Energy consumption of audiovisual devices in the residential sector: Economic impact of harmonic losses

Energy 60 (2013) 292e301

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Energy consumption of audiovisual devices in the residential sector: Economic impact of harmonic losses I. Santiago*, M.A. López-Rodríguez, A. Gil-de-Castro, A. Moreno-Munoz, J.J. Luna-Rodríguez Universidad de Córdoba, Departamento A.C., Electrónica y T.E., Escuela Politécnica Superior, Campus de Rabanales, E-14071 Córdoba, Spain

a r t i c l e i n f o

a b s t r a c t

Article history: Received 7 February 2013 Received in revised form 1 July 2013 Accepted 9 August 2013 Available online 7 September 2013

In this work, energy losses and the economic consequences of the use of small appliances containing power electronics (PE) in the Spanish residential sector were estimated. Audiovisual devices emit harmonics, originating in the distribution system an increment in wiring losses and a greater demand in the total apparent power. Time Use Surveys (2009e10) conducted by the National Statistical Institute in Spain were used to obtain information about the activities occurring in Spanish homes regarding the use of audiovisual equipment. Moreover, measurements of different types of household appliances available in the PANDA database were also utilized, and the active and non-active annual power demand of these residential-sector devices were determined. Although a single audiovisual device has an almost negligible contribution, the aggregated actions of this type of appliances, whose total annual energy demand is greater than 4000 GWh, can be significant enough to be taken into account in any energy efficiency program. It was proven that a reduction in the total harmonic distortion in the distribution systems ranging from 50% to 5% can reduce energy losses significantly, with economic savings of around several million Euros. Ó 2013 Elsevier Ltd. All rights reserved.

Keywords: Economic impact Harmonics Residential sector Single-phase power electronic loads

1. Introduction Around 30% of total average worldwide energy consumption between 1996 and 2006 corresponded to the residential sector [1,2], which constitutes a basic and integral component of a Smart Grid. In Spain, households consumed 17% of all final energy and 25% of electricity [3] in 2010, a percentage similar to those of neighboring countries. Due to the large energy consumption corresponding to residential buildings, any energy efficiency program that applies to this sector will have a high impact on reaching the objectives of energy consumption and CO2 emissions. The main actions of these programs focus on the use of more efficient equipment, which would reduce consumption and save energy. Nowadays an increasing number of devices contain power electronics (PE) in order to achieve a higher efficient energy use [4,5]. However, the employment of PEs could distort power quality because they introduce nonlinear loads into the low-voltage

* Corresponding author. Tel.: þ34 957218699; fax: þ34 957218373. E-mail addresses: [email protected], [email protected] (I. Santiago), [email protected] (M.A. López-Rodríguez), [email protected] (A. Gil-de-Castro), [email protected] (A. Moreno-Munoz), [email protected] (J.J. Luna-Rodríguez). 0360-5442/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.energy.2013.08.018

distribution system, which generate undesired frequencies, which are harmonics in relation to the fundamental frequency [4]. The presence of harmonics has a series of effects that must be considered. It implies a deviation of the ideal sinusoidal form (with constant amplitude and frequency) of the current and voltage signals in power grids, causing extra losses in the loads. Their presence changes the power factor of the system to a lower value as well as the reactive power demand, therefore increasing the total apparent power. Harmonic currents can also overload the neutral conductor and cause excessive heating [4,6]. In general poor Power Quality (PQ) might cause technical inconveniences that lead to large financial losses due to direct and indirect costs. Specifically, harmonics have a direct effect on utility companies’ costs and revenues [4]. Estimating the exact amount of losses and the economic consequences of a PQ event or disturbance in different sectors of daily life is quite difficult [7]. According to the analysis produced in 2000 by the EPRI (Electric Power Research Institute)-CEIDS in the USA, the cost of poor PQ, estimated by means of a survey, amounted to between 119 and 188 billion dollars a year. Another survey conducted by the Leonardo Power Quality Initiative in 2003e2004 that only considered industry and service sectors, determined that these annual costs in 25 countries of the European Union were 151.7 billion Euros. In Europe financial losses

