We recommend working through the following five steps when implementing a green desktop computing initiative.

  1. Estimate your energy consumption.
  2. Research what others have done to improve efficiency.
  3. Implement tools to reduce energy consumption.
  4. Communicate to help people do their bit.
  5. Share your experiences with others.

This process is informed by several years of experience working with Colleges, departments and museums at the University. It is designed to encourage you to implement a robust approach to power management and in so doing help others achieve similar results.

Quick Start

Whilst we recommend working through the full programme, if you have already decided to execute a project to reduce desktop power consumption then the following quick start can be used as an implementation check-list.

  1. Implement Power Monitoring

    In order to demonstrate the power and CO2 savings made, you need to implement power monitoring from the outset.

  2. Turn Off Desktop PCs

    Substantial power savings can only be made by powering down desktop PCs when they are not needed. Ideally this is done simply through cultural change - desktop users turn off their PCs at the end of the day to support an organisational goal of reducing unnecessary power consumption.

    However, various factors can make it hard to achieve the desired level of compliance. To help this, a number of technical tools are available to help. In particular the PowerDown tools, developed at Liverpool, offer a low-cost and effective automatic power-down scheme for Windows networks. There are also a number of commercial tools (see an Oxford assessment of the NightWatchman, PowerMAN and Surveyor products).

  3. Overcome Challenges with Wake-on-LAN

    Two of the most common objections to powering down of idle PCs are that it takes a long time for the PC to start the following morning (wasting time), and that PCs need to be turned on to allow remote access (e.g. to work from home).

    The Wake-on-LAN service overcomes these challenges to change by enabling desktops to be automatically powered up on a schedule, or on-demand.

1. Estimate

Here we consider energy consumption with respect to two policies for managing desktop computers:

  1. Leave switched on all the time
  2. Switch off at the end of each working day

We calculate financial costs and greenhouse gas emissions over a year and make the following assumptions:

  • A typical desktop computer (80 Watts) and LCD monitor (25 Watts) together run at 0.105 kilowatts (or 105 Watts)
  • Electricity is charged at £0.12 kWh (12 pence per kilowatt-hour)
  • One kWh of UK Grid electricity causes the emission of 0.537 kg CO2eq. (a measure of greenhouse gas emissions)
  • To calculate the number of hours a computer will be switched on over a year with Policy B we assume people use their computer for 8 hours a day, and 226 days over the year i.e. computers are powered down overnight, weekends and 25 days of holidays.
  • Desktop computers normally consume between 1-5 Watts when switched off, in standby (ACPI S3) or hibernate modes. To keep calculations simple we ignore this energy consumption.
  • There is no automatic power management e.g. monitors do not go to sleep during the day.

To calculate the total electrical energy consumed over a year with policy 1 we simply multiply the power the computer and monitor run at by the total time they are used over a year. So for our typical computer the sum would be: 0.105 kW x 24 hours x 365 days = 920 kWh. To estimate the financial costs we simply do 920kWh x 12p/kWh = £110. To estimate greenhouse gas emissions 920kWh x 0.537 kg CO2/kWh = 494 kg CO2.

The tables below use this calculation to show costs and greenhouse gas emissions for different stocks of computers. Table 2 also shows savings that might be achievable with a shift from policy 1 to 2:

Table 1. Policy 1: Leave computers switched on
Greenhouse gas
(kg CO2)
1 920 110 494
100 92,000 11,000 49,400
500 460,000 55,200 247,000
1,470,000 1,350,000,000 162,000,000 726,000,000

Table 2. Policy 2: Switch computers off at the end of each working day
Greenhouse gas
(kg CO2)
Policy 1 to 2
Policy 1 to 2
(kg CO2)
1 190 23 102 86 392
100 19,000 2,300 10,200 8,000 39,200
500 95,000 11,500 51,000 43,000 196,000
1,470,000 291,000,000 34,900,000 156,000,000 127,000,000 570,000,000

The figure of 1 470 000 computers is included as this is the estimate for the total number of desktop computers in UK Further and Higher Education, according to the SustainIT Report, P. James et al, 2009

These calculations are meant to illustrate the differences between the two policies. The actual savings that an organisation can achieve will be dependent on local conditions:

  • The power that desktop computers run at
  • The cost of a unit (kWh) of electricity
  • The amount of time computers are actually used over a year
  • Whether power management is currently implemented e.g. policies may already be in place to switch computers into sleep/standby (ACPI-S3), hibernate and off.

It is therefore important to use local measurements to estimate how much electricity consumption can be reduced. (The easiest way to estimate the power your computers when switched on is to use a plug-in power meter).

2. Research

Here we provide a variety of references to resources that range from the inspiring TED talks to highly detailed and specific papers on green computing. Our emphasis in selecting these resource is two-fold: developing low-carbon technology is a huge area of endeavour and there are many exciting projects emerging (2) IT professionals have a very important role in developing solutions, and green desktop computing (office and personal computing) can be achieved today.

Many groups have already achieved significant results but the lesson is clear: the problem is not as simple as it might first appear. Green desktop computing has often been cited as low-hanging fruit in terms of energy reduction. We suspect this assertion came about before people actually tried to tackle the problem in a realistic and complex IT environment. The main problem being that in the end in most situations power management is the responsibility of large numbers of individuals who have not typically had to change the way they work to consider energy consumption.

