This article gives a tidy summary of the key factors affecting the greenhouse gas emissions associated with data centers, and helps readers prioritize how best to reduce those emissions. The three areas for improvement are the efficiency of the information technology (IT) equipment (servers, storage, and communications), the efficiency of the infrastructure equipment (fans, cooling, pumps, power distribution), and the carbon intensity of electricity production.
These factors can be conveniently pictured using what we call a “data center energy-carbon performance map” like the one shown in Figure 1:
Figure 1: The data center energy-carbon performance map. The shaded area bounds the potential operational energy and carbon performance range of a prototype US data centre and illustrates the relative performance of different data centre characteristics. Coloured areas indicate general regions of energy–carbon performance. For some data centres, only subareas of this map will apply depending on equipment and electrical power constraints. Numbered points are discussed in the text of the article. See section S2 of the Supplementary Information for details. GHG=greenhouse gas, PUE= Power Utilization Effectiveness. Download a larger version.
The prototypical data center powered by coal-fired electricity is in the upper right hand corner, while the best place for a data center to be is in the lower left hand corner (high IT efficiency, low energy, low emissions). Note that you can have a high energy, high emissions facility with very low Power Utilization Effectiveness (PUE, the industry standard metric for infrastructure losses. A PUE of 1.0 represents zero infrastructure energy losses, with typical existing “in-house” facilities having PUEs of 1.8 or 1.9. In those facilities, there is 0.8-0.9 kWh of infrastructure overhead for every kWh of IT load).
The critical lesson from the analysis is that IT efficiency (which includes higher utilization and performance improvements as well as purchasing efficient hardware) is the most important issue on which to focus. Most recent efforts in the industry have been on improving infrastructure efficiency, which has many beneficial effects, but is not as important a lever as is the IT efficiency (in many new facilities we are reaching the limits of infrastructure efficiency, with PUEs as low as 1.04). The article also makes clear that just switching an inefficient data center to low carbon electricity isn’t a good choice, because it uses up scarce low carbon electricity that could otherwise be used elsewhere.
Here’s the key paragraph from the conclusions:
Here we offer the following recommendations to policymakers who seek to design effective incentives for low-carbon data centres: all existing data centres should maximize IT-device efficiency, especially as these devices can turn over quickly and thereby deliver rapid improvements. Decisions regarding when to upgrade remaining devices to more efficient models can be informed in part by a break-even analysis of the embodied emissions required to manufacture new devices versus the operational energy savings that would be realized. New data centres should locate in areas with ample free cooling and/or low-carbon electricity grids to further push operations towards better energy and carbon performance. In new or existing facilities where optimal IT-device efficiency is not feasible, significant reductions in PUE critically rise in importance as a policy aim (but still result in higher energy-use levels than efficient IT devices would deliver). Where such PUE reductions are constrained by location (for example, a lack of free cooling), procuring low-carbon electricity — either from local electricity providers or through the installation of reduced-carbon self-generation such as Solid Oxide Fuel Cells — becomes the next chief lever after energy efficiency has reached its practical limit. With these insights in mind, public- and private-sector policymakers can accelerate the transition to a low-carbon Internet by aligning their incentives with data centre characteristics that matter.
The article summarizes some important lessons for those thinking about low emission data centers, and I highly recommend reading it if you are interested in this area. It’s a short, crisply written paper, and one that should yield real insight if you’re thinking deeply about these issues. Please email me if you’d like a copy (it’s behind a paywall).
Masanet, Eric, Arman Shehabi, and Jonathan Koomey. 2013. “Characteristics of Low-Carbon Data Centers.” Nature Climate Change. vol. 3, no. 7. July. pp. 627-630. [http://dx.doi.org/10.1038/nclimate1786 and http://www.nature.com/nclimate/journal/v3/n7/abs/nclimate1786.html#supplementary-information]
Addendum: Katie Fehrenbacher of GigaOm just wrote a short summary of the article.