I. Santiago et al. / Energy 60 (2013) 292e301

for harmonics represent only 0.8% of the total losses in these sectors, other events such as voltage dips and supply interruptions being more significant due to their direct impact on customers, contributing in this case 57% of the total losses [6]. Nevertheless, a survey by the European Copper Institute (2001) identified harmonic distortion as one of the most important PQ issues for European countries [6]. In the residential sector the consequences are less drastic than those in industry, where an event can even cause the interruption in the operation of a whole plant [6,8]. However, a Laborelec and KEMA survey conducted in the Netherlands in 2004e2005 observed that the majority of Dutch PQ complaints were registered by domestic customers [6]. Furthermore, some of the equipment used in the households such as digital TVs, DVDs or personal computers, which contain power electronics, is very sensitive to PQ disturbances, specifically to the presence of harmonics. 62% of the Electricity consumed in Spanish homes is due to the use of electrical equipment (single-phase loads), and to a lesser extent, to lighting, cooking, heating and water heaters [3]. Audiovisual equipment has a relatively low power rating and each device’s individual contribution to the energy demand and to the additional losses could be regarded as negligible. However, the aggregated actions of this type of equipment can be significant enough to be taken into account in any energy efficiency measure. Accordingly, the main objective of this paper is to analyze the additional energy consumption in the Spanish residential sector due to the use of audiovisual equipment, to estimate the costs and the impact in the distribution systems caused by the increasing harmonic distortions of voltages and currents in the power grid. In order to seek solutions for both a more appropriate use of energy, as well as achieving what is known as Demand Side Management (DSM), it is essential that not only are energy efficiency specialists conscious of the characteristics and patterns of energy demand in homes, but also that they have an overview of this additional energy consumption, so important in planning and regulating electricity systems [4,6]. In Section 2 methodology used to determine the energy demanded and the economic impact related to the use of these audiovisual appliances is described. In Section 3, results are outlined and discussed. Finally, Section 4 is devoted to the conclusions and discussions. 2. Methodology The first step in performing this study is to obtain an estimation of active power consumption in the residential sector due to the use of some of the most widely used audiovisual equipment. Due to the limited available information concerning this aspect, data from Time Use Surveys (TUS) were analyzed, and information on household residents’ activities was extracted. In recent years some researchers have begun to use national TUS data to establish a more reliable causal relationship between human behavior and residential energy use [9e13], considering it as a complement, or even an alternative, to measuring energy uses. A Time Use Survey 2009e2010 was conducted by the National Statistical Institute in Spain for an annual period following the EUROSTAT guidelines for harmonizing time use data [14]. It referred to 19,295 people over 10 years old, living in a total of 9541 homes. This survey includes information about the daily activities, recorded in 10-min intervals, of the participants over the full 24 h of one random day. The interviewees used a diary to note down information about the activities they performed during the day, the place where the activities took place and whether someone accompanied them. As each person completes the diary for only one day, the results are statistically significant in aggregate mode

293

and not for individual consumers, in the same way that electricity demand only becomes significant at high levels of aggregation. From the diaries completed in the survey, the percentage of households in which one of their occupants was performing an activity related to the use of any of the appliances studied in this work (watching TV and/or DVD, using a computer, listening to music or the radio) was obtained for a complete day, recorded at 10-min intervals. These results were determined by distinguishing between weekdays and weekends. The percentages obtained from the population sample of the survey were extrapolated to the whole Spanish population. To do this, it was assumed that in the year to which the survey is referred, there were a total of 17,145,322 homes in Spain [15]. The percentages of houses equipped with the devices mentioned were obtained from the survey on Equipment and Use of Information Technologies and Communication in Households (2010) [16] and from the Homes and Environmental Survey (2008) [17], also conducted by the National Statistical Institute in Spain. All of this information is reflected in Table 1, together with the number of devices available per home [3]. This table also contains the percentage of households owning this equipment that uses the standby mode. These values were obtained from a report from the IDEA Institute (Institute for Diversification and Saving Energy) of Spain [3]. To determine the power consumption associated with each device, an individual standard model of each one was considered. Their characteristics are listed in Table 2. This information was obtained from the PANDA web database (Equipment Harmonic Database), containing information on measurements of different types of household appliances and office equipment, made in different laboratories around the world [18]. In the case of radios and CD players the values were obtained through measurements performed in our own laboratory because the information on these types of devices was not available in the PANDA database. A California Instrument 9003 iX programmable waveform generator power source, configured to pure sinusoidal waveform, was used. Both the current and voltage were measured using a data acquisition board. International Standard EN-61000-3-2 [19] establishes the allowed maximum current emissions for each of the individual harmonics up to the fortieth order. The maximum values of the THDi corresponding to specific models of devices reflected in Table 2, for the above allowed maximum for current harmonic emissions, were calculated. Table 2 also reflects the resulting values. To perform the calculation, it has been assumed that TVs and computers are included in the standard classification described in D, while the other remaining devices belong to class A. Although each appliance’s manufacturer provides a rated power value, the power consumption of each device is not constant but depends on the specific operation mode. For example, consumption in a computer depends on the particular function performed by the Table 1 Audiovisual equipment in Spanish households. Type of equipment

Percentage of households equipped with this appliance (%)

Number of devices per household

Percentage of households that use the standby mode (%)

TV DVD Desktop PC Laptop PC Radio CD player

99.5 78.4 50.1 42.5 82.0 62.1

2.2 1.2 1.2 1.3 1.0a 1.2

79.0 75.0 55.0 60.0 62.0 62.0

a Although it is assumed that in each house there is on average more than one radio, as the real value was not found in any source one device per household is assumed for this work. This would result in minimal consumption due to the use of this apparatus.

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I. Santiago et al. / Energy 60 (2013) 292e301

Table 2 Technical characteristics of audiovisual devices. Type of equipment

Year of purchase (approximate)

Active power (W)

THDv (%)

THDi (%)

Maximum THDic (%)

dPF

3200 LCD TVa DVDa PCa 2200 LCD monitora Laptopa Radiob CD playerb

2008 2008 2009 2008e2009

66.7 7.42 60.79 30.62

0.25 0.23 0.25 0.18

17.9 241.7 196.33 192.33

26.25 286.82 28.80 57.18

0.9157 0.9891 0.9921 0.9655

2008e2009 2006 2006

64.43 3.78 8.58

0.17 0.24 0.38

190.28 43.3 46.7

27.18 563.01 248.04

0.9766 0.5821 0.8462

different type of loads simultaneously connected [30]. Because this variation will be modified with each specific scenario, this work evaluates the economic impact that a change of 1% in power consumption would suppose, in the same way that Duarte and Schaeffer [4] made in their study. On the other hand, the presence of undesirable frequency components in voltage and current signals is quantified by means of the magnitudes named total current and voltage harmonic distortions, denoted respectively as THDi and THDv. These magnitudes, which measure the effective values of the harmonic components of a distorted waveform [28], are given by

