Ecological Transport Information Tool for Worldwide ... - Schenker

Page 80
IFEU Heidelberg, Öko-Institut, IVE, RMCON
Allocation of electricity from CHP and its environmental impacts
In some cases electricity for rail transport is produced in power plants producing both electricity
and heat (cogeneration or Combined Heat and Power - CHP). Therefore the environmental
impacts of running the power plant have to be burdened (allocated) on both output products. As
well. Amongst others the following allocation methodologies are feasible:
1. Allocation by Energy
2. Allocation by Exergy
3. Approach mentioned in /Directive 2004/8/EC/
The allocation by energy is based on the assumption that one unit of heat is equivalent to one
unit of electricity. This assumption is also the main disadvantage of this approach, because in
regards to thermodynamics electricity has a higher work potential than heat. So the more valuable
product of cogeneration is electricity and actually has to be burdened with more environmental
impact units than heat. Thus this allocation methodology favours electricity.
In contrast the allocation by exergy is considering the different valence of electricity and heat. In
/Heck 2004/ one unit electricity is equivalent to 0.17 unit heat. This methodology is favoured by
scientific institutions (e. g. IFEU) but does not represent an approved European standard for
CHP allocation so far.
Compared to the allocation by exergy the approach mentioned in /Directive 2004/8/EC/ (also
called “Finnish Methodology”) represents a European wide accepted methodology. It was developed
to calculate the efficiency of new CHP power plants. Therefore the difference (reduction)
between the production in CHP and the production in a separate heat and a separate electricity
power plant is estimated. The default values for the separate production are defined by
/Decision 2007/74/EC/. The methodology does not take the different valence of electricity and
heat into account (cp. exergy). But electricity gets a lower environmental benefit compared to
the allocation by energy. And this methodology is approved within the European Union. Thus
we use this approach to allocate the environmental impacts of cogeneration.
The following table shows the effect of using the three described allocation methodologies on
the overall efficiency and CO 2 -emission factor:
EcoTransIT World: Methodology and Data – July 15 th , 2010