Doesn't that sound like a strange question? Ironically, it isn't. It is a very important one. If you ask a dozen people what they mean, you will probably get all four of the following viewpoints:
Standby Generation: The energy customer is interested in having power during utility power outages brought on by weather or other utility system interruptions. The agendas may range from avoiding inconvenience to real financial losses due to lost data, business, or product (usually food).
Emergency Generation: Critical equipment and life safety concerns often require on-site generation that starts and picks up the loads within a few seconds of a power failure. Hospitals, tall buildings with elevators, and even commercial kitchens have these requirements as specified in the National Electrical Code.
Power Quality and Reliability: Some operations need even higher quality power than can be supplied by public utilities over transmission and distribution wires. They need absolutely pure power for temperamental electronics (such as a hospital's MRI) to large computer centers. Concepts such as motor generators, uninterruptible power supplies, and flywheels complement an emergency generator to produce a "premium power" system.
Peak Shaving and Cogeneration: Many energy customers are interested in owning a generator (for the reasons mentioned earlier) and believe they should operate that generator either during the on-peak period or all the time to "pay for it." After all, why should the asset simply sit there collecting dust? The careful economic evaluation of these concepts is beyond the scope of this module. Simply, understand that running engines for 3,000 hours a year or more is usually much less economic than simply operating the engines for less than about 100 hours a year under a peak load management agreement with the energy retailer and/or regulated electric utility.
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