Publications

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This paper describes the concept for augmenting the SEGIS Program (an industry-led effort to greatly enhance the utility of distributed PV systems) with energy storage in residential and small commercial applications (SEGIS-ES). The goal of SEGIS-ES is to develop electrical energy storage components and systems specifically designed and optimized for grid-tied PV applications. This report describes the scope of the proposed SEGIS-ES Program and why it will be necessary to integrate energy storage with PV systems as PV-generated energy becomes more prevalent on the nation's utility grid. It also discusses the applications for which energy storage is most suited and for which it will provide the greatest economic and operational benefits to customers and utilities. Included is a detailed summary of the various storage technologies available, comparisons of their relative costs and development status, and a summary of key R&D needs for PV-storage systems. The report concludes with highlights of areas where further PV-specific R&D is needed and offers recommendations about how to proceed with their development.

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Sandia National Laboratories, New Mexico, conducts the Energy Storage Systems Program, which is sponsored by the US Department of Energy's Office of Power Technologies. The goal of this program is to develop cost-effective electric energy storage systems for many high-value stationary applications in collaboration with academia and industry. Sandia National Laboratories is responsible for the engineering analyses, contracted development, and testing of energy storage components and systems. This report details the technical achievements realized during fiscal year 1999.

A flywheel is an electromechanical storage system in which energy is stored in the kinetic energy of a rotating mass. Flywheel systems under development include those with steel flywheel rotors and resin/glass or resin/carbon-fiber composite rotors. The mechanics of energy storage in a flywheel system are common to both steel- and composite-rotor flywheels. In both systems, the momentum of the rotating rotor stores energy. The rotor contains a motor/generator that converts energy between electrical and mechanical forms. In both types of systems, the rotor operates in a vacuum and spins on bearings to reduce friction and increase efficiency. Steel-rotor systems rely mostly on the mass of the rotor to store energy while composite flywheels rely mostly on speed. During charging, an electric current flows through the motor increasing the speed of the flywheel. During discharge, the generator produces current flow out of the system slowing the wheel down. The basic characteristics of a Flywheel system are shown. Steel flywheel systems are currently being marketed in the US and Germany and can be connected in parallel to provide greater power if required. Sizes range from 40kW to 1.6MW for times of 5--120 seconds. At this time sales are limited but growing. The suppliers of the composite type flywheel systems are currently in the prototype stages of development. Flywheel systems offer several potential advantages. FES systems, as their developers envision them will have exceptionally long service lives and low life-cycle costs as a result of minimal O and M requirements. FES systems are compact and self-contained allowing them to be placed in tight quarters, and they contain no hazardous chemicals nor do they produce flammable gases.

Sandia National Laboratories has been studying Energy Storage Systems since the late 1970s. To identify applications of energy storage, a two-phase Opportunities Analysis was conceptualized in FY94. Phase I of the project was completed and published in 1995. Phase II of the project is an extension of Phase I to reexamine the identified applications in the dynamic environment of today.

The Puerto Rico Electric Power Authority (PREPA) installed a distributed battery energy storage system in 1994 at a substation near San Juan, Puerto Rico. It was patterned after two other large energy storage systems operated by electric utilities in California and Germany. The U.S. Department of Energy (DOE) Energy Storage Systems Program at Sandia National Laboratories has followed the progress of all stages of the project since its inception. It directly supported the critical battery room cooling system design by conducting laboratory thermal testing of a scale model of the battery under simulated operating conditions. The Puerto Rico facility is at present the largest operating battery storage system in the world and is successfully providing frequency control, voltage regulation, and spinning reserve to the Caribbean island. The system further proved its usefulness to the PREPA network in the fall of 1998 in the aftermath of Hurricane Georges. The owner-operator, PREPA, and the architect/engineer, vendors, and contractors learned many valuable lessons during all phases of project development and operation. In documenting these lessons, this report will help PREPA and other utilities in planning to build large energy storage systems.

The Puerto Rico Electric Power Authority (PREPA) installed a battery energy storage system in 1994 at a substation near San Juan, Puerto Rico. It was patterned after two other large energy storage systems operated by electric utilities in California and Germany. The Puerto Rico facility is presently the largest operating battery storage system in the world and has successfully provided frequency control, voltage regulation, and spinning reseme to the Caribbean island. The system further proved its usefulness to the PREPA network in the fall of 1998 in the aftermath of Hurricane Georges. However, the facility has suffered accelerated cell failures in the past year and PREPA is committed to restoring the plant to full capacity. This represents the first repowering of a large utility battery facility. PREPA and its vendors and contractors learned many valuable lessons during all phases of project development and operation, which are summarized in this paper.