Eco-Friendly Solutions for Large Data Centre Backup Power

It's no secret that the Data Centre sector is continuously being driven towards 'Net Zero' aspirations, 'Zero Carbon' energy procurement, GHG emission & carbon footprint (CUE metric) reduction, in addition to increased regulatory restrictions, stringent tax regimes, permitting issues (emission standards) and finally, Scope 1 and 2 emissions reporting required under the EU's CSRD.

One particular focus point in this regard is the search for greener alternatives to the use of diesel generators for back-up power and maintenance operations. Additional challenges in this regard include lower emissions targets, improved air quality requirements and lower noise regulations being imposed on developers and operators alike.

Typical project viability considerations for DC developments include 'first cost', 'energy cost', 'operational cost' and 'GHG emissions'. Therefore, such factors need to be analysed when reviewing alternative methodologies. Another consideration includes emissions permitting and potential tax hikes that come hand-in-hand with the increased diesel generator capacity required for expanding campuses - which may hinder growth ambitions for some operators.

The Importance of Back-Up Power Generation

Mission critical facilities require a constant, uninterrupted source of high-quality electricity to avoid the loss or corruption of data. The role of back-up power generation cannot be underestimated as clearly seen during the role they played during the 'Deep Freeze' energy crisis in Texas, 2021.

Alternatives to diesel emergency generators also need to meet a number of technical requirements - including the ability to start-up and assume the required loads within the grace period provided by the UPS systems. Also, systems need to be designed to realistic requirements and not purely on 'nameplate power ratings'.

Alternatives to Traditional Diesel Generators

'Clean' Diesel Generators with Emission Reduction Technologies

Hydrotreated vegetable oil (HVO) is a biofuel that offers a promising 'stepping-stone' to cleaner alternative forms of back-up power that can be used with existing diesel generator infrastructure. Some operators are estimating up to 90% net-CO2 reductions can be achieved with this technology plus decreases in CO, NOx and particulate emissions.

Whilst it is touted as being 100% renewable, biodegradable, sustainable and non-toxic. There are wider environmental impacts concerning its source and production methods that shed light on potentially negative drawbacks linked to deforestation. Alternative sourcing methods that don't include key ingredients such as palm oil are also being established to help combat this. Alternative feedstocks are also being investigated including other renewable fuels based on 'tall oil' - sourced from forestry and paper production byproducts.

Natural Gas Generators

Natural gas is seen as an effective fuel due to its reliable, established distribution network and high capacity. A downside is that it is carbon-based (fossil fuel reliance) and thus contrary to the decarbonisation strategies of energy networks globally.

Data centers equipped with natural gas engines may be more successful in obtaining permits than those equipped with diesel generators due to their lower emissions, plus may receive permission for longer running times. In the UK, developers should refer to local regulations concerning 'Medium Combustion Plant' which include the Environment Agency's (EA) standard rules permit 'SR2018 number 7' and be wary of potential site locations that fall under an 'Air Quality Management Area'.

Unlike typical emergency diesel generators, gas engines are designed for continuous base load operation. Also, diesel generators typically boast better start-up and load assumption capabilities for a wider range of generator settings. Thus, due consideration should be given to the anticipated site mechanical load start-up profile, with alignment to the load acceptance profile of the proposed NG generator.

Gas engines typically come with higher CAPEX although a lower OPEX in the long run compared to their diesel counterparts. Medium-speed gas engines are typically used in heavy-duty applications for baseload and intermittent operation, e.g. like in power plants or ships. The key benefit is the use of a cleaner fuel source, coupled with output range which is well-suited for larger data centres requiring approx. >10MWe of continuous load.

Onsite fuel storage requirements should be studied in full alignment with local regulations and Tier 3 & 4 certification demands (I.e. for a minimum of 12 hours standby operation). Multiple utility connections, their reliability and respective costs should also be reviewed to provide the required redundancy in case of failure. Although underground gas grids are less prone to natural disasters than electricity and distribution grids - The notion that gas supplies are inherently reliable should also be validated, again taking lessons from the 'Deep Freeze' energy crisis in Texas, 2021. Also, in the event of failure of multiple sources simultaneously, the supply pipe storage capacity should also be assessed.

