Contribution of the recommended individual measures to CO2 reductionThe energy efficient renovation of Stuttgart's building stock (E1.1 Heat insulation) bears the most important additional CO
_{2} saving potential. Assuming theoretically that 100 % of the not yet renovated buildings are cleaned up, the possible reduction of CO
_{2} emissions beyond the trend scenario as a consequence of heat insulation measures in Stuttgart would amount to about 216,000 t/a. The predicted trend development covers only about 20 % of the reduction potential. Under the predicted conditions of the following years, the minimum scenario expects a reduction of 30 % of the declared potential.
The amount of CO
_{2} which can be additionally saved through the modernization of heating systems (E2.1 Modernization of heating systems) is confined by both the number of heating systems and the maximum annual use of 100 %. Assuming that 100 % of the installations are modernized and that mostly modern and perfectly regulated heating systems (e.g. condensing boilers) are used, about 75,000 t/a of CO
_{2} can be saved in addition to the trend scenario.
  
Absolute amount of CO2 reductions in 2010 according to different scenarios (energy)

 Absolute amount of CO2 reductions in 2010 according to different scenarios (traffic)


The predicted trend development covers already about 60 % of the reduction potential. The minimum scenario is based on the assumption that half of the potential can be additionally mobilized.
The maximum reduction of CO
_{2} through substitution effects (E3.1 Substitution of carbon fuels) is mainly confined by the fact that oil and coal cannot and usefully should not be completely squeezed out of the heat market due to market economy mechanisms. The minimum scenario is based on the assumption that, compared to the trend scenario, the percentage of oil and coal on the market can be halved, leading to an additional CO
_{2} reduction of about 31,000 t/a.
These three fields of measures alone make up for about half of the CO
_{2} reduction potential set out in the minimum scenario. And this already accounts for the fact that the measures in the fields of urban land use planning and industrial energy use won't lead to a net reduction of energy and CO
_{2} but are rather intended to reduce additionally expected energy requirements (e.g. through new buildings) to a minimum.
Furthermore, the minimum scenario is based on the assumption that currently unfavourable economic conditions for implementing measures in the fields of renewable energies, combined heat and power systems and the efficient use of energy by industry in Stuttgart will continue to exist in the foreseeable future.
The amount of possible CO
_{2} reductions through measures aiming at the saving or efficient production of electricity depends on the actual mix of power generation sources in Stuttgart. For a better understanding of the assessment characteristics, the values from the TWS power generation mix are compared with the values that result from extending the borders of the balancing area to the whole country (federal German energy mix,
see measures E1.3, E2.2, E2.3, E3.3, E3.5, E3.9).
Similar to the energy sector, the impacts of the measures from both scenarios were quantified for the traffic sector as well. As traffic measures usually influence each other, it is not possible to determine the exact effect of the individual measures without a separate model calculation. So the figure gives estimates of the dimension of the different saving potentials.
What has an outstanding effect in this context is the measures aiming at the improvement of the public transport's attractiveness (
see measures V1, V13, V14), which modify the modal split by reducing the motorized individual traffic and by increasing the use of means of public transport. This measure alone saves about 205 GWh/a of energy in the desired scenario, which is a CO
_{2} reduction of 56,000 t/a. And this is more than 40 % of the declared saving potential of the desired scenario. What has to be considered in the assessment of this measure, however, is the fact that its implementation requires significant investments.
The other savings are distributed between a range of further measures, of which only the introduction of a speed limit on federal motorways (V5) and the implementation of telematics measures (V16) have an energy saving or CO
_{2} reducing effect of more than 1 %.
Contrary to the energy sector, where the CO
_{2} reduction potentials of the minimum scenario are concentrated on room heat, i.e. heat insulation (E1.1), the modernization of heating systems (E2.1) and substitution effects (E 3.1), the saving potentials within the traffic sector are distributed on numerous measures with relatively weak effects each. But it becomes clear that the saving potentials of individual traffic measures are consistently higher than that of individual energy measures.
When assessing the results, one must not forget that adaptation processes will start already during the trend development. Further efforts are needed to meet the objectives of the minimum scenario.
In order to tap the full potential, a number of accompanying measures are advisable but cannot be quantified as for their saving potentials and financial requirements. These include above all consulting activities and conceptual research (measures
E1.2 bis E1.5, E2.4, E2.5, E3.7, E3.8 und E4.1 bis
E4.4,
V10, V11).
Ultimately, all measures aim at trying to overcome what prevents the realization of additional saving activities in order to initiate early and further investments compared to the trend development as well as changes in people's habits towards a more energy saving behaviour.
This shows that the objective must be the realization of the biggest possible savings with the help of the available financial means. In light of this, the examined measures are to be assessed in the following according to their cost efficiency, using the example of CO
_{2} reduction.
The first question is to know how much money will be needed so that a measure will reach a particular effect.
The next step is to determine the relation between the required costs of a measure and the expected benefit from the amount of energy saved within a specific time period and to analyze how the time staggering of measures is influenced by this. This method also provides first indications of how profitable the measures are. In case the annual costs for the CO
_{2} reduction are negative, the efforts for financing this measure are overcompensated by the energy cost savings which have been realized.
For each sector, different assessment criteria are established. In the energy sector, for example, it is the business aspect that counts as the investor usually profits from the amount of saved energy while the results in the traffic sector are rather considered in terms of the overall economy.




© City of Stuttgart, Office for Environmental Protection, Section of Urban Climatology 