PN

a

Ref. [16]. Measured in our laboratory. c Maximum THDi value calculated by using the maximum current emissions recommended by IEC 61000-3-2 for each of the individual harmonics until the fortieth order. b

THDi ¼

I1 PN

THDv ¼ device [20]. Televisions are also characterized by significant fluctuations in their power draw due to the variability of brightness and sound CRT (Cathode Ray Tube) or by typical power drops at channel changes (LCD) [21]. The data available in PANDA and data recorded in our laboratory indicate that a device’s consumption in different operation modes is usually lower than the value given by the manufacturer. Therefore, performing consumption estimation using the manufacturer’s rated power value would lead to an overestimation of the results. Consequently, the value of the active power used in this study for each device was obtained by averaging the different values of active power recorded in each different operation modes. With both the active power values and all the previous information obtained from surveys, the diary patterns of energy demand associated to each audiovisual device in Spanish households was determined. After determining the number of homes in which various audiovisual devices are being used, knowing the number of houses in which they are not being used is a forward approach. With this information, it is possible to determine the energy that these appliances located in Spanish homes consume in a standby mode. The impact that the consumption of only 1 W in standby mode for each device will suppose was determined. To perform these calculations, the penetration of standby mode use in Spanish households with regard to the number of homes that have these appliances, indicated in Table 1, was taken into account. These percentages are almost constant throughout the whole country [3]. Once the energy demanded related to active power consumption is known, the next step was to determine every device’s additional consumption associated with harmonic emission and its presence in the distribution network. Some papers in the literature are dedicated to the analysis of harmonic effects, determining the consequences of their presence in a specific office or commercial building, in both the commercial and industrial sectors [5,8,22e25]. In residential sectors, previous papers are mainly dedicated to determining or modeling the harmonic emissions of the usual loads and their contribution to signal distortion in customer and utility installations. Such research was mainly performed at a laboratory scale [25e29]. However, research into the impact of this type of perturbations extrapolated to a whole sector in general has only been carried out by Duarte and Schaeffer [4], with regard to the use of TV devices in Brazilian homes. First, the fact that nonlinear loads subjected to different feed waveforms can vary their electricity consumption was considered. This variation, quantified as belonging to the interval (3%, þ6%) in a particular case of association of three tubular lamps, one vertical freezer and two computers, depends on the characteristics of

2 h ¼ 2 Ih

h¼2

V1

Vh2

(1)

(2)

where I1 is the rms (root mean square) value of the fundamental component of the current (Amperes); Ih is the rms value of the hth harmonic current (Amperes); V1 is the rms value of the fundamental component of the voltage (Volts); and Vh is the rms value of the hth harmonic voltage (Volts). According to European Standard EN50160 [31] (IEC 50160), held by most European grid codes, the limit for total voltage harmonic distortion, up to the 40th harmonic, should not exceed 8%. The variation of THDi with harmonic voltage magnitude and phase angle depends greatly on load type [32]. Harmonic current limits are recommended by International Standards such as EN-61000-3-4 [33], EN-61000-3-2 [19] referred to electrical devices themselves, or by IEEE 519-1992 [34], which contains recommendations on harmonics at the point of common couple. For the scenario of a household (low-voltage circuits), a 20% value of THDi will be the maximum recommended [24]. As already indicated, domestic appliances have nonlinear characteristics that produce harmonic components of the current. The harmonic generated by each audiovisual device analyzed in this work, quantified through THDi, is reflected in Table 2. These values refer to the case in which devices are connected to an almost pure sinusoidal voltage waveform (low value of THDv). But in general, the total impact will depend on the number of appliances, their power ratings and their harmonic diversity [26]. Harmonic emission of individual loads will vary based on the differences in their circuits and operating conditions. In practice, the internal emission of two devices even if they are of the same type, will be slightly different in amplitude and in phase angle. Moreover, the presence of other devices modifies the emission of each one, because the current flowing between each device and the grid consists of two components, the “primary emission”, driven by the internal emission of the device itself, and the “secondary emission”, driven by the internal emission from the other devices [35]. When several loads are simultaneously connected at the same location, the emission can also be reduced by the cancellation effects due to differences in harmonic phase angles of different devices [27,29,35e38]. In addition to the audiovisual equipment studied in this work, other types of loads operate within a household. Furthermore, the combination of loads changes throughout the day, differing from one household to another [39]. Determining the harmonic emission of various combinations of appliances in a home is outside the scope of this work. In order to undertake the estimation of losses and assuming that voltage waveform is not distorted, three general scenarios with different THDi values were considered. These scenarios were: 1, corresponding to THDi ¼ 5%, the low harmonic emission; 2, corresponding to THDi ¼ 20%, the maximum

I. Santiago et al. / Energy 60 (2013) 292e301

recommended value; and 3, corresponding to THDi ¼ 50%, greater than the recommended value. For each of these three scenarios the additional harmonic-related losses in building wiring caused by the use of audiovisual equipment in Spanish households were determined. Copper wiring with a 10-m length both for the service drop and for the internal wiring, and with a section of 4 mm2 and 2.5 mm2 respectively was considered. Joule losses in wiring are given by I2R, where R is the total resistance of the segment, resistance of the segment, determined by its DC (Direct Current) value plus AC (Alternating Current) skin and proximity effects [22]. If the value of I increases by harmonic distortion, Joule losses will increase. Taking into account the frequency-related effects, a ratio of AC to DC resistance can be defined as

