Advanced Battery Technologies for Stationary Energy Storage Applications

At the grid level, lead-acid batteries account for just a fraction of a percentage of new energy storage deployments. So, what battery chemistries are developers and utilities using today, and why?

A radical energy transformation is under way today, one that we will likely fully appreciate only in hindsight. Auto manufacturers are transitioning to electric vehicles, which will enable new transportation paradigms and vehicle-to-grid services. Utility regulators and operators are beginning to rebuild the bulk power system to make it more resilient and better able to accommodate high penetration levels of variable renewable generation. The prime mover in these transitions is the rapid advancement in electrochemical energy storage technologies.

In this article, I briefly review grid applications for energy storage solutions, both in front of and behind the customer meter. I then provide a compendium of advanced energy storage solutions for stationary energy storage applications, looking at representative technologies, vendors and field deployments. Because there is much to cover here, this is less of a design guide for applications engineers than it is a snapshot of a very dynamic and exciting space, one that solar professionals would do well to keep tabs on.

Grid Applications for Energy Storage

It is with good reason that industry stakeholders, researchers and analysts often describe energy storage as the missing piece of the puzzle or the great enabler in the renewable energy revolution. Use cases for energy storage systems exist in front of the customer meter, at both the transmission and distribution level of the bulk power system, as well as behind the customer meter, in commercial and even residential applications. Depending on how and where developers deploy energy storage systems, benefits might accrue to a utility, reliability coordinator, balancing authority, third-party system operator, community, commercial or residential customer, society at large or some combination of these. As shown in Figure 1, a 2015 report published by the Rocky Mountain Institute (see Resources) identifies 13 different services that energy storage systems can provide to three general stakeholder groups.

Use cases for energy storage are generally built around opportunities to avoid incurring costs or opportunities to generate income. Examples of the former include energy storage deployments that allow utilities to defer transmission or distribution system upgrades, or that enable commercial and industrial customers to avoid demand charges. Examples of the latter include energy storage systems that participate in markets for ancillary services, such as frequency regulation, voltage support or demand response. Energy storage systems can also improve grid resiliency, provide generation capacity or facilitate the integration of more wind and solar. Some of these applications have broad societal benefits, such as disaster preparedness or greenhouse gas reductions, that are not easy to quantify in economic terms—at least not given today’s market structures.

Though there are many opportunities to deploy grid-interactive energy storage systems, it is important to recognize that different applications are not created equally. Frequency regulation is a relatively short-duration service, measured in seconds or minutes, intended to reconcile momentary differences in the generation-to-load balance; as such, it favors a fast response time but does not necessarily require large amounts of energy, because the battery is alternately discharging and charging in rapid succession. Applications that shift electric energy in time, over a period of hours or even days, are comparatively more energy intensive but may have more modest power requirements. Other applications are potentially both energy and power intensive. In demand management applications, for example, batteries store off-peak energy for a period of hours, then discharge stored energy during on-peak pricing periods as needed to offset the demands associated with heavy loads.

These different application characteristics underscore the need for different batteries and battery technologies. Some chemistries or technologies are better suited for short-duration power applications, whereas others are better suited for long-duration energy applications. Since deploying an energy-optimized battery in a power application or vice versa can degrade system performance in the long term, some hybrid utility-scale applications actually utilize both power- and energy-type batteries. While it is tempting to describe grid-interactive energy storage systems in general as a Swiss Army knife, no one battery is the ideal tool for all applications.

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