For Uninterrupted Power, Try Batteries
When it comes to uninterruptible power supply technology, batteries have proven to be one of the power source options.
Batteries are demonstrating themselves as a viable uninterruptible power supply (UPS) option. That's because they can be placed close to the user where they can generate electricity with or without grid backup. They also can generate enough power to serve thermal or cooling loads, generate a portion of electricity on-site to reduce peak price period purchases, improve the level of power quality and reliability, and serve remote sites where installing traditional power lines would prove costly or impossible.
But users, such as Needham Electronics, of Sacramento, CA, report that battery backup also is ideal even when operating in the middle of the metro area. "We use batteries to keep our computers on-line," explains Jim Purcell, an engineer with this company that specializes in building computer peripherals.
Needham Electronics has been using batteries for nearly four years, starting in 2000 when California began the practice of rolling blackouts as an answer to helping traditional line suppliers upgrade their technologies in an organized manner. "We needed to keep our computers on-line, properly powered up, but our UPS was not getting the longevity or reliability it needed, which is why we've switched to Optima's SpiralCell technology."
Purcell reports that gel-cell or flat-plate batteries tended to cease functioning after just a year. "We're a fairly small company, so it didn't take many of us to get together to decide what to do. I'd had experience with the brand before, so I was able to explain the technology to the others, and they agreed to give it a try."
He adds that since then there have been several times when they would have been without power but were unaffected. Purcell emphasizes, "An interruption of power, no matter how short, means an interruption of work. When you have no power, you have no production; when you have no production, you have no sales."
Speaking from Milwaukee, WI, Optima Commercial Marketing Manager Jay Kedia cited some other advantages with this advanced battery technology, especially for the vehicle market, whether off-road, on-road, mining, or logging. "For one, it allows for a longer shelf life than with traditional batteries. Our sealed batteries are lasting up to 500 days at room temperature versus four months to a year, depending on the other manufacturer. A second plus is a faster recharge time and a better recharge profile, which helps ensure a longer life." That is a particular advantage for those who work in remote areas and need to keep power on hand yet afford the inventory required for servicing their fleet.
At the same time, he emphasizes that the basic chemical reaction in this battery is no different than in a traditional lead-acid battery. "It's electrolyte reacting with lead to create an electrical current that is conveyed to a negative and positive terminal from which the user's electrical system draws power. Other elements include absorbent glass-mat [AGM] separators, much like water in a sponge. This mat is spiral-wound with the lead grids to create the necessary reaction.
"The acid is completely immobilized by the mat, making the battery fully leakproof. In addition, the fast reaction between the acid and the plate material allows for more efficient discharging and faster recharging. "Each of the six 2-volt cells contains a negative and positive lead grid and AGM separators. These components are locked tightly in place in a compressed cylinder. This means that the chemical reaction is not as susceptible to things like vibration and paste shedding that kill batteries." In addition, the high-purity lead grid makes the battery more resistant to internal breakdown and corrosion, especially at higher temperatures. This resistance is a factor for increased cycle life.
Two other advantages that have helped Optima's reputation for reliability since its beginning nearly 30 years ago as a battery supplier to the military market: the solid-cast connections and completely sealed case. Indeed, one of the photos in its product introductory packet shows an excavation machine's wheel resting atop the side of a battery case.
Kedia reports that the SpiralCell technology battery lasts twice as long as gel-cell or flat-plate models, whatever the application. Also, it is maintenance-free because it is completely sealed. "In many cases, when it comes to distributed energy, batteries are neglected. In this case, however, you can install the battery and forget about it. That's because a sealed battery cannot lose electrolyte, while a traditional lead acid can begin spilling when the case is placed at a 45° angle."
Kedia emphasizes, "The battery doesn't gas under normal operating parameters; it's closed to the environment." Which is why Optima can be shipped by air and is the only battery certified for air shipment. "If someone needs a battery immediately, they can order it for overnight delivery."
He adds yet another advantage to the technology: "Because of shelf life and shipping, companies and businesses not in the battery business can get into it. For example, equipment suppliers can offer batteries as part of their standard sales inventory and do so to an even wider market than they may be trying to reach with their wheeled equipment."
Industrial Battery Systems
John Kim, senior product manager for C&D Technologies in Blue Ball, PA, adds, "For example, major financial institutions need backup when the power goes out. If they lose a minute of their time, that can translate into millions of dollars. Also, when it comes to safety, nuclear plants need battery backup. During the Northeast blackout last summer, nuclear plants were able to continue operating safely because they had backup power."
Kim reports that their line of industrial batteries starts tipping the scales at just 30 lb., but the company produces others that weigh as much as 700 lb. The latter typically are constructed to supply a 10- or 20-year life. "That's for inside installation," Kim adds. "Companies running outdoor applications, such as huts or cabinets, tend to shop for the 10-year-life battery. It's the larger telecom, financial, and data centers that prefer 20-year batteries."
