External power adapters may lose 10 to 70 percent of the energy they consume, dissipated as heat rather than converted into useful energy. Battery charging systems have more avenues for losses: in addition to power conversion losses, power is consumed by the charging circuitry, and additional power may be needed after the battery is full charged to balance self-discharge. In 2005, the Environmental Protection Agency launched a new ENERGY STAR(R) label for external power supplies (EPSs) that convert line-voltage AC electricity into low-voltage DC electricity for certain electronic devices. The specification included power supplies for products with battery charging functions (e.g. laptops and cell phones), but excluded others. In January 2006, a separate specification was issued for battery charging systems contained primarily in small household appliances and power tools. In addition to the ENERGYSTAR(R) label, the state of California will implement minimum energy performance standards for EPSs in 2007, and similar standards for EPSs and battery chargers are in development at the national level. Many of the products covered by these policies use relatively little power and have modest per-unit savings potential compared to conventional energy efficiency targets. But with an estimated 1.5 billion adapters and 230 million battery charging systems in use in the United States, the aggregate savings potential is quite high. This paper presents estimates of the savings potential for external power adapters and battery charging systems through 2025.
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