By: Euan Cutting, Electrical Engineer, Black & White Engineering
As data centre operators continually look for ways to decarbonise their business operations, hydrogen has become a highly anticipated solution for storing and releasing low or zero-carbon energy.
When considering options for onsite electrical generators, there are very few practical options which can fit in a data centre campus and produce no carbon emissions. When excluding renewables from our options, it leaves us with gas generators and fuel cells. Of the two remaining options, fuel cells have higher efficiency (U.S. Department of Energy, 2015). The cost-effectiveness depends on how they are used, whether it is for backup or continuous power. In terms of cost, hydrogen at present is prohibitively expensive, not to mention the infrastructure required to store it, and the significant storage difficulties due to its low density (International Renewable Energy Agency, n.d.). While the cost of hydrogen is predicted to reduce over the next decade, making it more accessible, the issues around large-scale storage may prevent usage on many data centre sites. In the future, there will be locations with gas pipelines which could provide hydrogen, but this is unlikely to be an economical option when compared to consuming electricity from the utility grid.
As hydrogen can react with oxygen to release energy with no carbon emissions, it is no surprise that predicted investment into the sector has been estimated at up to $500 billion by 2030 (Hydrogen Council, 2021). Hydrogen fuel cells combine hydrogen and oxygen to generate low or zero-carbon electricity which can be used to power a data centre. The majority of fuel cells currently in use in data centres are solid oxide fuel cells (SOFCs), providing constant power. SOFCs can generate power through the conversion of fuels such as natural gas and biogas, into hydrogen, which is then reacted in the fuel cell to generate power. While using natural gas still results in carbon emissions, SOFCs are able to generate power with higher efficiency than combustion engines. SOFCs can also be fuelled directly with hydrogen, although this is not the norm due to hydrogen’s cost and availability.
While it is capable of providing constant power, hydrogen fuel cells are also being considered for providing backup power to data centres. This is greatly appealing to data centre operators as a more environment-friendly replacement for traditional diesel generators. This change would see the use of fast-start fuel cells, such as proton exchange membrane (PEM) fuel cells which could take the place of diesel generators (Roach, 2022).
SOFCs and PEM fuel cells differ from one another in their construction, materials, and operation. In a high-level view, the primary differences are the electrolyte materials (where the hydrogen and oxygen react) and operating temperatures. SOFCs operate at high temperatures, requiring longer start-up times and as a result, are suitable for continuous power supply (Equinix Inc, 2021). PEMs, by contrast, operate at lower temperatures and are capable of fast-start or continuous operation, but are a more expensive option.
How exactly fuel cells will be used in future data centres is still up for debate, with operators considering both backup and constant power options. There are significant trade-offs with each option; using fuel cells for backup power requires large quantities of hydrogen to be stored onsite, which is costly, space consuming, and high-risk, particularly when compared to current onsite diesel storage. Constant power usage, on the other hand, would see the fuel cells connected to a future hydrogen gas pipeline. The major disadvantage with this option is operating costs – as current data centre operators state that they intend to use zero-carbon “green hydrogen,” using renewable electricity to split water via electrolysis. This is almost guaranteed to be more expensive than just using utility electricity directly due to electrolyser efficiencies and losses in hydrogen distribution and storage.
Sustainability – a key driver in the use of hydrogen fuel cells
The key benefit and primary motivation for installing hydrogen fuel cells within a data centre is to reduce carbon emissions. As stated, some fuel cells such as SOFCs can use natural gas – while it is less damaging to the environment than diesel, it still results in significant carbon emissions. This may be attractive for data centre operators due to the cost of natural gas for industrial consumers versus the cost of utility electricity. Given the high efficiency of fuel cells, this allows data centre operators to produce lower cost electricity onsite, with the downside of carbon emissions when using natural gas and added energy system complexity.
Fuel cells powered directly with hydrogen rather than natural gas have the opportunity to be sustainable, provided that the hydrogen does not originate from fossil fuels. Depending on its source, hydrogen has commonly referred to ‘colour’ classifications to help differentiate how it has been produced and therefore how sustainable it is; hydrogen produced directly from natural gas is referred to as ‘grey,’ while hydrogen produced from natural gas with a carbon capture, utilization, and storage system (CCUS) is referred to as ‘blue.’ ‘Green’ hydrogen, produced via electrolysis with renewable energy, is often hailed as the gold standard. Additionally, there is ‘pink’ hydrogen – it is also produced via electrolysis like ‘green’ hydrogen however, it uses nuclear energy rather than renewable energy.
The goal to meet net zero-carbon targets, combined with the ongoing energy crisis, has also created a renewed interest in nuclear power which can provide vast quantities of low carbon electricity (Nordhaus & Lloyd, 2022; International Energy Agency, 2019). In addition to the low carbon electricity source which can be used for electrolysis, there are proposals to utilise waste heat from high temperature nuclear reactors, significantly reducing the energy required for electrolysis (World Nuclear Association, 2021). This potentially results in more efficient and economical hydrogen production.