RAC ¼ 1 þ Ys þ Yp RDC

(3)

where Ys is the resistance gain due to skin effect, and Yp is the resistance gain due to proximity effect. These magnitudes are used to calculate the increase in losses caused by an alternative current with an increasing frequency, mainly due to uneven distribution of the current within the conductors [23]. RDC was calculated by means of

l R ¼ r A

(4)

with r the resistivity of the conductor (2.03$108 U m at 70  C); l the length of the conductor (m); and A the cross-sectional area of the conductor (m2). For low-voltage (LV) power distribution facilities the ratio of AC to DC resistance can, as recommended in Annex 2 of the Spanish national electrical code [23], be approximated by

RAC ¼ 1:02 RDC

(5)

Considering only the non-sinusoidal load current, the total power loss can be obtained, including the THDi factor in the equation, as follows:



PL z1:02$RDC $I12 1 þ THD2i



(6)

The fundamental current can be divided in two components

I1 ¼ I1 j41 ¼ I1 ðcos 41 þ sin 41 Þ ¼ I1p þ jI1q

(7)

where I1p is the fundamental active current and I1q is the fundamental reactive current, respectively. Consequently, the minimum line power losses due to the fundamental active current, which are inherent to load operation and cannot be compensated, are given by

PLmin z1:02$RDC $I12 $cos2 41

(8)

Thus, dividing (6) and (8) results

PL PLmin

¼

1 þ THD2i 1 þ THD2i ¼ cos2 41 dPF 2

(9)

Determining PLmin, and considering the THDi values corresponding to each of the proposed scenarios, the additional losses can be calculated as:

DPL ¼ PL  PLmin ¼ PLmin $

! 1 þ THD2i  1 dPF 2

(10)

This magnitude was determined for one audiovisual device of each type, and afterward the values were extrapolated to those

295

used in all Spanish households, using the survey data previously indicated. Once these losses were evaluated, their economic impacts were estimated. Non-active energy due to the nonlinear loads that audiovisual equipment constitutes was also calculated. This non-active energy must flow in power grids, occupying the electricity system and reducing the supply of active energy available for sale to residential customers [4]. The total equivalent power (S) in the power grid can be obtained by

P ¼ P$ S ¼ DPF$dPF

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 þ THD2i dPF

(11)

where P is the total active power consumed by the audiovisual devices [4]. This equivalent power was determined by considering the three scenarios with different previously defined THDi values and the increment that takes place, compared with the situation of zero THDi, was determined as

DS ¼

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi  P $ 1 þ THD2i  1 dPF

(12)

Considering 20 Euros/kVA as an average cost of installing distribution transformers, the economic effects of increasing installed capacity were estimated. Once the apparent power is determined, the equivalent nonactive power can also be calculated by means of the expression

H ¼

pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi S2  P 2

(13)

In the same way as before, the total estimated distribution system non-active power flowing to the secondary transformer winding are determined by considering the three different values of THDi established for each of the three scenarios previously proposed. The increase experienced by this magnitude with regard to the situation of THDi ¼ 0, was calculated. 3. Results 3.1. Demand of active energy As explained in the previous section, the energy consumption values for audiovisual equipment use in Spanish households was determined for a typical day using the information recorded in some surveys [12e15]. The daily patterns of active energy demand associated with each audiovisual device in Spanish households, measured at 10-min intervals, and differentiating between weekdays (denoted by “wd”) and weekends (denoted by “we”), are depicted in Fig. 1. The sampling error given for the results of TUS surveys are of 0.52% for the use of TV- and DVD-related activities; 2.25% for computer use activities; and 4.66% for radio and recording device-related activities [14]. There is a >95% confidence that the true value is within the range determined by these margins of error. In Fig. 1 it was assumed that when a DVD is switched on, a TV set must be on simultaneously. Therefore power consumption corresponding to this appliance was calculated by means of the sum of the consumption of both devices, shown in Table 2. Furthermore it has been considered that laptops being used in the household are connected to the grid. The graphs represented in Fig. 1 reflect one typical day corresponding to the year in which the survey was conducted. The interval of values shown for the TV reflect either a single device or 2.2 devices connected simultaneously, this latter being the number of TV sets that to be found in the average Spanish household

296

I. Santiago et al. / Energy 60 (2013) 292e301 10

Energy (MWh)

300 250

TV we (2.2 TV per home) TV we (1 TV per home)

Daily consumption by the use of TV

200 150

Laptop wd

8

TV wd (2.2 TV per home) TV wd (1 TV per home)

Laptop we

9

Energy (MWh)

350

Daily consumption by the use of Laptops

7 6 5 4 3

100

2 50

1

0

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00

0

2

1 DVD we DVD wd

Daily consumption by the use of DVD

radio we radio wd

0.8

Daily consumption by the use of radio

Energy (MWh)

Energy (MWh)

1.5

1

0.6

0.4

0.5 0.2

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00

0 0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00

0

16

0.15 Desktop we

14

Daily consumption by the use of Desktops

CD we CD wd

Desktop wd

Daily consumption by the use of CD players

Energy (MWh)

Energy (MWh)

12 10 8 6

0.1

0.05

4 2 0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00

0 0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00

0

Fig. 1. Daily electricity consumption patterns corresponding to the use of TV (considering 1 or 2.2 devices simultaneously connected per housing), DVD, PCs (desktops and laptops), radio and CD player in Spanish households, on weekdays (wd) and at weekends (we).

