators discourages the use of diesel generators as the primary electric power source.

References

[1] Precedence Research, “Data Center Generator Market Size, Share, Growth 2024 to 2033,” Precedence Research, May 2024. [Online]. Available: https://www.precedenceresearch.com/data-center-generator-market. [Accessed 3 June 2025].

[2] Mordor Intelligence, “Data Center Generator Market Size & Share Analysis Growth Trends & Forecasts (2025-2030),” Mordor Intelligence, 2025. [Online]. Available: https://www.mordorintelligence.com/industry-reports/data-center-generator-market. [Accessed 15 May 2025].

[3] U.S. Environmental Protection Agency, “Construction General Permit (CGP) Frequent Questions,” U.S. Environmental Protection Agency, [Online]. Available: https://www.epa.gov/npdes/construction-general-permit-cgp-frequent-questions#aboutpermitting. [Accessed 11 June 2025].

[4] Texas Commission on Environmental Quality, “5+ Steps to Obtain Coverage Under the Construction General Permit (TXR150000),” Texas Commission on Environmental Quality, [Online]. Available: https://www.tceq.texas.gov/permitting/stormwater/construction/TXR15_5_plus_steps.html. [Accessed 11 June 2025].

[5] U.S. Environmental Protection Agency, “Submitting a Notice of Intent (NOI), Notice of Termination (NOT), or Low Erosivity Waiver (LEW) under the Construction General Permit,” U.S. Environmental Protection Agency, 8 April 2025. [Online]. Available: https://www.epa.gov/npdes/submitting-notice-intent-noi-notice-termination-not-or-low-erosivity-waiver-lew-under. [Accessed 12 June 2025].

[6] B. Stelzer, “EPA Requirements for Large Scale Diesel Emergency Standby Engines used In Data Centers, Hospitals, Water Treatment, Life Safety Applications,” safetypower.ca, November 2013. [Online]. Available: https://www.safetypower.ca/static/img/pdf/epa-requirements-for-emergency-engines.pdf. [Accessed 27 June 2025].

[7] U.S. Environmental Protection Agency, National Emission Standards for Hazardous Air Pollutants: Reciprocating Internal Combustion Engines and New Source Performance Standards: Internal Combustion Engines; Electronic Reporting, 169 ed., vol. 89, Washington D.C.: U.S. Environmental Protection Agency, 2024, p. 70505–70525.

[8] U.S. Environmental Protection Agency, “Timely Processing of Prevention of Significant Deterioration (PSD) Permits,” U.S. Environmental Protection Agency, July 2015. [Online]. Available: https://www.epa.gov/sites/default/files/2015-07/documents/timely.pdf. [Accessed 12 June 2025].

[9] Texas Commission on Environmental Quality, Title 30 Texas Administrative Code §106.4 – Requirements for Permitting by Rule, Austin: Texas Commission on Environmental Quality, 2023.

[10] Texas Commission on Environmental Quality, Title 30 Texas Administrative Code §106.511 – Portable and Emergency Engines and Turbines, Austin: Texas Commission on Environmental Quality, 2023.

[11] Texas Commission on Environmental Quality, Title 30 Texas Administrative Code §106.512 – Stationary Engines and Turbines, Austin: Texas Commission on Environmental Quality, 2023.

[12] Texas Commission on Environmental Quality, “NSR Permit Application Guidance for Combustion Sources,” Texas Commission on Environmental Quality, 2023. [Online]. Available: https://www.tceq.texas.gov/permitting/air/guidance/newsourcereview/rap/rap-eng.

[13] U.S. Environmental Protection Agency, “1990 Clean Air Act Amendments Summary: Title V – Operating Permits,” U.S. Environmental Protection Agency, November 2024. [Online]. Available: https://www.epa.gov/clean-air-act-overview/1990-clean-air-act-amendment-summary-title-v. [Accessed 12 June 2025].

