PERFORMANCE ANALYSIS ON SOLARROOF-TOP SYSTEM USING TEG

Solar is most commonly used form of Renewable energy. Solar energy is used nowadays for different purposes and the main use of solar energy is for production of electricity. There are many solar panels invented but they all are used when there is sunlight. Solar panel can be used with TEG (Thermo-electric generator) to improve the overall performance of the solar roof top system. Thermoelectric generators(TEG's) are energy conversion devices. This device is extremely reliable, safe, simple, compact and eco-friendly. The main aim of this paper is to implement and verify the mathematical modelling of thermoelectric generators with the help of MATLAB Simulink.


Introduction
At recent years, one of the most important problems at the world is lack of supplying energy in a continuous way due to increase in use of devices that mostly uses electrical energy. Nowadays the electrical energy which is being used is because of conventional sources like coal, diesel and nuclear. It is well known that this conventional sources are limited in nature and because of this environment is polluted. Therefore, it needed to use clean and non-enforceable energy which is "renewable energy" such as tidal energy, solar energy, wind energy, geothermal energy. And one of the easiest method to convert renewable energy into electrical energy is solar energy. But use of solar energy as compare to its presence is very less. Mostly solar panel is used for conversion of heat energy into electricity. Solar panel is used in the presence of sunlight. And this is the main drawback of solar panel, due to which the efficiency of solar panel is less, nearly less than 14%. And thus it must have to deal with this problem. Brief drawbacks of the current renewable energy sources have been tabulated below. Thermoelectric generator is based on the principle of seebeck effect. Seebeck effect is a phenomenon in which a temperature difference between two dissimilar electrical conductor of semiconductors produces a voltage difference between two substances. In this paper how electricity can be extracted from heat using thermocouples is explained.
The hardware model which is explained in this paper is THERMOGENERATOR, having more focus on energy generation by TEG during blackouts.
During day time when sun is having its light as well as heat energy with the help of a converging lens the heat energy provided by the sun is focused on heat exchanger and the fluid present in the heat exchanger gets heated up. Due to this transfer of energy the liquid which is also present in the thermos gets heated up to certain temperature during daytime. TEG's are already installed on thermos one side of the TEG is in contact with the hot liquid and another surface of TEG will be exposed to the atmospheric temperature. In this way the temperature difference is generated and electrical power is produced.

C. Specification of TEG.
For our purpose we are using the TEG model TEP1-24156-2.4.

D. Theoretical modelling of TEG
For the simulation of different parameter of thermoelectric module, it need different mathematical relationships. The output voltage of the TEG (a single unit) can be calculated using the following formula. [2] The output current of TEG unit is calculated using The output Power of TEG unit is given by

E. Simulation of TEG
Simulation of TEG is needed to obtain the characteristics, to study the voltage, current and power waveform with respect to time and with respect to temperature changes.
Simulation of the mathematical model of TEG in MATLAB Simulink by using equations (1), (2), (3). And the input characteristics is as shown in the Fig. 4 and the output characteristics is as shown in the Fig. 5.

Simulation Of Teg With Practical Conditions
Typically, in the practical scenario, when sun rises the ultraviolet rays of the sun are not that much effective therefore the heat energy that can be extracted from the sun is less. As the time goes on the heat energy that can be extracted is also increases gradually. During this period the temperature of the liquid increase gradually. Extraction of the heat is maximum during 12pm to 3pm and during this period thetemperature of the liquid has reached to its maximum value and it cannot be further increased, so temperature of the liquid remains constant for some time. In the evening, solar radiations from the sun are not available to heat up the liquid again. So the temperature of the liquid starts falling. Due to the insulation provided to the tank the decrease in the temperature is not rapid and does not reach to room temperature and its minimum value maintained to certain level.
Considering this practical scenario, input temperature signal that can be given to the simulation model is developed as shown in the

A. Steady state condition
Steady state condition is the condition where the temperature given to the simulation model is constant and not varying according to the proposed conditions. The temperature given is 2250C or 498 K, then the steady state results obtained are as follows in Fig. 7.
In Fig. 7, the steady state temperature is shown which is given as input to the simulation model. And the steady state values of the voltage, current and power are obtained are as follows. As the given input temperature is constant to the simulation model, the values obtained are also constant.