Where independent, on-site fuel storage is being considered, technologies such as bullet tanks, gasification and liquefaction units enable such capabilities - albeit the costs, safety risks, footprint and maintenance requirements should be fully analysed.

The Role of Biogas

Renewable natural gas - Known as Biomethane or RNG (produced via 'upgrading' biogas or thermal gasification of solid biomass) is another low-emission option that’s more sustainable since it can be endlessly sourced from trash, livestock operations, and wastewater treatment plants. Untreated biogas typically has impurities and inconsistencies thus for direct use, the firm 'Caterpillar' has engineered a suite of generators that specifically run on biogas - handling variations in methane and acidic blow-by gases.

Some countries offer financial incentives for the production of RNG and its export into the grid network. Such as the Renewable Energy Credit system in the USA and the Green Gas Support Scheme in the UK. Many EU countries view the use of RNG as an important strategy for decarbonising their respective grids, including heating and transport - with a large percentage devoted to fuelling natural gas vehicle fleets.

The Role of Green -Methanol and -Ammonia

Both Green Methanol and Green Ammonia are derived from the production of Green Hydrogen via water electrolysis using renewable energy. Green methanol production involves the combination of Biogenic CO2 (originating from biological sources) and Green Hydrogen, which both undergo catalytic conversion. For Green Ammonia - N2 is separated from air and mixed with Green Hydrogen using the Haber-Bosch process.

Both carbon-free fuels are receiving interest in a bid to reduce GHG emissions, especially in the maritime and aviation industries. Engine manufacturers are also making strides in research and development ahead of this transition - a key factor being the availability of the fuels in the required quantities.

Green Ammonia can be used in fuel cells and as a substitute/additive in ICE's (Internal Combustion Engines). When used as a dual fuel together with diesel, the diesel typically acts as a pilot fuel to ignite the ammonia-air mixture. Likewise, minor modifications are required to the original equipment - care should be taken to guarantee complete combustion of the ammonia to prevent N2O emissions (itself having an extremely strong greenhouse effect) - which would offset the carbon reductions intended. Thus, burning ammonia on the rich side leads to reduced NOx emissions.

Furthermore, it is typically liquified for storage purposes and can thus be stored at a pressure above 8.6 bar at 20°C, or 18 bar (non-refrigerated) to overcome evaporation in case the ambient temperature rises. In contrast, hydrogen must be maintained either in gas form at high pressure or as a liquid at sub-minus temperatures. Hence, Ammonia (non-explosive and transportable by road, rail and pipeline) is touted as a viable hydrogen carrier - with the hydrogen being converted back via a cracking process once it reaches its destination.

Its disadvantages include its toxicity and corrosive nature towards metals (especially in the presence of moisture) - in addition its potential to cause reactive nitrogen pollution in the case of modest leakage. Other sources state that despite its high toxicity to humans, a slip of ammonia to the environment, even in large amounts - leaves no significant long-term effects due to its ability to be readily diluted and disintegrated in the environment.

Mahle GmbH has a two-pronged approach for transitioning to ADDF (Ammonia-Diesel Dual Fuel) engines, both in the near-term and long-term. The former includes the retrofit of dual fuel arrangements to existing diesel gensets, with additional injectors added to the air intake to introduce ammonia. The latter includes a novel form of pre-chamber ignition system prior to hot gas entry into the main combustion chamber. The innovation also deals with another challenge - Ammonia's comparatively slower burn rate with that of diesel. Other developments include propulsion trials in the maritime industry, with Fortescue and NYK both running maneuverability tests using ammonia-diesel fuelled vessels.

Green Methanol includes both e-methanol (produced using renewable energy) and also bio-methanol (produced via sustainable biomass sources without the need for hydrogen). It is touted as having the ability to reduce carbon emissions by up to 65-95%, which is a higher potential than any other fuel being developed to displace traditional fossil fuels.

