Li-ion offers new opportunities for data centres

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A new white paper says that the falling cost of lithium-ion batteries is enabling data centre operators to review their electrical distribution topology and potentially generate additional income from their battery investment…

The European Data Centre Association (EUDCA) has announced the publication of a new white paper, entitled Battery Opportunities for Data Centres. Authored on behalf of the EUDCA Technical Committee by Gareth Williams, director at Arup, the white paper discusses the impact of lithium-ion batteries on the data centre space.

While uninterruptible power supply (UPS) vendors and customers have traditionally specified lead acid (VRLA) batteries in power backup solutions, recent reductions in the capital costs of Li-ion solutions have made them competitive with the older technology, offering a payback period of less than five years when the operational cost savings are considered.

The author says that within the US market, the capital cost differential has reduced even further, with some UPS vendors now able to offer their larger clients Li-ion battery solutions for the same price as VRLA-based solutions.

From reduced footprint to increased environmental range and lifecycle, Li-ion presents a number of advantages to the data centre designer such as increasing autonomy, load or white space; providing alternatives for the battery location and environment; or allowing the batteries to be considered for a range of functions that would not previously have been considered acceptable with VRLA type batteries. 

The author points out that sizing of UPS and battery systems needs to be carefully considered for these applications to ensure the site maintains sufficient battery capacity to achieve their Service Level Agreement (SLA) commitments. However, these operating modes could generate an additional income stream or operational savings.

In a recent trial of UPS for demand-side response applications, Basefarm’s data centre in Norway achieved the fastest response time of all operators following a power station failure event. Offering this type of service to the grid is expected to achieve an annual income of ¤50-100k/annum per MW of capacity that the operator is willing to make available for demand-side response.

Alternative electrical distribution topologies

Making use of the reduced footprint associated with Li-ion to install increased capacity allows the operator to move the batteries further upstream and protect even more of the site. The wider acceptable environmental range means the batteries could be relocated into the data hall and installed at PDU, row or even individual rack level. Locating the batteries this much closer to the IT load creates a range of further opportunities

Software defined power

Rack level battery capacity enabled by Li-ion technology is also an enabler for software defined power. Example uses include allowing power to be diverted or reserved to meet the demands of specific applications, racks or rows; power allocation based upon priority level of the application during failure scenarios; and deploying multiple SLAs within the same data hall.

In summary, Williams states that Li-ion batteries make it possible for today’s data centre operators to develop a range of alternative distribution topologies, increase available white space, reduce or eliminate the need for dedicated cooling for batteries. The smaller footprint and increased cycle-life options provide the potential to generate additional income through the provision of grid support services and relocating batteries downstream creates alternative opportunities for data hall level distribution.

Finite resource?

Responding to the report, Leo Craig, general manager of Riello UPS, welcomes the findings but cautions that Li-ion is a finite resource. He comments: “The benefits compared with traditional lead-acid are now well-established [ie more compact footprint, faster charging times, longer lifecycles]. But we’d be the first to admit there’s still plenty of work to do before data centre operators fully understand and embrace the possibilities. In such a naturally risk-averse industry, new technologies will inevitably be treated with suspicion, so the more positive examples and advocates there are, the better. 

“Hopefully, we aren’t far away from the evidence becoming so overwhelming that we reach the all-important tipping point where deploying UPS systems using Li-ion isn’t viewed as either an unusual or unnecessarily risky choice.”

Craig adds that one concept that could have a significant impact on data centre energy storage is the potential second life of batteries from electric cars: “Currently, it’s far cheaper to mine new lithium than it is to recycle. Electric car batteries typically last for around 10 years before they lose enough performance to require replacing, but they can still collect and discharge electricity for several more years. 

“Rather than simply sending these batteries to the scrapheap, doesn’t it make sense to repurpose them to store electricity generated from domestic renewable energy installations and commercial applications too?

“Not only is the cost of repurposing a fraction of the investment required for a new battery. But with electric cars set to become the norm, rather than the exception, in the coming years, it offers a practical solution to the issue of what to do with the millions of lithium-ion batteries that will eventually need to be reused or recycled.”

Several major car manufacturers already reuse EV batteries in large-scale storage projects. At the Johan Cruyff Arena in Amsterdam, for example, second-hand battery packs save power produced by thousands of solar panels installed on the football stadium’s roof. 

Craig concludes: “We should never forget that lithium is a finite resource and the only sustainable way to keep up with increasing demand is to think outside the box about ways we can both reuse and recycle.”

Application is key

When it comes to choosing battery technology, the best solution is application dependent, according to Stuart Cockburn, sales manager for Centiel UK.

“There will still undoubtedly be a place for VRLA batteries for many years to come but Li-ion can offer some useful advantages over VRLA batteries in certain situations,” Cockburn explains. 

“Li-ion batteries are happy running at a temperature of high 20/low 30 degrees centigrade, which makes them useful for applications such as hot works plant rooms like in medical facilities or hospitals for example which are generally kept at a higher temperature than a traditional air-cooled comms room. Li-ion batteries typically require less than half the physical space of the equivalent lead acid blocks and are less than 25% of the weight so could be more suited to installations where space saving is important or any installation in the upper floors of office buildings. Interestingly, the adoption of Li-ion within UPS systems, so far, has been greater in developing countries in Africa and the Middle East, where the main power grid is less reliable than in the UK and frequent power problems are more commonplace. 

“In these instances, the UPS and battery systems are required to be cycled several times per day. This greater take-up is primarily due to the higher cycling life of Li-ion: typically, 2,500 power-up and down cycles compared with around 300 for VRLA technology.” 

Discussing the financial implications of Li-ion adoption, Cockburn comments: “Although Li-ion is currently more expensive to purchase initially than VRLA batteries, most clients are looking for a 10 minute run time. However, consider this: your generator will start in 30 seconds so why do you need a 10 minute run time? VRLA batteries charge slowly so a 10 minute run time is usually necessary. 

“However, with Li-ion, because the charge goes back into the battery very quickly, just a five minute run time is sufficient. By halving the autonomy time, the number of batteries required is halved and therefore the cost of purchase is also halved. Further space is saved in the comms room too,” Cockburn concludes.

To obtain a copy of Battery Opportunities for Data Centres, email: alex.rabbetts@eudca.org

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