B. Dynamic state condition
Dynamic state condition is the condition where the temperature input given to the simulation model is of dynamic nature i.e. similar to the practical conditions which are stated above in the paper. The temperature is variable in nature according to the availability of sun during whole day. In Fig. 8 The dynamic state temperature is given as an input to the simulation model. And the dynamic state values of the voltage, current and power are obtained are as follows. As the given input temperature is variable to the simulation model, the values obtained are also variable in nature.
With the dynamic nature of input, it is seen that the values of voltage and current are varying according to the availability of sun. So output characteristics that is P-V characteristics will not be same as the obtained P-V characteristics that is obtained by using standard formulas as shown in Fig. 5.Therefore, the output characteristics obtained with the dynamic input is as shown in the Fig. 9.
In the P-V characteristics shown, it is increasing and then reached to its maximum point and this is the point needed for the charging of the battery or supporting other dc loads. This maximum point can be tracked by using proper maximum power point tracking system, after reaching maximum point its starts decreasing.

A. Power loss
The power output generated by thermoelectric module is proportional to the amount of heat flowing through the module. The amount of heat will be input power. The heat flowing is given by The amount of heat flowing through the module and the efficiency of the module for different temperatures is shown in the table given below

B. Insulation co-ordination.
According to the Newtons law of cooling the rate of fall of temperature is constant.

Proposed Hardware Model
The hardware model derived from the above description has following circuit diagram shown in the  The actual hardware results are with 3000 C at concentrated point the maximum temperature reached by the liquid is 800 C. The voltage generated by 6 Teg connected in series is around 18V and current 0.65A and this output can be given to charge the battery or can be given to the appropriate DC load.

A. Heat loss to environment
As very heavy insulation is provided to thermal tank the fall in the temperature with respect to the number of days is shown in the Fig. 12. The insulation which is provided to the tank consists of three layers one layer of thermal blanket, polystyrene and EPU foam. With such heavy insulation the loss of heat to the environment is very less and temperature fall is also less.
container. In this container, liquid is present and the heated liquid is circulated by the laws of thermodynamics.
The hardware includes 6 TEG's installed, one heat exchanger, one tank insulated with polystyrene and EPE foam, concentrating dish, circulating pipes. The insulation provided to the tank has three layers. First layer is thermal blanket. Second layer is polystyrene. Third layer is EPE foam which provide better insulation to avoid heat loss in the tank. So the actual model will look like Fig. 11.

B. Voltage and current varying with temperature
The variation of current with respect to the temperature difference is shown in the Fig.13 from the below graph it is seen that the current in the module increases as the temperature difference between surfaces increases. It is seen that with 80 degree temperature difference the current in the modules is around 650 mA. The variation of voltage with respect to the temperature difference is shown in the Fig.14 from the below graph it is seen that the voltage in the series connection increases as the temperature difference between surfaces increases. It is seen that with 80degree temperature difference the voltage in the modules is around 18V.

Conclusion
In this paper we have investigated and thought about the possibility of employing TEG's in order to make solar roof top systems more efficient. We have seen in detail the theoretical model of TEG and its various physical attributes as well as its input and output characteristics have been studied in detail.
And MATLAB Simulink model is generated to obtained the desired characteristics. The effect of environment has also been kept in mind and necessary calculations were carried out in order to incorporate the heat loss due to lack of insulation. It was later seen that with appropriate and sufficient level of insulation the loss of heat energy can be reduced and thus in turn the efficiency can be raised, this was illustrated using a sample case.
Finally, a hardware model was proposed and built which can be used along with the solar panels so that the maximum utilization of the solar energy can be done to have higher duty cycle of the equipment, along with the complete and organized details.