Hybrid life cycle assessment of energy use in laptop computer manufacturing

ALONG with the rapidly increasing number of personal computers, the energy consumption associated with a computer has attracted increasing attention. However, different Life Cycle Assessment (LCA) studies of computers report qualitatively different results. For example, a LCA by one of the authors (Williams) reports a total energy of 6,400 MJ required to produce a desktop computer with a 17-in CRT monitor [1], while a study commissioned by the European Commission under the developing Energy using Products (EuP) Directive reports a figure of 2259 MJ required, around half of the results of Williams [2]. While there are some differences in data used, the primary origin of the large gap between studies is the boundary of processes considered. The EuP study uses “process-sum analysis”, meaning that results are based entirely on a bottom-up construction of the supply chain based on facility level data on material and energy flows. Due to limited data the study does not account for energy used in manufacturing chemicals, equipment, manufacturing of some parts (such as hard drives) and services. The analysis by Williams uses a hybrid analysis which combines the bottom-up process-sum network with a top-down economic input-output (EIO) model to account for excluded processes.