# Evolutionary Maximization of Energy Amount Harvested by Means of Panel of Thermoelectric Modules
## 2 Thermoelectric Module  
The structure of thermoelectric converter module is illustrated in Figure 1. It consists of several dozen semiconductor N-P junctions electrically connected in series. Temperature gradient on opposite ceramic plates of the module causes valence electrons movement from the hotter to the colder side, generating pairs of electron-hole that affect electric current flow in a load circuit. Respectively to the [PERSON]'s phenomena, inner electric field produced on the semiconductor junction as well as voltage on module terminals are proportional to temperature difference \(T_{H}\)-\(T_{C}\) established between layers of oppositely doped materials. The figure of merit of thermoelectric module can be defined as [17; 18]:  
\[ZT=\alpha^{2}\frac{T}{\rho\lambda}\,, \tag{1}\]  
where \(\alpha\), \(\rho\) and \(\lambda\) are Seebeck coefficient, electrical resistivity and thermal conductivity, respectively, parameters specific to connected materials which are assured under average operation temperature point \(T\). The presence of electrical resistivity causes Joule heat energy dissipation on the inner resistance of the device and it requires MPPT algorithms usage for this inescapable energy loss minimization. However, thermal conductivity \(\lambda\) existingbetween opposite sides of module ceramic plates strongly limits temperature distance \(T_{H}\)-\(T_{\rm C}\) available for a real device with small thickness of few millimeters typically. Heat energy is transferred between converter sides and this results in temperature gradient degradation. Theoretical efficiency of thermoelectric module is associated directly with the Carnot principle and is formulated as [17; 18]:  
\[\eta=\left(1-\frac{T_{\rm C}}{T_{H}}\right)\frac{\sqrt{1+ZT}-1}{\sqrt{1+ZT}- \frac{T_{\rm C}}{T_{H}}}\, \tag{2}\]  
so electrical energy obtained strongly depends on thermal isolation achievable for assuring possible temperature difference between thermoelectric ceramic sides. Maximal efficiency of currently available thermoelectric devices reaches about 15% which was obtained for a module constructed from skutterudite materials operated at \(T_{H}\)-\(T_{\rm C}\) = 200 \({}^{\circ}\)C temperature gradient [12]. As may be concluded, relatively low efficiency and considerable production cost of thermoelectric generator modules are still main bottlenecks [19; 20]. It limits the wide offer possibility of this kind of panel, but the situation described should change due to intensive microtechnology [21] and new materials dominate research explorations [20; 21; 22], i.e., similarly as was observed previously for PV panels. On the other side, the crucial pros of thermoelectric modules are their durability and reliability guaranteed by thermal to electric conversion without any movement of mechanical elements and possibility of electric energy production in secluded places where application of another electricity source is impossible (e.g., space equipment). Besides, low power thermo-electric conversion is possible just now, i.e., with acceptable cost of TEG low-sized installation heated autonomically from thermal energy often wasted in exothermic processes (e.g., to automotive sensors wireless supply).