Hydrotreated vegetable oil is not an emission-free swap for diesel in datacenters

Biofuel lowers pollutants, but won't eliminate 'em, and could mean DCs compete for supplies

Datacenter operators are being encouraged to adopt hydrotreated vegetable oil (HVO) as a replacement for diesel in generators, however, analysts say the sustainable stand-in is not emission-free and has its own drawbacks.

With the number of bit barn builds on the up - thanks to trends like AI - and their energy consumption also ballooning, regulators including the European Commission have started to demand that operators detail their power use and greenhouse gas (GHG) emissions in an effort to nudge them into becoming cleaner and greener.

One quick fix that many are opting for is ditching diesel and replacing it with a more "sustainable" alternative fuel to power the backup generators that are meant to kick in if the electricity supply from the grid should fail.

HVO is held up as the optimal solution. It is manufactured by the hydrogenation and hydrocracking of various feedstocks including rapeseed oil, soybean oil, used cooking oil, and fats. It can be used in vehicles or equipment designed for standard diesel, without any changes to the engine, and is claimed to reduce GHG emissions considerably.

Global datacenter biz Digital Realty has tested out HVO, and last year started using the fuel source at its facilities in the US, following successful trials in Europe.

Fabrice Coquio, Digital Realty's SVP and Managing Director for France, told The Register that he started this in late 2022, with the region serving as the "guinea pig on the sustainability thing" for the rest of the group.

"We wanted to test the HVO 100 for a basic reason, even if it is a bit more expensive," Coquio said.

"I pay, on average, 25 percent more than an old liter of fuel. But over the life cycle, it has a reduced impact [on carbon emissions]."

Digital Realty's business in France is comprised of 13 datacenters in Paris and Marseille. A spokesperson told us:

"The use of HVO as a substitute for fuel oil has allowed us to avoid emitting 2,144 tCO₂ (across all scopes), equivalent to the annual emissions of 240 French citizens (assuming an average of 8.9 tCO₂eq per person per year. In other words, if we hadn't used HVO but instead used fuel oil, we would have had an additional 2,144 tCO₂eq emissions."

Kao Data switched to HVO in 2021, and Richard Collar, technical director, says its first project in Harlow, Essex, "involved several technical challenges."

"They included compatibility verification with our existing generators; the fuel transition process which required removal of traditional fossil fuel diesel and subsequent replacement with HVO; ongoing emissions testing; cost considerations; and addressing both the resiliency of the fuel, along with supply chain availability."

Generator maker Rolls Royce MTU ensured the HVO could "serve as a replacement" for diesel and "work without any engine modifications". This allowed its to swap upwards of 45,000 liters of diesel for HVO.

"Another key point is that during the early days, HVO was not accepted by statutory authorities as its use or adoption had not been incorporated into legislation. To address this, we undertook controlled experiments with our installed engines – measuring and comparing emissions from both HVO and fossil fuel diesel - and by engaging with our supply chain partners and the government to demonstrate the benefits," Collar told The Register.

In terms of Scope 1 emissions, he claimed replacing disel with HVO on the site "achieved a 13 percent reduction in particulate matter and a 6 percent reduction in NOx emissions." The generators are only used during testing or power outages, and so HVO didn't impact Scope 2 - electricity, heat, or cooling bought from external providers - he claimed.

"With regards to Scope 3, this is a key metric for both ours, and our customers' respective carbon emissions reporting, where HVO provides an overall reduction in CO2 emissions compared with traditional fossil fuels (diesel). At the same time, Kao Data supply chain emissions are also reduced due to the reduction in CO₂ arising from the production and transportation of said fossil fuels."

Fuel tankers powered by HVO transport the HVO fuel to all of Kao Data's bit barns from provider Crown Oils.

"While diesel has high upstream emissions (extraction, refining, transport etc), HVO is made from waste-derived food stocks, resulting in a lower lifecycle carbon footprint," Collar told us. "As such, HVO can reduce net CO2 emissions by up-to 90 percent compared to diesel, so has had a considerable positive impact on reducing our lifecycle emissions."

Alan Howard, principal analyst for Colocation and DC Building at Omdia, agreed the benefit of HVO is lower emissions, but said it is just not yet as readily available as diesel.

Apart from higher cost and being less widely available, there are other drawbacks to using HVO. Some of the feedstock inputs used for HVO, such as used cooking oils and fats, may have a limited supply, and if demand for the product grows, it will have to be fulfilled by drawing upon crop-based vegetable oils. This will mean using oils intended for food markets.

A report published [PDF] by the International Council on Clean Transportation in 2022 found that in the US at least, consumption of food-grade oils for biofuel production "is met by increases in vegetable oil imports, including palm oil and canola/rapeseed oil."

And while HVO may cut GHG emissions locally, it will cause pollution when combusted, according to Andrew Buss, IDC's Senior Research Director for European Enterprise Infrastructure.

"Whatever the source, it will still produce local air pollution when the generators are in use. Also, unless it can be made as a byproduct of other use of oils, creating HVO will often take agricultural land away from useful food production," he said.

Buss advised operators to consider other types of redundant power generation, such as smaller gas turbines, hydrogen fuel cells or large-scale chemical batteries.

However, despite its drawbacks, HVO is a better option than sticking with diesel. It is fully accepted by the UK government for many uses, which has classified it as a renewable fuel within the Road Transport Fuel Obligation (RTFO) scheme, for example. ®