Energy Storage Systems: A Primer

ESS, or Energy Storage System, is a new term to us electricians. What does it mean exactly? The NEC defines an energy storage system as one or more components assembled together, that are capable of storing energy for use at a future time. According to the Environmental Protection Agency (EPA), there are several ways to store energy including: pumped hydroelectric, compressed air, flywheels, batteries, and thermal storage. Another energy storage system is Fuel Cells

Types of Energy Storage System

The NEC recognizes three types of ESSs: self-contained, pre-engineered/matched components, or other. These types are based on how and where they are assembled. The components of a self-contained energy storage system are assembled, installed, and packaged as a singular energy storage container. Pre-engineered systems are systems with separate components that are pre-engineered and then field-assembled, and other systems are made up of individual components that are assembled entirely on-site. 

Universal Power Systems

A familiar term may be the Universal Power System, or UPS. This storage system provides storage power for a few minutes in order to safely shut down electronic devices (i.e. computers, data center hard drives) during a power outage. RealPars gives a good primer on the universal power system.

Pumped Hydro

Perhaps you have heard of Pumped Hydro. This is when a power plant pumps water from a lower-elevation reservoir or natural body of water to an uphill reservoir. When the power company needs more power, they release the stored water and allow it to run back downhill. This helps turn turbines faster to create more power. Recently, though, many power plants and commercial and residential customers want a way to store energy onsite without having to run water uphill. 

Battery ESS

Battery ESS (BESS) are the most common type of new installation. A sample commercial lithium BESS is from Samsung. Residential BESSs are increasing in popularity thanks to many residential customers installing solar panels, or Photovoltaic Systems (PV), on their rooftops.

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Courtesy of Clean Energy Review-Residential Battery Energy Storage Systems

The main components of a BESS in addition to the battery banks themselves are:

  • A charge controller, 
  • an inverter,
  • a battery management system, and 
  • disconnecting means. 

When installing BESSs, electricians need to be mindful of stranded energy — even after you disconnect the power, the batteries still have power across the leads. If you put your body across the leads you will still get a shock. 

NEC Requirements for ESS

There are two articles in NEC code that address BESSs: Article 480 and Article 706. Article 480 applies to all stationary installations of storage batteries. Article 706 applies to all permanently installed energy storage systems operating at over 50 volts AC or 60 volts DC that may be stand-alone, or interactive with other electric power production sources. 

The NEC introduced Article 706 as a new code article in the 2017 code cycle. There are five parts to this article: General, Circuit Requirements, Electrochemical Energy Storage Systems, Flow Battery ESS, and Other Energy Storage Technologies. Most of the article focuses on BESSs although it recognizes that there are other energy storage systems that electricians may install. ESSs for dwelling units shall not exceed 100 volts between conductor or to ground (706.30(A)). When installing BESS make sure you have the Material Safety Data Sheets for battery specifications and chemical composition. 

Future ESS systems to be aware of include Hydrogen Fuel Cells and Air Batteries. For now, according to Financial Times, lithium ion BESSs are what’s going to be installed in the near future. We as electricians need to be aware of these installations, and keep up with any new ESS-related additions or changes to the NEC.

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