Whether stored in fossil fuel, uranium atoms or chemical batteries, releasing stored energy has significant environmental and safety consequences. Power generation facilities have an excellent record managing large-scale operations, but many industrial operations need on-site power storage and generation capability to ensure continuous operation through power outages.

Lead-acid batteries have been the primary means of reliable electrical energy storage, yet they contain toxic and corrosive materials and pose risks of explosion, fire, and injury. Industrial and commercial sites often don’t have the capability to train personnel to operate and maintain these hazardous materials like large-scale utilities. Even normal handling can present hazardous waste disposal challenges.

Flywheel power conditioning and energy storage systems are suited to mitigate most power events. They are compact, safe to handle and maintain, and are non-toxic. Some recent innovations have made well-known flywheel kinetic energy storage systems attractive in many sites which previously had no alternative to lead-acid battery installations. Finally, they offer lower cost over their life span than batteries, require less maintenance, and operate more cheaply and efficiently.

MORE BATTERIES MEANS MORE LEAD
Most industrialized countries have stringent environmental protection legislation governing the use and transportation of hazardous substances. By volume, the typical lead-acid battery contains approximately 50 percent lead oxides, 24 percent electrolyte, and 26 percent lead.

The lead contained in uninterruptable power supply (UPS) battery strings in North America alone numbers in the hundreds of thousands often. Lead usually tops environmental hazard lists, and there is no argument that handling and disposal of lead-acid batteries pose environmental risk. In many areas, tax and other incentives are coupled with onerous financial penalties to encourage responsible and careful use, transport, and recycling.

Power outages are inevitable. Lightning, tree limbs, and small animals are ongoing causes of temporary electrical outages. Emergency and critical services have relied on stand-by electrical power supplies for years to operate hospitals, air traffic control, and other essential services and communications. The number of users now extends to numerous business-critical “7 x 24” operations running seven days a week, 24 hours a day.

What has changed dramatically during the past decade is the increasing reliance by industry on computers and sensitive microprocessors to control precision machinery, continuous process operations, and data centers with large concentrations of computers and communications gear.

Disruptions in microprocessor-controlled operations are far more common than the outages sufficient cause us to reset VCR and microwave clocks. Even one cycle (1/60 sec) of outage, or a 25 percent voltage dip lasting two cycles can cause microprocessors to malfunction. The consequences aren’t always life-threatening, but Business Week estimated power-related problems cost U.S. companies $26 billion in lost productivity and revenue each year.

Paper mills, textile mills, food processing operations, plastic and metal extrusion operations, and even computer-controlled machine tool operations share a growing concern for power quality. The first line of defense is a UPS which converts AC power to DC, and then back to AC. In this way, the electrical sags, glitches, and spikes are conditioned out of the facility’s power supply.

A critical adjunct to the UPS is a reserve DC power supply, commonly in the form of lead-acid storage batteries. Stored electrical energy is continuously available to “fill in” any gaps in the incoming electrical supply. The number of batteries required to provide stand-by power for a large industrial operation can require special battery racks and hundreds of square feet requiring special ventilation, air conditioning, and isolation.

Many operations must balance the cost of power quality with the cost of lost production, lost materials, damage to equipment and work in process, and down time. More and more operations are searching for a safe, cost-effective solution.

Batteries require regular maintenance, and their reliance on lead and sulfuric acid presents environmental and safety hazards. Lead enters the body primarily through ingestion, and sulfuric acid can enter the body through skin contact, eye contact, ingestion, and inhalation of acid mist. While skin contact is often prevented by gloves and aprons, eye contact from spilled or splattered electrolyte is the most dangerous threat. Sulfuric acid causes severe irritation, burns, cornea damage and potential blindness.

Lead-acid batteries are very reliable, but they produce hydrogen gas during charging cycles. Whether batteries are the vented type or so-called “sealed” Valve Regulated Lead-Acid (VRLA), the area must have adequate ventilation. As a precaution to control contamination from accidents, a model uniform fire code recommends enclosing battery banks with a four-inch curb and placing acid-absorbing mats beneath each battery.

Handled carefully by trained personnel, batteries provide safe service. But, “the No. 1 problem with battery service is poorly trained, or even untrained personnel,” according to Marco Migliaro, an industry expert in batteries, UPS, and DC power systems. Many organizations have recognized the importance of expertise and some have contracted battery maintenance to outside suppliers. Unfortunately, outsourcing by itself does not ensure the staff are aware of the special risks and hazards associated with batteries.

