Lixi Liu
University of Michigan
Lixi Liu is a second-year joint Ph.D. student in Mechanical Engineering and the School of Natural Resources and Environment at the University of Michigan. Her interests include renewable energy, energy efficiency, and sustainable systems. During her spare time, Lixi likes to do sudoku, cook, and go hiking.
Artificial lighting is an integral part of modern society but requires a significant use of electricity. In the U.S., 10% of the electricity is used towards lighting. As lighting consumption continues to increase in the next decade, upgrading to energy-efficient technologies such as fluorescent and light emitting diodes (LED) becomes increasingly important. LED lighting can potentially save the nation $50 billion in electricity cost and 5,000 trillion Btu of primary energy. However, given its high initial cost today and rapid technological improvement, estimating the right time to switch over to LED from a cost, energy, and emission’s perspective is not a straightforward problem. This is a multi-objective optimal replacement problem that depends on many determinants, including how often the lamp is used, the state of the initial lamp, the price and technological trajectories of lighting and of electricity generation.
In this study, a nonlinear deterministic optimization model is developed to analyze the replacement of 60 Watt equivalent A19 lamp in two case scenarios: 1) a new lamp is purchased at the start of the time horizon; 2) an existing lamp is in used at the start of the time horizon. The first scenario informs what type of replacement lamp is appropriate for purchase today while the second scenario addresses the time-zero question of whether to keep or replace an existing lamp. For each scenario, replacement policies are recommended based on the objective of the optimization: life cycle cost, life cycle energy, and life cycle greenhouse gas emission. A multi-objective that combines the life cycle cost with the social cost of carbon is also explored. In addition, the study examines the effect of regional difference in electricity grid mix on replacement policy across seven U.S. regions: Washington DC, Illinois, Kansas, Texas, Wyoming, California, and Hawaii.
Over the time horizon from 2015 to 2050, the study shows that, at an average use of 3 hours per day, it is optimal both economically and energetically to delay the adoption of LED lamps until 2020 with the use of fluorescent lamps, whereas the LED adoption is optimal today in terms of emissions. Therefore, rebate-providing utilities and energy reduction programs may not need to push for or incentivize the adoption of LED lamps at this time as long as their customers are using CFLs. The replacement policy varies slightly between different regions, with the greatest variance observed in the policy for Hawaii. Meanwhile incandescent and halogen lamps should be replaced immediately. In terms of research and development of LED lighting, increasing product service life and durability should not be a primary focus while energy efficiency is improving, since replacement benefits from early product retirement and adoption of newer lamps over keeping each lamp until its end of life. Instead, life cycle optimization strategies such as dematerialization and product modularization for recycling and remanufacturing should be pursued to minimize waste resulting from the early retirement.
• Products and services, design for the environment, product declarations and labelling , • Decision support methods and tools , • Sustainable consumption and production
