In order to make the Peltier effect economically viable, two conventional metals are no longer used to build a Peltier element. The resulting temperature difference here is less than 1 K.
Instead, one metal is replaced by an n-doped semiconductor (electrical conduction is done by negatively charged electrons) and the other by a p-doped semiconductor (electrical conduction is done by positively charged holes). A copper bridge connects the two semiconductor legs. If direct current is sent through the Peltier element in the direction shown, the copper bridge connecting the two elements cools down. The two connecting bridges, also made of copper, heat up. In other words, there is a constant heat transfer from the upper copper bridge to the lower copper bridges.
In order to obtain Peltier blocks that are suitable for technical applications, the individual Peltier elements are joined together in a meandering pattern. The Peltier elements combined to a Peltier block are thus electrically connected in series and thermally connected in parallel. The Peltier blocks themselves can now be connected electrically in series or parallel if large cooling surfaces are required.