TEFAVE

The increase in the European electric car market is backed up by international policies and the new paradigm of sustainable and intelligent mobility we are headed towards. One of the most important challenges of the industry is to increase vehicle range, improve battery efficiency and reduce consumption of the vehicles themselves.

The goal of this project is to incorporate energy optimisation solutions, including flexible thermoelectric generators (TEG) developed in-house, into electric vehicles, for two specific applications. On one hand, the goal is to achieve localised climate control to achieve individualised thermal comfort, taking the needs of individual users into account. And, on the other hand, the goal is thermal control of batteries.

Including the flexible thermoelectric generators (TEG) in the case studies involves eliminating the current fluid circulation system, and it leads to an increase in the useful life of vehicles. The solution was analysed in a very thorough way in the project. Both cases were researched from the point of view of thermal simulation, and work was done on the product design and on developing and manufacturing the TEG. An environmental analysis of the proposed solutions was also done.

Goals

The goal of TEFAVE is to include flexible thermoelectric generators (TEG) in strategic electric vehicle applications to improve energy efficiency and, consequently, increase range. Those applications are:

• Localised climate control for the comfort of user groups
• Battery temperature control

Results/Conclusions

A computational model that can simulate the complete behaviour of a TEG based climate control system was developed, and it can predict the behaviour of the system with a 10% margin of error. Likewise, a computational model was created for combining TEG with PCMs and a model with a 14% deviation was obtained.

Different avenues for manufacturing TEGs were explored and different technologies and materials were evaluated. Lastly, the combination of functional printing on textiles with conductive tracks with soldering points and the subsequent hybridisation with thermoelectric elements made it possible to manufacture large format TEGs in an automated way.

It was shown that the PCM combination in the system does not cause any improvements. Its low conductivity makes it act as an insulator, even with the addition of metal foam, and it is more effective to just use a TEG with a dissipater included. Work was done on manufacturing flexible dissipaters based on silicone pillars so the dissipation surface could be increased. Although there were some manufacturing difficulties, it was ultimately possible to put a flexible dissipater on a large format (120 x 80 mm2) TEG.

Using TEGs for the two applications examined was studied.

Options were analysed for using TEGs for localised climate control in vehicle seats. A configuration was chosen, (100 pairs, 3 mm semiconductors, 4 V power supply to reach temperatures below 30º C at 1 W in a stationary regime), that makes it possible to minimise the amount of material used and the electrical consumption of the fan and the TEGs, thus minimising environmental impact. In the comparison between a conventional climate control system and the one proposed in the project with the TEG, it is clear that the effects of the TEG are not relevant compared with a conventional system. Furthermore, it was observed that, like the conventional systems, the greatest impact is the “global warming” parameter. For the TEGs it is “depletion of fossil and mineral materials”. Likewise, it has been shown experimentally that the TEGs appear to be a reliable alternative for battery temperature control. They eliminate spikes near the maximum allowable temperature and prevent exceeding it.

After doing the environmental study, it was seen that the impacts from electricity consumption are negligible compared with TEG manufactured ones. It was concluded that the most impactful process in manufacturing the TEGs is obtaining the bismuth and tellurium semiconductors, followed by obtaining the silver ink. A test bench for evaluating the TEGs was set up. On one hand, an electroscopic impedance analyser was used. And, on the other, a test bench was put into operation under real conditions consisting of two thermal reservoirs with controlled temperatures and two variable thermal resistance heat exchangers. Large format modules were achieved, showing the robustness and reproducibility of the manufacturing process. The experimental results with the impedance device show that the modules are functional and have electrical resistance values within the expected margins. With a value of 10 μW cm-2*K-2 generation obtained the project can be considered to be successful.

The general assessment of the project is very positive. The activities were carried out according to plans, and it obtained results that are at the top worldwide. And it is also a technology with an enormous use potential, which is a success given the little time the consortium has existed. Furthermore, the collaboration between the two research groups, UPNA and NAITEC, was very fluid, which facilitated work and coordination with the groups, and it enriched the knowledge of both. It should also be highlighted that results from the project have been presented at three conferences, LOPEC 2022, the 12th International Conference of Thermodynamic Engineering and the 18th European Conference of Thermoelectricity, creating great interest at all of them. Several publications in scientific journals are also expected.