With battery prices dropping, an end to battery shortages on the horizon, and unprecedented deployment predicted over the next six years, the energy industry is likely at or near the tipping point for energy storage from pilot projects to prime time. As the size of the storage systems grow and the market matures, the criteria for how to house critical battery assets are also evolving. The container solution started out strong with its features of convenience, lower cost and modularity. However, because of its strengths in areas like safety, operational efficiencies, and system flexibility, the building envelope is no longer the storage underdog. From the outset, which solution will win possession of the batteries is no longer predictable.
After evaluating 150+ energy storage (ES) projects, we have developed the following benefits analysis framework to help decision-makers identify, establish and prioritize decision criteria and evaluate their options to determine which solution—container or building—“best” fits when it comes to the specific needs of the project, the site, and, of course, the customer.
Permitting and site constraints
Perhaps no set of criteria results in the dreaded “It depends” more than permitting issues. Aesthetics, exterior landscaping and physical plant security requirements are becoming increasingly prevalent and may preclude a container solution.
Physically restricted sites or the need for greater energy density also favor the building solution. For example, for the same 100 MWh storage capacity, a container solution will have a footprint of/require approximately 40,000 square feet but a building will require about 20,000 sf—less with a two-story building.
Ensuring that the batteries stay within their safe operating parameters is essential for warranties and performance guarantees and to prevent unwanted thermal events. Containerized systems have physical limits to their thermal management systems that constrain these systems in terms of size, efficiency, flexibility of controls, and life/resiliency. In contrast, a building solution offers significantly greater ability to customize airflow to critical areas, control humidity, and modify the system for future use cases. System backup, resiliency, and HVAC augmentations are also more easily achieved with a building solution.
Fire risk is a top concern in any energy storage project. With the release of NFPA 855 in September 2019, the energy storage market is working diligently to forecast and address the impacts this standard will have on projects for both containers and buildings. Water-based suppression is regarded as the most effective fire suppressant for lithium ion modules. Water-based systems are currently easier to deploy and less likely to fail in a building than in a group of containers. However, thanks to standards development, coupled with engineering methods, implementation methods for fire suppression are advancing quickly. When water supply is a concern, appropriately sized water supply tanks can be installed in remote areas with either configuration. Requiring water-based suppression systems in containers may level this differentiator between container and building solutions.
General operational & maintenance efficiencies
To illustrate the maintenance issues between these solutions, let’s compare two recent projects with 40 MWh storage capacity.
- Project 1 consists of 10 weather-resistant steel containers next to a remote substation. Each container has 20 doors, 20 locks, 8 individual HVAC units mounted within some of the doors, and approximately 500 lineal feet of weather stripping and seals, for a total of 200 doors, 200 locks, 80 HVAC units, and almost a lineal mile of weather stripping and seals.
- Project 2 is a 10,000-square-foot pre-engineered metal building in an industrial park. The building has seven doors and locks, 100 lineal feet of weather stripping and seals, two ground-mounted air handling units and two condensing units and associated balance of plant.
No matter the solution, any opening is subject to moisture intrusion and failure of seals, hinges, and locks, as well as other equipment. A failure mode comparison of these two projects will favor the building.
Compared with containers, building solutions also provide greater control over the structural envelope, as well as thermal and moisture protection. In addition to lower maintenance concerns, building solutions also provide a better-insulated space. Given the relatively fixed ISO dimensional standards for containers, there are limitations on the amount of insulation, potentially requiring more run-time on thermal management systems due to exterior “skin” heat gains when the batteries aren’t active. In addition to general maintenance efficiencies, buildings offer an increased ability to holistically integrate controls, fault detection, diagnostics, and service calls to the human-machine interface. They also often allow greater flexibility in voltage, system customization, and use case optimization.
Rules of thumb
In specific and rare cases, the choice between a building and a container solution can be straightforward:
- DC system coupling or prescribed modularity—Both of these situations require a containerized solution.
- Small capacity projects—Storage needs under 20 megawatts by four hours are probably best achieved through containers. Should battery energy density increase 2–3x current values, this figure will shift further in the container’s favor.
- Uncertainty in market conditions in some regions favors containers to ensure assets can be redeployed to more economically advantageous regions.
- Steel tariff mitigation—The most cost-effective containers are currently assembled overseas. As the debate on tariffs continues and as “Buy American” provisions develop, projects are more likely to benefit from a building solution.
- Larger capacity projects or very constrained parcels—Projects that require higher energy densities in a given footprint benefit from a building solution.
- A battery storage building can serve a dual role as an O&M building if desired.
- Tax incentives and depreciation can tip a project in either direction, depending on the project’s jurisdiction.
- The operational mindset is different for a container vs. a building, but neither solution should be considered “set and forget.”
A more comprehensive analysis featuring more variables is available here: https://www.mortenson.com/company/news-and-insights/2020/building-vs-container-energy-storage
When evaluating enclosure solutions for battery energy storage, many factors need to be considered before deciding which one ultimately has the home court advantage. The container solution still dominates when modularity, price and transportability are the key determinants. However, the building solution’s adaptability makes it a worthy competitor. Occasionally, regional market, permitting and regulatory conditions help one solution edge out the other. But when the choice is not immediately clear, the trade-offs in this framework can simplify the decision between building vs. containers in today’s fast-moving market and regulatory environment.
To learn more about how Mortenson’s Energy Storage team is enabling smarter power, click here: https://www.mortenson.com/energy-storage-solutions