By Jens Schoene and Robert Zavadil, EnerNex; Thomas McDermott, MelTran; Lavelle Freeman and Reigh Walling, GE Energy; and Jerry Fielder, CoServ Electric
The penetration of new load types has increased in the past few years and is expected to increase further. Some new load types such as compact fluorescent lightbulbs (CFLs) and appliances with variable speed drives (VSDs) are generally more energy-efficient and, therefore, are expected to reduce overall consumption and peak demand.
Lower peak demand can result in substantial cost reduction for utilities because this reduces the need for expensive generation or purchases to meet peak load. Conversely, the new technologies can negatively impact the power quality and operation of the utility supply system as a result of the active, nonlinear characteristic of these technologies’ electronic components, such as the ballast in CFLs and the converter in VSDs. These nonlinear loads can increase the harmonic levels of the supply voltage potentially to the point where the harmonic voltage distortion is unacceptably high, possibly resulting in problems such as overheating of transformers, nuisance tripping of breakers and fuses, and overloaded neutral conductors.
The voltage dependency characteristics of new loads can skew the aggregate mix toward constant power, potentially reducing the effectiveness of conservation voltage reduction (CVR) operations. Some new load types also can have a considerably lower power factor than the load they are replacing. For example, CFLs typically have a much lower power factor than incandescent lamps.
Energy-Efficient Lighting Energy Consumption
CFLs use about 20 to 30 percent of the electricity of incandescent lamps. White light-emitting-diode (LED) lamps are slightly more energy-efficient than CFLs, but the energy efficiency of LED lamps has a large potential to improve through technological advancements.
In Figure 1, electricity consumption is plotted against the initial luminous flux for incandescent lights, CFLs and white LED lights with phosphorous LED technology. The data in the figure are from manufacturer-provided specifications of commercially available lights.
The expected lifetimes of the CFLs in Figure 1 range from three to 10 times the life of incandescent lights, while the expected lifetimes of LED lights are 12 to 40 times that of incandescent lights. For the same lumens, an incandescent bulb draws four to five times as much power as a CFL. According to Energy Information Administration data from 2005, the electricity consumed by incandescent and energy-efficient lighting constituted 16 percent of the total residential electricity consumption. Considering the energy savings of energy-efficient lighting over conventional lighting, as illustrated in Figure 1, and the relatively large percentage of lighting-related residential electricity consumption, it seems apparent that further penetration of energy-efficient lighting has the potential to significantly reduce the overall residential electricity consumption.
Impact on Daily Load Curve
The heat generated by incandescent lights is not necessarily wasted because it can reduce the energy otherwise needed for residential heating. This incandescent heating is particularly beneficial in cold seasons where residential heating is required. Consequently, during these times the energy saved by replacing incandescent bulbs with CFLs is offset somewhat by the additional energy demand for heating. In some U.S. regions, particularly the Southeast, electric heating is prevalent, and this increases electric consumption. Incandescent lights are particularly wasteful, however, when air conditioning is used because of the additional energy consumed by the air conditioner to counter the heating effect of the incandescent light. This effect is illustrated in Figures 2, 3 and 4. Following are three simulated scenarios based on typical load curves and distribution of electricity consumption in a residential area:
- Scenario No. 1: Heating/cooling is not affected by lighting (see Figure 2).
- Scenario No. 2: Cold climate/season with electric heat (see Figure 3). The switch to energy-efficient lighting results in an additional need for heating, and, consequently, the energy consumed by the heat pump is assumed to increase by 20 percent.
- Scenario No. 3: Warm climate/season with air conditioning (see Figure 4). The switch to energy-efficient lighting results in less need for cooling, and, consequently, the energy consumed by the air conditioning is assumed to decrease 10 percent.
The figures show that the decrease in the peak load is -8.5 percent, -7.7 percent and -10.5 percent for scenarios 1, 2 and 3, respectively. The peak-load reduction is smallest (-7.7 percent) in a cold climate/season and largest (-10.5 percent) in a warm climate/season, as expected. The case study concludes that energy-efficient lighting reduces the overall electricity consumption, even if the incremental air conditioning use in warm climates is accounted for. The simulation results depend on the actual climate, heating, ventilation and air conditioning technology and efficiency, thermostat settings and lighting usage, but they illustrate the dual impact of energy-efficient lighting. Another less obvious consequence of the planned replacement of incandescent lights with energy-efficient lighting is the impact on the demand curve. A substantial reduction in lighting electricity consumption might shift the demand peak from the dark hours toward earlier hours. To illustrate this effect, the shape of the load curves in Figure 2 are normalized with respect to their peaks and compared. Figure 5 shows the results of this comparison. The peak of the curve for the high-CFL penetration scenario is shifted slightly to the left—toward earlier hours—compared with the base-case scenario.
Impact on Losses
The true power factor is a number between zero and 1 and is defined as the ratio of real power, P, to apparent power, S. The power factor often is used as a measure of the relative amount of useful power (i.e., the component of the total power that is consumed by purely resistive loads) transferred. For undistorted waveforms, the power factor depends only on the displacement of current and voltage of a single frequency (the fundamental frequency: 50 hertz or 60 hertz). Consequently, for the special case of fundamental-frequency waveforms, the power factor is called displacement power factor and is the ratio of fundamental-frequency real power and fundamental-frequency apparent power. Conversely, harmonically distorted waveforms are composed of multiple-frequency components and the displacement power factor for these waveforms, quantified by the displacement of fundamental frequency current and voltage, is different from the true power factor (the ratio of P and S). CFLs have a displacement power factor close to unity and a much lower true power factor because of the presence of harmonic distortion.
The nature of the losses because of the low true power factor of harmonic loads is nontraditional: The losses are results of the fundamental-frequency current and harmonic-frequency currents. This has implications for utilities and consumers.
First, harmonic losses do not create the same economic impact to the utilities as fundamental-frequency losses. The losses are paid for by customers having the nonlinear loads, not by utilities. This is because there is a two-way power flow related to the harmonics—the fundamental-frequency power from the system to the load that fuels the generation of harmonics and the harmonic-frequency power from the load to the system. Most meters are capable of measuring only the former and, consequently, this is the power for which consumers pay. Even if advanced meters capable of measuring harmonics and two-way power flow are employed, the question is: Should consumers be billed for the accurate net power flow measured by advanced meters or for the one-way fundamental power consumption measured by conventional revenue meters? The harmonic power produced by the nonlinear load and flowing back into the system does not have any value for utilities and other consumers. That harmonic power is detrimental to the overall power quality as utilities might need to mitigate the effects of harmonics through the use of filters.)
Jens Schoene is the director of research projects and modeling at EnerNex. Robert Zavadil is a co-founder of EnerNex, where he develops and oversees the company’s power system engineering consulting business.
Thomas McDermott is president of MelTran, a power system consulting company based in Pittsburgh.
Lavelle A. Freeman is a principal in GE Energy’s Energy Application and Systems Engineering group. Reigh Walling is a director of energy applications and systems engineering for GE Energy.
Jerry Fielder is the director of engineering for CoServ Electric based in Corinth, Texas.