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Denmark´s Second National Communication on Climate Change

Annex E: Electricity exchange and temperature corrections

Danish CO₂ inventory adjusted for electricity exchange and temperature variations

Electricity exchange

In some years Denmark imports considerable electricity while in other years electricity is exported. The variation is due to changes in precipitation in Norway and Sweden leading to fluctuations in the availability of hydropower.

The CO₂ emission inventory include a correction for this exchange of electricity. The correction is done from the assumption that the electricity is produced using the average fuels used at Danish power plants. The corrected emission is calculated as follows:

where:

Emi - is the calculated total emission from central power plants in tonnes.

H - is the heat production at the power plants, used for district heating in PJ.

En - is the total fuel consumption at the central power plants in PJ.

I - is the imported or exported electricity in kWh.

P - is the produced electricity at the central power plants in kWh.

Eff_h - is the marginal efficiency of heat production, estimated to be 2.0.

The correction for electricity exchange is intended to absorbe fluctuations due to varying availability of hydropower in Norway and Sweden caused by varying precipitation. The correction method assumes that all the actual variation in net exchange has this origin. However, the pattern seen in the latest years might include a more systematic change in the electricity exchange. In order to seperate such systematic changes from the fluctuations due to precipitation, work has been initiated on developing a revised correction methodology, which will guaranty that the ajustments, seen over several years, will be without systematic bias.

Temperature variations

Climate variation imply not only a variation in electricity exchange but also inter-annual fluctuations in domestic energy consumption due to variation in outside temperature. Consequently, correction for the impact of outside temperature variation has been applied as well.

The energy consumption for space heating in the service sector and in households is corrected for variations in outdoor temperature. Also consumption of district heat and 20% of the consumption of oil and natural gas used in industry is corrected.

Corrections for temperature variation is made by applying a correction factor to all space heating demands and the corresponding implied fuel consumption in the space heating, power and district heating sectors. The correction factor is based on the number of degree-days for the specific years, compared to the average number of degree days for a long period of years. The information source is the Danish Technological Institute.

The number of degree days for each year during the period 1990 to 1995 is shown in Table E.1. From the number of degree days, a correction index is calculated, assuming that 50% of the heat consumption depends on the outdoor temperature, while the other 50% is independent of the temperature (heat used for e.g. hot tap water).

Table E.1. Number of degree days and the corresponding correction factor for each year 1990 - 95.

The corrections for electricity exchange and for outside temperature variation are only significant for the CO₂ emissions and have therefore only been applied to these emissions.

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