[14] Texas Commission on Environmental Quality, “Petroleum Storage Tanks Registrations: Am I Regulated?,” Texas Commission on Environmental Quality, [Online]. Available: https://www.tceq.texas.gov/permitting/registration/pst/Am_I_Regulated.html. [Accessed 11 June 2025].

[15] Texas Commission on Environmental Quality, “Edwards Aquifer: Application and Review Process,” Texas Commission on Environmental Quality, 12 May 2025. [Online]. Available: https://www.tceq.texas.gov/permitting/eapp/review.html. [Accessed 11 June 2025].

[16] Phillips Tank and Structure, “Storage Tank Construction,” Phillips Tank and Structure, [Online]. Available: https://www.phillipstank.com/is/storage-tank-construction. [Accessed 11 June 2025].

[17] Prescient & Strategic Intelligence, “U.S. Diesel Genset Market,” Prescient & Strategic Intelligence , 2024.

[18] T. Park, “How to Avoid Ten Month Lead Times on Diesel Generators,” Global Power Supply, LLC, 11 March 2019. [Online]. Available: https://www.globalpwr.com/blog/avoid-ten-month-lead-times-diesel-generator-orders/. [Accessed 6 June 2025].

[19] CD & Power, “Timeline for Getting a New Stationary Generator Up and Running,” CD & Power, [Online]. Available: https://www.gotpower.com/new-stationary-generator/. [Accessed 11 June 2025].

[20] Generac Power Systems, Inc., “Modular Power System (MPS) Generator Brochure,” September 2016. [Online]. Available: https://gensetservices.com/wp-content/uploads/2016/09/0170220SBY-Generac-Modular-Power-System-Generator-Brochure-1.pdf. [Accessed 22 May 2025].

[21] National Electrical Code, “NFPA 110: Standard for Emergency and Standby Power Systems,” National Fire Protection Association, 1 January 2019. [Online]. Available: https://img.antpedia.com/standard/files/pdfs_ora/20200316/NFPA%20110-2019.pdf?v=2.0. [Accessed 20 June 2025].

[22] K. Dubin, “Oil-Fired Power Plants Provide Small Amounts of U.S. Electricity Capacity,” U.S. Energy Information Administration, 16 May 2017. [Online]. Available: https://www.eia.gov/todayinenergy/detail.php?id=31232. [Accessed 11 June 2025].

[23] Powerguard, “How to Run a Diesel Generator Efficiently,” Power Machine Systems Ltd, 2023. [Online]. Available: https://powerguard.co.uk/how-to-run-a-diesel-generator-efficiently/. [Accessed 4 August 2025].

[24] Issa M, Ibrahim H, Hosni H, Ilinca A, Rezkallah M. Effects of Low Charge and Environmental Conditions on Diesel Generators Operation. Eng. 2020; 1(2):137-152. https://doi.org/10.3390/eng1020009

[25] Cummins Power Generation, “ISO 8528 Genset Ratings and Transient Performance,” Cummins Inc., 2015. [Online]. Available: https://mart.cummins.com/imagelibrary/data/assetfiles/0058629.pdf. [Accessed 3 June 2025].

[26] Cummins Generator Technologies, “Understanding Alternator Inertia, AGN 183,” Cummins Inc, Columbus.

[27] Electric Reliability Council of Texas, “Inertia: Basic Concepts and Impacts on ERCOT,” Electric Reliability Council of Texas, Austin, 2018.

[28] A. Thiruvengadam, S. Pradhan, P. Thiruvengadam, M. Besch and D. Carder, “Heavy‑Duty Vehicle Diesel Engine Efficiency Evaluation and Energy Audit,” West Virginia University Center for Alternative Fuels, Engines and Emissions (CAFEE) and the International Council on Clean Transportation, Morgantown, 2014.

[29] Turnkey Industries LLC, “What Is the Life Expectancy of Industrial Generators?,” Turnkey Industries LLC, 8 July 2022. [Online]. Available: https://turnkey-industries.com/what-is-the-life-expectancy-of-industrial-generators. [Accessed 4 August 2025].

