A paper & calculator -based worksheet for working out your Carbon Footprint.
CRAGs Carbon Footprinting Worksheet |
updating query on green electricity, biomass and gas offsetting
written on 8/10/2007 01:25
John Cossham |
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I’d like to ask ‘anonymous’ why s/he would rate ‘green electricity’ as 90 – 100 % of the normal? The company I use, Good Energy Ltd, only buys and sells leccy from wind, solar and existing hydro. They asked customers about purchasing from landfill gas turbines, and we said no, and they don’t support new hydro dams as these can cause methane emissions from rotting vegetation. They seem pretty green to me and I wouldn’t be happy for a calculator to consider that my £200 a year (one unit per day) use is as much as 90% of the carbon footprint of a coal or gas – heavy electricity bill. I do understand that photovoltaic cells and wind turbines have a carbon footprint/embodied energy, but still cannot imagine how this might make it worth 90% of fossil based electricity.
I approve of a biomass rating, but think this should be flexible as some of us gather our biomass by bike and trailer. Hardly any of my 6 tonnes a year of logs are brought to me by motor vehicle, I’d say perhaps 5%, although many of the logs will have been cut using a petrol-powered chainsaw before I get to them.
Finally, what do people think of British Gas’ claim that their gas is green as they offset it? I buy my £50 a year of gas from them and have been asking them for about 4 years about a ‘green gas scheme’ and paying a bit extra for it whenever they’ve rang up and asked if I’d like to pay less for my gas. Should we be congratulating them? Are there greener gas suppliers? Is there a green gas supplier called Oxymoron Ltd?
John Cossham
Sorry – the
written on 8/10/2007 14:11
david |
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Sorry – the ‘anonymous’ is a bug on files’ comments – it’s David here. The rationale behind the green electricity is on the thread above. There’s also a “green gas” thread at 'Ethical' gas suppliers? Guardian article 15 March 2007.
Gas per pound & Ferries
written on 1/4/2008 10:07
david |
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The gas calculation per pound of gas bill is now severely out-of-date, by a factor of two or three, I think – because of rising gas prices. Also, we could do with a conversion factor for ferry trips.
Updates to footprinting worksheet 10/2008
written on 29/10/2008 18:13
david |
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Rick has kindly updated the footprinting worksheet, and I’ve added some corrections submitted by Kim Kaivanto of Lancaster University, as well as a bit of tidying up. If anyone wants copies of the older worksheet, please send us an email.
Rick’s changes
Rationale …
- DEFRA published a significantly updated & expanded set of conversion factors in June this year at http://www.defra.gov.uk/environment/business/envrp/pdf/ghg-cf-guidelines…
- OFGEM published revised proposed guidelines on green electricity in July which argue that the best proxy for the carbon intensity of all grid electricity regardless of tariff is the grid average. See the Green Electricity thread on the site for the URL.
And these are the changes to the worksheet
Gas
- Have given the kWh conversion factor to 3 decimal places. The cubic metre and feet conversion factors kept at 1 decimal place because fluctuations in the calorific value of the gas limit the accuracy anyway. Whereas the kWh on bills is accurate.
- Removed the “£1 of gas bill” line as the pace & degree of price changes has risen sharply.
(David: see also further corrections below)
Coal
Replaced the anthracite and bitumen coal lines with a single “domestic coal” line based on the new DEFRA figure of 2523 kg CO2 per tonne.
Wood Pellets
Added a new line for wood pellets. DEFRA have published a conversion factor for the first time.
Electricity
DEFRA only give figures up to 2006. The rolling average for the 5 years to 2006 is 0.537 kg CO2 per kWh, but the trend has been upward since 1999 and the figure for the single year 2006 was 0.562. So, I’ve chosen 0.55 as a guestimate of the likely current average.
OFGEM have not yet produced their final guidelines, but I think it is unlikely that 100% renewable tariffs will get a reprieve on the carbon intensity question. However, I don’t have a problem if you want to delay publication.
Car
I’ve added LPG as a fuel type, and amended & added to the car types in line with new DEFRA data.
Plane
I haven’t touched this.
Surface Public Transport
Not added. DEFRA have significantly revised the conversion factors & modes e.g. Coaches and London buses are now listed separately.
Kim’s changes
Gas conversion figures
CO2 conversion factor for gas: 2.05 kg CO2 / m3 or 5.80 kg CO2 / 100ft3, derived as follows…
Net CV basis:
- 0.206 kg CO2 / kWh for natural gas (net calorific basis) from Source#1, Annex 1
- 9.94 kWh / m3 average (net) calorific value of natural gas from Source#2, Annex A.1, p. 208. (calculated as (35.8 MJ/m3) / (3.6 MJ/kWh) = 9.94 kWh / m3)
- => 0.206×9.94=2.05
Gross CV basis:
- 0.185 kg CO2 / kWh for natural gas (gross calorific basis) from Source#1, Annex 1.
- 11.1 kWh / m3 average (net) calorific value of natural gas from Source#2, Annex A.1, p. 208. (calculated as (39.8 MJ/m3) / (3.6 MJ/kWh) = 11.1 kWh / m3)
- => 0.185×11.1=2.05
According to my calculations, regardless of whether one starts with a net or gross CV basis and working with three significant digits gives the result that the CO2 externality of natural gas is 2.05 kg CO2 / m3.
(David) For units of 100 cubic ft, based on these sources …
- there are 3.2808 ^ 3 = 35.31 cubic feet in one cubic metre
- 9.94 kWh.m-3 x 1/35.3 m3/ft3 = 0.282 kWh.ft-3
- giving 28.2 kWh.100ft3
- so kg CO2 / 100ft3 is …
- 28.2 kWh.100ft3 x 0.206 kgCO2/kWh = 5.80 kgCO2 / 100ft3
Sources:
- Defra (April 2008) Guidelines to Defra’s GHG Conversion Factors: Annexes.
- Defra (2007) Digest of UK Energy Statistics.
Updates
david
I think some updates need to be made:
Agree?