  1. The environmental debate has traditionally been characterised as a conflict between economic progress and preservation of the planet. Most TED speakers, insist that we can have both provided we're smart.
  2. Embodied energy is very difficult to calculate accurately due to the complexities of supply chains, and it is not the only consideration when trying to quantify the social and environmental effects of the full life-cycle of the stuff we consume. (We can also consider the impact of mining on local communities and the landscape, and the utility we gain from the particular tool). However the Embodied Energy Database, maintained by the team at http://www.wattzon.com/about provides a good start to quantifying the total environmental effects of things we use.
  3. HEFCE Carbon Management Strategy, published January 2010. The key message being: " From 2011, HEFCE capital allocations will be linked to carbon reduction. Higher education institutions (HEIs) in England are required to develop individual carbon reduction strategies, targets and associated carbon management plans."
  4. Green Desktop Computing at the University of Oxford, by Howard Noble, Kang Tang and Daniel Curtis, 2009. A summary of the findings from the Low-Carbon ICT project.
  5. Low carbon computing: a view to 2050 and beyond, by Paul Anderson, Gaynor Backhouse, Daniel Curtis, Simon Redding, David Wallom, November 2009. A comprehensive and detailed account of the considerations IT professionals will need to make when designing 'green' IT infrastructures for the future.
  6. Sustainable Energy - without the hot air, David JC MacKay. Chapters 11, 15 and 22 are the most relevant with respect to low-carbon computing.
  7. Sustainable ICT in Further and Higher Education, P. James and Lisa Hopkinson. Provides a comprehensive summary of all the issues pertinent to building and maintaining low-carbon computing infrastructures
  8. The PowerDown project at Liverpool University is an excellent practical guide to achieving significant energy savings with minimal effort. The approach described is being used at many Universities including the Centre for the Environment at Oxford.
  9. Energy Star provide a good guide to the issues and provide information about solutions on the Activating power management features in enterprises web page. The Energy Star website also provides guidance for people looking to buy more efficient computing equipment.
  10. "Energy Intensity of Computer Manufacturing: Hybrid Assessment Combining Process and Economic Input-Output Methods", Eric Williams, Environ. Sci. Technol. 2004, 38, 6166-6174. This paper provides an in-depth analysis of the methodologies used to calculate the 'embodied energy' associated with computing equipment.
  11. Oxford central machine room report written by Ramonet LTD, and commissioned by the University looking at ensuring the planned 'machine room' (data centre) is built to high sustainability standards, with respect to cost and in-use greenhouse gas emissions.
  12. Insomniac PCs An article about power management published for British Computer Society.

3. Implement

3.1. Monitor power management and switch computer on remotely

We recommend all groups first set up what we call FiDo software to plug into the University power management monitoring and wake on LAN facilities. Once installed you will have secure access to a graph of how many computers are switched on during the day and night, and the ability to switch computers on remotely:

Data from the power management monitoring facility installed at
                                the Computing Services (OUCS).
Figure 1. Data from the power management monitoring facility installed at the Computing Services (OUCS).

3.2. Safely and reliably power down computers automatically

The next step is to look at tools that safely and reliably put computers to sleep (S3), hibernate (S4) or off (S5) automatically. There are many ways to achieve this:

  • The PowerDown tools, developed at Liverpool University can be used to shut computers down automatically if they are idle, and nobody is logged in. A modified version of these scripts has been implemented at OUCE.
  • Use commercial software. Summaries of the NightWatchman, PowerMAN and Surveyor products were provided at the Keeping IT Clean conference at Oxford, and we have been sent through a case study relating to the use of Powerwise at a large UK University.
  • Energy star also provide a list of power management software.

If you have experience of any of these tools, or would like help in negotiating licenses with commercial vendors please send an email to OUCS at: greenit@oucs.ox.ac.uk.

3.3. Monitor electricity meter readings

The Environmental Change Institute has developed two tools to help analyse energy use. The first tool polls and compiles data from a specific networked meter, then uses the Simile software to produce a graph embedded in a web page, as below:

Electricity meter readings at the Computing Services
Figure 2. Electricity meter readings at the Computing Services department.

If you are interested in using a graph like the one above please send an email to greenit@oucs.ox.ac.uk.

The ECI has also developed SMEasure a web-based building energy analysis and carbon monitoring tool helping businesses save money and reduce carbon emissions.

Screenshot of the SMEasure tool developed by the ECI group at
                                the University of Oxford.
Figure 3. Screenshot of the SMEasure tool developed by the ECI group at the University of Oxford.

To learn more about the SMEeasure tool please get in touch with the SMEasure team directly.

4. Communicate

To achieve this we recommend:

  1. A manager with responsibility for budgets works closely with IT support staff and announces the initiative.
  2. The announcement should explain the initiative is driven by the need to reduce both greenhouse gas emissions and monetary costs. (The distinction here will become irrelevant if energy prices reflect their long term price i.e. include future damage to the environment).
  3. Provide regular updates on how well the initiative is progressing.
  4. Provide clear advice on how power management should be implemented on different types of computers e.g. those in training rooms, offices and those brought to the University (e.g. laptops). Advice will also vary depending on the operating system installed (e.g. Windows, Apple and Linux).
  5. Provide technical support during the transition phase e.g. how to use wake on LAN
  6. Your green desktop computing initiative will normally require everyone in your group to do their bit. Show a reasonable level of patience as people adjust to new ways of working but 'altruistic punishment' may need to play a role.
  7. It may be fruitful to use other means to motivate people e.g. gentle competition between groups. In general we recommend you relate energy saving to expressions of social capital rather than directly measures of energy use i.e. people are more motivated by each other than graphs and numbers.

5. Share

We encourage you to write up your initiative and publish it on your groups web site as this will help others learn from your experiences. Here we list a selection of case studies from different IT environments (departmental, College and museum) where a mixture of commercial, in-house and tools provided by OUCS have been implemented.

Most importantly the case studies listed here are currently the best examples of green IT initiatives at Oxford, each group has already achieved real and significant energy savings because of their efforts.

If you have published a green desktop computing initiative case study please let us know by sending an email to greenit@oucs.ox.ac.uk.