In this report we shall compare the energy used up in the creation of a single sheet of paper, printed on both sides, in print and in electronic media within a simplified system which excludes certain portions of the energy in both.
A full lifecycle analysis of both media, with due weight given to their inherent complexities, is beyond the scope of this work. Paper and electronic material aren't made from the same sources or by the same processes, and they aren't used in the same manner. Paper is recyclable, but electricity is not.
We shall consider one sheet of letter sized paper, weighing 5 grams (0.011 lbs), printed on both sides with a standard text, in both media. [1] We wish to examine the major processes which allow the production of this paper, and then those which enable reading two pages on a computer screen. We will consider only operational energy in each case, i.e., pulping, papermaking and paper transportation on one hand and coal transportation, thermal power generation and transmission on the other. We will specifically ignore the embedded/imbued energy of the equipment (computers, power station equipment, mill equipment, transport vehicles etc.) that make each process possible. These will be reused many times over, and their contribution to the net energy numbers of a single sheet is negligible. We will also not consider the energy cost of reagents for making the paper (dyes, water, land area, reagents and printing cartridges) because they are part of capital costs and are reusable over many cycles of production. We will also ignore the energy required for cutting and transporting lumber to the mill and for separating paper-based wastes from landfills.
As of 2006, the pulp and paper industry in the US used 2361 Trillion Btu of energy in all to produce 99.5 million tons of pulp and paper products. [2]
2,361 Trillion Btu /99,500,000 tons = 27.6 kJ/g (total process energy).
Of this quantity, the amount of energy purchased from outside sources (not generated onsite) was: 39.5% or 10.9 kJ/g net purchased energy.
For our 5 g sheet of paper, net energy input = 138.0 kJ (54.5 kJ purchased)
The energy required for commercial office printing (excluding manufacture of ink cartridge): (Annual energy for printer/Units Paper consumed annually) per printer = 4.2 kJ per page = 8.5 kJ/Sheet [3]
The total approximate processing energy required for producing a sheet of paper printed on both sides with text is therefore: 146.5 kJ. These figures match the ones suggested by Martin et al. as 26.4 GJ/ton of paper (processing energy) in the US in 1994, which equates to 145.5 kJ for a 5 g sheet of paper. [4]
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| Table 1: Machine Power Consumption [10] |
Freight transportation energy costs per ton-mile for a truck, inland shipping and train have been estimated at 4000, 500 and 500 Btu respectively, or roughly 4220, 530 and 530 kJ/ton-mile respectively. [5,6] The energy added for transporting our sheet (0.011 lbs) from the mill to the point of sale (conflated here with the point of use) per mile is therefore: 0.0028 kJ/mile. For perspective, say the mill is based in Portland, Oregon, and the paper is delivered to Houston, Texas by rail. [7,8] Transportation over this distance (roughly 2300 miles), for our one sheet, would add a value of approximately 6.4 kJ, which isn't a lot. The sum total process energy value for our sheet of paper in this example would amount to 152.9 kJ.
Reading on a computer, on the other hand, takes time, which adds to energy costs, unlike with print material. For computational purposes, let's consider the number of words per minute to be 200. [9] This gives us a 3 minute window in which the page will be read on an average and 6 minutes for two sides of a sheet. We can compute the following values (approximately) for various computer systems:
This energy, in the form of electricity, is produced and distributed at an energy cost, which is significant, especially if the energy is produced from a fossil fuel. Let us, for simplicity's sake, assume that the power required for the computer comes from a thermal power plant running off coal. [11,12]). Coal based thermal power has an average efficiency of 36%, and this power is transmitted with losses of up to 5% [13,14]. Thus the amount of energy as the heat content of coal used for generation by the power plant would be: 147.4 kJ (for a desktop) and 15.8 kJ (for a laptop).