[30] J. Marqusee and A. Stringer, “Distributed Energy Resource (DER) Reliability for Backup Electric Power Systems,” National Renewable Energy Laboratory, Golden, CO, 2023.

[31] A. Mott, “Best Practices for Standby Generator Operations and Maintenance,” Pacific Northwest National Laboratory, July 2021. [Online]. Available: https://www.pnnl.gov/projects/om-best-practices/standby-generators. [Accessed 22 May 2025].

[32] National Institutes of Health, “Design Requirements Manual: Generator Fuel Supply,” National Institutes of Health, Bethesda, 2013.

[33] M. Anthony, R. Arno, P. Saba Saad, R. Schuerger and M. Beirne, “Critical Operations Power Systems,” Institute of Electrical and Electronics Engineers, Piscataway, 2013.

[34] U.S. Environmental Protection Agency, “Nonroad Compression-Ignition Engines: Exhaust Emission Standards, EPA-420-B-16-022,” U.S. Environmental Protection Agency, Washington D.C., 2016.

[35] U.S. Environmental Protection Agency, “Regulation of Fuels and Fuel Additives: 40 CFR §80.510 – Applicable Standards and Requirements for Diesel Fuel,” U.S. Environmental Protection Agency, Washington D.C., 2005.

[36] U.S. Environmental Protection Agency, “Fact Sheet: Final Air Toxics Standards for Stationary Reciprocating Internal Combustion Engines,” U.S. Environmental Protection Agency, 15 May 2025. [Online]. Available: https://www.epa.gov/stationary-engines/fact-sheet-final-air-toxics-standards-neshap. [Accessed 4 June 2025].

[37] Texas Commission on Environmental Quality, “Texas Low Emission Diesel (TxLED) Program,” Texas Commission on Environmental Quality, 2023. [Online]. Available: https://www.tceq.texas.gov/airquality/mobilesource/txled. [Accessed 4 June 2025].

[38] California Air Resources Board, “Airborne Toxic Control Measure for Stationary Compression Ignition Engines,” California Air Resources Board, December 2011. [Online]. Available: https://ww2.arb.ca.gov/sites/default/files/classic/diesel/documents/finalreg2011.pdf. [Accessed 3 June 2025].

[39] Texas Commission on Environmental Quality, “Chapter 117 – Control of Air Pollution from Nitrogen Compounds, Rule Project No. 2023-117-117-AI, 2024,” Texas Commission on Environmental Quality, Austin, 2024.

[40] S. Adams, T. Baynard and G. Riegle, “Virginia DEQ Revises Proposed Backup Generator Rule to Apply Only to Loudoun County,” McGuireWoods LLP, 9 March 2023. [Online]. Available: https://www.mcguirewoods.com/client-resources/alerts/2023/3/virginia-deq-revises-proposed-backup-generator-rule/. [Accessed 3 June 2025].

[41] U.S. Environmental Protection Agency, “Diesel Particulate Filter (DPF) General Information, EPA-420-F-10-029,” U.S. Environmental Protection Agency, March 2010. [Online]. Available: https://www.epa.gov/sites/default/files/2016-03/documents/420f10029.pdf. [Accessed 4 June 2025].

[42] M. Wang, “Life Cycle Analysis of Biofuels with the R&D GREET Model,” Argonne National Laboratory, 24 October 2024. [Online]. Available: https://www.ieabioenergy.com/wp-content/uploads/2024/12/PS14-2_Wang-ANL.pdf. [Accessed 11 June 2025].

[43] U.S. Department of Energy Alternative Fuels Data Center, “Diesel Vehicle Emissions,” U.S. Department of Energy, [Online]. Available: https://afdc.energy.gov/vehicles/diesels-emissions. [Accessed 11 June 2025].

[44] K. Benton, “A Life Cycle Assessment of a Diesel Generator Set,” Montana Tech of the University of Montana, Butte, 2016.

