• • • ENERGY EFFICIENCY • • •
The changing landscape of data centre energy storage
By Ed Ansett, Founder and Chairman, i3 Solutions Group
apid technology advances are about to shift the landscape of energy storage options for data centre operators, whether running 250kW edge computing sites or 100MW hyperscale facilities. From battery banks to gravity, for emergency back-up discharge in seconds or long- term discharge over days, weeks, and months; how energy is stored on-site and off-site has the potential to radically shake up data centre power chain design and operation.
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Solutions already in use include the increasingly common Lithium-ion batteries and the familiar kinetic flywheels. Less familiar may be gravity and liquid air energy storage. Here we offer a high level ‘What is..’ list of just some of the new and not so new technologies that are in use today and those that could find their way into the data centres of the future. A more detailed technical analysis of data centre energy storage developments and emerging technologies will be available soon from i3 Solutions Group and EYP Mission Critical Facilities Inc.
1. LITHIUM-ION BATTERIES
Use of Li-ion has grown rapidly in data centres. As the Uptime Institute reported, this is mainly due to better energy density, rechargeability and management. It says “Li-ion energy storage is also regarded as a key component in renewable energy distribution, which is being adopted primarily to reduce carbon emissions.” In addition to being more compact and lightweight
than VRLA equivalents, advantages of Li-ion include energy capacity superiority, lower battery discharge through efficiency; extended lifespan; software optimisation enhancement and better remote management capability. While questions remain about how sustainable Li-ion is when measured across its entire lifecycle, from sourcing raw materials to operation, disposal and recycling, the use of Li-ion battery banks in data centres of all sizes will continue to grow in the near term.
The UTI says ‘there are now dozens of companies with Li-ion recycling services or technologies’, and it advises that ‘the best way for data centre operators to reduce the impact of Li-ion use will be to open a serious dialogue with suppliers.’ Meanwhile, large deployments are being planned. In late 2020 Google said: “In Belgium, we’ll soon install the first ever battery-based system for replacing generators at a hyperscale data center… batteries are multi-talented team players: when we’re not using them, they’ll be available as an asset that strengthens the broader electric grid.” (Source: Joe Kava,
googblogs.com) In every sector, data centres already make use of tens of thousands of cells in battery systems – they may also need to renew thousands of them each year. Lithium is not the only battery technology option available. More sustainable battery types, with high enough energy densities, are being developed and some may start to compete as they become more cost-effective; these include flow batteries, zinc nickel and sodium-ion. Using a less expensive and more common
element than Lithium, Sodium-ion cells can be recharged in around a fifth of the time. The technology is cost-effective and sustainable, which includes using local bio-based energy sources in the battery supply chain. For example, researchers in Germany are exploring the use of local agricultural waste in sodium-ion energy storage chemistry.
2. KINETIC
Flywheels have been used to store energy for thousands of years. Today in data centres across the world, tens of thousands of flywheels are used for short term energy back-up power. Kinetic energy as the name suggests is energy generated via motion of an object. In classical mechanics, kinetic energy (KE) is equal to half of an object's mass multiplied by the velocity squared. Kinetic energy = ½ (mass)*(velocity)2. A flywheel system
32 ELECTRICAL ENGINEERING • JULY/AUGUST 2021
stores energy mechanically in the form of kinetic energy by spinning a mass at high speed. Electrical or mechanical inputs spin the flywheel rotor and keep it spinning until called upon to release the stored energy. The amount of energy available and its duration are governed by the mass and speed of the flywheel. Kinetic flywheels have seen success as energy storage components in the UPS power infrastructure. These systems indirectly provide electrical energy for the data centre from low and high-speed flywheels.
3. COMPRESSED GAS STORAGE
Liquid air energy storage (LAES) stores liquid air inside a tank which is then heated to its gaseous form, the gas is then used to rotate a turbine. Compressed gas systems have high reliability and a long-life span that can extend to over 30 years. LAES, also referred to as Cryogenic Energy Storage (CES), is a long duration, large scale energy storage technology that can be located at the point of demand. The working fluid is liquefied air or liquid nitrogen (~78% of air). LAES systems share performance characteristics with pumped hydro and can harness industrial low-grade waste heat/waste cold from co-located processes. Size extends from around 5MW to 100+MWs and, with capacity and energy being de-coupled, the systems are well suited to long duration applications. (Source: Energy Storage Association) An Adiabatic Compressed Air Energy Storage (A- CAES) System is an energy storage system based on air compression and air storage in geological underground voids. During operation, the available electricity is used to compress air into a cavern at depths of hundreds of meters and at pressures up to 100 bar. The heat produced during the compression cycle is stored using Thermal Energy Storage (TES), while the air is pressed into underground caverns. When the stored energy is needed, this compressed air is used to generate
electricalengineeringmagazine.co.uk
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