As the world grapples with where energy will come from, now and in the future, the data center industry is at the forefront of the conversation. Driven by both government and industry initiatives, the imperative to offset data centers’ energy consumption with renewable energy sources resulting in reductions in greenhouse gas (GHG) emissions is higher than ever. And it doesn’t just apply to normal operations but also when backup energy is required.

Today, diesel-powered engines are still standard for generating backup power. But as data center operators evaluate the use of fossil fuels, including diesel, the door is opening for use of new, more sustainable backup fuels. As the search for fossil free fuel options evolves, HVO (hydrotreated vegetable oil) has proven itself a viable alternative to fossil diesel that’s also fully mixable with diesel in circumstances when it may be needed.

To explore the use case of HVO diesel usage in backup generation, the following is a closer look at the current backup generation landscape, the pros and cons of HVO, and the role HVO can play in short- and long-term energy sustainability.

Why does backup generation matter?

Achieving near perfect uptime within a data center’s operations is critical for customers to maintain productivity and revenue and avoid fines from SLA violations. Downtime can cost businesses $5,600 to $9,000 per minute, with Fortune 1000 companies losing up to $1 million per hour, and companies in high-risk industries such as finance, healthcare, manufacturing, and government losing an average of $5 million per hour.

Backup generation plays a key role in ensuring business continuity by providing power to the data center in the event that the main source of power fails — whether it’s because of a storm, power grid outage, natural or human-made disaster, or some other factor. If appropriate back up generation measures have been established, data center users (many of which provide critical services in their own right) can continue to receive reliable, uninterrupted service to operate their business even in the face of an external power failure.

Although occasions for using backup generation are rare, there are any number of situations that can pose a threat to the data center — among the worst, weather. According to theEnvironmental Protection Agency (EPA), heat waves in the U.S. are occurring three times more often now than in the 1960s, a higher percentage of precipitation comes from extreme, single-day events, and tropical storm activity has increased during the last 20 years.

With major weather events and natural disasters on the rise, and the always-present potential for human-driven catastrophe, the need for backup generation could become more common over time. It’s why discussions about renewable energy sources cannot exclude backup generation.

Enter HVO: pros, cons & other considerations

HVO was born out of the need to reduce carbon dioxide in the atmosphere. When fossil fuels are extracted and burned, carbon that’s normally sequestered underground is released, adding more carbon dioxide — CO2 — to the air and increasing the net carbon in the atmosphere. HVO is made with 100% renewable materials that, when refined, have a similar structure to fossil diesel and can help solve the ongoing problem of net new GHG emissions associated with fossil fuels.

HVO pros:
  • Net-neutral GHG emissions.HVO takes existing biomass — specifically vegetable oils, animal fat, and used cooking oils — and converts it into a fuel. When HVO is burned, CO2 is still emitted, but because the carbon from the biomass is already naturally in the ecosphere, no net-new carbon dioxide emissions are created, rendering its GHG emissions net neutral. HVO can also potentially reduce localized emissions by lowering the amount of diesel particulates and certain hydrocarbons in the air that can lead to various health issues within communities.
  • Reduction in overall GHG impact. Compared to fossil diesel, HVO can actually reduce GHG impact anywhere from 45-85%. For example, shipping HVO from a location like Singapore would see a reduction in GHG impact closer to the lower end because of the fuel burned during the lengthy transport. A domestic truck transporting HVO from one state to another, say, in the Midwest, would reduce impact even more. And if HVO is produced and used locally, that’s where the highest reductions in GHG could potentially be achieved.
  • Fully replaceable and mixable with #2 diesel. HVO is a full replacement fuel for most diesel generator sets. Any #2 diesel tank can be filled with HVO as needed, and vice versa. During a situation in which backup generators may have to run for days on HVO, the data center could still revert back to diesel in the event the HVO supply is exhausted and can’t be procured quickly enough.
HVO cons:
  • Scalability and supply. Because HVO mass-production is in its infancy, scale is still a challenge. But as awareness of HVO builds, production of the raw goods increases, and supply issues improve the justification for global HVO use will increase. To support this undertaking, major fuel refiners have recently announced they’re now making sizable investments in HVO refining and production, aiming to capitalize on the nascent opportunity.

There are a couple of engineering considerations as well:

  • Small reduction in horsepower. HVO has a slightly lower energy content which means it produces about 2-3% less horsepower than diesel. Performing an engineering study of finely tuned downstream services will register the difference, but the difference is small enough that it’s not noticeable from a user’s standpoint in most scenarios.
  • Slower transient response time. In a power failure scenario, the energy grid connection dies, the data center transitions to batteries, then once those batteries go out, the backup generator takes 100% of the battery load. In HVO’s case, it has a slightly slower transient response time than fossil diesel. Yet because the backup engine running on HVO is never hit with the full load all at once, but instead takes on the load in a measured way, the transient response difference is effectively negligible.
Beyond Theory

To expand beyond theory, STACK’s partner, Caterpillar®, conducted a test in early 2021 (performed in Lafayette, IN) to verify the use of HVO in one of their backup generators. Using a unit that had been purchased by STACK, tests were performed by Caterpillar® and subsequently both teams worked together to confirm testing criteria and goals. This testing just happened to coincide with the 2021 Texas Ice Storm which induced a massive regional power outage caused by extreme cold temperatures and winter weather. While testing occurred in a separate region, the HVO testing demonstrated one of the most important use cases for HVO: mitigating a sudden energy disaster.

The diesel engine successfully ran for several days on HVO during the outage, indicating that the engine was fully capable of supplying backup power fueled with HVO alone. Furthermore, if there had been a need to switch back to diesel at any point, the transfer would have been seamless since the engine could run effectively on either fuel type.

Leveraging existing infrastructure for a better future

HVO holds enormous promise as a renewable energy source, but the reality is that data centers around the world have already invested significant capital in diesel-based backup generation infrastructure, such as the generators and trucks delivering the fuel. Diesel engine technology has existed for over 120 years and is used in countless applications. Billions have been spent on diesel R&D and purchasing of those engines. Though decarbonizing data centers and redesigning them to be more green may be the overarching goal, retrospective costs loom large in the interim.

But there is an opportunity to reuse that retrospective capital in a way that’s much better for GHG emissions. HVO provides a real pathway to address and even reduce GHG emissions in the short term while still leveraging all the time and money invested in diesel power. The same diesel engines and tanks that data centers have already invested in can be used, while net-neutral emissions from backup generation can offset emissions from transportation until HVO can be produced at scale — helping to accelerate the data center industry’s course toward a more sustainable future.

Tim Hughes is VP of Strategy & Development for STACK Infrastructure.