On-site power systems traditionally have used to supply electricity to a facility in the event of a disruption of the supply from the electrical. Even then, most systems were installed to meet the facility’s safety requirements, including lighting for safe egress and power for critical equipment. Maintenance and engineering managers were not particularly interested in getting into the power-generation business.
Today, things are different. The explosive growth in the use of computers, telecommunications systems and computer-based building automation systems has increased the demand for a clean, stable source of power. Equally important is the widespread implementation of real-time pricing and time-of-day rates that has resulted in many managers rethinking the need to get into the power-generation business.
But getting into the power-generation business, even if only on an intermittent basis, requires careful planning. Economical loads must be determined, cost-effective fuel sources identified, and different power-generation systems evaluated.
And systems must be maintained once installed. Still, on-site power generation is an economically feasible option for many institutional and commercial facilities today. Before entering into a particular system, managers must understand the available options and the ways their use will impact their operations.
Three types of power systems are suitable for use in a range of facilities today: reciprocating engine-generator sets, microturbines, and fuel cells. Of the three, the most widely used systems to date are reciprocating engine-generator sets.
These sets use a conventional piston engine to drive an electrical generator. The sets can operate on a variety of fuels, including natural gas, gasoline, diesel, propane and methane. Waste heat from the engines can be recovered and used for space heating. Sets are available in sizes ranging from several kilowatts (kW) to as high as 6 megawatts (mW). Typical installed costs are $200-800 per kW.
Reciprocating engines are tried-and-true technology, having been widely used in both the power-generation industry and in facilities. A typical startup time of less than 10 seconds means they are well suited for standby applications. They offer slightly higher generation efficiencies than today’s microturbines, but one significant drawback is their relatively high maintenance costs.
Microturbines are small combustion turbines that recently have gained acceptance as power generators in facilities. They can burn a variety of fuels, including natural gas, propane, diesel, hydrogen and methanol. Waste heat from the microturbines can be recovered and used for space heating. Most currently marketed microturbines have generation capacity ranges of 25-500 kW. Typical installed costs are $700-$1,100 per kW.
Microturbines’ smaller footprints and quieter operations relative to reciprocating engines make them easier to install in existing facilities. Their maintenance costs are projected to be significantly less than those for reciprocating engines.
Fuel cells are the latest technology to be adapted for use as an on-site power system. Fuel cells generate electricity with a chemical reaction that combines hydrogen and oxygen, producing heat as a byproduct. Fuel cells can run on natural gas, methane, butane or any other fuel containing hydrogen. Like other on-site generators, fuel cells produce a significant quantity of waste heat that can be recovered for space heating. Fuel-cell capacities range from 3 kW to 3 mW. Typical installed costs are $2,000-8,000 per kW.
Fuel cells have not been in use long enough as facility power generators to develop an operational track record. But they have no moving parts, so their maintenance costs are projected to be significantly less than those for other types of generation systems.
Their biggest drawback is a rather lengthy startup time required to get the fuel cell operating and producing power; typically in the range of one hour.
Regardless of the type of systems in-stalled and the amount they are used, they require regular maintenance to function effectively and reliably. Technicians must perform maintenance on two levels: testing the operation of the entire generation system and performing maintenance tasks on individual components.
For systems that run only occasionally, it is important that they be test run in a simulated power failure. Operators should allow the system to sense the failure, start, reach operating voltage and speed, and automatically transfer and carry the designated load. This test run should continue for at least 30 minutes, and it should be performed at least once every two weeks.
For systems that run for extended periods of time, such as those that are used to base-load a facility, it is important that the system be monitored during operation to detect problems as they develop.
Technicians should start a maintenance log for the generator. If the system operates only during power outages, they should record the output voltage and frequency, oil pressure and operating temperature during the scheduled test run under load.
For systems that serve as the primary source of power or those that run for extended periods of time, record the operating parameters at least once daily. Keeping this log will help identify trends in system performance, as well as in identifying developing problems.
Technicians should inspect the entire system weekly for fuel, oil and water leaks. Check all belts for proper tension and integrity. Inspect the entire exhaust system for leaks, corrosion and signs of overheating. Top off and record engine oil and coolant levels.
They also should inspect and clean all battery and starter connections monthly, as well as check all coolant lines and hoses for leaks and overall condition.
For systems that have extended run times, managers can expect to have operating and maintenance costs for reciprocating systems that are $0.0075-0.02 per kWh generated.
One advantage of microturbines is that they have far fewer parts than reciprocating systems, resulting in increased reliability and reduced maintenance. Today’s microturbines also are designed for continuous operation, further reducing maintenance requirements.
Typically, fuel compressors will require service after 3,000-16,000 hours of operation. Air and fuel filters should be replaced after every 8,000 hours of operation. At 16,000 hours, the igniter, fuel injectors, and thermocouples will require replacement. And after 40,000 hours of operation — nearly five and one-half years of continuous run time — the fuel cell will require a major overhaul that includes rotor replacement.
A major advantage of fuel cells is their use of very few moving parts. Many believe this makes the units practically maintenance free, but since the units only now are moving into power-generation applications, no real data is yet available on long-term maintenance requirements. More likely, fuel cells will require some regular maintenance.
For example, some maintain that the fuel cell's stack will require replacement every 5-10 years because of carbon monoxide produced from hydrocarbons in fuel. Estimated replacement costs are in the range of 10 percent of the fuel cell’s total cost.
Another area in which maintenance will be required is the auxiliary equipment required for fuel-cell operation. As with other power generators, fuel cells produce heat. Auxiliary equipment is required to remove that heat, and that equipment requires regular inspections and maintenance.
Questions also have arisen concerning the length of the catalyst’s service life. The catalyst is the heart of the fuel cell, and any changes in its performance will impact its operation and efficiency.
Whatever the system that is chosen, managers must consider each technology specific post-installation costs. These considerations will be central to the technology’s ability to meet facilities short-term power needs and long-term performance expectations.
System-selection DecisionsWhen evaluating options for on-site power systems, maintenance and engineering managers must begin with an evaluation of the facility's needs:
Next, managers must consider the level of expertise available for operating and servicing the system, both in-house and from local, outside service companies. If a facility is to rely on on-site power generation, then system reliability is only as good as the reliability and availability of those who must operate and maintain it. Finally, managers look beyond first costs to life-cycle costs. Over the life of the system, what are the projected operating costs and potential savings of each possible system? What type of fuel is readily available near the facility? Can the supplier be locked into long-term price contracts? Failure to consider these issues can significantly reduce the benefits of on-site power generation. — James Piper |
