Changing the shape of datacentre power
Since their inception, datacentres have followed the same tried-and-tested formula for power generation, with diesel pivotal in safeguarding their power supply. As datacentres rapidly grow and society simultaneously transitions to a low-carbon economy, we must find a new approach to achieving continuous power supply without fossil fuels.
With hyperscale power demands ranging from 20 megawatts through to 1000 megawatts, in a power outage, the load is initially supplied with a battery-backed continuous supply, with diesel generators providing additional support through extended outages. While the duration of the battery may vary, this basic formula has been implemented again and again in different locations around the world.
Mains power for datacentre operations is typically supplied from a utility-backed power distribution grid, connected to supplies from various sources, which may include solar, wind, coal, gas, hydro and nuclear power stations. The grid is shared among all users to provide secure, readily accessible power. However, sometimes, that power fails, creating a short-duration blip in the power supply known as a brownout or a full-duration blackout.
In Australia, most outages last a relatively short time, with power restored within a few hours or, at most, a day. Datacentres are typically large industrial users connected to robust It takes a significant event to impact this supply, with acts of nature such as forest fires and flooding the most likely causes.
As a backup power supply, diesel is favoured given its high reliability, ready supply, and ease of storage. You can store a lot of energy in a very small space with a diesel tank, with most datacentres storing 12-24 hours of diesel on-site at a capacity of about 250 litres per hour. While diesel can go off, it will last indefinitely in storage if properly maintained. Given the rarity of power outages in most data centre locations, diesel supplies will last for many years on standby for a major event to occur.
Diesel’s carbon impact is an obvious downside as a fossil fuel. Additionally, as new hyperscale facilities become commonplace, diesel will be challenged by the size and scale of delivery required to support backup power requirements for hyperscale facilities.
So, what are the environmentally friendly alternatives, and why have we been so slow to include them in new designs?
Battery Energy Storage Systems
Increasing the size of our battery banks is one option. With the rise of Battery Energy Storage Systems (BESS) such as the Tesla Big Battery in South Australia[1], large-scale battery storage is a proven technology. A BESS could replace both local battery supply and diesel generator, sustaining operations longer than a traditional datacentre battery system. This would provide a solution with virtually no emissions and low levels of maintenance. With enough capacity, it could also be used similarly to other BESS systems to help firm up the electricity grid and compensate for peaking energy supply from renewables. However, datacentres are rapidly growing, and maintaining a 24-hour supply to a 500-megawatt hyperscale datacentre would require 12,000 megawatt hours of batteries, equivalent to over 60 of Teslas 193 megawatt hours Big Battery, and would be a huge space footprint.
Hydrogen
Hydrogen is a clean burning fuel, producing only water as a byproduct. When produced via electrolysis using renewable energy sources (for example, solar), hydrogen is a low-carbon fuel that can be consumed to generate power, with a range of generation technologies available including engines, turbines and fuel cells. However, with energy lost at each conversion stage, more than 60 percent of energy[2] is lost from “solar panel” to rack. While fuel cells provide a slightly higher power generation efficiency, they are currently more expensive and not readily available at hyperscale capacities. Hydrogen also suffers from a relatively low level of volumetric energy density compared to diesel, so storage on-site is relatively difficult for large scale facilities, but still vastly higher density than BESS. , but such distribution infrastructure is limited and unlikely to be readily available unless provided as government-backed infrastructure.
Nuclear power
Significant hype is building for nuclear power with Small Modular Reactors (SMRs)[3] offering up to 500 megawatts of carbon-free power and micro reactors[4] offering up to 10 megawatts. While these solutions would provide ideal base-load power for a datacentre facility, significant work is needed to develop and deliver this type of facility. Social licence for the use of nuclear power in many countries will also be limited, particularly in Australia where it remains a contentious issue in public forums.
The last alternative is to make a bold choice and remove generators entirely, relying solely on a utility connection. To do this, datacentres must be much closer to power sources and connect to multiple independent distribution paths or sources of supply. By connecting to diverse grid distribution paths, you lower the supply risk if one of the paths fails. Batteries are still needed to manage short duration switching and brown out quality issues, but the need for extended on site generator capacity is reduced. This does mean that datacentres need to be relocated towards more industrial locations and away from urban areas, which is becoming increasingly likely as new datacentres grow into the megawatt range.
Ultimately, there is no single solution and understanding each datacentre's operating needs is essential. The first consideration should be a robust discussion of necessary uptime – the datacentre’s level of availability and which option best serves this. It’s clear that as social licence diminishes for carbon-emitting diesel generators and the practicalities of diesel at hyperscale become challenging, a change in approach must come next.
References:
[1] South Australia's giant Tesla battery output and storage set to increase by 50 per cent - ABC News
[2] Green hydrogen as a power plant fuel: What is energy efficiency from production to utilization? - ScienceDirect