By Beth Splittgerber, Product Manager for the Small Diesel Product Line for Kohler Power Systems, North America

Figure 1: The Doughnut of social and planetary boundaries.
Credit: Kate Raworth and Christian Guthier. CC-BY-SA 4.0. Citation: Raworth, K. (2017), Doughnut Economics: seven ways to think like a 21st century economist. London: Penguin Random House.

Our climate crisis has resulted in an urgent demand for more sustainable mission-critical power technologies. To balance environmental impact against the need for mission-critical power, the doughnut economics model is useful – the concept shows that we need to use enough resources to provide the basics for all people, without causing damage to nature and our planet.

For mission-critical power, diesel generators are a proven solution, and the most popular option. They offer flexible outputs across a broad range of power nodes and can be accurately sized within a small footprint. 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.

But diesel generators do emit greenhouse gases and other pollutants. Switching entirely to another backup power source is unrealistic in the short term, and for some applications, diesel gensets are the only practical option.

Therefore, generator manufacturers have invested heavily in reducing emissions. The focus has been on the engine, with environmental standards such as EPA Tier 4 in the US, pushing engineers to reduce nitrogen oxides (NOx) and particulate matter levels.

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

For example, high-pressure common rail fuel injection systems improve combustion efficiency, while exhaust gas recirculation (EGR) is commonly deployed to reduce NOx, by recycling exhaust gases back into the combustion chamber.

Significant advances have been made in after-treatment. For example, diesel oxidation catalysts break down pollutants in exhaust gases into less harmful components. Other technologies such as diesel particulate filters and selective catalytic reduction can also cut contaminants.

In practice, mission-critical generators are often used for less than 12 hours per year and at low loads, for monthly maintenance. This means the engines cannot sustain the optimal operating temperatures needed to burn the fuel completely, thus causing 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 monthly at 30% of their rated capacity to burn off unused fuel or prevent build-up. However, some advanced generators can now be run at 30% of rated capacity as little as once per year, which can cut total pollutant emissions by up to 82%.

Another advance is the development of renewable fuels. Hydrotreated Vegetable Oil (HVO), for example, is a liquid fuel that is synthesized from waste vegetable oils or animal fats. Unlike first-generation biodiesel, HVO does not impact crop resources, and it can translate into up to 90% fewer greenhouse gas emissions than diesel.

HVO is similar in grade and quality to traditional diesel, and so can be used as a drop-in replacement, or as a blend with diesel. It is resilient in cold weather, safe in hot climates, and can be stored for up to ten years.

Technical teams around the world are also evaluating new medium-term technologies for mission-critical power, such as batteries and fuel cells.

Battery performance has matured rapidly in recent years, and the technology is already available with an efficiency of nearly 90%. Generator manufacturers have forged several joint ventures with industrial partners to develop battery-powered systems.

However, mission-critical applications would require many large battery packs – presenting cost, complexity, and footprint challenges. And batteries contain high levels of rare metals, which are becoming difficult and expensive to acquire.

Fuel cells have a lower footprint compared to batteries, and the possibility of quick refuelling with pressurized or liquid hydrogen. But they can only really be considered ‘green’ if the hydrogen used to power them comes from renewables, nuclear, or biomass. Achieving this fully is many years away from being practically available at scale, and the hydrogen produced is difficult to store in bulk.

Mission-critical power is clearly becoming more efficient and sustainable. Intense research and development efforts have delivered advances in several critical areas – from engine optimization to the use of renewable fuels. The challenge is to continue this progression while embracing other exciting technologies, such as batteries and fuel cells. However, meeting such ambitions will require ongoing innovation and collaboration to deliver the mission-critical systems of tomorrow.


Beth Splittgerber is the Product Manager for the Small Diesel Product Line for Kohler Power Systems, North America. She has been with Kohler for 30 years, committed to bringing the best quality product to market, including the latest focus towards clean energy, which is a key part of Kohler’s sustainability journey.

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