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Energy storage and energy density: an EPC’s view  

By Ben Echeverria and Josh Tucker, Burns & McDonnell

Energy density is becoming a key tool in optimising the economics of battery energy storage projects as suitable sites become harder to find. Ben Echeverria and Josh Tucker from engineering, procurement and construction (EPC) firm Burns & McDonnell explore some of the considerations of designing projects on constrained land.

This is an extract of a feature which appeared in Vol.37 of PV Tech Power, Solar Media’s quarterly technical journal for the downstream solar industry available to Premium subscribers. Every edition includes ‘Storage & Smart Power,’ a dedicated section contributed by the team at

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When transmission authorities in the USA first began to realise that utility-scale storage facilities would be necessary to help manage the intermittency of renewables being connected to the grid, land availability was not a concern. With Arizona, California and Texas leading the way, land was readily available for large project footprints.  

Given both space and favourable market conditions, buildout was not an issue and, as a result, those three states currently contain more than 75% of today’s battery storage capacity nationwide.    

Those early market conditions are no longer the reality. Sites with large amounts of available land near transmission interconnections are becoming increasingly less available, and that can make today’s project sites more challenging, especially as demand for these facilities continues to grow.

Sites may still be available near interconnection locations, but they typically have much smaller footprints, and as a result of constrained supply and high demand, land prices in these situations are increasing. As a consequence, developers are seeking to significantly increase the amount of energy storage per acre. This drive to optimise project economics is being pursued by seeking more energy-dense batteries while also optimising the available site footprint.  

To be clear, we will be referring to energy density in this article as volumetric energy density. The industry has progressively improved upon battery energy density, with lithium-ion batteries increasing the energy available in the same footprint by about 10-12% over the last year.  

Building up, not out 

In densely populated metropolitan areas like Los Angeles, New York City and Boston, decarbonisation efforts are creating unique challenges for battery energy storage projects.  

However, the reality is that within large, dense urban areas, only small plots of land are available. The only realistic and economically viable option is to design these projects vertically, either with batteries installed in enclosed building structures or with vertically stacked battery enclosures. If the building is the preferred solution, this may involve stacking multiple racks to increase total rack heights up to 15 feet, versus the conventional 7-foot racks. This could involve the building having multiple stories of these taller racks.  

With this configuration combined with higher energy density within battery modules themselves, the overall energy capacity will come close to meeting higher energy demands of these metro areas.  

Going vertical is more complex  

Though numerous projects are now on the drawing board, it must be noted that no high-rise BESS facilities are currently operational.  

That’s because going vertical requires careful evaluation of operations and maintenance impacts, including installation of robust safety systems. These analyses shift the focus from performance and design of modules toward a holistic look at the entire site. Considerations will be given, for example, to the broad operational effects of utilising heavy mechanical equipment in compact spaces that must operate safely.   

Operating conditions for vertical BESS projects — as well as conventional projects — must be evaluated for each site. Storm and flood risks, relative humidity, seismic considerations and prevalence of salt within coastal air are among the environmental factors that can affect how the site will be designed and operated. The development of an operations and maintenance programme should include evaluating tolerances of all critical battery chemical processes in parallel with design, safety and equipment decisions.   

Other options for density  

Battery suppliers are modifying cell and module designs and footprints, along with enclosure designs, to maximise battery density and to decrease spacing between enclosures. Numerous creative designs are currently being developed to make maximum use of space, thus increasing energy density for the project site.  

One realistic constraint is the tonnage that can be feasibly transported to the job site and then lifted into place either by crane or forklift. This becomes a logistics challenge that starts as a total turnkey operation from the original manufacturer (primarily in Asia), transport to a container ship, offloading to a truck, transporting to the project site and final offloading to be set in place.   

What about safety?

Thermal runaways start as a short circuit within or external to the battery cell that triggers an exothermic reaction. These reactions produce enormous heat and explosive gases that can lead to fires and/or explosions if the event occurs within a contained space that is not ventilated.  

Placement of racks in vertical configurations can add another element of thermal management by creating different heat zones and hot and cool aisles. 

No project is identical 

Energy density has become a priority for both operational and financial reasons, but to date most of the advances have come primarily from the batteries and secondarily from space optimisation within enclosures, along with creative enclosure configurations.   

One possible sign to indicate the technology advancement for the energy storage market is shifting is the development of battery cell types geared specifically to meet the needs of the power industry. The energy storage market previously used battery cells generally designed for the EV market and not necessarily designed with a use case for the storage market. By optimising the cell design for storage applications, improvements in degradation and cycle life (i.e., life of the battery) can be achieved. Some manufacturers are starting to offer a 25-year performance guarantee (one cycle per day) for certain battery types.  

As more fossil-based thermal generation will be exiting the market, that capacity must be replaced by other sources along with energy storage playing a key role. As these energy storage systems are moving into more urban areas, energy density and land availability will be topics of great interest for the foreseeable future.   

This is an extract of a feature article that originally appeared in Vol.37 of PV Tech Power, Solar Media’s quarterly journal covering the solar and storage industries. Every edition includes ‘Storage & Smart Power’, a dedicated section contributed by the team, and full access to upcoming issues as well as the nine-year back catalogue are included as part of a subscription to Premium.

About the Authors

Josh Tucker is engineering manager for the Energy Storage Department at Burns & McDonnell. He is responsible for all engineering for the energy storage business. 

Ben Echeverria, energy storage regulations and compliance at Burns & McDonnell, is responsible for assisting the EPC project teams on energy storage projects globally, focusing on the safety, regulations and overall compliance of the interconnected systems.  

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