The calculation instrument divides the energy sources into the three categories fossil, nuclear, and renewable. Hereby, the following assignments are used:

 Fossil:
gas, fuel oil, coal,
district heating (fossil fuels incl. waste incineration),
electricity (conventional: fossil fuels)

 Nuclear:
electricity (conventional: nuclear power)

 Renewable:
wood, solar (thermal),
district heating (biomass, solar [thermal]),
electricity (conventional: renewable sources), electricity (PV)

For the school building of example C almost all of these values are already available, except for the contribution of different primary energy sources to the overall energy mix used for the production of conventional electricity. The calculation instrument takes the data published in the Monthly Electricity Survey in October 2003 by the IEA which shows the contribution of primary energy sources in the three categories for a certain country. The further proceedures are described in example C.

Example C: Falk Comprehensive School
The school building in this example has consumed 150.000 kWh of electricity that were purchased by using an electricity contract that does not specify a certain contribution of different energy sources to the overall energy mix.
The primary energy consumption related to the use of electricity amounts to 435.000 kWh. Since the school building is situated in Germany, 66 % of the primary energy used to produce electricity comes from fossil fuels, 30 % is nuclear, and 4 % is renewable. Consequently, 287.100 kWh of electricity is produced using fossil fuels, 130.500 kWh using nuclear, and 17.400 kWh using renewable energy sources.
These results are added to the primary energy consumption previously calculated. In the category of fossil energy sources 250.800 kWh of primary energy have been used for space heating. Therefore, a total amount of 532.575 kWh of primary energy is coming from fossil energy sources. The figures for nuclear and renewable energy remain the same. Therefore, a total of 544.500 kWh of primary energy consumption for the school building is fossil, 130.500 kWh is nuclear, and 17.400 kWh is renewable. Their sum equals the overall primary energy consumption amounting to 692.400 kWh. In conclusion, the percentages showing the contribution of different energy sources to the overall energy consumption in the building are: 78 % for fossil energy, 19 % for nuclear energy, and 3 % for renewable energy. Figure 14 shows the corresponding extract of the Display® poster.

Figure 14: Extract of the Display® poster showing the contribution of different energies to the overall primary energy mix