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 There are many schemes that offer consumers the opportunity of making a pledge to reduce their carbon dioxide (CO2) emissions, with the aim of helping to reduce the risk of damaging climate change. At the National Energy Foundation, we offer one such web-based scheme ourselves: the award-winning Carbon Workout. Like the best of these schemes, the Carbon Workout follows the Best Practice Guidelines issued by Defra. However, if you are thinking of running a local scheme yourself, we can work with you to design a compliant scheme, and can help you measure its success.
This page is designed to give some additional, unofficial guidelines, for how you can quantify the carbon dioxide (CO2) savings made by people who have signed up to a Climate Change Pledge Scheme. It is designed to complement the Defra Best Practice Guide to Designing and Operating Climate Change Pledge Schemes (issued June 2008) which contains a section on measuring success in qualitative terms, but not in quantitative terms. However, firmer estimates of savings may be required by some funding organisations to determine Value for Money or may be regarded as best practice if, for example, you are a charity wishing to report your effectiveness to stakeholders such as members or the Charity Commission. However, you should bear in mind that is impossible to calculate exact numbers and that any estimates of CO2 savings may have a large margin of error.
You will need to decide whether or not you are attempting to evaluate the potential CO2 effect of all pledges made, or only the CO2 savings from those pledges actually implemented. Although it is easier to estimate the former value, this will usually over-estimate the real savings made. You may decide to use market research or an ongoing programme of communications with pledgers to provide an estimate of the number of pledges that have been kept.
If you lack firm data on the proportion of pledges achieved, you should use conservative estimates, which may vary with the type of pledge, for example:
- around one half of behavioural (no-cost) pledges may be kept
- only one third of pledges requiring a significant time or financial investment are likely to be kept
The effects of some pledges may last for a long time if they involve investing in new low energy equipment, such as installing a condensing boiler or fitting solar panels. In contrast, many behavioural pledges will only last for a shorter period, as old habits creep back.
When calculating CO2 savings, it is usually easier to start by calculating energy savings, in kWh by type of fuel, and then converting them to CO2 equivalents. In doing this:
- use the Defra conversion factors where available
- take extra care in how carbon savings from switching to renewables or green electricity are calculated, especially as commercially purchased green electricty should normally now be accounted for as having the same carbon content as average grid electricity
- indicate your assumptions clearly if they have not come from a recognised UK source
In calculating carbon savings, there are two main approaches: Top Down and Bottom Up.
Top Down methods start with the total carbon emissions (or energy used) by an entity, typically a household, and so should only be used if fuel bills or similar records are available. They then calculate the CO2 emissions by each fuel, using an estimated percentage of the total fuel used. For example gas savings may be:
- 15% for installing a gas condensing boiler
- 3% for turning the thermostat down by 1°C
- 20% for adding cavity wall insulation
In calculating the total saving, you must remember that each measure reduces the total demand after implementing the other measures, so that the effect of combining the 3 shown above is to reduce gas consumption to:
85% x 97% x 80% = 66% of its initial level, with a combined CO2 saving of 34%
and not a saving of (15 + 3 + 20)% = 38%.
You may need to distinguish between homes that use electricity for heating and hot water and those that use other fuels, as the percentage savings from non-heating pledges (such as switching TVs off standby or using CFLs) will be much lower in electrically heated homes.
Bottom Up methods will typically look adding up at the actual energy or CO2 savings from an individual measure for a typical household. As with top down savings, it is not possible to add together savings from two measures that both reduce demand for a single purpose (such as adding a new boiler to adding insulation). Where possible, you should try and use bottom up numbers that reflect either the size of the home or the number of occupants.
Top Down methods are generally thought to give more accurate estimates of saving, as they start with real fuel bills (and CO2 emissions), reflecting actual homes and lifestyles, and can be checked against bills received in future years. Both methods may over-estimate savings from physical measures if pledgers take some of the benefits by having a warmer home, rather than lower costs and emissions.
There are a number of reliable sources for estimated saving numbers, including the Act on CO2 website, the Energy Saving Trust and Good Practice Guides as well as the NEF website. However there are many actions, especially behaviour changes, where you may need to make your own estimates of savings, or where you may believe that nationally available numbers are unlikely to be appropriate to your pledge target groups. In these cases, you should try and be conservative in your estimates and include the key assumptions in any reporting.
Finally, bear in mind that many savings achieved following pledges may also be reported as savings by other bodies. For example, if as a result of making a pledge, someone has loft insulation installed by a contractor part funded through the energy utilities' Carbon Emission Reduction Target (CERT), then the utility company involved will also take credit for the CO2 saving.
For more information about how the National Energy Foundation can help you set up a local Climate Change Pledge Scheme, please contact our Communities Team. For help in calculating CO2 savings on a project, please contact our Carbon Calculations Consultants.
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