tE eFFect

The term "thermoelectric effect" encompasses three separately identified effects: the Seebeck effect, Peltier effect and Thomson effect. This separation derives from the independent discoveries of French physicist Jean Charles Athanase Peltier and balt-German physicist Thomas Johann Seebeck. Joule heating, the heat that is generated whenever a voltage is applied across a resistive material, is related though it is not generally termed a thermoelectric effect. The Peltier–Seebeck and Thomson effects are thermodynamically reversible, whereas Joule heating is not.

 

            The Seebeck effect is the conversion of temperature differences directly into electricity and is named for the balt-German physicist Thomas Johann Seebeck, who, in 1821 discovered that a compass needle would be deflected by a closed loop formed by two metals joined in two places, with a temperature difference between the junctions. This was because the metals responded differently to the temperature difference, creating a current loop and a magnetic field. Seebeck did not recognize there was an electric current involved, so he called the phenomenon the thermomagnetic effect. Danish physicist Hans Christian Ørsted rectified the mistake and coined the term "thermoelectricity". The voltage created by this effect is of the order of several microvolts per kelvin difference. One such combination, copper-constantan, has a Seebeck coefficient of 41 microvolts per kelvin at room temperature.

            The Peltier effect is the presence of heat at an electrified junction of two different metals and is named for French physicist Jean-Charles Peltier, who discovered it in 1834. When a current is made to flow through a junction composed of materials A and B, heat is generated at the upper junction at T₂, and absorbed at the lower junction at T₁.

            The Thomson effect was predicted and subsequently observed by Lord Kelvin in 1851. It describes the heating or cooling of a current-carrying conductor with a temperature gradient. Any current-carrying conductor (except for a superconductor) with a temperature difference between two points either absorbs or emits heat, depending on the material.

            In metals such as zinc and copper, whose temperature is directly proportional to their potential, when current moves from the hotter end to the colder end, there is a generation of heatand the positive Thomson effect occurs. Conversely, in metals such as cobalt, nickel, and iron, whose temperature is inversely proportional to their potential, when current moves from the hotter end to the colder end, there is an absorption of heat and the negative Thomson effect occurs. If the Thomson coefficient of a material is measured over a wide temperature range, it can be integrated using the Thomson relations to determine the absolute values for the Peltier and Seebeck coefficients. This needs to be done only for one material, since the other values can be determined by measuring pairwise Seebeck coefficients in thermocouples containing the reference material and then adding back the absolute thermopower of the reference material. Lead is commonly stated to have a Thomson coefficient of zero; in fact, it is non-zero, albeit being very small. In contrast, the thermoelectric coefficients of all known superconductors are zero.

 

            For monitoring the performance of photovoltaic and thermoelectric, LabView has been used. Basically each renewable energy plant or system plants needs the monitoring control systems. Same as hybrid system, where the performances and parameters must be closely monitored and controlled, thus allow adequate data acquisition system.  The data acquisition system requires large number of measured data where very frequent recording necessary needs to be automated to eliminate the probability of human error as well as to save time. This project is mainly about computer based real time monitoring system center which use LabView as Graphic User Interface (GUI) to provide graphical display output chart, graph or pie chart.