Improving Electrical Reliability Through GenSet Battery Selection and Maintenance
An overview of possible power outage risks and what you can do about them.
RISK OF POWER OUTAGES
Power outages are a significant problem. A 2012 Ernest Orlando Lawrence Berkeley National Laboratory study, titled, “An Examination of Temporal Trends in Electricity Reliability Based on Reports from U.S. Electric,” analyzed 10 years of electricity reliability information collected from 155 U.S. electric utilities (accounting for roughly 50% of total U.S. electricity sales). The study reported “reliability is getting worse, on average, over the [past] 10 years,” a finding that is especially true among smaller utility firms. While there has been some improvement in the last four years, “this reversal is not large enough to offset the overall trend for the entire 10 years.”1
The result is an increase in outages. According to research at the University of Minnesota, there has been a steep increase in non-disaster-related outages affecting at least 50,000 consumers during the past two decades. The university’s research showed that blackouts have increased 124%, from 41 blackouts between 1991 and 1995, to 92 between 2001 and 2005.2
More recently, researchers at Carnegie Mellon University estimated that the average U.S. electricity consumer experiences an average of 214 minutes without power each year. This is in stark contrast to Germany and Japan, in which only 21 minutes and six minutes, respectively, are spent without power each year.3
Unfortunately, this is not a problem that is likely to go away any time soon, as the root cause — our aging infrastructure — is under a tremendous amount of stress. The U.S. power grid — a complex network of power lines and substations — was built back in the 1950s and ‘60s. A report by National Public Radio, titled “Power Hungry: Reinventing the U.S. Power Grid,” likened the grid to “a highway system — one that has been seriously neglected and is now being pushed to its limits with the demands of our growing and changing energy needs.”4 Our country’s expanding population and increasing dependence on electronics is increasing our collective appetite for electricity.
According to “A Word to the Wise: Know Your Power,” an article from May 2012 in The Data Center Journal, U.S. demand for electricity is forecasted to grow by 40% over the next two decades.5
Additional stress is placed on our electrical systems as utilities and businesses increase our use of renewable energy sources. Some sources estimate that the share of electricity coming from renewable sources of electricity is projected to grow from 10% in 2012 to 16% in 2035.6
Decreasing reliability and increasing outages are costing both consumers and businesses money. According to the Environmental Protection Agency (EPA), “cost of a service interruption varies by customer and is a function of the impact of the interruption on the customer's operations, revenues, and/or direct health and safety.” In one study, Pacific Gas & Electric Company (PG&E) estimated the total annual cost of power outages to its customers at $79 billion per year.7
Power outages or service interruptions can impose direct costs on customers in the following ways:8
- Loss of data: Information can be damaged or lost in storage, transmission, or processing. Some data loss can be temporary, while other losses may be permanent. Data spills also can result in sensitive information being lost and acquired by an outside party.
- Equipment damage: A brownout or voltage sag can cause equipment to perform poorly or incorrectly. A blackout or complete outage can damage sensitive circuitry in computers, data networking equipment, and critical alarm systems.
- Extra maintenance costs: An outage can require many additional man-hours to service hardware and to bring systems back online.
- Cost for replacement or repair of failed components: Out-of-pocket expenses may be required to replace damaged hardware and software.
- Permanent loss of revenue from downtime: An 2010 online survey by CA Technologies of 2,000 information and technology (IT) executives found that, on average, companies lost $26.5 billion in revenue each year from IT downtime, translating to roughly $150,000 lost annually for each business.9 In another report by Emerson Network Power titled, "Calculating the Cost of Data Center Outages," the average cost of data center downtime across industries was approximately $5,600 per minute.10
- Costs for idle labor: According to the CA Technologies survey, IT downtime costs businesses, collectively, more than 127 million person-hours per year — or an average of 545 person-hours per company — in employee productivity. This loss is equivalent to 63,500 people being unable to work for an entire year.11
- Liability for safety/health: Depending on the location, outages can have serious, life-threatening ramifications. For example, hospitals and health care facilities need up-to-the-minute patient information in order to make accurate life-and-death decisions; this information is not accessible during a power outage.
