Since there are a lot of suppliers offering electricity that is produced using very different energy sources the calculation instrument cannot take into account every possibility. It implements four possibilities:
The first possibility is to purchase conventional electricity. Hereby conventional electricity signifies that it is purchased with supply contracts that do not contain an agreement about the contribution of specific primary energy sources to the overall energy mix. Therefore, it can be assumed that this electricity is composed similarly to the national electricity production. For this purpose the data were obtained from the results of the GEMIS version 4.14 calculation published by the Öko-Institut.

The possibility to specify the global mix of the electricity production is used for the distribution of the energy sources (Fossil, Nuclear, and Renewable).

Example C:Falk Comprehensive School
150.000 kWh of electricity were used for other purposes than space heating. Since no weather correction is necessary this value is directly multiplied by the corresponding CED factor which depends on the country. It amounts to 2,90 for Germany. Therefore, the primary energy consumption needed to provide 150.000 kWh of electricity for the example school building comes to 435.000 kWh.

The purchase of “green” electricity means that it is provided by using supply contracts that define a certified “green” energy mix. The calculation instrument assumes that wind power and hydro energy contribute each by 50 % to the overall energy mix since both are the most frequently used renewable energy sources for the production of electricity. The specific factors are sourced from GEMIS version 4.13 calculation made by the IWU.
If the building is equipped with photovoltaic panels for which a production of a certain amount of electricity has been declared the calculation instruments assumes that the system consists of polycrystalline silicon. As this is by far the most widely used technique, this simplification will normally not result in a false calculation. The conversion factors were obtained from the ProBas database.
In case of a cogeneration unit in the building the calculation instruments takes into account the possibility of supplementary electricity fed into the grid. However, there are no further credits given for this extra electricity. The justification for this proceeding is that the corresponding amount of electricity should normally already be rated at the point where it is finally consumed. The following example gives a detailed description of the calculation process for a cogeneration unit in the building.

Example B: Cogeneration unit in the building
In the form sheet on the page “Details about energies and their
consumption ” you have entered the information that your cogeneration unit in the building has produced 100 000 kWh of electricity and that 10 000 kWh have been fed into the grid.
Therefore, 90 000 kWh are produced and used within
the building. In order to obtain the gas consumption that was used for the production of electricity the calculation tool assumes an efficiency of the plant of 85 %. Starting with this factor the instrument calculates the overall gas consumption for the cogeneration unit i.e.100 000/0.85 =117 647 kWh gas. This figure is then subtracted from the from the total gas consumption of he building in order to calculate the amount that was necessary to heat the building i.e. 300 000 – 117 647 = 182 350. This figure is then multiplied by he climatic correction factor.
The quantity of gas used to produce he 90 000 kWh =105 880 i.e.90 000/0.85 is then added to the previous climatic corrected total i.e.182 350 X CC.This final total is further multiplied by the primary energy conversion factor for natural gas and
CO2 conversion factor.