It has the capability to be blended with diesel or used in its pure form, whilst it is a liquid at ambient temperatures. It has a higher flammability than that of diesel (with a flashpoint of approx. 10°C), whilst partial combustion can create pollutants including formaldehyde and formic acid. Interestingly, pure methanol when burnt alone produces an invisible flame. This can also be addressed via fuel blending.

Another characteristic is that it must be stored tightly, and sealed and away from moisture - since it is readily miscible with it thus diminishing its combustion qualities. Improved phase stability can again be achieved by blending methanol with other fuels that have a higher water tolerance. Another option is the addition of a co-solvent such as ethanol.

A dual-fuel approach (methanol-diesel) is also commercially available, with both MAN and Wärtsilä using it in their two- and four-stroke engines respectively. Generator sets that run on 100% methanol are also commercially available together with ready-assembled retro-fit kits. Conversion methods include using 'glow plug' assisted ignition to enable compression ignition engines to run solely on methanol (without a pilot fuel source) - in this case, the glow plug temperature and proximity to the fuel jet are critical. Also, as we saw with Mahle GmbH's approach for ADDF engines - retrofit options also exist by way of a separate low-pressure methanol fuelling system and port fuel injectors. Various operating modes can be utilised including 'homogeneous charge compression ignition' and 'partially premixed combustion' - both of which are related to the autoignition timing of the fuel-air mixture.

The maritime industry is showing a preference towards Green -methanol over its -ammonia counterpart due to its cost, safety and technological readiness for implementation. As suggested at the beginning of the section - a big challenge includes the need to scale up production volumes in line with potential demand in addition to the production costs of going 'green', which are still significantly higher than traditional fossil fuel-based methanol production. Costs though are expected to reduce as lower-cost biogenic CO2 becomes more widely available, coupled with decreasing renewable electricity costs. That said, the price of electricity is a primary cost driver - with excess renewable energy commanding low prices due to its dispatch during periods of low demand. Companies such as Thyssenkrupp, are developing methods to harness excess renewable energy and captured excess CO2 in order to create green methanol. Their concept is illustrated below;

Credit: Methanol: A Future-Proof Fuel A Primer Prepared for the Methanol Institute (2020)

There are ongoing concerns that the limited available feedstock to create biogenic CO2 is a factor that may prevent economies of scale being achieved. However, there is potential to link several biogenic sources via common infrastructure to tackle this, namely from sectors that include ethanol production, biomass power, waste to energy, cement, paper and food manufacturing.

Likewise, the cross-utilisation of water electrolysis (associated with e-methanol production) and biomass gasification is a hybrid production method under significant development expected to increase methanol yield with lower production costs compared to pure e-methanol methods - particularly if renewable energy sources are not available all-year round. The waste heat from electrolyser processes can also be used to dry biomass thus further increasing efficiencies. Demonstration projects such as 'BioReFuel' in Denmark are also advancing this technology. Furthermore, biomass-to-hydrogen (BtH2) plants together with carbon capture and storage are also being developed. The economic feasibility of biomass feedstocks also includes challenges such as the high cost and environmental impact of growing, harvesting and transporting the biomass itself. Conversion efficiency limitations and the potential need for commercial additives are other challenges. Finally, countries with excess forest biomass such as India, China and Brazil look the most likely to benefit from such technological advances.

In summary, when comparing both green -ammonia and -methanol; both are hazardous chemicals with the former at much lower concentrations. Therefore, the cost of managing safety is potentially higher for green ammonia installations due to the need for corrosion-resistant tanks, enhanced safety measures which include safety zoning, double piping, leak detection and engineered ventilation systems.

Green -methanol is more expensive to produce, whilst -ammonia is more expensive to handle. Thus, the choice between them depends on factors such as CO2 availability, safety, handling costs, overall sustainability goals. Wartsila Engines have conducted numerous tests for diesel engines running on both green -ammonia and -methanol, with various mixing ratios. They concluded that Light Fuel Oil (FLO) or HVO would generally be required as a pilot fuel, without significant drops in power or mechanical efficiency - albeit the changes to the fuel supply setup add approximately 15% to the plant outlay.

