Power System Design: Why Lithium is Taking Over Stationary Energy Storage

Figure 1: This chart contains the most common commercialized sub-chemistries of lithium-ion batteries. Different applications require different performance characteristics and can be better served by selecting the correct chemistry.

Today, you don’t have to look very far to find a device that is powered by a lithium-ion battery. Chances are, you’ve got one in your pocket, or sitting somewhere on your desk. You might be reading this article using a lithium-ion powered device! Lithium-ion batteries are the hidden power source behind billions of consumer products, everything from smartphones, tablets, and laptops to cordless power tools and digital cameras. Also, lithium-ion batteries are being developed and used as power sources for hybrid and self-driving vehicles, and finally are making a debut as energy storage solutions for electrical grids, wind turbines, and solar panels.

Lithium-ion batteries are well known to be smaller and lighter enabling portable devices to shrink and run longer. Now why would stationary applications, where space and weight are rarely an issue, benefit from a lithium-ion battery? Lithium-ion batteries have a few more benefits than just size and weight. These benefits include lower costs, higher reliability, increased flexibility, and remote monitoring. Telecom network, data center, and edge computing operators are finding these benefits fit their needs and are deploying more lithium-ion batteries than ever before.

The advantages of lithium-ion batteries often make them a more practical option for UPS backup power, especially in small-scale and remote deployments.

Reliable Power

The failure of lithium-ion batteries in UPS applications is extremely rare. Today’s battery providers utilize quality materials, superior design, and improved manufacturing methods to produce lithium-ion batteries that are built for reliability in all kinds of mission-critical environments. Research and investment in EV lithium-ion batteries has spilled over and benefits all lithium-ion batteries. Battery management systems (BMS) have evolved and improved over the past 20 years. These advanced BMS paired with modern cells create highly reliable backup batteries, as well as add monitoring, and advanced algorithms to monitor health of the cells.

Battery Management Systems are required on all Lithium-Ion batteries. Typically these are integrated into the design, and are the true differentiator between assemblers and integrators. Battery Management Systems can be extremely complex, monitoring voltages, currents and temperatures. They use this information to run algorithms that calculate the State of Charge, Time to Empty, Time to Full, and State of Health. Even more sophisticated BMS can operate thermal control systems, remote monitoring communications and even control energy conversion devices like inverters and chargers.

Since a BMS comes with every lithium-ion battery it is extremely attractive to Telecom, Network, and Data Center operators. No longer do you need to spend more on a separate BMS, integrate/program it yourself, and then try to find time to interpret the data. In today’s data centric world this functionality provides new value to operators.

Energy Density & Faster Recharge

Lithium-ion batteries have a higher power density (watts per kilogram, or W/Kg) and energy density (watt hours per kilogram, or Wh/Kg) than lead acid batteries. They provide the same amount of energy in a lighter, more compact design. There are a few sub chemistries to choose from, as shown in Figure 1.

Also, most lithium-ion batteries can be recharged over 90% capacity in under two hours, while VRLA batteries may take anywhere from four to 24 hours to fully recharge. If an edge data center or 5G cell station has multiple utility outages in a single day, the lithium-ion batteries can quickly be recharged to provide ride-through time for each outage. Additionally, Lithium-Ion batteries can be paired with Solar, Wind, or fossil fuel generators to charge quickly and discharge slowly, optimizing energy harvesting when it is available.

Extended Lifespan & Cycle Life

Lithium-ion batteries have a lifespan of 10-15 years, which is 2-3 times as long as the average 5-7 year lifespan of lead acid batteries. A lithium-ion battery may easily last the entire 15-year lifespan of your UPS. Also, lithium-ion batteries have a predictable degradation curve, which makes it easier to determine when they are approaching “end of life” and will need to be replaced; unlike lead acid batteries, aging lithium-ion batteries are not subject to “sudden death syndrome.”

