Published In February 2001
Blackouts, brownouts, surges, and outages cause downtime—costly downtime in many cases. With billions of dollars at stake, backup power strategies are no longer optional. They are a necessary way of ensuring reliable power. That peace of mind requires carefully planned strategies. Before selecting a system, decide the total wattage requirements for the items that will run off the generator. The starting watts also require consideration, as they can range anywhere from 50 to 300 percent more than the normal watts required. Items that create radiant heat, such as toasters and ovens, do not require additional watts when starting. A single fossil fuel-driven engine generator with an automatic transfer switch that monitors the normal electric service and transfers power is among the most popular units. This system is used to power life-safety systems and other building elements that can sustain lighting, air conditioning, and other interruptions. An uninterruptible power system is typically based on battery storage linked with inverters to convert AC voltage to DC and back to AC for critical equipment power. This system protects specialized equipment from being damaged by short-term outages. The backup power is limited to the size of a generator, batteries, inverter, or other backup power system. Many homes and large companies today require an uninterrupted power supply (UPS), especially for computers to remain operational. “There are many trends in the utility area because there are increasing demands on utility providers,” Nev Carmichael, Invensys Secure Power vice president of product management, said. “Technology is dependent on good quality and reliable power. More industries are paying attention to backup power because today, just having power is not the only answer—uninterrupted power is the key.” A smaller generator may be coupled to an inverter or battery charger and battery bank to optimize efficiency. If emergency backup is required only for brief periods or only on weekends, a gasoline or propane generator may be preferable. An increasingly popular system is an industrial-rated, slow-speed 10kW diesel generator that provides around-the-clock operation. When connected to a 275-gallon home-heating tank, it may run without interruption for one and one-half weeks at full load or three weeks at half load. Most generators are set up to supply standby uninterrupted power immediately when power fails. The most common residential power source is a gas, propane, natural gas, or diesel generator. Diesel units, which cost more, are generally the most effective. A natural gas generator will provide about 750 hours of uninterrupted power (nearly three months using the power eight hours per day). If the unit has overhead valves and an oil filter, it may double its efficiency and run for 1,500 hours (about six months at eight hours per day). Some systems exceed the structural capabilities of most office buildings and full support poses storage difficulties, so a diesel generator may be difficult to install in a commercial office building. If a company expects to grow dramatically over the next few years, the building structure must be examined to accommodate this growth and determine its needs. High-speed, 3,600 rpm diesel units that use less fuel than the gas-fired, slower-speed models (1,800 rpm) will last longer, use less fuel, and have four poles instead of just two. A microprocessor control center monitors continuous utility voltage. Once the voltage drops below a preset value, the generator engine will start automatically. When the power is restored, the generator transfers the electricity back to utility power. “There has been an increasing need for more reliable systems,” Mike Proffitt, American Power Conversion product marketing manager, said. “It is important to find a centralized system to provide power when it otherwise becomes unavailable. More and more people are finding ways to optimize efficiency in their homes or offices.” Electrical contractors are also seeing this as a growing market. According to Proffitt, “Most units need to be hard wired into a network environment. This is opening up more opportunities for electrical contractors. The units generally consist of a single- or three-phase power system and they all require a form of hardwiring the system to the electrical infrastructure of the building. It is going to be a good market for electrical contractors to optimize on.” Diesel generators can be stored indoors more safely and for longer periods of time without deterioration. If a generator is running at 50 percent or more of its capability, efficiencies are increased. The units without battery banks run continuously and result in an increased cost of operation per kilowatt-hour of electricity. A generator should be in the range of 120 to 200 percent of the maximum charge rate delivered from the battery charger to the battery bank. Even with equal fuel consumption, a small generator using 100 percent power and no reserve power and a larger generator at 50 percent power may run out. It may be beneficial to increase electrical loads when selecting a generator for a washing machine, air conditioner, or water pump, which use larger electrical loads than televisions and radios do. Infrequent large loads may be run directly off the generator, which alleviates