Navigating the route to more sustainable mission critical power

Which mission critical power option is right for your next building application?

By Beth Splittgerber November 7, 2022
Courtesy: Kohler Power Systems, North America


Learning Objectives

  • Learn why diesel generators remain a preferred option for backup power.
  • Understand how generators have been modified in recent years to design for optimization and efficiency.
  • Clarify the role of renewable fuels, such as HVO, in the future of sustainable mission critical backup power.

Mission critical power insights

  • To balance sustainability against the demand for mission critical power, this article discusses alternative fuel sources and how design engineers and manufacturers are working to reduce the emissions from mission critical power.
  • Emissions from mission critical power sources should be carefully taken into consideration.

Buildings rely on resilient mission critical power for business, health, sanitation, safety and security. However, the threat of climate change has resulted in urgent demand for more sustainable mission critical power technologies.

While diesel generators are the most commonly used emergency power solution, they create carbon dioxide and emissions of particles such as soot and their environmental impact is widely seen as undesirable.

To balance sustainability against the demand for mission critical power, it’s useful to consider the doughnut economics model. First published in 2021 in an Oxfam report, this model aims to help balance the needs of people with the resources available on our planet. It proposes an approach for the 21st century that makes sure no one is left short of life’s essentials while ensuring we don’t exceed safe limits for environmental impact. Reducing the emissions from mission critical power is a prime example of where the industry is looking to achieve this balance.

Why diesel for mission critical power?

When a power outage occurs, diesel generators start quickly and reliably to provide electricity and allow continuity of operation. Generators are a tried and trusted option, the estimated total industrial generators market (diesel, gas, marine) is predicted to reach $23.6 billion by 2025, with many of these products being used for mission critical applications. For some mission critical power environments, diesel generators are the only option, particularly in remote areas where the grid is unreliable and there is a lack of supporting energy infrastructure.

Why are diesel generators often the preferred option? Firstly, they offer flexible outputs across a broad range of power nodes and can be accurately sized within the small footprint required. Diesel provides an efficient and readily available fuel that can be stored safely on-site and works in most climates. Additionally, most generator suppliers offer well-established maintenance and support, giving end-users peace of mind.

Power outages can be rare, so backup diesel generators are only used occasionally and for short periods — therefore emissions are relatively low. That said, there is a genuine and growing demand for more sustainable operations, from original equipment manufacturers and end-users alike.

Kohler Power Systems ushers in a future powered by sustainable fuels, earlier this year approving their entire line of mission critical diesel generators to run on Renewable Hydrotreated Vegetable Oil (HVO). Courtesy: Kohler Power Systems, North America

Optimization and efficiency of mission critical power

Generator manufacturers have invested heavily in the pursuit of more environmentally friendly technologies. This has been concentrated on the engine, with environmental standards such as Environmental Protection Agency Tier 4 in the U.S., pushing engineers to rethink engine architectures to reduce nitrogen oxides (NOx) and particulate matter levels.

Emissions reduction technologies have cut the amount of pollution created, via in-cylinder reductions and treat created pollution before it enters the environment through after-treatment technologies. Engineers have also used advanced computer-aided tools and computational fluid dynamics to predict performance and optimize designs.

For example, high-pressure common rail fuel injection systems increase the injection pressure of diesel fuel, allowing for finer atomization, improved air-mixing and greater control of injection timing. Meanwhile, electronic fuel injection means the engine can be programmed to inject fuel at the ideal time during the combustion cycle — with multiple injections carried out within milliseconds. By using closed-loop feedback controls, the engines can also adjust the fuel injections to account for transient events, steady-state operation or environmental operating conditions.

Exhaust gas recirculation is commonly deployed to reduce NOx. Exhaust gases are recycled back into the combustion chamber and mixed with the intake air to reduce oxygen content and therefore combustion temperature.

Significant advances have been made in after-treatment technologies. Diesel oxidation catalysts, consisting of a honeycomb structure coated in precious metal in a stainless-steel housing, cause a reaction in the hot diesel exhaust flows as it passes through, breaking down pollutants into less harmful components. Other technologies such as diesel particulate filters and selective catalytic reduction can also reduce the release of contaminants.

In practice, mission critical generators are often used for less than 12 hours per year and at low loads because most of the runtime is for monthly exercising. This limited use means the engines cannot sustain the optimal operating temperatures needed to burn the fuel completely. This can cause a build-up of unburnt fuel in the exhaust system — known as wet stacking — which can lead to decreased engine performance and higher emissions.

In the past, the solution for wet stacking has been to run the generators once a month at 30% of the rated capacity to burn off unused fuel or prevent build-up. However, technological advances are reducing the need for this procedure. Advanced generators can be run at 30% of rated capacity as little as once per year to maintain optimal performance and stay within emissions guidelines. Revisiting maintenance programs and switching from monthly to yearly load testing cuts total pollutant emissions by as much as 82%.

Renewable fuels for power systems

Another advance in sustainability is the development of renewable fuels. Hydrotreated vegetable oil, or HVO, for example, is a liquid fuel that is synthesized from waste vegetable oils or animal fats using a special hydrotreatment process. Unlike first-generation biodiesel, HVO does not impact crop resources and it can translate into up to 90% fewer greenhouse gas emissions over its entire life cycle. It is resilient in cold weather, safe in hot climates and can be stored for up to 10 years.

HVO is similar in grade and quality to traditional diesel and can be used as a drop-in without modification. HVO is also completely compatible with the standard mix of petroleum-derived diesel fuels and can be used as a blend with traditional diesel. The ability to mix HVO and conventional fuels provides flexibility to the end-user, who could introduce HVO as a renewable fuel and then revert to diesel should the need arise.

While HVO is available right now, global generator and power systems manufacturing technical teams are also evaluating new technologies for mission critical power, such as batteries and fuel cells that might be deployed. Battery performance has matured rapidly in recent years and the technology is already available with an efficiency of close to 90%. Many companies have already forged several joint ventures with industrial partners to develop battery-powered generators.

However, scaling battery solutions is difficult. Mission critical applications would require a substantial number of large battery packs — presenting cost, complexity and footprint challenges. Also, batteries contain high levels of rare metals, which are becoming more difficult and expensive to acquire.

Fuel cells are also attracting attention. They have a lower footprint compared to batteries and the possibility of quick refuelling with pressurized or liquid hydrogen. These factors mean fuel cells could be adapted for backup applications and more extended storage periods.

However, fuel cells can only really be considered “green” if the hydrogen used to power them comes from sustainable sources such as renewables, nuclear or biomass. Achieving this fully is many years away from being practically available at scale and the hydrogen produced is hard to store in bulk without significant investment in associated infrastructure.

Choosing the correct power system options

The route to cleaner mission critical power will be achieved through a transition period — it will not happen overnight. There is no “one size fits all” solution, with regional and industry-specific variations.

In some circumstances, diesel will always represent the best technology and remain the fuel of choice  and reductions in diesel genset emissions will make this a more sustainable option. But in other applications, renewable fuels such as HVO will offer more flexible alternatives without compromising performance. In the future, fuel cells and batteries could present a step-change in sustainability, with little or no at-source emissions.

As companies continue to invest heavily in backup power, end-users will be able to reduce their emissions, thanks to a diverse range of technology options. Together, these different options will enable mission critical power to remain effective and reliable, while becoming significantly more environmentally friendly.


Author Bio: Beth Splittgerber is a product manager at Kohler Power Systems. In her 30 years at Kohler Power Systems, Splittgerber has been committed to bringing the best quality product to market, including the latest focus toward clean energy, which is a key part of Kohler’s sustainability journey.