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CO2 assessment methods for electric heating in France

Panel: 4. Monitoring and evaluation for greater impact

Authors:
Florence Khayat, ENGIE Lab CRIGEN Lab Future Buildings and Cities, France
Christian Muresan
Benjamin Haas

Abstract

Calculation of CO2eq content is a rather straight-forward task for fossil fuels as it derives mainly from combustion equations. It is much more complex for electricity, since it is not a naturally available energy but an energy vector (it does not emit greenhouse gas (GHG) at the time of consumption, but during production). At a given moment, the kilowatt hour (kWh) consumed on the grid comes from a mix of the different energy sources used to produce it.

The CO2eq content of the electric kWh corresponds to the CO2eq emissions generated by the production of this kWh of electricity. Thus, to know the emissions related to the consumption of an electrical appliance, one question arises: how the electrical system responds to the corresponding demand and by what means of production? GHG emissions depend on the plants called to meet the demand, and therefore the production mix.

Determining the exact relationship between electricity consumption and the corresponding CO2eq emissions requires precisely associating a means of electricity production with this consumption. The electrons circulating freely on the electrical network, it is however impossible to know the exact origin of the current supplying electrical use at a given moment.

Therefore, how to estimate the GHG emissions generated by an electrical appliance knowing that the means of production mobilized vary at each moment to respond to the variability of demand? The choice of the method depends on the objectives sought.

What calculation method can be used to evaluate the CO2eq content of electricity in the two following cases: the achievement of an overall measurement of GHG emissions and the establishment of a long term action plan to reduce these emissions? This article is dealing with all these questions using various calculation methods.

Each question involves selecting the most relevant allocation method:

– To define an overall balance, the average calculation methods are the most suitable : The average methods are all based on the simple principle of dividing GHG emissions from a given electricity production by all the electricity produced or consumed associated with that electricity production. Various variants are existing seasonal and per usage ones and with various time steps (yearly, monthly etc). For the French context where an important part of the power production is done by nuclear power plants the results are the following ones: monthly method by use provides a CO2eq content about 80g/kWh, seasonalized method by use (focused on the generation sources requested by the peak load) provides a CO2eq content up to 210g/kWh. These methods have structural limitations but also related to the integration of various renewables sources to the grid. Moreover if these average methods make possible to differentiate the CO2eq content of a kWh according to its use and period, it does not make possible to asset the effect of a variation in consumption, upwards or downwards, on the electric production plants.

– The marginal methods are consequential methods focused on the generation systems that, at the margin of the mix (current or prospective), can respond to an increase or a decrease in demand. These methods are based on physical, technological and economical behaviors of the electricity ecosystem and dedicated to support energy policies. In order to properly decide investment choices in the framework of an energy policy, it is necessary to use a prospective vision, to take into account future changes in the generation fleet (e.g. construction or not of a new nuclear power plant) and the impacts on the power demand and associated GHG emissions. The use of the marginal method on the historical French mix, the marginal CO2eq content values are between 450 and 550g/kWh.

A European standard on the topic, under CEN/TC371 is being published for public inquiry. We will expose the variety of methods introduced in this standard, as well as impacts on policy makers.

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