Do diesel gensets have a role in the future sustainable digital infrastructure?

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To discuss the future for diesel gensets in the drive to a net-zero future we spoke to Tobias Bertler, senior manager direct sales at Rolls-Royce Power Systems

How concerned about sustainability are data centre operators when it comes to backup power?
Data centre operators are extremely interested in sustainable back-up power solutions. This is partly because the entire data centre market is dominated by the large technology companies that are very much in the public eye and feel a social responsibility to reduce their carbon footprint. Carbon neutral as well as carbon negative targets from Microsoft, for example, are terms that have entered the public discourse in recent years.

This has also brought data centre emergency power systems into focus. Although they have only a few operating hours, gigantic capacities with an extremely high available power are being built for these mission-critical data centres. Their standards, also about lower exhaust emissions, are constantly being tightened and emergency power generators are sometimes equipped with exhaust aftertreatment systems. This green trend is also spreading from the hyperscale operators to smaller data centres, which often lease capacity as collocation data centres to the large technology companies, which do not build data centres themselves in every country but have similar specifications for their leased capacity.

Is there still a big demand for diesel gensets from data centre operators?
Definitely. Every mission-critical data centre has back-up power systems built into it that typically run on diesel fuel. Last year’s exceptional situation caused by the COVID-19 pandemic showed once again how important it is to ensure an uninterrupted power supply for sensitive and critical infrastructures such as global continuous Internet traffic.

Only individual companies have currently opted for a solution with gas gensets or battery storage systems without diesel generators. Gas gensets have less dynamic behaviour than diesel gensets, meaning they take slightly longer to deliver full power and have less transient behaviour to respond to load changes. Those that do not have access to a gas pipeline, but must store gas, require more space and have more demanding and expensive storage overall compared to diesel.

In addition, in many regions the gas network is not independent of the power grid, and in the event of a power outage, the gas supply may also fail. Therefore, even if gas is connected, larger quantities of gas must be stored locally. In the case of batteries, the storage capacity is limited, while the diesel genset, if it is fuelled, can generate electricity permanently and supply the data centre.

Accordingly, diesel gensets are currently still the perfect solution for mission-critical facilities that can provide power for several days in an emergency. As an exception, we see non-critical data centres, which do not incur major costs or damage even in the event of an outage, but only have their computing process suspended. One example is cryptocurrency mining, whose potential loss of power in the event of a power outage is calculated in a risk assessment. In some cases, they only have batteries that allow for a controlled shutdown.

Given the very infrequent use of these backup gensets do you consider the problem of emissions a concern?
Exhaust emissions are always a critical issue, and the diesel scandal has not made this any easier. That is why emergency power generators are now also in the spotlight, despite their short run times, and certain limits must be met to get the systems approved. Emissions (both noise and exhaust) are also part of the building permits for the entire data centre and can delay them accordingly if the issues are not considered early on.

Authorities look at worst-case scenarios and assume that if a power outage occurs, several 100 MW diesel generators will then be running, even if only for a relatively short time. Since it is crucial for data centre operators how quickly a data centre can come online (time-to-market), the operators look very sensitively at the emission values and possibilities to shorten approval processes via lower values. In addition, the sustainability goals of data centre operators also consider ways to optimise the emergency power supply.

How are you attempting to reduce emissions from your diesel gensets?
We have different ways of reducing emissions from diesel gensets. On the one hand, we continue to work on reducing exhaust emissions through internal engine measures. In addition, we offer exhaust gas aftertreatment systems from our own development and from third-party suppliers. We thus offer different, flexible, and project-specific solutions for the very heterogeneous market, where there are different directives and legislation depending on the region.

What are the challenges you face in reducing emissions?
We come up against technical limits when it comes to engine-internal measures, as it is not possible to improve emissions of all pollutants to the same extent. When integrating exhaust gas aftertreatment, we have the challenge of the increased exhaust backpressure with which the engine is operated. It is therefore important to consider these issues at an early stage of engine development.

For example, the current MTU engine series were prepared in good time for combination with exhaust gas aftertreatment systems and developed for corresponding exhaust gas back pressures.

The space required for exhaust gas aftertreatment can also be a challenge, especially if a system must be retrofitted. Due to the wide variety of directives and legislation in different countries, regions and sometimes even cities, it is not possible to offer customers a standard solution. Already in the design and planning phase, the requirements must first be clarified with the local authorities on site to plan for the appropriate solution and the corresponding installation space. Nevertheless, as a manufacturer, we try to offer modular, expandable solutions as far as possible to be able to respond to the different requirements and offer customers the best possible solutions.

With companies such as Microsoft saying that they will stop using diesel gensets, is it forcing the industry to look at alternatives?
The current announcements are definitely accelerating the process of offering greener solutions for emergency power solutions as well. Rolls-Royce has set its own goals in this regard and has already been investing in environmentally friendly future solutions for lower emissions, reduced energy and raw material consumption since 2015 through its Green and High-Tech Programme. To drive development forward more quickly, Rolls-Royce Power Systems has established the new ‘Power Lab’ business unit in 2020.

Our propulsion and energy systems are designed to help meet the societal challenges of climate change, increased energy demand, and the mobility and energy needs of a growing global population. That is why we see it as important to expand renewable energies and Power-to-X technologies, make alternative fuels available, prepare combustion engines for alternative fuels, and develop alternative energy and propulsion systems.

Accordingly, we are expanding our portfolio to include fuel cells and are currently testing hydrogen engines for energy supply. We see great potential in hydrogen as a fuel. The numerous initiatives by various countries to further expand the infrastructure are also encouraging. In addition to hydrogen, we are working on other fuels produced from renewable energies such as e-diesel, e-methanol, and e-methane.

