performance optimization of hybrid solar heating system using thermoelectric generator

http://www.iaeme.com/IJARET/index.asp 9 [email protected]

International Journal of Advanced Research in Engineering and Technology

(IJARET) Volume 7, Issue 2, March-April 2016, pp. 09-20, Article ID: IJARET_07_02_002

Available online at

http://www.iaeme.com/IJARET/issues.asp?JType=IJARET&VType=7&IType=2

Journal Impact Factor (2016): 8.8297 (Calculated by GISI) www.jifactor.com

ISSN Print: 0976-6480 and ISSN Online: 0976-6499

© IAEME Publication

___________________________________________________________________________

PERFORMANCE OPTIMIZATION OF

HYBRID SOLAR HEATING SYSTEM USING

THERMOELECTRIC GENERATOR

Sabah M. Hadi, Aed Ibrahim Owaid and Rasim Abbas Ahmmed

Solar Researches Centre, Renewable Energies Directorate,

Ministry of Science and Technology, Republic of Iraq

ABSTRACT

The hybrid solar system assumed to be consist of thermoelectric generator

(TEG) and evacuated tube with efficiency extracted under standard condition

of 1000 w/m2and ambient temperature 25 C, then the efficiency of hybrid

system measured at different solar radiation and temperature. In addition the

thermal efficiency and electrical efficiency are extracted. The study was done

with different figure of merit (ZT) (0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4) of

thermoelectric generator (TEG). The heat transfer coefficient of evacuated

tube 0.89 W/k.m and temperature dependent that transfer coefficient

0.001w/k2. m the calculation and graphs were done by MATLAB program.

Key words: Solar, Evacuated Tube, TEG, Efficiency, MATLAB

Cite this Article: Sabah M. Hadi, Aed Ibrahim Owaid and Rasim Abbas

Ahmmed, Performance Optimization of Hybrid Solar Heating System Using

Thermoelectric Generator. International Journal of Advanced Research in

Engineering and Technology, 7(2), 2016, pp. 09-20.

http://www.iaeme.com/IJARET/issues.asp?JType=IJARET&VType=7&IType=2

1. INTRODUCTION

The greatest advantage of solar energy as compared with other forms of energy is that

it is clean and can be supplied without any environmental pollution. Over the past

century fossil fuels have provided most of our energy because these are much cheaper

and more convenient than energy from alternative energy sources, and until recently

environmental pollution has been of little concern [1].

The solar energy is available in abundance and has potential to meet the current

heating and electricity needs. However in most cases the solar systems are limited to

providing either heat or electricity. Recently, hybrid systems are developed, either

with photovoltaic or thermoelectric to generate both electrical power and thermal

energy or heat [2]. Thermoelectric power generation is one of the current interests in

clean energy research in view of direct solar power generation. Thermoelectric power



generation be-comes an attractive application. Recent research analyses were

proposed in the open literature to cover the various aspects of energy

generation[3]Thermoelectric have large potential to become an alternative power

source for electrical power supply, as they could provide co-generation system

anywhere thermal gradients exist. The most efficient way for improving the

performance of thermoelectric power generation systems is to use it with hybrid

systems. Thermoelectric module can be used with flat plate collectors, parabolic

collectors and parabolic dish or evacuated tube collectors to generate heat and

electricity simultaneously. Such hybrid system improves the overall performance of

the thermoelectric power generation system which can be made cost effective [2].

This hybrid system takes several form using for example Fresnel lens which is

concentrate the solar rays on the thermoelectric generator and produce the electrical

power with electrical conversion efficiency of 15%from the incident solar energy.

The hybrid system depend on three subsystem solar absorption system,

thermoelectric system and electrical energy management [4, 5] also dish concentrator

can be used within the hybrid system as the energy conversion and also it is highly

suitable for isolated energy demand where the conventional grid is not feasible or

available [6].

2. THEORETICAL PART

2.1. The Hybrid System

The conversion process of the solar energy indirectly can be done by several ways and

by several kinds of the thermal units. Which depend on dish concentrator and the

other on dish concentrator and so on.

The thermal units convert the solar energy to thermal energy become electrical

energy by mechanical way, so in order to prevent the mechanical way which needs

special maintenances and another requirements, the researchers followed the way

(STEG) which still in the process of research and training.

