# Superinsulation Materials for Energy-Efficient Train Envelopes
## 5 Discussion
### Application Aspects
Thus, one calculates an annual saving of about 45.0 kWh/m\({}^{2}\) of train envelope for VIPs and of about 22.5 kWh/m\({}^{2}\) for silica aerogel boards--in both cases compared to conventional melamine foam resin. One can consider the economic payback of using superinsulation materials for the example of an ICE 4 train. A new ICE 4 train costs about 39 million EUR [47]. At a length, height and width of 375, 4.1 and 2.9 m, respectively, it takes just under 90 m\({}^{3}\) of insulation material to insulate such a train with 20 mm of insulation (subtracting 25% of window area on the side walls). Considering a thermal superinsulation cost of 4000 EUR/m\({}^{3}\) and a conventional insulation material cost of 500 EUR/m\({}^{3}\), the use of thermal superinsulation would incur an additional cost about 70 EUR/m\({}^{2}\) of opaque train envelope and make the whole train roughly 0.8% more expensive. Assuming an electricity price of 0.1 EUR/kWh (e.g., 0.11 CHF/kWh for Swiss trains [48]) and not considering any transforming losses when using this electricity for heating, the thermal superinsulation would only be paid back in about 16 years for VIP and in about 31 years for silica aerogel boards. Since no energy savings for cooling due to the better U-values were considered here, the actual payback time would be somewhat shorter. The same holds if electricity prices would become higher. On the other hand, discounting and opportunity costs for such an investment into a more expensive insulation are not considered, which would increase the payback period. This very rough estimation indicates that using thermal superinsulation in trains may be financially interesting or not depending on the specific train and climate at hand. Thus, the individual situation needs to be considered and evaluated in detail in order to answer the question of financial feasibility of thermal superinsulation in that case. The same approach can be used to estimate the ecological payback of superinsulation materials in trains, at least in terms of embodied energy. Considering the density and embodied energy of VIPs, silica aerogel boards and melamine resin foam according to Table 4, one can calculate the difference in embodied energy per square metre of 20 mm insulation between the superinsulation materials and the conventional melamine resin foam. This difference would be 156.9 kWh/m\({}^{2}\) for the VIPs and 127.6 kWh/m\({}^{2}\) for the silica aerogel boards. Dividing by the yearly energy savings of 45.0 and 22.5 kWh/m\({}^{2}\) for VIPs and aerogel, respectively, the result is an embodied energy payback period of about 3.5 and 5.7 years for VIPs and silica aerogel boards, respectively. This is much shorter than the operation duration of trains of about 30 years or more. Hence, this rough estimation of embodied energy payback shows that the use of superinsulation materials to achieve lower U-values in trains is clearly indicated from an ecological point of view. This holds in spite of the fact that many train operators in Europe use already renewable energy, since overall, Europe is still far from a completely renewable electricity production with 34% renewable electricity for 2019 [49]. Therefore, any energy saved in the transport sector--be it renewable or not--can be used in other sectors where the energy mix is not completely green yet.