A typical lead acid battery has a cycle life of 200, meaning you can discharge the battery to 50% capacity and recharge it to 100% capacity, up to 200 times before the battery dies. But we know when you use a battery, you usually discharge it all the way to empty, damaging the lead acid battery. The lithium-ion chemistries used in batteries for UPS applications each have a longer cycle life – 1,000-2,000 cycles for the Nickel Manganese Cobalt (NMC) chemistry, and 2,000-4,000 cycles for the Lithium Iron Phosphate (LFP) chemistry. Figure 2 summarizes the uses and benefits of these two chemistries. Additionally, you can discharge lithium-ion batteries from 100% to 0%, which is twice the available capacity of lead acid batteries without doing any damage to the cells at all!

Figure 2: The main two Lithium-Ion sub-chemistries used in the stationary storage market LFP and NMC. LFP is a stable, long lasting, low cost solution, but when energy density matters nothing beats NMC.

Smaller Size and Lower Weight

Lithium-ion batteries are up to 70% more compact than lead acid batteries. The smaller size of lithium-ion batteries makes it easier to install them in space-constrained deployments, such as modular or containerized data centers, 5G micro nodes, and data closets.

Also, lithium-ion batteries typically weigh about 1/3 less than most VRLA batteries. The lower weight makes lithium-ion batteries easier to carry, transport, and install, especially when delivering them to remote locations. Just talk to an installer, their knees and backs will thank you!

Temperature Tolerance

In outdoor settings, lithium-ion batteries can tolerate higher (and lower!) ambient temperatures, and are less susceptible to sudden temperature changes that would shorten a lead acid battery’s useful life. In indoor settings, lithium-ion batteries provide a savings in cooling costs, since server rooms and data closets can be kept at a higher ambient temperature without fear of damaging the batteries.

Less Maintenance

All lithium-ion batteries have a built-in Battery Management System (BMS) that monitors battery performance, reducing the risk of sudden battery failure. The BMS provides automatic status and fault monitoring, cell balancing, and power optimization for each individual battery.

A well-designed lithium-ion battery is virtually maintenance free, making it a “set it and forget it” solution. The BMS allows technicians to monitor battery health, in either a local or remote deployment. This allows you to maximize battery life, minimize downtime, and reduce labor and maintenance costs.

Cost Comparisons – Lithium-Ion vs. Lead Acid Batteries

Although the costs have decreased significantly over the last decade, lithium-ion batteries can require a higher initial investment than lead acid batteries. However, depending on the costs of the application, lithium-ion batteries offer long-term savings in Total Cost of Ownership (TCO) when used in 5G and IT network deployments. Figure 3 shows some of the categories to consider when selecting a backup power chemistry for your long-term deployment. Each deployment is different, but stationary battery applications typically operate for very long periods, many more than 15 years.

Figure 3: Lead Acid batteries may cost less up front, but when considering all of the costs associated with 10+ years of battery life Lithium-Ion’s initial capital investment is paid back by lower maintenance and replacement costs.

Figure 4 shows the cumulative cost differential over the 15-year lifespan that is typical of a UPS. While the initial costs of lead acid battery systems are lower, the total costs steadily increase over time, as the VRLA batteries must continuously be maintained and periodically replaced. Meanwhile, over this same period, the recurring costs of lithium-ion batteries are minimal, producing a Return On Investment (ROI) within five years of the initial battery deployment.

Figure 4: In this particular application the cumulative cost of Lead Acid batteries, their maintenance and real estate costs outpace lithium-ion in 5 years. In 15 years the costs associated with lead acid batteries are double that of lithium-ion.

As mentioned, the longer lifespan and reliability of lithium-ion batteries means that they may last for the entire life of your UPS. This eliminates the cost of replacing batteries every few years, and also provides potential savings in labor, maintenance, shipping, and transportation that would otherwise be needed to service and replace the batteries in remote locations.

All in all, Lithium-ion batteries benefits for stationary applications are at a tipping point. Many network operators are considering lithium-ion batteries as a cost saving, higher performing alternative to the traditional Valve Regulated Lead Acid batteries they are used to using. Is it time to consider using Lithium-ion batteries to backup your mission critical loads?

Read the original article at Power System Design.


Category: In the News
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