Dec 17, 2007 at 00:00
Is off really off? When you leave your home, do you leave your TV set on? Do you unplug the ac wall adapter every time you take your cell phone with you?
Even if you switch your TV off, most sets continue to draw current. Did you know that US households pay more than $1 billion annually to keep TVs and appliances in standby? Many products waste as much electricity when they're supposedly off -- in a ready-to-go mode -- as when they're on.
A few years ago a European study showed that the power dissipated in digital converters for satellite receivers was virtually the same in both active and standby modes (averaging about 20 W). This was wasted energy primarily from inefficient standby operation and excessive no-load power.
Some Definitions
Standby power is dissipated when a product isn't performing its primary function (eg when a TV is ready to be turned on by a remote control). No-load refers to the power used in a power supply even though the product isn't connected to it. A cell phone charger is a good example. If left plugged into a wall socket, it will draw current even though it isn't charging a phone's battery.
It's not unusual to find a dozen or more wall adapters in homes. These little continuously running wall warts and bricks provide low-voltage power for everything from security systems and cordless screwdrivers, to rechargeable vacuum cleaners and answering machines. A typical brick, left plugged in with nothing connected to it, wastes as much as 4 W. Touch one of these bricks. Is it slightly warm?
The annual cost of a watt of this wasted energy in the US is a dollar. While this may seem like a trifling sum, consider the fact that in an average home this adds up to fifty watts of continuous leakage.
Terawatt-Hours Wasted
A Lawrence Berkeley National Laboratory study showed that the total annual leakage from homes is 45 terawatt-hours (45 x 1012 W-hr). The annual cost to consumers from this is a whopping $3.5 billion, and might be closer to $5 billion (based on rather low utility rates ranging from 7 cents/kW-hr to 12 cents/kW-hr).
Salt mines are a problem, too. Computers, printers, and networking subsystems are an essential part of today's office environment. Offices usually run multiple fax machines, copiers, laser printers, and postage machines. Most of these devices remain plugged in all the time.
A study sponsored by the German Federal Environmental Agency (Umweltbundesamt) showed that leakage in German homes and offices cost over $2 billion annually. That comprises about 10% of total electricity consumption in Germany. The amount of energy wasted (20 terawatt-hours) was more than the total power requirement of 14 terawatt-hours for the entire city of Berlin annually. Worse, total carbon dioxide emission associated with this wasted energy was over 10 million tonnes (metric tons).
Look back at a typical household back of the 1970s. It likely had a single TV, an AM/FM stereo (with a turntable or 8-track deck), and a telephone. In contrast, today's average home has at least two TV sets, a DVD player, one video game, multiple cordless phones, and a microwave oven. Most homes also have PCs, modems, printers, fax machines, and cell phone chargers. Other widgets and systems on the consumer electronics radar screen include the likes of large-screen home theater systems (Sony has a system that's so complex the company provides a tutorial to help consumers select the right modules). The list keeps growing.
Take heart. Some efforts to address energy waste are scoring results. In Japan, legislation now mandates that devices meet a specified level of dissipation. In the US, the Energy Star program mandates compliance with power limits. To qualify for the Energy Star label, appliances in standby must dissipate less than about 4 W.
Outdated power supply technology is a problem, too. Most sophisticated products such as cell phones and DVD players continue to use older power supply technologies.
Intelligent Design
Switching supplies, if carefully designed, can help, though. IC maker Power Integrations, for example, has a family of chips that let switching power supplies dissipate only about 100 mW under no-load conditions. This dramatic reduction in energy waste (compared to 1 W to 4 W no-load for most linear supplies) can reduce the cost of wasted energy from dollars to dimes. Switching supplies can also cost less than regulated linear supplies, and they're lighter.
If you make your designs greener, the real green may be the payoff in higher product sales to energy-conscious consumers.
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