The Infuriating Inconstancy of Carbon Emission Factors

Dr. Bob EverettOpen University

It is essential that carbon counting is done properly. A decision that one number is larger than another may set off a whole train of policy action.

Just as the ‘financial engineering’ of a wind farm project may be as important as the nuts and bolts, so it will be with serious carbon counting.

The importance of getting the right numbers and accounting procedures

The problem seems to be to get the numbers to lie down on the paper and stop wriggling.

1. BIOFUELS Is all bio-ethanol equally green? Some figures on ethanol from maize and wood….

If you were offered a tanker-load of bio-ethanol could you be sure of its source?

2. ELECTRICITY

SAP 2005 uses a carbon emission factor of 0.422 kg CO2/kWh for electricity consumed 0.568 kg CO2/kWh for electricity ‘displaced from the grid’

The current average UK factor is probably about 0.54 kg CO2/kWh

It would be nice to have just one number.

Alas - it’s all rather complicated...

The demand on the grid varies over the year….

And different plant is brought in to supply the load...

Source: Peacock & Newborough

Source: Bettle, Pout & Hitchen

The higher the load on the grid, the higher its carbon intensity

Pithy Questions:

Should a saved kilowatt hour be credited with cutting transmission losses from the power station?

Is a saved kilowatt hour an ‘average’ one or a ‘marginal’ one?

What happens if gas prices go up?

Where have we come from and where are we going to?

Source: Batey & Pout, 2005

3. COMBINED HEAT AND POWER GENERATION

Low carbon heat

or

Low carbon electricity?

CHP plants produce both electricity and heat. Their overall fuel efficiency is higher than electricity-only power stations.

It is a low carbon technology, but which does it produce - low carbon heat or low carbon electricity?

We could take waste heat from a large power station (such as Barking). Doing this will reduce the generation efficiency slightly, so we could see this as ‘low carbon heat’.

This could be used as an alternative to embarking on expensive retrofit insulation in local housing.

What about a Stirling engine domestic micro-CHP unit? This is essentially a gas boiler that makes some electricity as well.

Shouldn’t this be seen as something that provides ‘normal’ gas fuelled heat but ‘low carbon electricity’?

Between these two extremes are a host of other types of CHP plant and potential ‘disharmonies’ between the UK assessment method (CHPQA) and the European Co-generation Directive assessment method.

A lot of further research and discussion will be needed…….