For C&D Technologies, the emphasis is on two types of batteries: the VRLA, or valve regulated lead acid, and the traditional flooded battery. "With VRLA batteries the acid is self-contained with the use of glass mat separator material, and they operate under slight internal pressure, which facilitates the recombination of internal gases. These are used mostly in restricted areas," Kim explains.
Flooded batteries have a longer history of reliable service life but require active maintenance and ventilation. "Flooded batteries normally go into large central offices and data centers in a separate battery room," he points out.
Looking toward the future, Kim comments, "Customers are looking for reliability. Will the battery provide backup power when needed? That is be the number-one thing customers want, and I don't think that will change, no matter what comes up in the way of new technology." He then emphasizes, "Lead-acid batteries are still the most effective way to provide reserve backup power."
Meanwhile, on the Power Grid
One of the newest users of battery backup on a power grid–wide system is Golden Valley Electric Association Inc. (GVEA), headquartered in Fairbanks, AK. GVEA owns and maintains 2,200 mi. of distribution line, 335 mi. of transmission line, a 25-MW coal-fired generation facility, and 200 MW of diesel- and oil-fired gas turbine generation. GVEA has a system peak of 182 MW during the winter months while serving 38,000 meters spread across 2,200 mi.2
Several layers of data acquisition and control systems allow GVEA's dispatchers to monitor the battery energy storage system.
"During the past three years our total power sales has reached more than a million megawatts," reports Tim DeVries, manager of engineering services. "Alaska is an electrical island. We are not connected to Canada or to the lower 48 [states]. Small loads, small population, long distances, few roads, and challenging conditions make for an interesting life. Outages are a fact of life, and in Fairbanks, total system blackouts are not unknown."
Before the mid-1980s, GVEA was electrically isolated from the Anchorage area and relied on coal- and oil-fired generation to supply electricity to its members. "In order to keep costs down, we implemented an underfrequency relay load-shedding scheme and ran our generation with minimal or no spinning reserves. Decisions for how much spinning reserves to have on hand were made daily, depending on time of year, weather, and system configuration." Though reduced, outages due to load shedding plagued GVEA.
In the mid-'80s, thanks to the addition of a 186-mi. 138-kV transmission line known as the Intertie, GVEA was electrically connected to the Railbelt power system, which supplies electric power to 75% of Alaska's population. (The Railbelt consists of an area from Homer to Fairbanks that is connected by railroad, electrical, and road systems.) DeVries emphasizes that while the Intertie gave GVEA access to cheaper power from hydro and natural gas–fired generation, it also increased their exposure to outages and line disturbances. "The entire combined Railbelt power system has incredibly low inertia and is susceptible to large changes in frequency for relatively minor losses in generation."
One effort to minimize the impact has been a stipulation that all Railbelt utilities provide a share of the spinning reserves required due to loss of the largest operating generation on the Railbelt system. "The shares are proportioned to each utility based on the largest unit each utility has operating and the largest unit that is on-line. No distinction is made as to the type of spin that a utility provides or its response time to accepting the load obligation." Unfortunately, while GVEA had the technology in place, it could not provide real spinning reserves cheaply, so it took on more solutions that were economical, practical, and easy to implement. "A Shed in Lieu of Spin [SILOS] application was developed that used a SCADA [supervisory control and data acquisition] controlled load-shedding scheme."
The purpose? DeVries bluntly states, "This way you could ensure that every member shared the pain equally. This system has been historically proven to be able to respond in less than two seconds to power supply system disturbances caused by generator trips, and the rate of frequency decay [0.8 hertz per second] was slow enough for the SCADA-based SILOS system to react." There were times, however, when this system was too slow to handle faults on the Intertie. Under heavy import conditions, the loss of the Intertie required GVEA to shed 50-70% of its load quickly to allow the transmission system and the remaining generation and load to stabilize. In some instances the rate of frequency decay ranged from 2.0 to 7.0 Hz/sec. "As the number of outages have decreased, our customers have become less enthused about having their lights turned off, even though they are extremely interested in low rates."
He points out that small-but-consistent load growth, coupled with fuel price declines due to competition from natural gas-fired and hydro generation over the Intertie, has allowed GVEA to maintain electric rates at the same level for the last 20 years. This has helped make for happy customers. Still, the need to reduce the number of power failures—and do so affordably—remains. After pointing out that state aid was needed for a multimillion-dollar investment, including installation of a second transmission line to span the 105 mi. between Healy and Fairbanks, the need still existed to ensure power backup and to provide voltage compensation for the Northern Intertie. (The original transmission line has been in service for some 40 years.)
Bring on the BESS
After assurance of a state grant, Railbelt power providers began seeking other solutions. GVEA joined six other providers in that effort: Homer Electric Association, Matanuska Electric Association, Anchorage Municipal Light and Power, Fairbanks Municipal Utilities Services, Chugach Electric Association, and the City of Seward. Says DeVries, "One of the subcommittees for the Intertie Participants Group investigated more than a dozen options using life cycle cost analysis and determined that a battery energy storage system [BESS] was the best option and provided the greatest benefit potential. The incremental costs of choosing a BESS over traditional SVC [static var compensator] voltage support solutions were mitigated by additional project benefits in three primary areas: transmission and distribution, generation, and strategic [aspects]." Examples of strategic benefits are a reduced risk of high system investment by acting as an "any fuel" source, quick design and installation, flexible siting, improved power quality, reduced demand peaks, and enhanced reliability through the reduction of power supply–generated outages.
