Reference Publication: Floyd, D., Webber, C., "Leaking Electricity: Individual Field Measurement of Consumer Electronics," Presented at the American Council for an Energy-Efficient Economy, Asilomar Conference Center, Pacific Grove, California, August 23-28, 1998.
Disclaimer: The views and opinions expressed in this article are solely those of the authors and are not intended to represent the views and opinions of the Florida Solar Energy Center.
Electricity: Individual Field
Measurement of Consumer Electronics
B. Floyd and Carrie Webber
Florida Solar Energy Center (FSEC)
Leaking electricity or "parasitic load" is energy wasted by electronic devices when they are not performing any useful function, typically in an "off" or "standby" state. Before this study, little was known about the magnitude or source of this waste. While whole house losses have been estimated to be approximately 50 watts, little data has been available to quantify energy waste from individual loads. This paper summarizes measurements of over 600 consumer electronic devices taken by researchers at both the Florida Solar Energy Center and Lawrence Berkeley National Laboratory. Combined they form the largest data set of consumer electronic loads ever assembled. Measurements were recorded at national electronic stores, a nationwide retailer and in individual's homes. Measured loads include heat pumps, televisions, videocassette recorders, digital video disk players, cable boxes, portable stereos, DSS receivers, telephones, and other miscellaneous residential electronic appliances. Detailed power consumption of each device was measured in the most common modes of operation (on, off and standby) and the features most likely to affect energy consumption were recorded. Loads for each product type and category are summarized in all modes of operation and methods to reduce parasitic loads are proposed.
While all consumer electronic devices consume energy while performing a particular task or service, many also consume energy while "off" or in a powered down state. Loads of this nature have been labeled vampire, parasitic, or simply leaking electricity because often no obvious function is being performed for the energy consumed. Individual loads of this type are often small (<30W) but collectively add to a substantial load. Estimates range from 37 to 50 TWh consumed annually in the US alone (Thorne & Suozzo 1998) or approximately 5% of an average household electrical load. European stand-by power consumption was estimated to be 10 TWh per annum (Molinder 1997), which confirms the global significance of this problem.
Leaking electricity plagues a variety of consumer electronics. Leaks originate in the design of the product or component(s). More specifically leaks are from (Rainer et al. 1996):
The various sources of leaking energy create some confusion about terminology. Some of these functions can be thought of as standby functions. That is, the device is waiting to be turned on and requires power either to be able to respond to a signal (e.g. remote control), to maintain an environment beneficial to the user (memory) or to speed up the device's response to an on signal. Other functions, such as clocks on microwaves and VCRs, offer a legitimate service to the user, although it is not the primary function of the device. Other loads are pure losses and offer no service to the user. We refer to these loads collectively as "standby losses."
While it can be argued that some standby losses perform a useful service, it is often possible to reduce or entirely eliminate the load without reducing the service performed. For the majority of these leaks there are solutions that could be implemented, however, there is little incentive for manufacturers to redesign products to reduce parasitic loss. It is also doubtful if consumers would demand the improvements, especially if conveniences such as remote control are eliminated. This report examines a large variety of consumer electronics to identify the magnitude of individual device standby losses.
Readings were taken using watt meters that measured true root mean square voltage and current. This is critical in measuring these loads since few loads are purely resistive in nature (Stiles & Fuller 1997). Measurement errors caused by phase shift between the voltage and current waveforms as well as waveform distortion must be considered when selecting metering equipment. All of the meters selected for data collection were of this type and ranged in accuracy from 0.25 to 1.5%. Careful attention was also taken to select the appropriate range for each reading. This is especially important when taking watt readings since the accuracy can be diminished if the meter is set to an inappropriate range.
Our primary interest was in measuring standby power. For most devices, standby power was measured with the device plugged in and the power switch (if any) in the off position. For devices without a power switch, standby power was taken to be the lowest sustained power draw. For battery chargers, power draw may drop once the battery is fully charged. Standby measurements, therefore, were taken either with a fully charged battery or no battery at all in the device. Whenever possible, we also measured active power with the device in a common operation mode (e.g. charging a battery, playing a videocassette, etc.). Because active power varies far more widely than standby power (depending, for example, on volume setting and the nature of the signal for audio and video equipment), our data on active power should be used with caution.
Our data set now consists of 633 devices. Of these, 598 consumed at least some power when ostensibly turned off. The average standby power for the sample was 3.8 while the median was 2.5. Figure 1 shows the distribution of standby power consumption in the sample. The distribution is skewed significantly toward the low end of the range. The cumulative distribution is given in Figure 2, which shows the percent of the sample at or below each standby wattage level.
