Energy Warehousing

Nov. 1, 2012
The role of the 21st century substation continues to expand.

Remember when smart grid burst onto the scene? It was heralded as the latest, greatest and most modern technology available. It was the silver bullet that would slay all the dragons in the realm. Well, that was more than 10 years ago, and it did not quite have that effect. That's not to say smart grid technology is not solving problems, it is, but it's just one of the tools available. Now, another new technology is getting attention: energy storage. Even more interesting is the unlikely location in which it is being used: the electrical substation.

The electrical substation is becoming the big-box store of energy storage, the warehouse for electricity. For a place that has been called the edge of the grid, the electrical substation is attracting a great deal of attention, which really makes a lot of sense. Large wind and solar power enter the grid at the substation. The consumer is attached to the substation taking power from the grid.

With advancements in distributed generation (rooftop photovoltaics [PV] and community wind), these same customers are pumping megawatts back into the grid at the electrical substation, too (see “Renewables Challenging the Grid,” T&D World, July 2012). In its “Annual Energy Outlook 2012,” the Energy Information Agency predicts this end-user type of distributed generation (wind and PV) will double in the next 10 years, so it should not be ignored.

The Evolving Grid

The grid has been evolving into a smarter, more dynamic electric system and distributed energy storage (DES) systems enhance this dynamic. With DES located throughout the distribution system, it improves reliability. With the ability to disperse power at key points throughout the distribution network, DES meets peak demand without the need for additional generation, transmission and distribution infrastructure.

Some are proclaiming distributed storage will replace the smart grid by solving all of the electric industry's problems such as demand response and peak shaving, but it is really a complementary tool for the toolbox. By combining energy storage with power electronics, sensing technology and high-speed communications, the potential of the smart grid is really being released.

Pike Research's “Energy Storage Tracker 2Q12” reported, “In the face of rising electricity consumption and increasing levels of variable renewable energy generation around the world, energy storage technologies are being pursued as a means of increasing the flexibility and efficiency of the power grid. In the first half of 2012, new projects were commissioned and announced, utilizing a variety of energy storage technologies.”

Deploying DES systems from the substation to the consumer is one way of dealing with this challenge. It provides backup power, voltage correction, time shifting of loads, congestion relief, and deferral of upgrades or system additions.

By taking advantage of these ancillary services, many utilities are reinforcing their systems and improving frequency regulation, load following, spinning reserves and short-duration renewables integration. This allows utilities to manage the uncertainty of evolving consumption patterns and inconsistent resources.

Power Electronics with Storage

One of the more interesting approaches introduced the distribution network to power electronics combined with energy storage. Basically, it is a flexible ac transmission system (FACTS) controller using the static compensator concept, employing voltage source converter technology. ABB calls such a device DynaPeaQ.

The heart of the DynaPeaQ system is ABB's SVC Light system combined with Saft's high-capacity lithium-ion (Li-ion) battery storage. It's high-speed switching using insulated-gate bipolar transistors (IBGTs). The DynaPeaQ can be connected to the transmission grid as well as at the subtransmission and distribution levels.

The energy storage part of the system receives and stores power from renewables, such as wind, or surplus power from the grid. Using power electronics, it feeds the grid with exactly the right amount of reactive and active power needed at each instance, independently of one another, and with a minimum of bulky filter arrangements.

The first DynaPeaQ system was installed in Norfolk, England, on EDF Energy's 11-kV distribution system in 2011 (see “UK Deploys Battery Storage,” T&D World, January 2012). It has a 200-kWh capacity with a real power rating of 600 kW and a reactive power rating of 600 kVAR. By combining the SVC Light technology with the Saft Li-ion batteries, the system provides continuous dynamic voltage control and frequency regulation, which are essential for grid stability.

Established Technology with a New Twist

Improvements to battery technologies have led to a new class of battery systems in the substation and on feeders. One such project is the U.S. Department of Energy's (DOE's) PJM Regulation Services (Pennsylvania-New Jersey-Maryland interconnection) demonstration project using a 3-MW Deka UltraBattery. This project provides continuous frequency regulation services on its system in Lyon Station, Pennsylvania, U.S.

The storage system has been developed by East Penn Manufacturing Co. and its subsidiary Ecoult. This system includes both storage and the power-conversion system. The Ultra-Battery is an advanced lead-acid technology that combines the advantages of a lead-acid battery with the quick-charging and discharging abilities of a capacitor.

Another advanced battery technology comes from Xtreme Power of Austin, Texas, U.S. The company has introduced a battery system it calls a chemical capacitor. These batteries are inert, use dry materials and operate at room temperatures unlike other technologies in the marketplace. Xtreme has installed more than 22 MW of these batteries on systems such as Kodiak Island, Alaska, U.S., and Oahu, Hawaii, U.S.

Flow batteries are gaining attention because they are scalable, can be discharged completely without decreasing their capacity and the electrolyte never wears out. A DOE-sponsored project funded by the American Recovery and Reinvestment Act (ARRA) installed five 500-kW TransFlow zinc-bromine battery systems, from Premium Power, on the Sacramento Municipal Utility District (SMUD) and the National Grid systems. Two of the units are installed in substations and the rest are deployed as community energy storage (CES) systems on feeders and in customers' homes.

A Smarter Grid

Technically, CES technology is outside the substation, but it certainly extends the influence of the substation and it's a step toward solving the pesky problem of the last mile. The last mile is the feeder extending to the customer, which is the most under-monitored portion of the grid. In much of the world, the distribution operator knows there's a problem when the customer calls and says the lights are out.

