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By Mohammad Qayoumi
March 2003 -
Energy Efficiency Article Use Policy
The effect of computers on facilities goes beyond their influence on productivity and communication. The proliferation of computer technology impacts energy considerations, as well. A decade ago, the percentage of electricity used by computerized equipment was negligible. Today, these pieces of equipment consume close to 15 percent of the nation's total electricity.
But their impact goes well beyond quantity. In the future, the quality of electricity that facilities will need to power this often-sensitive equipment will be much more stringent than traditional electrical loads.
Maintenance and engineering managers have grappled with the reliability of electricity for some time. Because of their central role in overseeing facilities' power distribution systems, they often get the first call when problems arise.
To address facilities’ need for high-quality, reliable power, many facilities have installed uninterruptible power supplies (UPS). But increasingly, managers are exploring emerging technologies to handle facilities’ onsite power requirements.
With the advent of small-scale electrical-generation systems, one technique that can address facilities’ electrical needs is small-scale distributed-generation systems (DGS). These systems enable managers to seriously evaluate onsite generation as an economically viable and attractive option.
Traditionally, in-house power systems have consisted of passive equipment. The utility provides most of the power in these facilities, except in rare occasions when the emergency generator of a UPS might provide some power.
In a DGS arrangement, a large percentage of energy is generated in a limited geographic area using small generation units. Similar to utility distribution power grids, these small units are connected to each other in a micro-grid. An analogy for the DGS would be the centralized mainframe computers of the past and a large number of PCs and servers connected via a network.
In the case of a power utility, the size of electrical generators ranges from 150 megawatts (MW) to 800 MW per unit. With a DGS, the generation units could be as small as 20 kilowatts (KW) and as large as 100 KW.
The key to the commercial feasibility of these small units is the development of new technologies that have significantly lowered their cost. For instance, the cost of installing one such technology, a microturbine, is roughly $600 per KW, which is very comparable to the unit cost of generation for large-scale units that utilities use.
Also known as virtual power plants, DGS offer new possibilities for reliable, low-cost power. Numerous small generation units are connected to create a totally self-sufficient environment. In some cases, the local utility can supplement a facility's electrical power needs. In other words, sometimes power comes partially from the local utility, while at other times, DGS units supply excess power to the utility.
New technologies enable customers and utilities to remotely monitor the energy use of major loads, and managers can make decisions on real-time basis as to whether any units must be taken off line.
Micro-grids use the Internet for communication and system control. So, unlike traditional systems, they require no dedicated communication system. Micro-grid systems also can be AC or DC. The use of DC systems also can help facilities avoid most power-quality issues present with AC power systems.
DGS use a variety of technologies, including microturbines and fuel cells.
Microturbines offer great potential for many facilities. The technology is very robust and reliable, due to microturbines' inherently simple design. Many units can be connected in parallel to supply power to larger loads. In fact, because of their modularity, the overall reliability of the power system is significantly higher than that of one large traditional generation unit.
Based on supercharger turbine technology, these units can use a relatively wide range of primary fuels, including some that otherwise would have been vented or flared.
The net efficiency of these units is better than that of traditional utility sources. For instance, typical utility plants have an efficiency of about 38 percent, with roughly 7 percent wasted due to transmission and distribution losses. By comparison, microturbines have an efficiency of about 30 percent. But when used in cogeneration applications that use both the units’ power and thermal energy, the combined efficiency can be 70-90 percent.
Another important characteristic of these units is low emission rates. Nitrogen oxide (NOx) emission rates can be less than 9 parts per million, or less than 0.5 pounds per megawatt-hour (MWh). By contrast, the emission level from a typical power plant is 10 times higher.
The contrast between a microturbine and a diesel engine is even greater. A diesel engine generates more pollutants in one hour than a microturbine produces in nine days. For this reason, in many metropolitan areas, a diesel generator can only operate as an emergency unit and cannot operate on an ongoing basis.
Microturbines require relatively low maintenance, due to their inherent design. The units only have one moving part — namely, a compressor and turbine mounted on a rapidly spinning shaft. For this reason, the availability of these units often exceeds 99.8 percent.
Finally, microturbines are compact and create negligible vibration. These characteristics mean that, unlike traditional generation units, they require less space and can be installed and ready for service rather quickly.
During the past few decades, fuel cells have received attention as a viable electrical generation source. As with regular batteries, they generate electricity using hydrogen and oxygen. Unlike regular batteries that contain a fixed amount of charge that is depleted, in a fuel cell, the process is continually regenerated, so the unit can stay on line for long periods of time.
Fuel cells have a number of potential benefits, including no moving parts and few emissions, other than water and heat. Typically, the NOx emission of a fuel cell is less than 0.01 gram per kilowatt-hour (kWh), or roughly 600 hundred times less than that of a utility power plant. Also, their low maintenance features make them prime candidates for reliable power.
Many utilities have demonstration projects using fuel cells. One barrier to fuel-cell technology is installation cost, which can be $4,000-8,000 per kW. So without a utility subsidy, the technology is not commercially viable. Some industry experts believe that fuel cells might become commercially viable within a decade or so, while others point out they have heard such projections about fuel-cell technology for four decades.
Given the continuing trend toward microprocessor-based technology in facilities, the need for reliable, high-quality power seems destined to continue. As these alternative power-generation technologies emerge and advance, the challenge for managers is to specify the technology that best meets the specific needs of their facilities and does so cost-effectively.