[3]. It can be observed that each of the electronic devices analyzed in this paper presents different energy consumption patterns at different times of the day. Although the profiles are similar for both weekdays and weekends, consumption is higher at weekends. In Fig. 2 the total daily energy consumption due to the use of all the appliances studied (TV-considering 2.2 devices simultaneously connected per housing-, DVD, computer, radio and CD player) is reflected. The most significant contribution to this energy consumption corresponds to the use of television sets. TV use accounts for more than 80% of consumption, while TV and computer use accounts for almost 98% of the energy consumed by the equipments analyzed. This is because TVs and computers are the mostused equipment and their power consumption is also higher than that of DVDs, radios or CD players. Extrapolating the data corresponding to the curves represented in Fig. 1 to a whole year, an estimation of the total energy

demanded to power these devices in Spanish households can be obtained. The annual energy consumption for each of these devices is reflected in Table 3. Although they have such a low power consumption at an individual level that could even be regarded as negligible compared with other appliance types, their total annual energy demand can be greater than 4000 GWh. This means that, at an aggregated level, the contribution of this type of devices to energy efficiency measurements must be taken into account. In Spanish households the daily consumption profiles, broken down into individual appliances, were not previously available and therefore a comparison with the results of other authors is not possible. Only annual power consumption results for TV and computer use can be compared with those revealed in the IDEA’s SECH-SPAHOUTECH report [3]. The results obtained in this paper are of the same order of magnitude. The values may be even more realistic if TUS were able to provide the number of devices of the same type that are simultaneously connected in each household, or

I. Santiago et al. / Energy 60 (2013) 292e301

400

Total_we

350

Total_wd

Energy (MWh)

300

Daily consumption by the use of TV (2.2 devices per home), DVD, computer, radio and CD player

250 200 150 100 50 0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00

0

Fig. 2. Total daily electricity consumption patterns corresponding to the use of TVs-2.2 devices simultaneously connected per housing, DVDs, PCs (desktops and laptops), radio and CD players in Spanish households, on weekdays (wd) and at weekends (we).

if it were possible to obtain real information concerning the percentages of the different types and sizes of devices (TVs, computers, etc.) to be found in Spanish homes. As already indicated, the main contribution obtained is due to TV use. In Spanish households the TV is the most widely used audiovisual device and it also has the greatest penetration. In this paper a model corresponding to an intermediate-sized LCD was used in order to perform the calculations. Now, however, demand for larger LED (Light-Emitting Diode) and plasma TV devices is increasing, with per-device power consumption greater than 100 W [40]. Therefore, in a future scenario consumption would increase by more than 40%. 3.2. Active energy demanded by standby mode The daily patterns of active energy demand associated with keeping each audiovisual device on standby mode in Spanish households is reflected in Fig. 3. In this figure it was assumed that each device consumed only 1 W in this mode. Obviously the consumption that corresponds to each real device in standby mode is higher than 1 W and therefore these figures reflect the impact that the consumption of each watt in this mode would suppose. These consumption profiles were also determined every 10 min, differentiating between weekdays and weekends. Although the consumption of each device is different and varies within a certain range, the use of the standby mode in some equipment represents a constant level of energy consumption in homes. The most significant values again correspond to the TV sets, because they are the audiovisual devices to be found most commonly in Spanish households.

Table 3 Annual energy demanded by audiovisual devices in Spanish households, distinguishing between weekdays and weekends.

297

Fig. 4 represents the total daily energy consumption corresponding to their simultaneous use in standby mode of all audiovisual equipment analyzed in this paper for all Spanish households. It can be observed that only 1 W per appliance supposes a fixed daily national energy consumption of between 10 and 11.6 MWh the maximum values being reached at night. This implies a total energy consumption of 1.6 GWh per day e almost 590 GWh per year. This energy that corresponds to around 135 million kg of CO2 [41] emitted annually into the atmosphere by the Spanish residential sector alone. These emissions could be avoided by changing the usage habits at a domestic level, disconnecting equipment that is not in use from power supply. The active power consumption from the use of audiovisual equipment, plus consumption due to their use in standby mode (considering in this case only 1 W per device in standby mode), give a daily power consumption in Spain that can be in excess of 16 GWh at weekends and 11.5 GWh on weekdays. The total annual energy demanded by each type of audiovisual device and the economic impact that the consumption of 1 W per device in standby mode supposes are shown in Tables 4 and 5, respectively. These data correspond to the year to which the TUS data refer. The values obtained, which correspond to a complete year, are not negligible. The economic impact, calculated without taxes and expressed in Euros, suppose an aggregated expenditure of all users of over 65 million Euros. Since this work has only evaluated a standby consumption of 1 W per device, the results cannot be compared directly with the values given by other authors. However, if this consumption is multiplied by a factor of 2 or 3, the wattage that domestic audiovisual equipment usually consumes in this mode, the values obtained are of the same order of magnitude as those obtained in the SECH-SPAHOUTECH report [3]. This represents 10% of the total consumption of household appliances [3] and it is similar to TV consumption in active mode. The present tendency among manufacturers is to reduce the consumption of equipment in the standby mode. For example some recent LED TV devices have a standby power consumption of 0.3e0.5 W [40]. Therefore in coming years this type of consumption could decrease. However, it would still represent significant energy losses that could be reduced or even eliminated by changing the usage habits of domestic residents. 3.3. Variation in active energy demand due to the presence of harmonics As has already been indicated nonlinear loads subjected to different feed waveforms can vary their electricity consumption in a proportion that depends on the specific situation. The economic impact due to a change of 1% caused by harmonic emission in the active power consumed by these audiovisual devices in operation, is illustrated in Table 6. These values are expressed in Euros and they correspond to a whole year. These costs were calculated without taxes. As already stated, although the additional cost per household may be negligible, it can be observed that at an aggregated level these figures should be taken into account, because a variation of 1% in active power consumption of these devices, due to the presence of harmonics, would imply an additional annual cost in Spain of between 2.5 and 5.0 million Euros.