Dual-Fuel (Natural Gas & Hydrogen) & 100% Hydrogen Generator Sets

Some generator suppliers, such as 'Generac' offer dual-fuel (bi-fuel) generator set options running on both diesel (for start-up) and natural gas (once load is applied) thus reducing the amount of diesel fuel required on site. In the event of emergency, they can also run 100% diesel.

Blending hydrogen into natural gas pipelines is also an approach under rapid development for achieving near-term emissions reductions and early market access for hydrogen technologies such as electrolyzers. It is also touted as the most economical way to transport large volumes of hydrogen over long distance without the need for new infrastructure.

According to 'Wartsila', there is potential to blend up to 25% hydrogen into the natural gas whilst still maintaining its classification. Some success stories include suppliers such as Hawaii Gas and New Jersey Natural Gas. The UK is also trialling up to 20% hydrogen blending (sourced from both 'green' and 'blue' hydrogen) into the natural gas networks as part of their 2050 net zero carbon targets, with early trials hinting signs of success with no modifications needed for existing systems. Similar US trials also yield the same results (SoCalGas >20%) The above approach does face some resistance though, with opponents raising concerns that it could prolong reliance on natural gas.

The effect on blending may cause safety risks and operational issues for natural gas transmission systems due to the differing combustion properties - thus modification requirements should be reviewed taking into account considerations such as meter & valve accuracy and durability (hydrogen is more prone to leakage than methane), fatigue and fracture resistance in pipelines, increased pressure drops, gas velocities and compression power requirements, etc. To combat the latter issues, solutions such as increased flow rates & delivery pressures and increasing the number of compressor stations are options being investigated to overcome transmission losses. Specific safety concerns include the risk of flashback, preliminary studies suggest that for blends up to 30% it isn't a major factor however the risk increases as the percentage ratio of hydrogen increases.

Caterpillar also offer generator sets with hydrogen blending capabilities up to 25% hydrogen by volume (after default system configuration), in addition to 100% hydrogen combustion engines, such as those used in their G3516 (1000kW) gas gensets. This technology boasts lower GHG emissions compared to natural gas and diesel variants - however the resulting NOx emissions remains a focus point for researchers with potential exhaust aftertreatment requirements. On a positive note, JCB appear to be pioneering in-cylinder NOx reduction techniques, while pre-intake control measures are also available.

Finally, hydrogen combustion engines are generally noted as having a lower energy efficiency than that of their fuel cell counterparts - approximately 10-15% less. However, they do not require rare earth elements such as those used in batteries and fuel cells.

Hydrogen Fuel cells

Hydrogen Fuel cells are gaining immense research focus in automotive applications due to their high-power density, low operating temperatures and noiseless operation. Albeit their rapid start-up capability in cold climates remains a challenge due to their slower heat-up time when compared to IC engines. A special focus should be given to durability and subsequent life span covering a range of environmental scenarios (temperature, humidity & corrosion) to mitigate degradation of fuel cell components over time such as the membrane and the catalyst and subsequent losses in efficiency, which may govern the need for enhanced materials or coatings.

In order to consider fuel cells as backup systems, they need to be cost competitive and/or offer significant advantages over uninterruptable power supply from batteries or diesel systems. Also, should redesigns of system configuration be required for their integration, the disruptive and cost impacts need to be assessed fully. Data centre developers can use operational fuel cell experience in back-up systems to assist their transition away from fossil fuel reliance on a larger scale.

The National Renewable Energy Laboratory (NREL) remarks that the use of fuel cells as a means of backup power does not require a complete redesign of existing electrical infrastructure, redundancy and support systems; at the same time noting the increased (bulk) gaseous or liquid hydrogen storage requirements compared to diesel due to the differences in density. Fuel delivery options must be considered for hydrogen fuel cell applications, either via tube trailers, intermediary fuels (e.g. transport via ammonia) or hydrogen infrastructure including pipelines, delivery, on-site production, etc. Regarding footprint, in Microsoft's pilot project mentioned below, two 40ft shipping containers of fuel cells were considered the equivalent of one diesel genset.

This makes use of hydrogen fuel cells for primary data center power impractical today. It is, however, feasible for backup power, as enough hydrogen to support 48 hours of continuous operation for large data centers can be stored on site. Furthermore, site selection choices for future data centres could depend highly on their proximity to natural gas pipelines.

