Diesel Generator Alternatives for Facility Owners

Amid growing concerns over grid reliability, many are looking to expand backup power capabilities.

Diesel-fueled generators remain the predominant resource, offering resilient, dispatchable power at a moment’s notice. Yet diesel generators are major contributors to local air pollution and global climate change — and, in some instances, present reliability concerns of their own.

To ensure resilient backup power while reducing environmental impacts, more energy users are considering alternative backup power sources.

Diesel Generators Are the Go-to Backup Power Source

Generators form the dispatchable backbone of emergency power supply systems. These critical assets provide electricity for life safety systems and high-value equipment in the event of a primary power failure.

Code requirements determine how quickly generators must turn on, how much fuel must remain on site, and how to design essential electrical systems. Following the National Fire Protection Association (NFPA) 110 Standard for Emergency Standby Power Systems, many jurisdictions only allow the use of liquefied petroleum (diesel), liquefied petroleum gas (propane), or natural gas.

That said, some jurisdictions are starting to issue waivers for the approval of certain alternative backup power systems. Recently, the Centers for Medicare and Medicaid Services clarified that, if a waiver is issued, hospitals could rely upon alternative power sources for emergency power.

Despite the availability of alternative backup power sources, diesel-fueled generators remain by far the most popular choice. Diesel generators account for 85 percent of systems used in U.S. critical facilities and commercial buildings. Generator use is growing — since 2021, manufacturer Generac has seen a 70-percent increase in diesel generator sales as grid failures, wildfires, and extreme weather events become more common.

Why do diesel generators remain so popular? They are generally reliable and relatively cheap. Benefits include:

• Superior load carrying capacity
• Proven ability to deliver high-quality electrical power
• Rapid response time
• Easy access to fuel supplies
• Self-contained fuel storage
• Expansive network of service and support professionals

Diesel Generator’s Environmental Challenges

Diesel generators certainly have drawbacks. Most noticeably, diesel emissions contain harmful levels of nitrous oxide (NOx), sulfur dioxide, particulate matter, and volatile organic compounds.

Modern units pollute significantly less than older models. Tier 4 generators emit 94 percent fewer NOx and 91 percent less particulate matter than Tier 2 engines. Still, any diesel-fueled generator contributes to local smog, exacerbating asthma, lung disease, and other health conditions. Particulate matter produces black carbon, a greenhouse gas and toxic air contaminant.

Source: U.S. National Renewable Energy Laboratory

A recent study found the San Francisco Bay area’s diesel generators have a carbon footprint equivalent to the annual carbon emissions of more than 20,000 combustion engine vehicles. When released into the atmosphere, black carbon particulates absorb sunlight, emitting radiation into the surrounding air. If deposited onto mountaintops, black carbon can accelerate the rate of snow and ice loss, contributing to declines in regional water supplies.

Diesel Generator’s Reliability Concerns

Diesel generators come with some reliability concerns. When not properly maintained, generators are prone to mechanical issues that can prevent equipment from starting or running as intended. As seen following 2024’s Hurricane Helene, disaster events undermine the availability of critical refueling supplies.

Diesel generator reliability issues tend to fall into three categories:

• Failure to Start: If generators are run infrequently, common issues include mechanical failure of the voltage controllers, dead starter battery, oil lubrication system, or fuel injectors. Among regularly maintained and tested generators, risks are more often related to failure of worn-out components.
• Failure to Run: After the generator starts, mechanical failures could include engine overheating, component structural issues, or clogged filters due to degraded or spoiled fuel supplies.
• Failure of Fuel Supply: Diesel generators can only last for as long as fuel supplies are available. Hospitals are required to store at least 96 hours of fuel onsite. Commercial facilities typically have enough fuel only to last 36 hours. If diesel resupply shipments are disrupted due to a natural disaster or supply chain issues, the generator will eventually become useless.

Running diesel generators can also present reputational concerns. Facilities that remain tied down to a fossil fuel system may be met with complaints from neighbors, residents, or corporate stakeholders — especially as momentum toward electrification continues to grow.

Alternative Backup Power Solutions

Diesel generators are no longer the only technically and economically feasible backup power option.

Alternative Fuels

Many generator models are now available with dual-fuel capabilities. This flexibility enables facilities to use diesel, natural gas, or alternative blends — provided the facility has installed necessary storage infrastructure. Such alternatives include:

• Renewable diesel: Chemically equivalent to petroleum-based distillate, produced using fats, oils, or greases
• Biodiesel: Chemically equivalent to petroleum, manufactured from vegetable oils, animal fats, or recycled restaurant grease
• Hydrogen: Clean-burning fuel that emits water vapor as its only byproduct, produced through chemical reactions powered by natural gas or renewable energy

Source: U.S. Energy Information Administration

Natural gas and — eventually, perhaps hydrogen — offer the benefit of established pipeline networks. The existence of hardened infrastructure makes such options more economical. That said, extreme weather events such as 2021’s Winter Storm Uri demonstrate that even hardened pipelines at times experience pressure loss and production curtailment.

Solar Photovoltaics and Battery Storage

Solar energy can be harnessed and stored using lithium-ion battery technology. To work as a resilient backup power source, the battery energy storage system (BESS) will need to remain charged and ready in the event of a power disturbance. Capacity is dependent on battery size and solar output.

BESS technology is not generally relied upon for long-duration events (greater than four hours). Energy storage technology is still in its infancy. For applications where long-duration storage is required, a blend of technologies should be considered.

Renewable energy systems enable owners the opportunity to take advantage of federal, state and/or utility incentives. Notably, the federal Investment Tax Credit (ITC) was recently expanded, allowing for-profit as well as tax-exempt entities who install certain clean energy systems to lower their upfront costs by up to 30 percent.

Fuel Cells and Linear Generators

Courtesy of Mainspring Energy

Fuel cells and linear generators produce power through chemical or electromechanical reactions. For both systems, new models are available that are fuel flexible, relying on natural gas, hydrogen, or other alternative fuels. Fuel cells and linear generators are dispatchable and energy efficient.

When deciding among these options, factors to consider include:

• Grid Reliability: In areas where an aging grid is more prone to outages, facility owners may want to think twice before relying entirely on intermittent backup power. A solar + BESS configuration may be sufficient if the local grid has proven to be generally resilient.
• Existing Infrastructure: The capital costs of replacing a backup generator’s mechanical, electrical and plumbing equipment pose significant barriers. Diesel generator alternatives are generally more practical during a site expansion or new construction project.
• Regulatory Environment: Across the country, local jurisdictions are imposing more stringent pollution control measures, restricting permits or increasing the operational costs of diesel-fired systems. New measures include enforcement of performance standards aimed at reducing on-site emissions or improving a building’s energy efficiency.

Gauging Risk

Any backup power system comes with some level of uncertainty.

To identify the right system, it is important to understand the facility’s unique operational demands and infrastructure-specific requirements. Burns works with our clients to perform detailed engineering analyses that assess the feasibility of alternative backup power systems. Evaluations balance site-specific circumstances, financial considerations, and long-term planning goals.

Facility owners looking to mitigate their environmental impact and align with broader electrification efforts must tread carefully. If a power disruption occurs, having an appropriately designed system will prove crucial. The facility’s backup power strategy must maintain code compliance, operational resilience, and financial performance. Partner with a consulting engineer who will understand these risks and who will ensure that critical campus facilities are ready for whatever the next emergency brings.