Why Nickel-zinc Beats Lead-acid and Lithium-ion in Data Center UPS

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Steve Jennings is senior VP, sales and marketing, at ZincFive

Lead-acid battery technology has been the workhorse for data center UPS for decades, but      newer technologies introduce fresh opportunities to improve performance, safety, sustainability, and TCO. Lithium-ion and Nickel-zinc (NiZn) chemistries are the primary competitors displacing lead-acid in the marketplace. Both promise smaller footprints and longer operational life than lead-acid batteries. While the tradeoffs of lithium-ion batteries are more well known, given their wide use in other energy storage applications, NiZn technology has specific advantages in terms of reliability, safety, and sustainability over both lead-acid and lithium-ion solutions in data center UPS facilities. These advantages can lead to lower TCO for data center operators.

High Power Density with Small Size and Weight

Two of the most obvious drawbacks of lead-acid batteries are their cumbersome size and weight. NiZn batteries offer dramatically higher power density than lead-acid batteries when measured by either weight (Watt-hours per kilogram) or by volume (Watt-hours per liter). To illustrate the impact of upgrading to NiZn batteries, we compared a 50kW NiZn UPS backup system to comparable lead-acid systems and found these advantages for the UPS facility:

More Reliable Performance

To harness this high power density, the data center operator must be sure the battery backup is highly reliable. The key consideration is battery string reliability. When a lead-acid or lithium-ion battery cell fails, it creates an open circuit that halts string operation. A weak or depleted NiZn cell, on the other hand, remains conductive, allowing the string to continue operating. This turns an emergency situation with other battery chemistries into a simple battery replacement at the next planned maintenance cycle, with little cost and no operational impact. In addition, NiZn battery strings tolerate string imbalances to a greater degree than either lead-acid or lithium-ion strings.

In mission-critical applications such as data center backup, NiZn battery chemistry is capable of fast recharging and excels at high discharge rates while retaining thermal stability. It does not require trickle charging to maintain capacity performance, which simplifies system design and is more energy efficient. Moreover, unlike lead-acid batteries, NiZn is an alkaline battery that does not sulfate over time, which contributes to a significantly longer life with low maintenance. In combination, these reliability behaviors directly lower TCO.

Safer Data Center Facilities

In addition to uninterrupted uptime, data center operators are responsible for the safety of their facilities and personnel. NiZn battery technology has clear safety advantages over lead-acid batteries, eliminating the caustic chemicals and regular maintenance required to keep the batteries fully functional. Furthermore, NiZn batteries do not outgas during normal operation as lead-acid batteries do.

While data center operators would like to consider lithium-ion technology as a replacement for lead-acid systems, they may have read about indoor thermal runaway events at utility energy storage facilities. To evaluate the relative safety of new battery technologies, they can consult the results from any battery or energy storage system that has been tested to the UL9450A Test Method for Evaluating Thermal Runaway Fire Propagation in Battery Energy Storage Systems. Testing under the UL 9540 Test Method can occur at levels defined in the method including the cell, module, unit, or installation level. Cell level testing is the fundamental indicator of whether the battery chemistry will or will not propagate a thermal runaway. ZincFive’s NiZn batteries have been rigorously tested by UL according to the UL9540A Test Method at the cell level, and they did not exhibit thermal runaway in any of the five arduous and destructive test types.

Lithium-ion battery systems that pass the higher unit-level tests rely on a controlling mechanism (a Battery Management System or BMS) designed to prevent the propagation of a cell-level thermal event. Mechanical and electronic devices are known to fail and may not preclude a thermal event if they do fail, hence the superior safety value provided by a battery chemistry able to be tested at the cell level and not exhibit thermal runaway.

Advantages for Sustainability

Given the rapid growth in size and number of data centers worldwide, operators are under pressure to mitigate their environmental impact. This is another driver for replacement of lead-acid batteries that contain significant amounts of hazardous materials that necessitate a highly pollutive recycling process. In fact, environmental organizations have identified used lead-acid battery recycling as one of the world’s top pollution problems.

Upon end-of-life, lithium-ion batteries do not yet have a clear, self-funded path to recyclability. They require extra transportation-safety provisions, because they contain both a chemical and an electrical hazard. They are treated carefully to prevent the possibility of fires with associated toxic outgassing.

NiZn chemistry delivers sustainability advantages over both of the alternatives. Consisting mainly of common highly available materials, NiZn batteries are non-flammable and fail-safe. Even better, with useful life up to three times as long as lead-acid batteries, data center operators do not have to replace them nearly as often.

In addition, NiZn is one of the most recyclable battery chemistries on the market. In fact, the California Department of Transportation (Caltrans) has defined a Green Technology Battery Backup System (GT-BBS) standard that utilizes NiZn battery-based backup systems as a green alternative to traditional lead-acid battery backup systems.

NiZn Attributes that Lower TCO

The TCO for UPS backup encompasses more than just the upfront capital expenditures (CapEx) of battery solutions and facilities to house them. For lead-acid batteries, operating expenditures (OpEx) over the life of the UPS system can be more expensive than CapEx. NiZn solutions dramatically lower OpEx through their much longer useful life and simplified maintenance.

There are other important contributors to TCO for data centers. The size and weight advantages of NiZn batteries compared to lead-acid batteries can lower the investment needed to build UPS facilities within data centers. What’s more, NiZn batteries have a wider operating temperature range than other technologies, which reduces demands on data center cooling systems and enables placement of UPS backup closer to the load.

By lowering OpEx, ZincFive solutions reduce TCO by up to 28 percent over lead-acid-based UPS products when looking across the total UPS useful life.

The Battery Technology for Safer, High Performing Data Center Backup

NiZn technology has emerged as the best choice for replacing lead-acid batteries in data center backup. With high power density and smaller size and weight, as well as longer life and higher temperature operation, NiZn-based batteries are the heart of reliable high-performance UPS. These batteries are safer to operate and a greener alternative than both lead-acid and lithium-ion backup options. Overall, NiZn technology can help data center operators lower the TCO of data center backup.

Opinions expressed in the article above do not necessarily reflect the opinions of Data Center Knowledge and Informa.

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