However, companies are increasingly facing pressure from investors to comply with Environmental, Social, and Governance (ESG) standards which is another reason why hydrogen fuel cells are appealing to data centre operators (HSBC UK, 2023). This pressure is already pushing companies, including data centre operators, to explore alternative technologies such as fuel cells, which may attract more investment and improve public image.
The practicalities of hydrogen fuel cell usage in data centres
Implementing hydrogen fuel cells in place of diesel generators results in a significant change to the overall energy system of a data centre. As data centre designers, it is our responsibility to design the electrical and mechanical infrastructure to provide constant power and cooling to the servers.
From an electrical perspective, fuel cells and diesel generators have fundamentally different properties. To begin with, diesel generators produce alternating current (AC), whereas fuel cells produce direct current (DC). Additionally, they have varying properties when powering up and assuming high loads. This may provide novel options for DC systems within a data centre, although depending on the size of the data centre and the distances that electricity may have to travel, this could become inefficient.
From a mechanical perspective, designing a hydrogen storage system is significantly more complex than a diesel storage system. Hydrogen has more storage options available however, it presents higher risks than diesel such as greater flammability and explosivity, higher pressures, potential for low temperature, or chemical storage methods which are all hazardous. This therefore requires the mechanical design for such a system to comply with rigorous safety standards. Consequently, local planning restrictions may prevent a data centre from storing hydrogen onsite – a particular issue for data centres in Europe which are often located in urban and industrial environments.
There are various ways that hydrogen fuel cells could be implemented within a data centre. As mentioned, there are significant costs associated with adopting this technology, and in many cases, they are not a feasible replacement for existing diesel generators as current data centre sites have not been designed with hydrogen in mind. This is less of an issue in markets such as in United States where data centres have a greater access to available land. In typical European data centre locations, land comes at a premium and many data centres are located in relatively urban environments.
One suggestion is for greater integration of energy systems, which would see data centres located adjacent to energy industries or having data centres integrated with hydrogen generating plants and fuel cells. This solution sidesteps planning problems by locating data centres alongside low carbon energy industries. A major issue with this (aside from the available land) is blurring the lines between the data centre operators, utility providers, and energy companies. While this gives data centre operators direct access to low carbon energy, there will have to be a clear demarcation between data centre operators and utility operators, as the data centre operators’ primary business is data rather than energy.
In addition to the above design considerations, cost is another hurdle for hydrogen uptake. While it is hard to predict exactly how costs will vary over the coming decade, especially with recent cost fluctuations due to the energy crisis, there are a range of investments and subsidies being launched. These aim to produce cost-competitive hydrogen at scale. This could take the form of subsidies such as contracts for difference (CfDs), which can help increase investment in low carbon technology. In the last decade, CfDs have played a major role in bringing down the cost of renewables for developers. This has been a success story in the UK, with the grid gaining large quantities of renewable energy (National Grid ESO, n.d.).
Design-first greener, cleaner data centres
There are countries in which the local utility grid generates power from highly polluting fossil fuels such as coal. In this scenario, the carbon emissions per kWh of electricity from these girds are higher than the emissions from a fuel cell utilising natural gas. This allows a data centre to utilise SOFCs with a natural gas supply, which reduces or eliminates the data centres’ demand on the local utility grid, while also reducing the carbon footprint of the data centre (when compared to a scenario in which the data centre used electricity from a carbon intensive grid). There is also the potential to utilise waste heat in a vapour absorption machine (VAM) chiller, to provide cooling and power for further carbon mitigation (U.S. Department of Energy, 2017). Black & White Engineering has designed data centres that use SOFCs in this capacity, which can provide the dual benefit of reducing carbon emissions and costs, while additionally mitigating demands on local utility grids.
However, a caveat to the sustainability benefits of this kind of onsite power generation is, as a country begins to decarbonise its utility grid, the emissions reduction which the data centre operator previously had will be diminished, until eventually they may generate more carbon emissions per kWh than the electricity available on the utility grid. While this is highly dependent on the country in question, a good example of this would be the combined heat and power (CHP) plants in the UK. A decade ago, these plants provided “low carbon” electricity in comparison to the grid at the time, but now in many cases, emit more carbon than local grids. Countries which already have decarbonised grids, France, Sweden, and Scotland, for example, will not benefit from a continuous system which uses natural gas to begin with.
An ideal scenario for a data centre operator utilising this system would be for a zero-carbon hydrogen pipeline to become available as the local utility grid becomes decarbonised. However, this also requires the hydrogen supply to be cost-competitive with utility electricity. As more fast-start PEM fuel cells enter the market, there will be greater flexibility on how fuel cells can be used. PEM fuel cells would allow for dynamic changes in power generation, potentially allowing backup power options or the ability to provide services for the utility grid. Again, this would necessitate significant onsite hydrogen storage or a ‘green’ hydrogen pipeline.
In the coming years, if ‘green’ hydrogen that is made from renewable energy can be made as cost-competitive and as available as current fossil fuels, it will offer a sustainable alternative to diesel for data centre operators. While hydrogen technologies offer a promising solution, they are complex technologies which must be carefully implemented to ensure real carbon mitigation, practicality, and cost-effectiveness.
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