By Marty Ellman, Project Director at Nexus Engineering Group
For renewable energy to meet growing global demand, engineers must solve the complex problem of energy storage. Electric utilities are exploring utility-scale battery technologies ranging from lithium-ion to new hydrogen fuel cell systems to bridge the gap between when renewable power is generated, and when it is used. These energy storage solutions are especially critical for intermittent power sources like wind and solar.
Simultaneously, developers have pursued smaller-scale energy storage systems to offset peak demand power pricing, integrate with other distributed generation energy assets in microgrids, and provide reliability and resiliency to campus power systems during operational disruption and generation-loading transitions.
The IEA’s stated goal of net-zero carbon emissions by 2050 has accelerated the need to have utility and commercial scale storage battery systems at the heart of our electricity grid. Today, utility and industrial facility engineers have limited options for their energy storage solutions, with lithium-ion installations the clear leader in the category. But two more technologies that have come to market over the last decade show promise and are worth watching.
Here’s what to consider when evaluating your facility’s energy storage system needs, and what’s on the horizon for the latest battery technology.
The current leader: lithium ion battery systems
Lithium battery containers storing intermittent solar and wind farm energy
Lithium-ion batteries are one of today’s preferred energy storage solutions because they are commercially available and highly efficient. Lithium batteries power rechargeable electronics and electric cars, and they dominate the energy storage landscape with megawatt installations now common, and gigawatt installations under development.
Components:
- These systems are made up of individual lithium-ion batteries stacked in 1-2MW modules that provide up to 4MWh of capacity.
- Multiple modules interconnect to form large-scale installations, with even larger utility scale installations possible within a common building enclosure.
- Installation components consist of batteries, inverters, transformers, fused switches, and surge arresters. They connect to the power grid through conventional substation and transmission line design.
Considerations:
- Lithium-ion battery life expectancy and return on capital investment are directly related to their daily charge-discharge deployment. Consider the number of charge-discharge cycles expected when choosing this storage technology.
- Due to the potential fire hazard of lithium-ion batteries, mechanical ventilation and temperature monitoring and control are important safety factors.
- The National Fire Protection Association recently issued NFPA 855, a new standard that provides guidelines for addressing fire risk and other safety issues connected to energy storage systems. The standard includes specifications on the ventilation, signage, and emergency operations related to battery systems based on their technology, location, and size.
The next contender: flow battery systems
A 60MWh flow battery system on the Japanese island of Hokkaido; image: Sumitomo Electric
Flow batteries, also known as redox flow batteries or flow cell batteries, have been featured in mostly demonstrational installations to test the technology and determine its ability to be implemented commercially in larger-scale applications. In a flow cell battery two chemical components are dissolved in liquids and then pumped through the system on separate sides of a membrane. While not yet broadly available for commercial use, their greater longevity will likely come with added system complexity.
Components:
A typical vanadium redox (VRB) flow battery system is made up of electrolytes, tanks, pumps, and cell electrode membranes.
Future Considerations:
- These installations will require a larger footprint and process system interconnectivity.
- Expect a significant amount of full system discipline design compared to a lithium-ion installation.
- The primary advantage of flow battery systems is a discharge longevity in the 12-hour range, with little degradation of system life expectancy when operating in a daily charge-discharge deployment.
Future potential: hydrogen fuel cell battery systems
Energy storage for renewable hydrogen gas
Hydrogen fuel cells (HFCs) have recently gained much attention for their potential in electric and battery powered vehicles. Fuel cell powered systems use clean energy to produce hydrogen through electrolysis, and then compress and store the hydrogen to produce electricity when needed. Considered a potential distributed energy game-changer for decades due to their very high efficiency, they have not yet proven economically viable in commercial applications.
Use as fuel in hydrogen cars to replace internal combustion engines have popularized and accelerated the technology, but it’s use in the distributed energy marketplace in energy storage solutions is still largely theoretical.
Components:
- Electrolysis equipment, compressors, pipelines, fuel cells, and electrical grid interconnection.
Future Considerations:
- Hydrogen could be produced at or near the site of use in distributed production or at large facilities and then delivered to the point of use in central production.
- Fuel cells have operational efficiencies up to 60%, and no harmful emissions. It may be possible to integrate a hydrogen fuel cell battery system in a CHP facility and use the fuel cell waste heat.
- Installations are currently theoretical. Their high cost makes their use for practical energy storage uncertain.
Battery Storage Sizing
Utility and industrial facility engineers responsible for selecting and implementing battery storage installations will be actively following these technologies as they look to determine the ideal solution given their desired battery storage capacity, watt hour sizing, charge and discharge rates, impacts on voltage/frequency response, battery life, and overall life cycle return on investment.
Here are some additional considerations:
- The relative size of a battery installation is not determined by its base MW rating, but by its MWh rating and the number of hours it can provide the nameplate rated output level.
- In addition to longer time durations, overall MWh sizing relates to charge/discharge ratings and system life expectancies. Therefore, determining the desired functional and economic requirements of the system is the first step in choosing the right storage system.
- Advancements in Grid and Microgrid Control Systems utilizing Model (Algorithm) vs. Rule (Logic) Based Control are optimizing battery charge/discharge cycles, and maximizing their contribution to load profiles, energy economics, and reliability/resiliency when the battery systems are brought on-line to boost system stability.
