Community Energy Storage

Executive Summary

The concept of community energy1. Energy is the potential of a physical system to perform work. (A common unit of work is foot-pound—the amount of energy needed to lift one pound up a distance of one foot.) Energy exists in several forms such as electromagnetic radiation ... storage (CES) has captured the imagination of the growing ranks of stakeholders with interest in electricity storage (storage). It involves electricAn adjective meaning “needing electricity to operate” such as electric motor or wire. IEEE: Containing, producing , arising from, actuated by or carrying electricity. utility owned storage that is distributed, being located at the periphery of the utility distributionThe practice of and infrastructure for distribution of electricity to end-users by utilities. Typical voltages range from 12 to 138 kiloVolts (kV) system, near end-users. The potential benefits of distributing the storage capacityThe rate at which equipment can either generate, convert or transfer energy. rather than using one or a few large units can be significant. 
 
Although it is not a value propositionOne or more individual benefits associated with a specific use. A value proposition is said to be attractive if the total value of all benefits exceeds all costs, including required return on investment, if any. per se, CES embodies many attractive facets of the broader storage value proposition for the electricity grid and marketplace of the future; one that is smarter, more sustainable, more diverse and more distributed and modular. 
 
CES is especially important as an example of grid-connected and utility owned and operated distributed energy storage systems (DESS). DESSs are modular storage systems that are located at or near end-user homes and businesses. 
 
Another unique facet of CES is that, to some extent, the concept was developed as a way to characterize modular electricity storage in a way that gives it a “look and feel” that resembles conventional utility alternatives and equipment. The objective is to present storage as a mainstream alternative rather than a new, novel or even exotic concept for the future.
Discussion
 
Community energy storage entails utility deployment of modular, distributed energy storage systems (DESS) at or near points in the utility distribution system that are close to residential and business end users. The genesis of the CES concept was investigations by American Electric PowerThe rate at which energy is generated, converted, transmitted, distributed or delivered. (AEP), starting in about 2005, to evaluate the prospects for and merits of locating advanced sodium sulfur (NaS) battery1. Two or more electric cells connected together electrically. In common usage, the term “battery” is also applied to a single cell, such as a household battery. 2. A system comprised of identical electrochemical cells. storage, rated at about two MegaWatts (MW), at substations. An example is shown in Figure 1. 
 
Eventually, AEP added a different twist on the concept involving numerous much smaller units – rated at 25 kiloWatts (kW) for three hours, or 75 kiloWatt-hours (kWh) – that are distributed and located at or near end-user sites. So, instead of deploying one or two large battery systems with a power output of 2 MW at the utility substation the alternative is to deploy 80 individual systems, at or near end-user homes and businesses whose power output is 25 kW. An example is shown in Figure 2. 
 
AEP describes the approach as “a fleet of small distributed energy storage units connected to the secondary of transformers serving a few houses controlled together to provide feederAn electrical wire/circuit which “feeds” energy to the next lower level of distribution. A feeder may be an underground or an overhead wire. level benefits.” Special design attention was given to making the CES resemble conventional utility equipment (as shown in Figure 2). 
 
One notable advantage of using many smaller units is “unit diversity”. Because there are so many units, it is unlikely that a substantial amount of CES power will be out-of-service at any time. Said another way, at any time one or maybe a few CESs may be out-of-service. That is helpful if reliabilityThe degree of performance of the elements of the bulk electric system that results in electricity being delivered to customers within accepted standards and in the amount desired. May be measured by the frequency, duration and magnitude of adverse... is especially important. 
 
CES is designed to “island” which means that when a localized portion of the distribution system becomes electrically isolated from the rest of the grid, CES can “pick up” the end-user demand1. The rate at which electric energy is delivered to or by a system or part of a system, generally expressed in kilowatts or megawatts, at a given instant or averaged over any designated interval of time. 2. The rate at which energy is being used by... and can serve that demand while there is stored energyThe energy available in the storage system to perform physical work through the conversion of its chemical or mechanical energy, stated in kWh or MWh.. So, CES functions autonomously to provide “back-up” power when, for example, a traffic accident or a fallen tree. 
 
Though the actual value proposition for any specific CES deployment will vary significantly, important elements of the rationale for CES include: a) it can provide numerous benefits, b) it is a flexible solution for many existing and emerging utility needs, and c) to one extent or another, eventually, utility engineers will include modular distributed storage as a standard alternative in their growing toolkit of solutions and responses. 
Utilities’ conventional toolkit includes a fairly narrow set of solutions, primarily generators, transformers and wires. Before utility engineers can and will accept storage as a standard alternative, it is important to standardize utility specifications for the storage systems. (AEP published “Functional Specifications for CES” as an open source standard). 
 
CES is expected to provide numerous benefits in many possible combinations. It can serve as a robust, fast-responding and flexible alternative to generationThe manner in which electricity is generated. The electricity that flows through California. It can store low priced energy and use that energy when the price is high. CES can also be used to provide most types of “ancillary services” that are needed to keep the electrical1. An adjective meaning “pertaining to electricity”. Electrical Engineer. 2. Related to, pertaining to or associated with electricity but not having its properties or characteristics. grid stable and reliable. Depending on the location, CES may reduce the need for transmissionAn interconnected group of lines and associated equipment for the movement or transfer of electric energy between points of supply and points at which it is transformed for delivery to customers or is delivered to other electric systems. and distribution (T&D) capacity because CES provides power locally, so less T&D equipment is needed to serve the local “peak demand.” CES can also improve the local electric service reliability and power qualityA measure of the level of voltage and/or frequency disturbances.. Of particular interest is CES used to maintain a stable voltage in the distribution system. 
CES can play an important role in the integration of renewable energy (RE) generation into the grid, including large scale/remote wind generation and distributed (e.g. rooftop) photovoltaics. CES addresses two notable RE generation integration challenges. First, CES can be charged with wind generation output, much of which occurs at night when the energy is not very valuable. In some circumstances,demand for energy is less than the amount being generated, so wind generation is “curtailed” (turned off) or the system operatorAn individual at a control center (Balancing Authority, Transmission OperatorThe entity responsible for the reliability of its “local” transmission system, and that operates or directs the operations of the transmission facilities., Generator Operator, Reliability Coordinator) whose responsibility it is to monitor and control that electric system in real time. must pay someone to take the energy. By charging at night, CES takes advantage of the time when transmission systems are less congested and more efficient. Second, CES can be used to manage localized “power quality” related challenges posed by high penetrations of photovoltaics systems, especially in residential areas. Of particular note are undesirable voltage fluctuations that occur such as those associated with rapid variations of output due to passing clouds.

Conclusions and Observations 

Although CES is not a value proposition per se, the concept is powerful. It entails use of a flexible, standardized, modular utility-owned solution to important existing and emerging challenges faced by utilities in the new electricity marketplace. It can be added as needed while providing numerous benefits. It is enabled by and enhances the value and effectiveness of the expanding suite of elements of the Smart GridCollectively; devices, practices and protocols that enable rich monitoring and situational awareness and flexible and robust control of various parts of or entire power systems under varying conditions. Among other objectives, Smart Grid is expected to.... CES or some variation of CES could well become a standard solution used by the electrical utility engineer of the future.