Power Electronics

Energy Efficiency Is a Global Issue

Improving energy efficiency continues to be a focus around the globe as the cost of energy rises and significant attention is being drawn to lighting. The International Energy Agency estimates that approximately 19% of the electrical energy consumed globally is for lighting. The recently signed U.S. energy bill calls for the phasing out of certain incandescent bulbs starting in 2012, to be replaced by energy-efficient lighting solutions such as compact fluorescent and LED-based solutions.

While incandescent bulbs are an easy target, approximately 70% of energy used for lighting is outside the home and involves a wide variety of sources such as fluorescent, halogen and metal-halide high-intensity-discharge (HID) lamps used in the industrial, services, commercial, governmental and retail sectors for large-area lighting applications among others. They’re used in parking structures, parks, public areas, factories, warehouses and large retail stores. A considerable installed base of low-efficiency lighting technologies exists such as mercury vapor lamp.

Beyond energy consumption, these applications involve public-safety issues and maintenance concerns. For example, a typical HID streetlight is on for 3500 to 4000-plus hours per year and might need to be replaced every two to four years. For an underground parking garage or tunnel, this is accelerated since lamps are lit 24 hours per day. Bulb lifetimes are commonly specified to a 50% failure rate, so it is not uncommon to have streetlights on a preventive maintenance schedule to replace them all, even if they have not failed. This is one of the reasons why there’s a wide adoption of LEDs for traffic signals, which have similar high-use characteristics.

High-brightness white LEDs have been coming into the mainstream over the last few years. Their performance (lumen output) and efficacy (lumens/W) has been improving rapidly and they’re starting to be deployed for large-area lighting applications. They’re directional in nature compared to lightbulbs, which emit light in all directions, most of which must be redirected by fixtures to where it needs to be pointed, resulting in fixture losses.

High-power LEDs can achieve greater than 50,000 hours of lifetime, which is defined here to 70% lumen maintenance. Using LEDs, fewer lumens are required and light pollution and glare can be reduced from the luminaire.

One initiative aimed at deploying and promoting LED lighting is the LED City program. Austin, Texas, is the newest to join LED City, of which Toronto, Raleigh, N.C., and Ann Arbor, Mich., are all members as well. These cities are evaluating and deploying state-of-the-art LED lighting technology across their municipal infrastructures.

In December 2007, the City of Austin and Austin Energy retrofitted a floor of a parking garage with 47-W LED fixtures. The mayor anticipates that Austin could achieve an annualized savings of $10,178 per year with a payback of 6.5 years. LED fixtures have also been installed at a hallway at Austin Energy headquarters, in an events center marquee sign, in a water fountain at the events center and in traffic signals. Additional test installations are planned throughout the city.

The City of Ann Arbor is replacing a significant number of its streetlights with LEDs. It is replacing 120-W bulbs with LED fixtures consuming less than 60 W, resulting in longer light-source lifetimes, lower service and replacement costs, and reduced energy consumption.

The European Union has an initiative as well. The Intelligent Energy Initiative includes the Intelligent Street Lighting Initiative, called E-street. This project includes investigating the impact of networking streetlights that can be centrally controlled by power-line networks or other communication techniques. Lights would be dynamically adjusted, based on the time of day, season and weather conditions, for maximum energy savings while simultaneously meeting community and public-safety requirements.

While networked lighting is not unusual for commercial buildings, it is a shift for street lighting which has been traditionally controlled by autonomous light sensors mounted on streetlights. As part of the E-street initiative, it is estimated that approximately 60 TWh/year of energy is used for outdoor lighting just within the European Union. Projections are that intelligent lighting could save 38 TWh/year.

In the E-street project, there have been field trials to verify the energy-savings potential. In Oslo, Norway, the trial resulted in a 70% energy savings, 40% of which was achieved by new energy-efficient luminaries while the remaining 30% was achieved by intelligent dimming control.

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