The device with the highest measured load while "off" was a residential heat pump. Source of this load was attributed to the compressor's crankcase heater and was measured at 65 watts (sample average of 30 watts). Crankcase heaters extend the life of the compressor by minimizing oil migration out of the compressor, but some control strategies leave the heater connected when it is not needed. Since the heater does perform a function at times and our sample size is small, care must exercised when interpreting the results. One design only activates the heater when the compressor's discharge line temperature falls bellow 70oF (Stamp 1998). This resulted in the crankcase heater on for only 15% of the time where ambient temperatures varied between 53oF and 93oF (Parker 1998). Another design had the crankcase heater energized continuously.
The next highest standby power consumption, 29 watts, belonged to a mini-system. Mini-systems are compact audio systems small enough to fit on a shelf. They combine a receiver, CD player and/or cassette player in a single unit but have separate speakers and are typically less portable and more powerful than a boom box. Unlike other high active power devices, losses for mini-systems are highly correlated with rated power. This suggests that a single power supply is used in both active and standby modes. Because the power supply is sized for active power, it is significantly oversized for standby loads, thus increasing standby losses. The unit with the highest rated power of 275 W had losses of almost 29 W, while the device with the lowest rated power, 20 W, leaked only 3.3 W.
The highest leakers were concentrated in a surprisingly narrow number of products. Forty-one products leaked 10 watts or more. These represented only 10 product types, primarily audio and video. Set-top boxes were among the worst offenders: five of the seven cable boxes we metered and all eight of the digital satellite systems used more than 10 watts in standby. Forty percent of TV/VCR combination units, 36% of mini-systems and 33% of powered speakers used more than 10W. Two of the three security systems we metered also consumed more than 10 watts in standby, as did two of the three heat pumps metered. Some TVs, VCRs and receivers were also among the highest leakers; however, these units represented only a small share of the total sample for those products.
There were 58 products with standby losses of one watt or less (excluding zero losses). Well represented were receivers (24% of our total sample), power supplies, battery chargers and rechargeable products. Power strips with surge protection were the lowest consumers at 0.2 W. Four TVs, three clocks/clock radios, two cassette players, a CD player, three boom boxes, a turntable, a baby monitor, a timer, a ground fault circuit interrupter (GFCI) receptacle, a heat pump and a modem rounded out the lowest leakers. The devices were categorized first by product type (e.g. TVs) and then by product category (e.g. video equipment). While many groupings of the products were possible, it was decided to classify them by industry, which would facilitate policy-making. Divisions included:
Table 1 shows metering results for each product type, grouped by category. Included are the largest standby loss, the smallest standby loss, the smallest non-zero standby loss, and the average active power. Because the number of products metered for active and standby power differs, sample sizes were reported separately. Why was it necessary to look at products with non-zero standby losses separately? For some products it may be easier to eliminate standby losses than to reduce them. This is because most of the products in our sample have power supplies. If the device is using any power at all, that power must pass through the power supply. Since power supplies typically lose 0.5 - 1 watt even when not supplying a load, very few (less than 2%) of the products in our sample consume under 0.5 watts. Some products do not require power for functions during standby; these can be reduced to zero standby by placing the power switch on the primary side of the transformer (some products could do this but do not) (Meier & Huber 1997). The minimum non-zero standby power consumption provides a better measure of the technical potential for units which provide some sort of service in standby (e.g. remote control or memory) than the overall minimum.
One quandary that arose in categorizing our product list was what to do with the array of rechargeable products. These ranged from an electric lawn mower to a rechargeable shaver. In spite of their obvious differences, these products are very similar in terms of their standby mode operation. Therefore, rechargeable products and battery chargers were broken out in a separate group. The results are presented in Table 2. For these products the active power shown is power when the charger is actively charging. All of these products had standby losses.
Parasitic Load Reduction
Energy is a function of both power (watts) and time. Strategies to reduce parasitic power consumption should therefore strive to reduce the devices energy use or simply reduce the time it is consuming electricity. Each strategy is useful, however the function of a particular device will ultimately determine which strategy is most appropriate. For example, increasing the efficiency of the power supply (watt reduction) would be the most appropriate strategy to reduce leaking electricity in a security system since the electronics must be powered all the time to monitor sensors. Rack audio system components although would benefit more from total disconnection (reduced operating time) since they are used infrequently.
substantial effort has been concentrated on reducing the energy
waste from transformers or power supplies (Thorne & Suozzo 1998).
