Emergency back-up facilities to cope with an unforeseen loss of mains electricity supply are a standard attribute of data centres. Until recently this option has almost invariably comprised a bank of usually lithium-ion batteries that can kick in immediately to allow operations to continue in the short term supported by an on-site generation capability that can maintain operations for an extended period.
That second layer of capability has usually been provided by electrical generators driven by diesel-fuelled motors. But as businesses of all sorts look to find more environmentally benign ways of operating data centres are also looking to find alternatives to the use of fossil fuels even for dealing with occasional contingencies.
No place for diesel in sustainable future
Perhaps the most immediate strategy is simply to replace diesel with a different, less polluting fuel. This is the option that has been implemented by Kao Data, provider of colocation services based on hyperscale principles at its data centre site in Harlow, Essex, in the UK. That description is provided by chief technology officer Gérard Thibault, who explains that the site currently comprises one fully operational building with an 8.8MW capacity and an identical second in construction with planning permission granted for two more.
Thibault says that just over 18 months ago the company took the decision to swap from diesel to HVO (Hydrotreated Vegetable Oil) as the fuel for the engines that power its back-up generators. The decision was prompted, he says, by two factors. The first was the adoption of a corporate policy aimed at taking a proactive approach to sustainability. The second was that HVO was literally a ‘drop-in’ option that, as he confirms, required no physical alterations to the engines or engine controls. As such they preserved all our existing investment in the engines and generators.
At the time the building had three generators each rated at 1808kW. The actual conversion procedure, Thibault says, involved no more than draining their existing diesel content and replacing it with HVO without disturbing any sludge. Since then two more have been added as the business has grown which have, he confirms, been HVO from the start.
“In normal operation the building has two electrical feeds from a sub-station and uses a series of low-voltage UPSs further down in the distribution scheme providing 400V three-phase power with a five minute battery store on each,” Thibault, says. “Generally the engines will start in a range of 18-32 seconds.”
Emphatic results for HVO
So far there has been no occasion to use the engines in a real emergency. But, Thibault explains, they have been operated in realistic simulations on a regular basis. “They are run from one to two hours a month in a test scenario that runs the generators up to speed, parallels them with mains supply and then drops the mains supply to ensure we can get an uninterrupted supply to the building,” he states. During those test phases though the AC output of the generators does support the real operations of the data centre.
Moreover testing has also proven out the much enhanced environmental performance of HVO. Late last year the company carried out a specific benchmarking exercise in which emissions from one of the engines were directly compared in HVO operation and a temporary reversion on the same machine to diesel fuel. The results were emphatic. “The figures are a 90 per cent reduction in CO2 taking into account growing the vegetable oil in the first place and a six per cent reduction in NOx,” Thibault says. “We lose sulphate emissions completely because there are no sulphates in vegetable oil.”
More subjective impressions are also positive. “We have not created black smoke and there is no ‘chip fat’ odour,” Thibault, says. “There have been no surprises.” There is, Thibault concedes, an initial cost penalty as HVO is about 15 per cent more expensive than diesel fuel. But he says that Kao has accepted that as a given in its drive to achieve environmental efficiency and that is mitigated slightly by the fact that HVO has a marginally higher energy density than diesel. With security of supply also assured through Kao’s relationship with its preferred supplier Crown he confirms that the first engine and generator combination in the second building on the site which should be completed in the middle of this year will also run on HVO.
The case for hydrogen
But is there a perhaps more radical if not yet immediately practicable option to provide sustained back-up power for data centres? One company that thinks so is Vertiv, which provides critical infrastructure elements such as UPS and battery combinations. In this case the technology it is focussing on is that of hydrogen fuel cells.
Vertiv’s thinking is explained by Arturo DiFilippi, global offering manager for large AC power UPS. DiFilippi, who is based in Bologna, Italy, says that while the company is not a supplier of power generation equipment it does have to address how its products will be integrated with power generation technologies and what those technologies might be.
In that context, DiFilippi is convinced that diesel generation is not a sustainable option. Fuel cells, however, would be and, as he further explains, they represent the company’s preferred option as the power generation technology it could couple with its own products. He confirms that Vertiv is now well-advanced in proof of concept development work that could see the first real implementations of the technology in this application by the middle of this decade.
DiFilippi says Vertiv has focussed initially on the potential of PEM (proton-exchange membrane) fuel cells that utilise a solid polymer electrolyte and require a supply of hydrogen and atmospheric oxygen to operate at the relatively low temperature of up to 80OC. Indeed late last year it published a white paper setting out some of the basic economic and performance parameters for the technology it has so far established.
Requirements for PEM fuel cells
The essential elements for the use of PEM fuel cells in this context, DiFilippi confirms, are threefold. First sufficient on-site hydrogen storage with four trailer loads identified as the necessary amount to provide 48 hours of back-up for a 1MW facility. Second a fully contained PEM fuel cell system with integrated thermal management, air filtration and DC output to the UPS. Finally a UPS with lithium-ion batteries able to control the fuel cells and featuring an integrated DC-to-DC converter able to operate continuously for several hours.
In this context, says DiFilippi, PEM fuel cells offer several advantages. “They are clean with no CO or CO2 emissions, they involve an electro-chemical reaction with no combustion and their efficiency is probably slightly higher than diesel generation,” he states.
A crucial difference between fuel cells and diesel-powered generators is that the former generates DC power and the latter AC. As DiFilippi explains this means that the output of the fuel cell can be fed directly into the lithium-ion batteries which can then act as a buffer between the cells and the data centre load. In turn this means that if the load requirement drops below the output of the cells the excess can be used simultaneously to recharge the batteries. Indeed DiFilippi identifies this ability to effect transience absorption as a key distinguishing feature of the fuel cell approach.
DiFilippi says that testing of the concept late last year involved proving out the integration of 500kW UPS with a 200kW fuel cell. The work was carried out in Europe and involved a fuel cell supplier which he will not for the moment identify. Right now, though, Vertiv is looking to scale up that work by setting up a demonstration centre at its Delware site in Columbus, Ohio, in the US that will involve a 400kW fuel cell with a 1.2MW UPS. Testing so far, he confirms, has proved that it is feasible technology and he remains cautiously optimistic that 2025 could see its first commercial rollout.