Many companies are willing to pay to protect their businesses from the damage caused by outages. This is referred to as value of lost load (VoLL). The amount they are willing to pay varies greatly and is based on a number of conditions, including the activities affected by the outage, the number of interruptions, whether or not there was advance warning, types of weather conditions, and the duration of the interruption.12
Generator and emergency-power failures can result from several common maintenance issues. These include the following:
- Starting-system issues, batteries, and cables
- Bad fuel, fuel piping failures, and clogged fuel filters
- Mechanical equipment issues
- Light loading of generators
- Control and software issues
A strong preventative maintenance program is one of the easiest and cost-effective ways to reduce the level of risk and raise the uptime percentage of a facility’s critical power system. Managing the common failure areas allows managers to harden potential weak links in crafting preventative maintenance programs.
However, negligent battery maintenance remains the most common reason for failure of critical backup power systems, and the main reason why standby generators fail to start is due to dead starting batteries. In his white paper, titled “Improve Genset Availability by Detecting Bad Batteries Early,” Bill Kaewert of Stored Energy Solutions LLC, claims “failure to start is the most significant avoidable cause of diesel generator malfunction. Weak or undercharged starting batteries are the most common cause of standby power system failures. Over 80% of failures to start are caused by battery problems.”13
Good monitoring and maintenance, however, are the keys to minimizing failure of batteries — particularly lead acid gen-set batteries. For proper maintenance, adequate watering of flooded batteries is important to replenish lost water and to keep the battery’s plates from going dry, which can cause permanent loss of capacity. Correctly charging the battery also is crucial: overcharging can accelerate water loss, while undercharging can cause sulfation. Both can result in permanent capacity loss.
NOT ALL GEN-SET BATTERIES ARE THE SAME
While maintenance is important, choosing the right gen-set battery is even more important. The key is knowing your application and its requirements. Here are several questions to consider when determining your gen-set battery needs:
- Environment. What is the “true” environment for your installation? It is important to fully understand the environment to which your battery will be subjected. Will it be exposed to high heat during the day or long periods of cold at night? Will the battery be in an enclosure and/or a temperature-controlled environment? Has your battery been tested and designed for these conditions?
- Duration. Does your application require your battery to stay on continuous or trickle charge? Is your battery designed for longevity under these circumstances? Will it have the starting power it needs when necessary?
- Rechargability. Is your application subject to frequent outages? Does your battery have quick recharge capability to meet these needs?
- Size. Is your battery properly sized for your application, accounting for typical depth of discharge? Does it fit within the system footprint?
- Protection. Are your batteries properly concealed to avoid theft at the installation site? Are the individual cells monitored to protect against thermal runaway?
OVERVIEW AND COMPARISON OF GEN-SET BATTERIES
Batteries for generator starting applications must, at a minimum, meet two key requirements:13
• First, they should have high power density so the most amount of energy can be packed into the space. This will allow extra energy to be stored when needed, such as on extremely cold days, as well as to reduce the depth of discharge, thereby increasing longevity.
• Second, they must be able to last several years under continuous trickle charge and be ready to fire up the gen-set whenever necessary. Combining these two key requirements makes it easy to see why one needs a dual-purpose battery — one that is strong enough to last many years and powerful enough in a compact package to start large diesel engines, even in very cold weather.
Nickel cadmium. Nickel cadmium (NiCd) designs consist of a nickel hydroxide positive electrode and a cadmium negative electrode in an electrolyte solution of potassium hydroxide, resulting in a nominal voltage of 1.2V. The traditional design is pocket plate.
NiCd batteries have a high self-discharge rate and require more maintenance than lead acid batteries. However, they can endure an overcharge situation much longer than other technologies without serious damage. They also can be stored in a fully discharged state without detrimental effects, such as sulfation, which can make it harder to recharge. As a result, NiCd batteries are favored in applications where they can tolerate a certain amount of abuse. However, they exhibit memory effect and, as a result, often deliver a shorter life than that for which they are rated.
In addition to the standard NiCd battery, the industry has developed specialized designs with refined attributes, such as sintered plates, fiber plates, plastic bonded electrodes, and foam plates for specific applications.