Annual energy demanded by the use of each audiovisual equipment (GWh)

TV DVD Desktop Laptop Radio CD

Weekdays

Weekends

Total

1048.7e2307.3 5.1 169.3 109.7 8.22 0.8

622.6e1369.8 6.8 86.9 56.3 4.70 0.5

1671.4e3677.1 11.9 256.2 166.0 12.9 1.3

3.4. Losses in conductors Furthermore, annual losses due to conductor resistance in the service drop and in the internal wiring of all Spanish households and their corresponding costs, in Euros, are indicated in Tables 7 and 8 respectively. These values, with regard to the audiovisual devices analyzed in this work, were determined by considering the

298

I. Santiago et al. / Energy 60 (2013) 292e301 6

0.96 Daily consumption by the use of TV in standby

Daily consumption by the use of Laptops in standby 0.94

4 3 TV we (1 TV on per home) 2

Energy (MWh)

Energy (MWh)

5

0.92

0.9

TV we (2.2 TVs on per home) 0.88

TV wd (1 TV on per home)

1

Laptop we Laptop wd

TV wd (2.2 TVs on per home) 0

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00

0.86

2.04

1.5 Daily consumption by the use of DVD in standby

Daily consumption by the use of radio in standby

2.02

Energy (MWh)

Energy (MWh)

1.45

2

1.98

1.3

radio we radio wd 0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00

1.2

0.98

1.34 Daily consumption by the use of Desktops in standby

0.96

Daily consumption by the use of CD players in standby

0.94

1.33 Energy (MWh)

Energy (MWh)

1.35

1.25

DVD we DVD wd

0.92 0.9 0.88 0.86 0.84

1.4

1.32

1.31 Desktop we

CD we CD wd

Desktop wd 1.3

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00

0.82

Fig. 3. Total daily electricity consumption patterns corresponding to 1 W per device due to the use in standby of audiovisual devices in Spanish households, on weekdays (wd) and at weekends (we).

three scenarios corresponding to a value of THDi equal to 5%, 20% and 50%. As could be expected, the higher the THDi, the higher the losses. It has been shown that moving from a scenario of THDi ¼ 50% to one with a value of 5%, would suppose a saving of between 196 and 380 MWh per year, avoiding their corresponding costs, ranging between 12,000 and 45,000 Euros. These figures only refer to some of the audiovisual equipment in the houses. If all housing loads were taken into account, some of them with a greater use and with a greater energy demand than audiovisual equipment analyzed in this work, the reduction of harmonic emissions would represent a considerable energy saving. It is noted that an energy efficiency program should not disregard this information, and the aim should be to demand more strict regulations and to enforce their compliance. Comparing the results with those obtained by other authors is not easy, since there are no similar studies, except the paper by Duarte and Schaeffer [4]. In this case the authors analyzed the

impact of TV use. Their study was performed in a Brazilian state, between 1997 and 2005. Our study relates to Spain 2009e2010, so any comparison between the two is of no real value. 3.5. Increase in installed capacity The presence of harmonics due to nonlinear loads will increase the total equivalent power (S) in the distribution systems. The rise in installed capacity with increasing harmonic emission is reflected in Table 9. The values in this table correspond to the peaks recorded at weekends, constituting the maximum values obtained. If harmonic emission due to the working of these devices is high, as reflected by a higher THDi value, the installed capacity of the electric system must therefore be greater, and the losses that electricity utilities must absorb can become significant. Accordingly, new distribution transformers have to be installed to take care of increased installed capacity. Therefore moving from

I. Santiago et al. / Energy 60 (2013) 292e301

12.5 Daily consumption by the use of audiovisual equipments in standby

12

Energy (MWh)

Table 5 Economic impacts of the annual energy demanded for a consumption of 1 W by each audiovisual device working on standby in Spanish households, differentiating between weekdays and weekends. Annual cost, in Euros, corresponding to a consumption of 1 watt for each audiovisual device in standby in Spanish households

11.5 11

TV

10.5 DVD Desktop Laptop Radio CD

10 9.5

299

we wd

Weekdays

Weekends

Total

18,801,266.3e 20,572,871.3 8,990,424.9 4,094,939.2 4,105,341.8 6,321,929.4 5,883,889.19

6,891,072.9e 7,942,857.8 3,590,339.8 1,624,203.7 1,628,329.8 2,501,200.8 2,352,393.3

25,692,339.1e 28,515,729.1 12,580,764.7 5,719,142.9 5,733,671.6 8,823,130.2 8,236,282.5

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00

9

Fig. 4. Sum of total daily electricity consumption patterns in Spanish homes, on weekdays (wd) and at weekends (we) of audiovisual devices in the standby mode corresponding to 1 W per device.