As a plug in power pack or integrated into the device, power supplies
comprise a significant portion of leaking electricity. There are
basically two types of power supplies, Linear Power Supplies (LPS)
and Switch Mode Power Supplies (SMPS). LPS are inherently inefficient
in nature (50-60%) but appeal to manufacturers due to their low
cost. SMPS are more efficient (85%) and can be controlled to match
loads (Frizzell). SMPS, can however, effect power quality similar
to electronic ballasts and may not be appropriate where line noise
is a concern (audio equipment). Power supplies also waste electricity
because they are often switched on the low voltage side (output)
rather than the high voltage side (input). This is most likely due
to the added expense of manufacturing a transformer with switching
on input side and instant on features required by devices that are
Reduction of leaking electricity in other areas will be harder to achieve. Manufacturers will be hesitant to remove conveniences such as instant on and remote control capabilities due to feared market rejection. LED/LCD displays and memory retention consume relatively little energy and improvements would be costly. Displays can be made to activate only with operator interaction, however, often displays present information that is useful even when the device is off such as a clock on a VCR. Memory retention could be retained either through the use of "flash memory" or backed up with a battery as in a PC's bios.
Devices that charge batteries offer some opportunities for improvement since often the chargers continue to draw energy after the battery has reached full charge. Smart chargers that vary the current supplied to the battery as it charges as well as the incorporation of SMPT would improve efficiency.
Table 2. Battery Chargers and Re-chargeables
|Cell Phone Charger|
|Rechargeable Personal Care Product|
|Cordless Power Tool|
|Rechargeable Lawn Care|
|Handheld Vacuum Cleaner|
|Multi-Purpose Battery Charger|
|Total Battery Charger|
Reducing Operating Time
Reducing the operating time of a device can be as simple as using a manual switch to disconnect the load or more elaborately through clocks or sensors. Unfortunately some consumer electronics rely on some power to maintain memory (clocks) or for instant-on convenience (remote control). This could easily be overcome if the devices incorporated backup batteries or capacitors to supply current when the device is disconnected or through the use of non-volatile memory. In fact, some devices already incorporate this technology (e.g. computers).
There is a myriad of ways to reduce the operating time of loads and often this strategy will go above and beyond simply reducing the parasitic portion of the load. For example an occupancy sensor could be connected to disconnect selective loads, as the space becomes vacant. In new home construction a portion of the home's circuits could be designated for occupancy-based control. Another simple idea is to connect all audio components to the switched outlets normally provided by the amplifier. When the amplifier is switched off the components are as well. Other control strategies include proximity sensors, timers, and activity monitors that monitor (internally) if the device is in use.
This report examined, in detail, a variety of consumer electronics that contribute to leaking electricity. Average standby power for the sample of over 600 products was found to be 4 watts. The majority of the products were found to consume less than 10 watts in standby mode. Only 38 products were found to leak more and these were primarily audio and video products. Set-top boxes such as cable boxes and digital satellite systems almost all consumed more than 10 watts. Products that leaked little power included some receivers, power supplies, battery chargers, and rechargeable products.
Data for this paper was gathered in two distinct regions of the US at multiple different locations. Given this diversity and the number of items measured, the averages should give an indication of where improvements can be made. It is now possible to examine in more detail the product types that contribute greatest to this waste. In the Parasitic Load Reduction section, several general strategies were presented that could be applied to most of the devices measured. However, policies or standards designed to reduce parasitic load loss would have to be formulated for each product type (or possibly a group of product types) and would require a more in depth investigation of manufacturers designs and associated loads.
While many methods exist to minimize or eliminate parasitic loads, product redesigns will not happen automatically. Manufacturers have little incentive to redesign products to reduce parasitic loads since consumers do not demand the change. Also it is doubtful if manufacturers or consumers would be willing to sacrifice convenience or reliability to save a few watts. Some reductions may happen automatically, however, as manufacturers switch to more efficient SMPS primarily to reduce weight and size. Many options do exist to reduce parasitic loads and not affect performance or convenience but will probably only materialize through government intervention.
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Huber, Wolfgang. 1997. Standby Power Consumption in US Residences. M.S. Thesis, Technical University, Munich, Germany.
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Council for an Energy-Efficient Economy, Washington, D.C.
American Council for an Energy-Efficient Economy
August 23 - 28, 1998.
Asilomar Conference Center
Pacific Grove, California