[45] Generator Source, “Site Planning for an Industrial Generator Installation,” Generator Source, [Online]. Available: https://generatorsource.com/generator-services/site_planning_for_generator_installation/. [Accessed 3 June 2025].

[46] Eaton, “VacClad-W 5–15 kV Metal-Clad Medium Voltage Switchgear Design Guide,” Eaton Corporation, 2021. [Online]. Available: https://www.eaton.com/content/dam/eaton/products/design-guides—consultant-audience/eaton-vacclad-w-5-15kv-metal-clad-medium-voltage-switchgear-design-guide-dg022001en.pdf. [Accessed 3 June 2025].

[47] D. Austin, “Electrical Room Basics,” National Fire Protection Association, 30 November 2022. [Online]. Available: https://www.nfpa.org/news-blogs-and-articles/blogs/2022/11/30/electrical-room-basics-part-1. [Accessed 3 June 2025].

[48] Our Generator World, “How Loud is a Diesel Generator?,” Our Generator World, 28 March 2025. [Online]. Available: https://www.ourgeneratorworld.com/archives/11198. [Accessed 2025 15 May].

[49] Cummins Power Generation Inc. , “Sound-Attenuated and Weather-Protective Enclosures,” Cummins Power Generation Inc. , Minneapolis, 2008.

[50] International Agency for Research on Cancer, “IARC: Diesel Engine Exhaust Carcinogenic,” World Health Organization , Lyon, 2012.

[51] S. Whitehouse, “Diesel Emissions Reduction Act of 2025,” 10 July 2025. [Online]. Available: https://www.congress.gov/bill/119th-congress/senate-bill/2235/text/is. [Accessed 2025 July 21].

[52] U.S. Department of Energy, Office of Energy Efficiency & Renewable Energy, Alternative Fuels Data Center, “Biodiesel Laws and Incentives in Minnesota,” U.S. Department of Energy, [Online]. Available: https://afdc.energy.gov/fuels/laws/BIOD?state=mn. [Accessed 12 June 2025].

[53] Rockefeller Foundation, “Electrifying Economies: Detailed Cost Models and Benchmarks,” Rockefeller Foundation, New York, 2020.

[54] DirecTank Environmental Products, “Understanding the Cost Benefit Analysis for Aboveground Tanks,” DirecTank Environmental Products, 10 August 2023. [Online]. Available: https://directank.com/aboveground-tanks-understanding-the-cost-benefit-analysis/. [Accessed 16 May 2025].

[55] LAZARD , “Lazard’s Levelized Cost of Energy Analysis – Version 11.0,” LAZARD Inc., November 2017. [Online]. Available: https://philipwarburg.com/wp-content/uploads/attachments/lazard-levelized-cost-of-energy-version-110.pdf. [Accessed 19 June 2025].

[56] Cummins, “Generator Set Data: Model DQLH,” Cummins, Columbus , 2017.

[57] J. Lenard, “Who Makes Money Selling Gas?,” National Association of Convenience Stores, 4 February 2025. [Online]. Available: https://www.convenience.org/Media/conveniencecorner/Who-Makes-Money-Selling-Gas. [Accessed 16 May 2025].

[58] Pilot Flying J, “Fuel Prices,” Pilot Flying J, May 2025. [Online]. Available: https://pilotflyingj.com/fuel-prices. [Accessed 4 June 2025].

[59] U.S. Energy Information Agency, “U.S. No 2 Diesel Retail Prices,” U.S. Energy Information Agency, 2024. [Online]. Available: https://www.eia.gov/dnav/pet/hist/LeafHandler.ashx?n=pet&s=emd_epd2d_pte_nus_dpg&f=a. [Accessed 28 July 2025].

[60] U.S. Energy Information Administration, “Gasoline and Diesel Fuel Update,” U.S. Energy Information Administration, 2 June 2025. [Online]. Available: https://www.eia.gov/petroleum/gasdiesel/. [Accessed 4 June 2025].