2013-01-11

Amortization Periods of Energy Efficient Notebooks

87 years! That's the amortization period of a notebook that is 10% more energy efficient than a usual notebook.

A recent Life Cycle Assessment (LCA) study of the German Federal Environment Agency (UBA) examines the carbon footprint of notebooks and tries to determine the time span after which a notebook should be replaced by a new one seen from an ecological point of view. The study is available in German and English language.

Summary

The study presents four scenarios based on three different life cycle data sets. Two of these scenarios are based on the same data set but are modeled to represent the disposal and recycling phase as a “business as usual” scenario and a “best practice” scenario. Both differ slightly regarding credits for recycling and reuse of precious metals. In all four scenarios, the usage phase is modeled in accordance to the utilization profiles of the Energy Star program1:3-5,8-9.

The study calculates the Global Warming Potential (GWP) of one notebook over five years for the best data set with 230 kg CO2e (data from a research on behalf of the European Commission, aka “EuP Lot 3”) and for the above mentioned “best practice” scenario with 380 kg CO2e (data from a research on behalf of the UBA and from the EcoInvent 2.2 database). The usage phase accounts in all scenarios for 138.5 kg CO2e1:29.

The amortization periods are calculated as the periods one has to use a more energy efficient new notebook until the emission savings from the use phase fully compensate the emissions from production, distribution, and disposal. The calculations are done in improvement steps of 10% ranging from 10% to 50% and a single calculation for 70%. However, notebooks are naturally designed to be energy efficiency due to the to longer battery run-time. Therefore the study treats energy improvements of more than 10% between two notebook generations as unrealistic1:30-33.

For the 230 kg CO2e data set (EuP Lot 3) the amortization period is 33 years. However, for the 380 kg CO2e “best practice” data set (UBA + EcoInvent) the amortization calculation results in 87 years. The following table illustrates the results for the various energy efficiency improvement steps1:30-33.

Amortization periods of notebooks under consideration of different LCA data sets and energy efficiency improvement steps1:30-33
LCA Data Set GWP
[kg CO2e]
10% 20% 30% 40% 50% 70%
EuP Lot 3 230 33 17 11 8 7 5
UBA + EcoInvent
"business as usual"
382 89 44 29 22 18 13
UBA + EcoInvent
"best practice"
380 87 44 29 22 17 12


Results

The study reveals that the GWP of a newly purchased notebook cannot be compensated with an improved energy efficiency in a realistic usage period due to the high impacts of production, distribution, and disposal compared to the low energy efficiency gains between notebook generations1:41.

Therefore, it does not make sense to replace a notebook with a new one for ecological or energy saving reasons (except for longer battery run time). Instead, a notebook should be used as long as possible, which makes it necessary to produce and buy notebooks that allow hardware upgrades, e.g. memory or disk space1:41.

Conclusion

Software product managers and software engineers should be aware of the ecological necessity of hardware usage times beyond the usual three to five years time horizon, especially regarding notebooks and probably also other kinds of mobile devices or nettops. This means for example to produce efficient code that performs well on such old hardware or to allow users to disable features that consume processor time, that they do not use, or that are not really necessary to use a software (e.g. indexing in the background to speed up search operations).

  1. Prakash, S., Ran, L., Schischke, K., Lutz, S.: Timely replacement of a notebook under consideration of environmental aspects. Dessau-Ro├člau (2012). http://www.umweltdaten.de/publikationen/fpdf-l/4317.pdf