Every battery leaks to some degree around the jar and terminal seals. Careful and regular inspections can prevent any real danger, but if overlooked, leaking electrolyte can create a path to ground or a short circuit, causing fire. Few personnel would risk open flames around batteries, but many are unaware of the risks of static discharge. In one case, just sliding a heavy battery across a mounting rack generated enough static to trigger a cell explosion that blew out a 6- by 13 -inch section of the battery. Luckily, it was on the side facing away from the worker. Fires are not common, but loose connections which produce substantial heat energy are most often the cause.

Another battery hazard is “dryout.” Dryout is a normal (and desirable) occurrence in the first six to eight weeks of VRLA battery life. The new battery’s electrolyte is saturated with water, which dries out during the initial charging cycles and is vented safely. The battery then enters a stable phase. If the charging voltage is too high, further dryout drives out more water and can lead to thermal runaway, a condition in which the battery continues to generate more heat than it can dissipate. The end result is explosion and fire.

If the battery charger does not automatically adjust to the battery temperature and resistance, thermal runaway is a constant threat. And since most purchases are awarded to the low bidder, the additional protection is often absent.

Battery recycling is widespread, but even so, the amount of lead disposed annually is in the thousands often. Sulfuric acid used in the electrolyte is dilute and must be neutralized with soda ash (sodium carbonate) or quick lime (calcium oxide) before disposal as hazardous waste.

FLYWHEEL TECHNOLOGY DEVELOPMENTS
Plant engineers who would like to avoid the environmental risks inherent with chemical storage batteries have previously had no practical, affordable alternative to batteries. But new developments in flywheel technology present a proven promise for improved environmental safety and superior performance at lower total cost than batteries.
Recent developments have combined the advantages of simple, low-cost materials with a modem bearing design that delivers a continuous stream of DC power for up to several minutes. The flywheel incorporates rotors machined from a solid block of forged high-strength steel riding on a combination of magnetic and conventional bearings inside a vacuum enclosure. Proprietary generator technology minimizes eddy current losses and provides for complete control of developed voltage throughout the speed range of the flywheel. The standby losses for a 400 kW system are below 2 kW, which delivers significantly higher standby efficiency than traditional electromechanical battery strings.

Several forms of rotary energy storage have been available which involve mass added to a motor-generator set feeding a critical load. The additional rotating mass adds approximately one-half second of ride-through to alleviate the majority of power sags and glitches. Variations on this approach extend the ride through to about 15 seconds, or integrate the flywheel with a quick-start engine-generator system which must come on line in only a few seconds. The two main drawbacks of these systems are high cost and large space requirements (about 150 square feet). The systems tend to be noisy and quick-start systems are subject to frequent nuisance starts even in sub-second outages.

The new series of flywheel energy systems require only 10 square feet of floor space and can deliver up to 800 kW. With a life span of 20 years or more, flywheels offer two key advantages over battery-based UPS installations: lower cost of ownership and longer life. As a rule, these flywheel systems represent about one-half the total life cycle cost of battery-based alternatives. The flywheel system requires no special environmental considerations like air conditioning or ventilation. Maintenance requirements are minimal compared to battery installations, and there are no environmental hazards or safety concerns associated with them.

One of the primary advantages of the flywheel technology is that it is ideally suited to the most commonly occurring power events. The vast majority of power events are momentary glitches, sags, and surges lasting less than a second or two. Lead-acid batteries are most efficient in long discharge cycles rather than the “bursts” of demands presented in most industrial and commercial applications. The short duration of power outages constitutes a harsh operating environment for batteries and standby gensets. Frequent discharge cycles shorten life and create wear. Ambient temperature can be a major performance and life factor, since batteries don’t function efficiently in extreme heat or cold.
By contrast, the flywheel has only one moving part and is ideally suited for short-duration discharge cycles. One installation with a flywheel system has monitored an average of more than 200 power events per day, many of which are the result of motor starts and stops. A precision machine tool facility uses a flywheel to “ride through” short power events, and if power isn’t restored after a few seconds, alarms notify all employees to shut down equipment. This arrangement allows an orderly process to protect precision work and tooling that amounted to tens of thousands of dollars in losses.

Other operations use a flywheel in conjunction with a smaller battery string, providing longer-term power at lower total cost. The flywheel absorbs the majority of”hits” and conserves battery power for longer outages. An additional benefit is longer battery life from fewer “bursty” discharge cycles. Another alternative is to use the flywheel as a standby power supply and to provide starting power for an emergency generator.

In each of these scenarios, the number of batteries in service is reduced and their life cycle is extended. Existing facilities often do not offer the space required, either in terms of square footage or environmental requirements, for a battery~string of adequate capacity to sustain facility operations. A flywheel alone or in combination with a genset or smaller battery string can offer a solution that is as appealing and friendly to the user as it is to the environment