one scenario with a value of THDi ¼ 50% to another with a value of 5% could lead to a decrease in investment of between 2.2 and 4.6 million Euros (Table 10). As previously indicated, the current emissions of each of the individual harmonics of different orders up to the fortieth generated by the residential devices analyzed in this paper, are limited by the IEC 61000-3-2 standard [19]. As reflected in Table 2, the real THDi value emitted by computers and monitors is higher than the THDi values calculated from the maximum current emissions indicated by this standard. However, each of their individual harmonics emissions should be analyzed, as well as those of the rest of the devices, in order to verify if each one complies with the standard, and, therefore, whether manufacturers reach this standard. The impact of some appliances on the total THDi upon buildings’ low-voltage (LV) feeders is likely to be minimized due to their lower typical power draw [26] which might be the case in DVDs, radios or CD players. The contribution of TV or computer devices will be more significant, due to their greater power consumption. In an even less favorable scenario, with a total contribution of THDi ¼ 150% in the LV power distribution facility, TV consumption alone would represent an increase in total equivalent power (S) between 670 and 1470 MVA, requiring an investment in new transformers of between 16 and 36 million Euros. As well as increasing the required capacity of the facility, the presence of harmonics causes additional losses in transformers due to, among others, eddy magnetization currents flowing through them. These losses, which increase with the square of the harmonic order number, also generate a higher operating temperature and, in some cases, additional heat which exceeds permissible limits, thus, decreasing the transformers’ useful life. If not addressed, such

Table 4 Annual energy demanded for a consumption of 1 W by each audiovisual device working on standby in Spanish households, differentiating between weekdays and weekends. Annual energy demanded by the use in standby of each audiovisual equipment, considering 1 W per device (GWh)

TV DVD Desktop Laptop Radio CD

Weekdays

Weekends

Total

158.2e173.1 75.6 34.4 34.5 53.2 49.5

58.0e66.8 30.2 13.7 13.7 21.0 19.8

216.2e240.0 105.8 48.1 48.2 74.2 69.3

problems may result in insulation failure and hence the failure of distribution transformers, interruption of the electricity supply with a consequent revenue loss for utilities. In such a situation a transformer rated for an expected load will have insufficient capacity. The reduction must be determined based on the range and magnitude of the harmonic emissions. Standard ANSI/IEEE C57.110 1998 [42] specifically establishes criteria for the power dimension of transformers feeding nonlinear loads. This standard establishes the equivalent or useful value of kVA for transformers, compared to their nominal value, using what is known as the K-factor. To determine this, harmonic pollution must be known. Therefore the most usual recommendation is that traditional transformers’ nominal capacity needs to be de-rated between 60 and 80% [42]. The extra cost of a transformer dimensioned using the K-factor varies from 30 to 60% within the range of power ratings from 15 to 500 kVA. When the current distortion rate exceeds 5%, an efficient method for treating harmonics in power transformers is to install such K-factor transformers, which are a special type of transformer manufactured to include an additional coil in order to cope with the extra losses caused by eddy current harmonic distortion [43,44]. However these transformers are not used in distribution systems. This might, therefore, be a solution for an office or commercial building, but not for the LV installations in residential buildings. 3.6. Increase in non-active power In the same way, a rise in harmonic emissions originates an increment of non-active power flowing through the network, as reflected in Table 11. While for a scenario with THDi ¼ 5% non-active power flowing in the power grid (due to the use of these devices) varies between 50 and 90 Gvar per year, for a scenario with THDi ¼ 50% it could be between 3500 and 6700 Gvar. These values should not be neglected because if this energy did not exist, it could be sold as active power with the corresponding profits for utilities.

Table 6 Economic impacts of a variation of 1% of the annual power consumption caused by harmonic emission corresponding to audiovisual devices in Spanish households. Annual cost, in Euros, corresponding to the 1% of annual energy demanded by audiovisual devices in Spanish households

TV DVD Desktop Laptop Radio CD

Weekdays

Weekends

Total

1,246,477.4e 2,742,250.3 6109.2 201,222.8 130,342.1 9774.3 975.9

740,021.4e 1,628,047.7 8069.0 103,270.6 66,893.6 5584.6 646.5

1,989,499.1e 4,370,298.0 14,178.2 304,493.4 197,235.7 15,358.9 1622.4

300

I. Santiago et al. / Energy 60 (2013) 292e301

Table 7 Total annual additional losses in conductors by the use of audiovisual devices in Spanish households due to the presence of harmonics. Annual losses in conductors (MWh)

Table 9 Increase in installed capacity of electricity system (kVA) demanded by the audiovisual devices in Spanish households due to the presence of harmonics. Increase of installed capacity (kVA)