For Rolls-Royce Power Systems’ applications, the compactness of the PEM fuel cell resulting from its high-power density, its high scalability, the possibilities of modular design and the resulting flexibility are ideal. Fuel cells can be integrated directly into battery-electric or electrified energy systems, for example. The cell achieves high electrical efficiency (approx. 50 per cent), a high current density and is also very safe to use. It thus offers the necessary prerequisites for use in stationary power generation systems – such as emergency generators or uninterruptible power supplies.

If fuel cells take over the backup power supply – be it as an uninterruptible power supply or a grid backup system – only heat and humid exhaust air are generated. The fuel cell system has no moving parts, which minimises mechanical maintenance. The fuel cell also scores points in a comparison of efficiencies: Whereas with the internal combustion engine, the mechanical energy must be converted into electricity by an additional generator, the fuel cell supplies electrical energy directly. Another advantage is that it can be excellently scaled: More modules mean more power – fuel cell systems can also be easily integrated later and grow with it when a data centre expands. This makes fuel cell systems a long-term and future-proof investment.

Fuel cells can play a central role for CO2-free data centres. In the future, the basic power requirements of a data centre could be covered by solar and wind power plants. If sufficient green electricity is available, hydrogen can be produced from water by electrolysis and stored on site. In addition, the hydrogen demand can be covered by a supply network that will be available in the future and used to operate the fuel cell: It would immediately take over the supply of the data centre to maintain the infrastructure in the event of a power failure.

Rolls-Royce and Daimler Truck are planning to cooperate on a CO2-neutral emergency power supply for mission-critical facilities such as data centres using stationary fuel cell generators. These are to offer emission-free alternatives to diesel engines, which have so far been used as emergency power generators or to cover peak loads. Daimler Truck and Rolls-Royce have signed a memorandum of understanding to this effect. At the end of 2019, Rolls-Royce Power Systems and Daimler agreed on a pilot project to develop a demonstrator for the use of this technology for stationary energy supply based on fuel cell modules from automotive production. It will go into operation in early 2021 and contribute to the energy supply of Rolls-Royce Power Systems at its headquarters in Friedrichshafen.

Another development that we have been driving forward for several years is the upgrading of gas gensets for emergency power systems. The focus here is on improving transient behaviour, particularly regarding starting the plant and its response to load changes. Gas gensets are also used for continuous power supply for data centres.

For example, SpaceDC officially launched its new 25.45 MW data centre campus with Rolls-Royce technology in early November 2020. It is the first green data centre in Indonesia. Three MTU gas and diesel systems with the latest exhaust aftertreatment technology provide efficient and clean base-load and emergency power and cooling.

Are you considering using or are you currently using any fuels other than diesel to power the gensets?
For the synthetic fuels according to EN 15940, we have run extensive tests on the test bench and in the field in recent years. We expect to be able to release these fuels for our Series 4000 engines from 2021. The synthetic EN 15940 fuels are as follows: GTL (Gas-to-Liquid), BTL (Biomass-to-Liquid) and HVO (Hydrotreated Vegetable Oil), which are produced using the Fischer-Tropsch process and are similar to diesel in terms of their properties. However, they also offer some advantages, such as storage stability, which is much better compared to conventional diesel (especially with increased bio content). BTL and HVO are largely made from biological feedstocks and can be produced in a CO2-neutral manner.

What about biodiesel – is it a viable fuel given the sporadic use of gensets that are only used at backup power?
Biodiesel has a higher bio and water content and thus has a poorer storage capability than regular diesel. Biodiesel is more susceptible to aging due to microorganisms in the fuel and can even tip over. This is referred to as the diesel plague, where a bio-sludge forms in the fuel that can cause equipment malfunction and damage. Since fuel is often stored for long periods in emergency power systems, we view this fuel rather critically for this area. We consider other alternative fuels, such as the synthetic EN 15940 and e-fuels, to be more suitable for this purpose. Nevertheless, we have approved an admixture of seven per cent biodiesel without further measures. For blending of up to 20 per cent biodiesel we recommend various accompanying measures such as additives, a tank maintenance system or engine flushing. If the admixture exceeds 20 per cent, this must be considered on a project-specific basis.

There has been talk of connecting these backup genset units at data centres to the grid. Is that a viable option?
Absolutely! Emergency gensets offer excellent conditions for feeding control power into the power grid and thus compensating for fluctuations in the grid (frequency and voltage) caused by the increased integration of renewable energies. The gensets can thus play a significant role in supporting the energy transition (and integration of renewables). To this end, there are various capacity markets in different countries in which to participate. For many years, Rolls-Royce Power Systems has had cooperative agreements with various national and international companies that enable our gensets to be integrated into the respective capacity markets. Another advantage for the operators is the creation of another source of income with the installed emergency power systems. Rolls-Royce has some reference installations in both the diesel and gas sectors. However, data centre operators have been very reluctant to implement them and the references are mostly from other industries.

Any other thoughts on the future of diesel gensets for data centres?
In the short to medium term, we continue to see diesel gensets as the established technology for mission-critical emergency power systems. They currently offer the highest level of safety and the most coherent technical characteristics for this use case. More environmentally friendly solutions that contribute to decarbonisation will become established and are part of the development roadmap for the future Rolls-Royce portfolio. These include gas gensets, alternative fuels, battery storage and fuel cells. In the long run, new topologies and architectures will develop from the data centre power supply via the integration of the new technologies to be able to use all the advantages of the corresponding technologies. A major challenge will be the (sufficient) availability and storage of alternative fuels, as well as the integration of the data centre into more decentralized flexible power grids.


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