In the case of electronic media, the transportation of coal from mine-mouth to the thermal plants must be considered. Here we must evaluate the energy added as a fraction of the heat content of coal, which is assumed at 8000 Btu/lb. [15] This gives us a transportation energy addition of 500 Btu on 16,000,000 Btu per ton of coal per mile of railroad transport 0.003%/mile. For perspective, we could assess the example of the Monticello Thermal Power Station, which gets its coal from the Powder River basin in Wyoming, roughly 1200 miles away, by rail. [16] This gives a net addition of 3.75% to the energy value in question which is 5.9 kJ (for a desktop) and 0.6 kJ (for a laptop).
The total energy in consumed in reading our two standard text pages in Houston for the above example would be 153.3 kJ (desktop) and 16.4 kJ (laptop), compared to the 152.9 kJ for a sheet of printed paper.
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| Table 2: Unit conversions. | |||||||||||||
Better technology like LCD, power efficient computers and laptops are indeed reducing energy required for reading electronic material. But paper can be re-read without additional cost any number of times, which isn't true for computers. So where one time reads are required (like e-mail), use a laptop. Where a document must be read only once with normal reading speeds (like e-mail), it is better to use a laptop. If it is to be reused many times over, it certainly wouldn't hurt to print. It's a really bad idea though, to be doing both simultaneously.
© Tejo Pydipati. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] 600 words per page of 10pt New Roman Lorem Ipsum random pseudo-Latin.
[2] Institute of Paper Science and Technology, "Report for American Institute of Chemical Engineers: Pulp and Paper Industry Energy Bandwidth Study," August 2006.
[3] K. Kawamoto et al., "Electricity Used by Office Equipment and Network Equipment in the U.S.," Energy 27, 255 (2002).
[4] N. Martin, "Opportunities to Improve Energy Efficiency and Reduce Greenhouse Gas Emissions in the U.S. Pulp and Paper Industry," Lawrence Berkeley National Laboratory, LBNL-46141, July 2000.
[5] D. Sperling and J. S. Cannon, James S, "Climate and Transportation Solutions: Findings from the 2009 Asilomar Conference on Transportation and Energy Policy," Institute of Transportation Studies, University of California at Davis, Working Paper 1316812, UCD-ITS-RP-10-09, 1 Mar 10.
[6] A. J. M. Bos, "Direction Indirect: The Indirect Energy Requirements and Emissions from Freight Transport," PhD Dissertation, University of Groningen, 1998, p. 15.
[7] T. M. Power, T. M., "Public Timber Supply, Market Adjustments, and Local Economies: Economic Assumptions of the Northwest Forest Plan," Conservation Biology 20, 341 (2006).
[8] K. J. Kramer, E. Masanet and E. Worrell, "Energy Efficiency Oportunities in the U.S. Pulp and Paper Industry," Lawrence Berkeley National Laboratory, LBNL-2268E, 20 Jan 10.
[9] M. Ziefle, "Effects of Display Resolution on Visual Performance, Human Factors," 40, 555 (1998).
[10] K. Kawamoto et al., "Electricity Used by Office Equipment and Network Equipment in the U.S.," Energy 27, 2555 (2002).
[11] U.S. Energy Information Administration / Annual Energy Review 2009 Table 2.1f pp 45
[12] R. E. H Sims, H.-H. Rogner and K. Gregory, "Carbon Emission and Mitigation Cost Comparisons Between Fossil Fuel, Nuclear and Renewable Energy Resources for Electricity Generation," Energy Policy 31 1314 (2003).
[13] S. Sengupta, A. Datta, A. and S. Duttagupta, "Exergy Analysis of a Coal-Based 210 MW Thermal Power Plant," International Journal of Energy Research 31, 14 (2007).
[14] J.-T. Bernard and C. Guertin, "Nodal Pricing and Transmission Losses: an Application to a Hydroelectric Power System," Resources for the Future, Discussion Paper 02-34, June 2002.
[15] G. D. Stricker et al., "Coal Quality and Major, Minor, and Trace Elements in the Powder River, Green River, and Williston basins, Wyoming and North Dakota," U.S. Geological Survey Open-File Report 2007-1116, 2007.
[16] J. Javetski, "Monticello Steam Electric Station," Power Magazine, 15 Aug 06.