When complete in December 2003, the BESS will consist of 13,760 battery cells.
All in all, the BESS technology will provide voltage regulation, first swing stability, loss reduction as well as generation of spinning reserves, ramp-rate constraint relief, load following, black start, load leveling, and reduced or deferred turbine starts.
After a thorough review of more than 110 outages from 1994 to 1997, GVEA determined that the association needed to install a BESS with a minimum output of 40 MW. It then selected Power Engineers of Haley, ID, to draw up the specs, which it did, basing them on the experience of the BESS owned by Puerto Rico Electric Power Authority in San Juan, along with input from Abbas Akhil of Sandia National Laboratories, Phil Symons of Symons/EECI, Black & Veatch, and GVEA.
Basically their BESS is required to operate in the full power circle and to provide continuous, infinitely adjustable control of real and reactive power over the entire operating range. The specification required that the vendor guarantee that the BESS could supply 40 MW for 15 minutes, with a 4-MW/min. ramp-down after the 15-minute mark, and be prepared to do it anytime in the next 20 years. DeVries explains, "Our group also required the BESS be able to operate in seven distinct modes: VAR support, spinning reserve, power system stabilizer, automatic scheduling, scheduled load increases, automatic generator control, and charging."
DeVries, who has explained the process in several industry meetings, points out, "We knew from the start that the evaluation process was going to be complex and difficult. Different power converter systems [PCSs], different battery technology, different configurations, guarantees, warranties, and modularity issues would make an apple-to-apple comparison impossible. Our primary focus would be to verify that each proposal could meet the technical aspects of the specification and then evaluate the total cost of ownership over a 20-year period. Personnel from purchasing, operations, power supply, dispatch, engineering, accounting, as well as our consultant, helped with the evaluation."
There were 10 factors evaluated by GVEA and the other participants. These included life cycle cost calculations, warranties and guarantees, operational considerations, overall design, risk, commercial and contractual aspects, flexibility of the proposed design, corporate proactiveness on the part of vendors, exit strategy, and other. "[The exit strategy] item included that if the BESS ultimately failed, what were our options? Could the equipment be redeployed throughout our system or could it be resold? We also looked at how the building [that houses] the system could be reused," DeVries explains.
The broad "other" category included an evaluation of training available, site security, completeness of testing plans. "And it included another catch-all subcategory called ‘green stuff,' which evaluated battery disposal, how preexisting building conditions were handled, noise, and other hazards," he describes.
DeVries adds that BESS is composed of the power converter system, battery, converter transformers, and supporting subsystems. "It is being installed in an existing 500-foot by 120-foot building. The PCS interfaces the battery to the AC system using standard ABB medium-voltage, three-level, two-phase modules utilizing integrated gate-commutated thyristors. Maximum sustained output of the PCS is 46 MVA [megavolt ampere]. The PCS is water-cooled utilizing a SwedeWater fine filter/raw water system. The fine-water system can flow over 400 gallons a minute of 100% demineralized water and uses a heat exchanger in the raw water [glycol] side to dissipate heat." External cooling towers help the raw-water side dissipate heat.
He explains that the battery consists of four strings connected in parallel, with each string containing 3,440 cells arranged in 10-cell modules. Each cell is a Saft-type SBH920 liquid-filled Ni-Cad. "This is a high-performance, 920-amphour, pocket plate Ni-Cad that can withstand repeated deep discharges with little effect on battery life. Each cell is 16 inches high by 21 inches long and 8 inches wide and weighs 150 pounds. There will be a total of 13,760 cells installed, with 10 spare modules on-site.
"Each module will be tied to the battery monitoring system [BMS]. At each module a Philadelphia Scientific Sentry Unit will monitor the module voltage, electrolyte level in one cell, temperature in one cell, and the presence of any liquids in the bottom of the module. Each Sentry Unit will relay its information to a single Sergeant Module dedicated to each string. That module will collect the data and send the information to the BMS supervisory computer."
As GVEA prepares to fully activate its BESS, Devries concludes with a look at the timeline for such a project. "The project began the end of October 2001. About 30% of the design review was completed by December 15, with 90% design review completed in late March 2002. Last April, construction and installation were nearly complete, and during the summer we started up with two strings of batteries. In late September, with three of the four strings on-line, we began gathering data for the 18-month availability test." By then, they also had completed employee training. For December, the goal is to have all battery strings installed, with a provisional acceptance certificate issued by the end of January 2004.
Whether it's a vehicle, an office complex, a manufacturing plant, or even a city, batteries are able to meet the challenges involved in providing electricity—permanently or temporarily—when other sources have failed or are not practical. Batteries help make for success instead of excuses.
Author's Bio: Journalist Joseph Lynn Tilton specializes in land and building issues.