How turbochargers keep the internet flowing

Data centers put considerable effort into ensuring their power supply remains constant even if power from the national grid becomes unavailable. That includes uninterruptable power supplies (UPSs) powered by batteries, along with backup generators boosted by turbochargers.

Modern society depends on secure, fast, uninterrupted data flows. The ways we work, shop and entertain ourselves in the twenty-first century have become significantly reliant on the availability of data services in the cloud.

‘The cloud’ is, of course, a rather romantic euphemism: what we’re actually referring to are hundreds of purpose-built data centers scattered across every country, each housing hundreds, perhaps thousands of server racks, and all of their associated needs for power, cooling, service, security and connectivity.

Data center operators are selected by their customers based on cost and reliability. It’s become usual for operators to advertise ‘Five Nines’ uptime guarantees in their Service Level Agreements (SLAs). That is, that the data center will be operational for 99.999% of the time. Achieving this level of reliability without becoming unprofitable is a continual challenge: operators need to build in backups and contingencies for everything, but without significantly increasing costs for customers compared to competitors.

Power outages are disastrous for data center operators. Because they need to offer such robust SLAs, any downtime is extremely expensive – 0.001% of a day is just under a second. Any period offline beyond that second means they have to start paying compensation to their customers. According to the data center consultancy Uptime Institute, over half (54%) of the operators polled in its most recent survey said their most recent significant, serious or severe outage cost more than $100,000, with 16% saying that their most recent outage cost more than $1 million.

Christoph Voser, Global Product Line Manager, Accelleron Christoph Voser, Global Product Line Manager, Accelleron

Power Up

Thus, data centers put considerable effort into ensuring their power supply cannot be knocked over even if power from the national grid becomes unavailable. The moment power from the grid falters, uninterruptable power supplies (UPSs) powered by batteries kick into action to restore the current. At the same time, backup generators situated beside the data center, in containers, fire up.

It’s legitimate to ask why the backup generators are required, over and above added insurance, given the presence of battery power. This is because of two factors. First, typical data centers consume as much power as a small town. In Ireland, admittedly an extreme case, data centers consume nearly one third (32%) of all the country’s power. The volume of battery cells they’d need to continue to supply power for more than a few seconds would be extremely large, while diesel backup generators are often designed to bridge a power outage of 24-48 hours. Second, batteries are expensive, while diesel-powered generators are typically a lot less so. Any way to ensure reliability at a lower cost is very much welcomed, given the financial constraints of these businesses.

So, these generators need to be capable of reaching full power fast, typically in less than 30 seconds. In North American and Europe, operators will typically choose a series of smaller 3MW generators, providing redundancy. The higher the engine is turbocharged the less space and materials, and thus cost, are required to provide the power. The turbochargers need to achieve a high compression ratio in a short amount of time. Therefore, the turbochargers are optimized for part-load efficiency in order to accelerate fast so that the generator can start to output electricity in the shortest period possible.

Engine builders for these applications will often turn to Accelleron for their turbochargers, given the availability of units with high compression ratios, fast transient response and the company’s reputation for reliability. The TPX family of turbochargers is the best fit for this market, offering a fast transient response and high compression ratio. The generators have zero margin for error when every extra second could cost $1000s.

Green data?

The choice of diesel oil to power these generators is because it’s familiar, inexpensive, has a long shelf-life and is readily available. And, of course, they don’t produce any emissions if the engine isn’t switched on, which is every operator’s hope. Normally, the generators are tested briefly every two months, to ensure they work, and sit dormant for the rest of the time.

Operators are seeking to become more sustainable, however, and with more businesses required to report on Scope 3 emissions (those created by their suppliers), a commercial advantage to finding better alternatives is developing. As with alternative fuels in the marine industry, these alternatives have complications. A quick win and a step in the right direction would be natural gas powered generators, and some data centers – notably in the US – have made the switch. The complication comes with how the gas grid operates. In many countries, such as most of the EU, the gas grid’s flow is controlled by electric switches, which would be rendered inoperable in the case of an electric grid outage.

A promising alternative is HVO fuel (Hydrotreated Vegetable Oil). This is carbon neutral but otherwise available as a direct replacement for diesel oil. It’s not as abundant as diesel, and it is unlikely to be a major replacement for fossil fuels across other industries where engines are continuously operated. But for these small power generators, which are hardly ever switched-on and thus have tiny fuel supply requirements, HVO may well provide a usable route to becoming carbon-free.

The data center market is predicted to grow significantly in coming years. It was growing significantly over the last two decades as our lives became more and more digital, and the AI-boom that started in late 2022 has accelerated this growth significantly. Expectations of reliability rarely decrease over time, and so we hope that Accelleron turbochargers which enable the high power density required will continue to be a small but essential ingredient of the digital economy for a long time to come.