Battery storage developments
This renewable energy storage sector includes many supplier companies and active developers. Various battery technologies are advancing through process refinements, and new technologies are under development. Greater storage capacity and power density—along with system cost reduction—are targets for the developers. Power output and storage duration are relatively low compared to other energy storage methods, but continue to improve over time.
While batteries strive for a niche within large-scale integrated energy storage systems, physical size requirements pose a limiting factor, as is the case for other storage technologies (This is online Ref. 4; see main article, CE Nov. 2012). Battery-based energy storage applications are progressing toward the 50-megawatt (MW) level, with more operating experience being accumulated. Most commercial installations today are for individual plants or facilities. However, projects at the lower end of utility-scale are starting to emerge (see examples below).
Among various battery types available, the following are some technologies applicable to larger-scale energy storage—or may develop to that category with further advances. These are actually battery systems that include controls, flow circuits as applicable, and means of battery management:
- Sodium sulfur (NaS)—a battery structured with a molten liquid sulfur positive electrode and a molten liquid sodium negative electrode, separated by solid beta-alumina electrolyte. It needs high temperature process (>300 C/572 F) to maintain chemical reactions and has been demonstrated in long-duration energy storage. Its high operating temperature characteristic is not a downside for typical renewable energy applications. A major supplier is NGK Insulators Ltd. of Japan.
- Lithium ion (Li-ion)—consists of cylindrical or rectangular cells, typically built into multi-cell modules in series/parallel arrays, which are linked into a “battery string” for the required voltage. A battery management system controls each battery string. Advantages include high energy density (300-400 kWh/m3), near 100% efficiency, and long cycle life (3,000 cycles at 80% discharge depth), according to the Electricity Storage Association (ESA). Suppliers include Electrovaya Inc. and Saft Batteries.
- Vanadium redox (VRd)—a type of flow battery that uses vanadium redox electrochemical couples dissolved in a liquid electrolyte (sulfuric acid) solution. “Redox” refers to chemical reduction and oxidation reactions that store energy in the electrolyte flowing through the battery cells from two external tanks. During charge and discharge, hydrogen ions are exchanged between the electrolyte tanks through a hydrogen-ion-permeable polymer membrane. Net efficiency of VRd batteries can reach 85%, the ESA noted. Prudent Energy Corp. is one supplier of this battery type.
- Zinc bromide—a fuel cell regenerative type battery where metallic zinc is plated from an electrolyte solution to negative electrode surfaces in the cell stacks during the charge process. Metallic zinc dissolves in the electrolyte during discharge and is replated in the next charge cycle. It allows 100% discharge of stored energy. A major supplier is ZBB Energy Corp.
- Sodium metal halide—an advanced battery type with high energy density, where chloride ions released from sodium chloride combine with nickel to form nickel chloride when charging. Sodium ions then migrate from the cathode reservoir through a beta-alumina separator into the anode reservoir. This chemical reaction reverses during discharge. Individual battery cells, sealed in a metal case, are linked to form a battery module. While internal process temperatures are high, thermal insulation holds the module’s external surface temperature within 10-15 C of ambient. General Electric’s Durathon battery is a product example.
No single battery type is expected to dominate large-scale energy storage markets. Other technologies under development could also be future contenders.
Batteries in the wind
Addition of a 36 MW battery storage system is ongoing at the 153 MW Notrees wind power project in West Texas near Kermit. The system will permit storage of excess wind energy and means of discharge to the grid during high electricity demand periods. Duke Energy, owner of the wind farm, and storage technology provider Xtreme Power Inc. have teamed to develop the project. A U.S. Department of Energy (DOE) grant and matching funds from Duke Energy support the project. Completion date for the battery storage project at Notrees was estimated as mid-December 2012 by a Duke Energy spokesperson.
Xtreme Power’s energy storage offering consists of a proprietary dry cell technology (modular power cells), power electronics, and a control system that includes SCADA functions and grid connection. These elements are integrated into an overall energy storage and digital power management system named Dynamic Power Resource.
Meanwhile, a notable wind energy and battery storage facility went into commercial operation near Elkins, W.Va., in September 2011. Integrated with AES Wind Generation’s 98-MW Laurel Mountain wind farm is a 32 MW battery-based energy storage system from AES Energy Storage. The two entities are part of parent company AES Corp. Lithium-ion batteries supplied by A123 Systems represent the largest advanced energy-storage installation of its kind, according to AES. The wind farm part of the facility comprises 61 General Electric 1.6-MW wind turbines.
Battery storage will allow Laurel Mountain wind farm to smooth fluctuations in power generation, and help maintain power grid reliability. AES Energy Storage claims 76 MW of battery-based storage in operation or construction, plus in excess of 500 MW energy-storage projects under development. The Laurel Mountain storage facility more than doubles the size of any of the company’s previous projects.
Thermal energy storage is compatible with concentrated solar power (CSP) technologies—as discussed in the main article in CE Nov. 2012 and online Ref. 3. However, solar photovoltaic (PV) generation, where solar panels transform sunshine directly into electricity, presents a definite opportunity for battery storage.
Solar PV with battery storage has been demonstrated and test installations have taken place in the U.S. and elsewhere. These applications have been mainly at isolated PV generation sites and for individual users.
One indication of progress is the October 2012 announcement by Acciona Energy of the first utility-scale installation of battery storage for a solar PV plant in Europe. The 1.1 MW lithium-ion battery was integrated with an existing Acciona solar PV facility in northern Spain. Global renewable operator Acciona Energy and advanced battery manufacturer Saft Batteries collaborated on the solar energy storage project, named ILIS (Innovative Lithium-Ion System management design for MW solar plants). The Li-ion battery developed by Saft can store and discharge 560 kWh of electricity, according to the company.
The grid-connected Tudela PV plant has been running since 2002 and was the largest of its type in Spain at that time. A plant control system connects to Acciona’s Renewable Energies Control Center (also located in the Navarra region) where the company monitors operation of all its installations worldwide.
- Frank J. Bartos, PE, is a Control Engineering contributing content specialist. Reach him at email@example.com
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