In 2022, a collaborative pilot project between Microsoft and Plug Power announced the installation of a containerised 3MW (PEM) fuel cell system fed by 'blue' hydrogen made from industrial by-products able to replace traditional diesel generators in the data center sector using simulated loads. The project aimed to demonstrate the viability of this technology at the same scale as that of a traditional backup generator. Detailed information can be found on a recorded session published here.

Again in 2022, NorthC - a Dutch DC developer, also planned to install hydrogen fuel cells in 500kW phases up to 1.5MW at its Groningen data centre.

Credit: Microsoft - 48hr liquified hydrogen storage

Credit: Microsoft; warm (50'C) water vapour output from hydrogen fuel cells.

Honda and Mitsubishi Cooperation also announced a demo project (2023) supplying waste hydrogen from an industrial facility to retired automotive fuel cells, powering a small data center. American Honda Co. have another operational demo hydrogen fuel cell power station (500kW - scalable) providing emergency backup power to their data centre campus in California (2023) - the facility again uses retired automotive fuel cells and is intended as a proof of concept for future commercialisation efforts.

Further recent developments (2024) include recent collaborations between Caterpillar, Microsoft & Ballard Power Systems, deploying a large-format 1.5 MW hydrogen fuel cell and BESS system at a live data centre in Wyoming (testing performance at high altitude, below-freezing conditions), whilst simulating a 48-hour backup power event supporting critical loads. Also, Ballard Power Systems are currently collaborating with ABB to develop high-power, scalable 3MW hydrogen fuel cell applications in the maritime industry.

Credit: Caterpillar, Microsoft & Ballard Power Systems

At the time of writing, our understanding is the that the 2022 Microsoft and Plug Power 3MW demonstration noted above is the largest to date for a DC back-up power application. Whilst a pre-requisite for adoption of this technology appears to the availability and economic viability of green hydrogen. Also, industry forums remark "The industry won't move from pilot projects to large-scale use of fuel cells without a greater understanding of the technology".

Other concerns include reliability, fire safety, leakage (the global warming effect of hydrogen leaks is almost 12 times stronger than carbon dioxide) and the cost of ownership. Global green hydrogen production capacity is likely to increase in the next 5-10 years, with cost reductions expected as supply chains mature. In parallel, convertible natural gas-powered fuel cells also offer a stepped approach to supplement the learning process for data centre operators and their integration of such technologies whilst hydrogen infrastructure develops further. Other DC players, such as Google, have been investigating the use of large-scale batteries to replace diesel generators at one of their Belgium sites.

Performance wise, there is a concern that fuel cells underperform during significant load surges due to the lower dynamic response, struggling with power peaks during start-up and acceleration (in vehicular applications). Thus, an auxiliary battery power supply with advanced energy management is required for highly dynamic scenarios - giving birth to the FC-BAT hybrid concept as seen in 2024 collaboration above. TLS Offshore Containers also offer innovative BESS and hybrid hydrogen fuel cell battery containers, with academic studies relating to hybridisation boasting reduced fuel cell power adjustment range, and slower rates of performance decay.

Equinix have recently published updates regarding their FC-BAT demonstration plant sited at one of their facilities in Dublin - housed in a 20ft shipping container (250kW electrical output, 216kWh battery storage), scalable to 2MW using green hydrogen. They are also experimenting with smaller 100kW systems for use in critical fire suppression and tropical climate adapted demonstration units in Singapore.

From an energy management perspective, the operational challenges include balancing the use of UPS (for immediate power to critical loads), BESS (mid-duration energy storage & backup power) and fuel cells (longer-term backup power).

Credit: Hitachi's HyFlex™ demonstration unit - 400–600 kVA (Temp. Systems) and 1MVA (Perm. Installs)

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This article was written by Luay Zayed, founder of Biyat Energy & Environmental Ltd. A global energy and environmental consultancy specializing in turnkey engineering solutions that protect the environment and improve energy efficiency in the manufacturing & industrial sectors.