Advantages of NiCd batteries include:
- Works well in extreme temperature applications
- Tolerates abuse, including over-discharge
- Long shelf life
- Limitations of NiCd designs include:
- High self-discharge rate
- Flooded technology making non-spillable certifications difficult to obtain
- Requires watering and in some situations special charging algorithms
- Difficult to charge and maintain full charge, making it increasingly difficult to come back online after a disturbance
- Exhibits memory effect, in which it gradually loses its maximum energy capacity if they repeatedly recharged after being only partially discharged
- Contains toxic metals, making it costly to recycle
Flooded lead acid. Flat-plate flooded lead acid batteries are the principal plate design found in stationary applications throughout North America. The flat plate consists of a grid structure of lead calcium or lead antimony. The grid serves the dual purpose of being the electrical conductor and the mechanical support for the lead dioxide positive plate material and the spongy lead active material of the negative plate. The flat plate design has proven to be a robust, cost-effective design. It is a flexible design, in which plate characteristics — such as thickness, alloys, wire radius, and placement — can be modified with relative ease to create a battery design that is optimized for a particular application (such as float service, cycle service, long duration, high rate, general purpose, etc).
Advantages of flooded lead acid batteries include:
- High reliability
- Easily recyclable
- Well-understood technology
- Economical solution
- Services a broad range of applications
Limitations of flooded lead acid batteries include:
- Flooded technology, making non-spillable certifications difficult to obtain
- Reduced life in high temperatures
- High maintenance; requires watering
Thin-plate pure lead (TPPL). Pure lead plate designs have a low corrosion rate because they do not have impurities or alloy additives in the pure lead. This allows for a long float life expectation. They also have a low gassing rate, which reduces water usage and reduces maintenance costs. TPPL batteries can provide considerable energy density improvement over NiCd and flooded lead acid battery technologies. TPPL batteries can easily be charged and recharged, minimizing downtime. The mechanical design, using high compression, not only supports a longer life but also provides a robust design to combat against vibration and other onerous conditions. A trusted and proven technology, TPPL batteries are being embraced for applications in telecommunications; multiple military applications, including starting batteries for tanks; police; ambulance and fire; starting batteries for large trucking fleets; silent watch, and submarine microgrid/hybrid applications. TPPL batteries also offer an excellent solution for switchgear applications.14
Advantages of TPPL batteries:
- Long life
- Ability to handle abusive situations
- Ease of getting back online
- Low maintenance, no need to water
- Easy to recycle
- High energy density
- Ability to handle high temperatures
- Limitations of TPPL batteries:
- Higher than normal initial cost.
Improving electrical reliability for gen-set systems begins with an essential building block — the battery. Batteries traditionally have been the weakest link in the gen-set system. It is important that designers fully understand their application needs and the various battery chemistries available to meet those needs. Lead acid technology, especially TPPL, is a preferable solution for most applications — offering long-life, strong performance, and low maintenance requirements that offset the somewhat higher investment.
Joseph H. Eto, Kristina Hamachi LaCommare, Peter Larsen, Annika Todd, and Emily Fisher, Ernest Orlando Lawrence Berkeley National Laboratory. “An Examination of Temporal Trends in Electricity Reliability Based on Reports from U.S. Electric Utilities.” January 2012.
Thom Patterson. “U.S. electricity blackouts skyrocketing.” October 15, 2010. http://www.cnn.com/2010/TECH/innovation/08/09/smart.grid/index.html.
Karl Rusnak, Economy in crisis: Power Outages Highlight America’s Aging Infrastructure. July 02, 2012. http://economyincrisis.org/content/power-outages-highlight-americas-aging-infrastructure.
National Public Radio's "Power Hungry: Reinventing the U.S. Power Grid." Heather Philipp, Renewable Choice Energy. 05/12/2009.
Jeff Spence. “A Word to the Wise: Know Your Power.” The Data Center Journal. May 7, 2012.
Cassandra Profita, Energy Outlook: Your Carbon Emissions Will Fall (A Wee Bit). Oregon Public Broadcasting’s Ecotrope. Jan. 23, 2012.
“CA Technologies Survey Reveals IT Systems Failures Cost Businesses 127 Million Lost Person-Hours.” May 23, 2011. http://www.ca.com/us/news/Press-Releases/na/2011/CA-Technologies-Survey-Reveals-IT-Systems-Failures-Cost-Businesses-127-Million-Lost-Person.aspx
National Survey on Data Center Outages, Sponsored by Emerson Network Power, Ponemon Institute. September 30, 2010.
Peter Cramton and Jeffrey Lien. “The Value of Lost Load.” University of Maryland. February 14, 2000.
Bill Kaewert. SENS – Stored Energy Systems. “Improve Genset Availability By Detecting Bad Batteries Early.” 2006.
Kalyan Jana, EnerSys. “TPPL — A Cost-Effective Solution for Genset Starter Batteries.” 2008.