THDi

5%

20%

50%

THDi

5%

20%

50%

TV DVD Desktop Laptop Radio CD

101.68e223.69 0.65 3.13 2.90 0.18 0.04

124.93e274.84 0.80 7.22 5.13 0.19 0.05

255.13e561.29 1.65 30.10 17.61 0.25 0.06

TV DVD Desktop Laptop Radio CD

1042.2e2292.7 14.0 88.8 57.9 12.3 0.9

16,521.3e36,346.9 222.5 1.407.9 917.6 194.8 13.9

98,469.3e216,632.5 1320.4 8391.1 5471.1 1160.9 83.1

4. Conclusion and discussion This work has shown that the greatest contribution to electricity consumption in Spanish households due to the use of audiovisual equipment corresponds to TV devices, followed by computers. The contribution of equipment such as DVDs, radios or CD players is much lower. Although in general, the individual consumption of these audiovisual devices is very small, their use at an aggregated level in an important proportion of houses for some hours per day leads to highly significant values for demanded energy. The energy consumption from the use of these appliances in standby mode, which can be several hundreds of GWh per year, is not negligible. This highlights the fact that any measurement taken to reduce energy consumption in homes should not only consider major appliances, but also the contribution of these types of small appliances. Due to the fact that these electronic devices constitute nonlinear loads in the power system, in order to know the real energy impact corresponding to the use of such devices, in addition to active power consumption, the not insignificant consumption caused by the emission of harmonics generated by the presence in the power grid of this type of equipment needs to be taken into account. The presence of harmonics will result in negative effects such as distorted supply voltage, losses in the distribution network, additional losses in transformers, neutral overload, overheating and thermal stress, the malfunction or damage of electronic equipment, and even communication interferences. In this paper it has been revealed that some of these additional losses experienced in the Spanish residential sector reach several million Euros per year. Although at the individual level effects might be negligible, at an aggregated level the contribution of these devices to reactive power demand or to overloading the neutral conductor can be significant. So, it is noted that an energy efficiency program should not disregard this information. The impact of harmonic emission on the installations can be mitigated or compensated using different methods. As has been explained, some of these effects can be relieved by oversizing the facilities, which involve a consequently greater investment in them. The use of passive, active or hybrid filters, with different topologies, or transformers with specific characteristics can be used

to compensate device emissions, yet these solutions present several installation difficulties [25e45]. Another measure proposed by numerous authors is to achieve harmonic reduction or even cancellation by mixing different types of loads [26,27,37,38]. In the case of Spanish homes, it is not always possible to combine single and three-phase loads [37]. On the other hand, when multiple single-phase appliances are simultaneously operating, it leads to a reinforcement of harmonic magnitudes, resulting in significant harmonic voltages on the power grids. This would exacerbate the problem and increase the contribution of even lower power appliances. However, harmonic angle diversity or dispersion is relevant because if they are out of phase, this could result in a cancellation of harmonic magnitudes [26,38] as well as in a voltage distortion reduction. This issue should be further investigated in order to be able to provide users with potential load combinations that would contribute to reducing the problem. It might even be possible to analyze a method for penalizing domestic users possessing harmonic-generating devices, such as that which could be applied at the industrial level. In the former, however, such measures would not be very effective because perhousehold emission levels are not significant. Key and Lai [22] demonstrated that, in the case of a commercial building, the greatest potential for harmonic impact would require the adoption of solutions near to the generating loads. They even affirmed that the most effective option was to eliminate harmonics at their source, reducing them inside electronic equipment. This was also stated by Duarte and Schaeffer [4]. Therefore, reducing or mitigating harmonic emissions in each individual device would represent a considerable energy saving at global level and also improve the profits of electricity companies. However, the different options will require further investigation in order to compare their cost and effectiveness. This present study will be extended in a future paper to cover the rest of the typical loads found in a household. Problems associated to harmonic emissions could be accentuated in the coming years due to the fact that new nonlinear appliances, which will replace present linear loads, such as water heaters, fridges and freezers are now being commercialized [26]. The solution would be to demand stricter regulations regarding harmonic emissions, Table 10 Economic impact of the installed capacity increase in electricity system (Euros) demanded by the audiovisual devices in Spanish households due to the presence of harmonics.

Table 8 Economic impacts of additional losses in conductors.

Cost of the installed capacity increase (Euros)

Annual costs of losses in conductors (in Euros) THDi

5%

20%

50%

THDi

5%

20%

50%

TV DVD Desktop Laptop Radio CD

12,084.7e26,586.3 77.7 372.6 344.6 21.4 5.14

14,848.1e32,655.7 95.7 858.3 609.6 22.6 5.42

30,323.0e66,710.5 196.3 3.577.7 2.093.8 29.4 7.05

TV DVD Desktop Laptop Radio CD

20,844.0e45,854.0 280,0 1776.0 1158.0 246.0 18.0

330,426.0e726,938.0 4450.0 28,158.0 18,352.0 3896.0 278.0

1,969,386.0e4,332,650.0 26,408.0 167,822.0 109,422.0 23,218.0 1662.0

I. Santiago et al. / Energy 60 (2013) 292e301 Table 11 Annual flow of non-active energy (Mvar) in the distribution system due to the emission of harmonics by audiovisual devices in Spanish households.

[17]

Annual non-active energy in the distribution system (Mvar) THDi

5%

20%

50%

TV

33,934.6e 74,656.0 250.3 10,463.7 5848.0 204.5 22.7

514,923.3e 1,132,831.2 3782.3 137,514.0 80,162.0 3228.2 351.3

2,624,187.8e 5,773,213.1 19,063.4 545,951.9 335,667.9 18,838.6 1915.0

DVD Desktop Laptop Radio CD

together with the means of enforcing their compliance. Compelling manufacturers and local distributors to provide suitable information about the power quality of their products in order to raise users’ awareness of this issue will also be a very important factor.

[18]

[19]

[20]

[21]

[22]

[23]

Acknowledgments This work was supported in part by the Spanish Ministry of Industry, Tourism and Trade, and FEDER under grant no. TSI020100-2010-484 and by Spanish Ministry of Science and Innovation under grant no. TEC2010-19242-C03-02.

[24]

[25]

[26]

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