Why do I need an on-line UPS with my generator?

  1. Many times the generator will take a few minutes to start up when utility is lost. The UPS supplies battery backup during that period of time for seamless power to the connected load. To handle this situation, most any UPS type (off-line, line-interactive or on-line) will probably work.
  2. Generators typically exhibit poor voltage regulation due to loads turning on and off on the output of the generator. This affects the generator speed, which then results in a change in its output voltage. Off-line UPS units are not acceptable for this problem.
  3. Generators are also prone to poor frequency regulation due to loads turning on and off on the output of the generator. This also causes the generator to change speed which results in a change in its output frequency.


Bottom Line:
Only a true on-line UPS will protect against all three of these problems.


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Within the electric utility industry, diesels serve as prime power, standby power and emergency power applications, ranging from 8 kW generators to 4000 kW power units.

  • Diesel generators serve as backup power to nuclear power plants because of their reliability. They are used to power critical systems and maintain plant safety in emergencies.
  • Portable rental power units have been used in disaster situations as a temporary source of power, providing critical community services, thus saving lives.
  • During preparations for the possible “Y2K computer problem,” diesel generators served as a critical backup power supply for individuals as well as businesses and industry. It was almost impossible to find a generator for sale in some parts of the country, as year-end 1999 approached.
  • Coal-fired power plants also rely on diesels for materials handling – such as conveyer equipment and heavy trucks.


As in many diesel applications, diesel engines used in the electric utility industry are faced with emission challenges. Environmental benefits of diesels – such as low greenhouse gas emissions – are balanced by concern with emission of nitrogen oxides and diesel particulates. Increasingly tighter environmental regulations worldwide call for advanced emission controls and near-zero diesel emission levels in the years to come.

In the United States, the USEPA has published regulations which impact diesel engine emissions in the “non-road” category, which covers most heavy equipment, as well as for stack emissions from power plants. The European Union and other countries are adopting similar regulations.

Engine manufacturers and the utility industry are rising to these new challenges and are already producing and designing engines and diesel generators to meet the US and international regulations. The diesel industry has expressed confidence that the new emissions standards can be met without disruptive impacts on the power output, reliability, ease of maintenance and fuel economy of diesel engines.

EPA regulations are intended to reduce emissions of nitrous oxides (NOx), total hydrocarbons (THC), carbon monoxide (CO) and particulate matter (PM). MARPOL regulations are intended to reduce NOx and SOx emissions.

Engine manufacturers and suppliers are addressing the reduction of emissions through: engine design, fuel and lubrication formulations, and exhaust aftertreatment.

Engine design enhancements include: compression chamber redesign; enhanced turbo charging; common rail fuel injection; exhaust gas recirculation; water injection and advanced electronic engine control systems.

The use of low-sulfur diesel fuel is one strategy designed to reduce emissions both directly and by enabling exhaust aftertreatment. Other diesel fuel options include raising the cetane number in diesel fuel; which improves the combustion process. New lubricants that reduce friction thereby lowering emissions are another technique.

Exhaust aftertreatment consists of using catalytic converters and particulate traps to control emissions after the combustion process.


In terms of power generation, diesel generators are one means to produce electricity. Hydro-electric, nuclear power, various types of fossil fuel boilers, and alternative technology such as wind and solar, make up the range of options being employed to meet electric needs. But as noted, many of these power sources rely on diesel engines at some point in their power production process. Diesel engines will continue to be an integral part of the world power generation picture for the foreseeable future.

To help businesses protect critical facilities during a power outage, the Diesel Technology Forum offers the following tips:

  • Assess the Risk. Identifying your facility’s critical loads is an important first step. Assign a cost to the risks associated with utility power interruptions, production losses and downtime.
  • Install a standby generator. Frequent outages of a few seconds, a few minutes or more can often disrupt production lines and have significant cost implications to businesses. While other fuel sources take up to two minutes to engage, diesel-powered standby generators are uniquely qualified to provide power quickly and continuously during a power outage. And, the combination of greater fuel efficiency and lower fuel costs for diesel generators means that they offer the most cost-effective source of reliable backup power available.
  • Have sufficient fuel storage. For extended outages, running out of generator fuel before the outage is over may mean you’re out of luck. The chemical structure of diesel fuel allows more energy to be released per unit that any other source of commonly used power. This greater power density means less fuel consumption than other sources. Still, it is important to make sure that you have sufficient fuel storage capacity on-site for an extended outage of several days. Additionally, diesel fuel degrades over time, so be sure to use and replenish the supply on an annual basis.
  • Maintain your equipment and exercise the standby generator monthly. As required by electrical codes, standby generators should be “exercised” monthly to insure they will operate as designed in the event of an emergency. Be sure to operate the generator under load to make sure the entire system works, and keep up with recommended maintenance procedures.
  • Contract rental power. If installing your own standby generation is not feasible for your business, you might consider contracting with a firm to reserve rental generator power for use in the event of an extended outage. In the case of disaster, it may be too late to secure rental power after the fact.


Domestic and international emissions laws-along with advances in technology and competition among engine suppliers-will continue to serve to reduce emissions while maintaining diesel power as an important part of our total energy picture.