the need for an inverter and additional battery capacity. During a large power surge, the battery charger will back down and the generator and inverter power will be added for the total output power available. “We think it’s a quick-growing market while other markets are declining. It will increase the importance for residential and commercial users to have their own emergency backup system,” said Mike Carr, Generac Power Systems Inc. manager of marketing communications. Since the generator’s inverter is continuous, occasional surges pose no conflicts. A generator, when turned online, will manage all surges. The inverter powers the AC loads from the batteries around the clock when the generator is off. In all backup systems, a transfer switch (either automatic or manual) must be used to prevent back-feeding the power line. This switch receives power from the generator or power company, but it will only pass one source to the loads through the inverter. The inverter must be online and battery-powered to pick up any AC loads if the power fails. Many inverters offer automatic generator start and stop control functions to provide further automation to the system. More efficient appliances may also be used, including fluorescent lighting and a propane refrigerator. Generally, a minimum of four to six parallel banks of 6-volt batteries are required to absorb the power to either the battery charger or inverter. This provides sufficient power storage. To compute battery capacity for power storage, take 25 percent of the watt capacity (volts times amps) under normal conditions and 50 percent during emergency conditions. The maximum safe charge rate to prevent battery overheating and damage uses a capacity/10 charge rate. “The demand for backup power systems is increasing,” Carr added. He said fewer power plants are being built due to environmental issues or community opposition. Carr believes there is an increasing need for emergency backup power. “The trends in emergency backup power are growing more compelling,” Carr said. “In addition to the normal but unpredictable disruptions of power caused by weather or natural disasters, there is a crisis brewing because of rapidly declining utility reserve margins. The demand for power is increasing every year but utility generating capacity is not keeping pace. That’s because power plants and transmission lines take years to put in place. The normally long lead times for large projects are further extended by regulatory delays and public opposition. The end result is that reserve margins—the excess capacity of the utilities to produce power beyond normal demand—are declining significantly. In times of peak demand (such as hot summer days), power interruptions, outages, and brownouts are growing increasingly likely with each passing year. Because of that, the need for homeowners and businesses to have emergency backup power on-site is only going to increase.” Solar-, wind-, or water-powered generators may also be used as renewable energy systems, reducing generator use. Power interruptions occur as nuisance interruptions, brownouts, short-term outages, and long-term outages. Nuisance interruptions, which generally range from momentary blackouts to power surges, may prevent data from being accessed offline and can even damage stored information. Transient increased voltages may damage the physical components of a voice/data system. Brownouts are utility-imposed reductions in voltage on the power distribution lines to decrease the demand on the utility generator equipment. Most brownouts occur during the summertime and reduce the air conditioning output when cooling is most necessary. A brownout may result in further problems to hardware. Short-term outages most frequently occur when there is a problem on the utility distribution system that cannot be repaired quickly. These outages last less than four hours. While most companies may survive a short-term outage, they will also realize a significant loss in productivity. Long-term outages last more than half a business day and result in a prolonged power failure with a loss of data. These outages may require operational procedures to backup the site and offload work to other sites. “Deregulation is a growing trend in the United States, causing uncertainty in the supply and cost of power, which was not a concern in the past,” Bill Treffert, Generac Power Systems president, said. “Having a reliable source of power is even more imperative today with computer systems being so important to businesses. Grocery stores rely on scanners and computer control systems and they can’t operate without power. Other businesses of all kinds are similarly dependent.” Backup power generator systems are expensive, so one of the most critical factors in budgeting is to determine whether the system fits the needs of the business. The type of backup system selected largely depends on what type of outage may affect a business and where the space itself is. In rural locations, power is often fed from a basic single service site via aerial distribution lines. These lines may be susceptible to traffic accidents, which can lead to a power outage in multiple locations. Urban sites usually have reliable underground services fed from dual networks. SPEED, a Weymouth, Mass.-based freelance writer, can be reached at firstname.lastname@example.org.