The Independent Sent 27 December 2007
Sir,
the article 'My carbon-free year' (Independent Thursday 27 December 2007) claims that Donnachadh McCarthy's home was `carbon-negative for energy' during 2007. This would be great if it were true, but the claimed carbon footprint of -141 kg was obtained only by using a carbon carousel fraud.
The home sometimes exported and sometimes imported green electricity. For every kWh of electricity exported, the net footprint was credited with -430g of CO2. Fair enough. But when the home imported a kWh of electricity, the effect on the footprint was declared to be zero. This is a fraud, since under this accounting system a building that imports 1 kWh on Monday and exports 1 kWh on Tuesday (and thus makes no net contribution) would be judged to have removed 430g of CO2 from the atmosphere! When this error is corrected, we find that Donnachadh McCarthy's impressive home is not carbon negative. It has a CO2 footprint of +24 kg.
It is a terrible struggle to make a British home carbon neutral!
yours
David MacKay
PS
Here are the details of the correct spreadsheet
``How the eco-savings add up''
| CONSUMED | CO2 footprint | |
Gas usage | 609 kWh | 116 kg |
NET export of green electricity (598-384) | 114 kWh | -92 kg |
Solar electricity produced and used on-site | 420 kWh | zero |
(Other items in the table all as before, zero.) | ||
Net footprint | +24 kg | |
PPS - They didn't publish my letter.
2 comments:
This ties in with the intuitive notion that none of the technology that the author is using, directly or through the grid, abstracts carbon dioxide from the atmosphere and locks it away from the atmosphere.
Without such technology (growing wood for furniture would count) the concept of carbon negative only arises if there is a carbon positive allowance somewhere else, such as granting a pollution rate.
I'm assuming the fraud here is from claiming that a 100% green tariff is utterly carbon neutral when there are other financial obligations on the supplier that mean that it is no longer the case? Not to mention that its grid electricity so could be anything and you are thus relying on the honesty and success of the generator to supply additional green electricity
I've done a quick worksheet lookup here for reference:
http://spreadsheets.google.com/pub?key=pYDw6GR4D-S5SKXpYDNMwVg
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