The concept of CES is a simple one. Troy Miller, S&C Electric's manager of business development and product management, said, “Basically, a CES system provides megawatts for many hours broken up into small units installed at or near the point of consumption. S&C has developed the PureWave CES system that can monitor the feeder to prevent overloading padmount transformers, detect loss of grid power, isolate the customers from the fault and provide power until reliable grid power is available or the battery is depleted.”

Broad-scale deployment allows the utility to aggregate them to be used for phase balancing, which flattens the feeder's voltage-regulation curve. Miller reported, “S&C has provided the PureWave CES system to utilities such as Scottish and Southern, American Electric Power (AEP), Southern California Edison (SCE) and Duke Energy.”

The Irvine Smart Grid Demonstration is another DOE ARRA project testing the benefits of smart grid technologies, substation storage and CES applications. The project is led by SCE, with the Boeing Co., GE, A123 Systems, SunPower Corp. and Itron Inc. The substation portion consists of two 2-MW, 500-kWh containerized Li-ion batteries. The distribution storage portion consists of 25-kW, 50-kWh CES units located on feeders. The residential energy storage consists of 4-kW, 10-kWh units located in residences.

Grid Applications

Li-ion battery systems have improved their capacities and are now available for utility-scale applications. SCE is taking part in a DOE ARRA Li-ion battery test project at its Tehachapi storage project. SCE is working in partnership with A123 Systems to install an 8-MW, 32-MWh phosphate high-power Li-ion battery at the Monolith Substation in the Tehachapi Mountains. This project is scheduled for operation in late 2012. It will evaluate a utility-scale Li-ion battery's ability to increase grid performance and integrate wind generation.

With total capacity of approximately 365 MW installed worldwide, sodium-sulfur (NaS) batteries are getting attention. They are putting power where it is needed — in the substation. AEP has been a leader with installations of NaS battery systems. Its first was in 2002 with the Dolan Technology Center NaS system near Columbus, Ohio, U.S.

Dolan was followed by the 1.2-MW, 7.2-MWh system installed in its chemical station on a 12-kV feeder in 2006. This storage system allowed AEP to defer building a new substation, enabled it to shave the peak and improved the feeder load factor by 5% (from 75% to 80%).

In 2008, AEP installed three additional NaS facilities, rated 2 MW each: one in Churubusco, Indiana, U.S., one in Balls Gap, West Virginia, U.S., and one in Bluffton, Ohio. AEP's latest NaS installation is a 4-MW facility located on the transmission system in Presidio, Texas, U.S. The NaS battery can supply Presidio power for about six hours in the event of an outage on the radial transmission line feeding the city. It also will address voltage fluctuations and momentary outages.

The batteries have been manufactured by NGK Co., and they are controlled through S&C's PureWave storage management system (SMS). PureWave is a fast-response, automatic power converter and controller that provides the ability to store energy in a variety of battery storage technologies and to control the discharge of the power into the electrical grid.

SCE awarded S&C a turnkey contract for a 1-MW PureWave SMS with NGK batteries to be installed on Catalina Island, California, U.S. The NaS system will allow SCE to reduce the amount of time diesel generators are run, decreasing carbon emissions. BC Hydro also has awarded a contract to S&C for two 1-MW SMS with NGK NaS battery systems, at the communities of Golden and Field, to support peak loads and limit carbon emissions.

Integrated Systems

Last year, EKZ, a Swiss distribution utility, partnered with ABB to install ABB's packaged DES scheme in Dietikon, Switzerland. The ABB DES is an integrated system consisting of a Li-ion battery, inverter, transformer, and medium- and low-voltage switchgear. It is rated 1 MW and configured for 500 kWh. It will be used to evaluate balancing peak loads, intermittent power supply and viability of a solution for grid optimization.

Arizona Public Service is testing a Li-ion energy storage system on its Flagstaff, Arizona, U.S. distribution system. The utility is installing Electrovaya Inc.'s 500-kW, 1.5-MWh Li-ion battery system. The project will test the battery system in the substation environment to determine whether the steadier flow of electricity would be less stressful on the substation equipment than the variable output of the nearby PV system. The system will then be moved to the Doney Park Renewable Energy Site, a 500-kW PV solar park, where its operation will be evaluated.

Italy's largest power company, Enel, has installed a Siemens Siestorage energy storage system on its system this year. The Siemens system has a capacity of 500 kWh and has been installed in Enel's medium-voltage network. It is being used to evaluate voltage regulation, integration of renewable resources into the network, integration of electric-vehicle charging stations and to study black-start capabilities. The Siestorage system is an integrated battery management system that can be scaled up to 8 MW.

Batteries Must Be Included

Taking storage to the substation level has brought about applications that cross all manner of barriers between utilities, generators and customers. It has brought new solutions to some old technical problems, and it's addressing some pretty thorny societal issues, too. Placing storage closer to the consumer can reduce the need for traditional generation by peak shaving, stabilization can be improved with faster frequency regulation and load leveling on the feeders can add to reliability.

Unfortunately, there is no such thing as a free lunch. Storage is expensive on a kilowatt-hour basis. When a battery is charged or discharged, there are losses and losses cost money.

But some of distributed storage's greatest benefits may be with the emotional issues of altering usage patterns. Utilities have invested hundreds of millions of dollars in smart meters, demand-response software and time-of-use rates in an attempt to modify consumer behavior. The customer has not responded favorably. Studies have found incontinence or discomfort trumps conservation and outweighs any desire for cost savings every time.

Distributed storage offers a “no customer involvement” solution. It does not require consumers to make any changes to their behavior nor does it hassle them to program their appliances. As previously stated, energy storage is a tool to be used where it makes sense, and the benefit to cost-ratio analysis just got a little more complicated.

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