This system consist of thermoelectric generator unit made of semiconductor

materials with higher afford range of temperature than the stagnation temperature of

the evacuated tube collector, which converts the solar energy to thermal energy.

Figure 1 Schematic diagram of the System Arrangement.

Performance Optimization of Hybrid Solar Heating System Using Thermoelectric Generator


2.1.1. Thermoelectric Generator (TEG)

The global energy crisis has motivated researchers to explore alternative means of

generating power. One approach to providing electrical energy is by direct conversion

of heat to electricity using thermoelectric generators (TEGs). It is attractive to use

TEGs because they have no mechanical parts, resulting in a power system that is

silent, reliable, environment-friendly, and virtually unlimited lifetime [7].

The basic theory behind this TEG is "seebeck effect". Seebeck effect was

discovered by Thomas Seebeck in 1821. When a temperature difference is recognized

between the hot and cold junctions of two dissimilar materials (metals or

semiconductors) a voltage is generated, this voltage is called Seebeck voltage. Indeed

this phenomenon is applied to thermocouples that are extensively used for

temperature measurements. When a Thermoelectric material (Thermoelectric Module

or Thermocouple) held in-between temperature gradient it generate some voltage. In

fact, this phenomenon is applied to thermocouples that are extensively used for

temperature measurements. Base on this Seebeck effect, thermoelectric devices can

act as electrical power generators [8] .as shown in fig. (2)[9]

Figure 2 Illustration of Seebeck effect

Seebeck coefficient can be found by the equation (1) where ΔT, ΔV are

temperature difference and potential difference respectively through the two junction

between the two equations (2):

α

α

As mentioned above the thermoelectric generator consist of two different

materials, So the conversion efficiency of thermal energy depends on the physical

properties of thermal conductivity and electrical conductivity for this materials, so

find efficiency was associated with finding (Z)figure of merit which can be defined

as it is one of the most important concepts of thermoelectric that is ability of heat

conversion to electricity[10], So the finding of (Z) figure of Merit for any material

concerning the thermoelectric generator must be found by the equation (3) so

that()represent the electrical conductivity and can be measured by ampere. volt-1

.

meter-1

and (λ) is thermal conductivity for the material and can be measured by

watt.meter-1

.kelvin-1



To find (ZT) unitless figure of merit without units by multiplying the parties of

equation by (T) as shown below:

Then the equation(3) will become as in (5) which represent (ZT) figure of merit

which is unit less , this for one material but in case of two materials which the

thermoelectric generator depends on, the equation will become (6) where ρρ represent

the electrical resistance for the first and second material respectively:

The conversion efficiency of the thermal energy to electrical energy for the

thermoelectric generator can be expressed in the equation (7) where P,η,Q represent

the electrical power ,conversion efficiency ,and thermal energy respectively. The

efficiency of the thermoelectric generator depends on (ZT) figure of merit for two

materials and on the temperature difference at both sides of the generator [4] and

expressed by the equation (8), the first part of the equation represent Carnot efficiency

:

ƞ

2.1.2. Evacuated Tube

Each evacuated tube consists of two glass tubes made from extremely strong

borosilicate glass. The outer tube has very low reflectivity and very high transitivity

that radiation can pass through. The inner tube has a layer of selective coating that

maximizes absorption of solar energy and minimizes the reflection, thereby locking

the heat. The ends of the tubes connected to the copper header are fused together and

a vacuum is created between them. This process is called as evacuation, as by

definition, it means that the air is pumped out from the cavity.

The vacuum is created to recreate the thermos flask effect as vacuum acts as an

insulator and does not allow short wave radiation to escape through the glass tube.

This traps the solar radiation much more effectively and hence higher temperatures

can be achieved [11]. As shown in fig, (3). The resulted thermal energy from the

evacuated tube collector can be found by the equation (9) and this equation is

considered as a basic equation to find the thermal energy for several types of solar

collector.

Where Qcoll, A, η,a1,a2,Tm,Ta, and G are the thermal energy emerging, the area of

the thermal collector, the greatest efficiency, heat transfer coefficient ,heat transfer

coefficient in terms of the temperature, the average of the fluid temperature in the

solar collector , the ambient temperature ,and the solar radiation on the solar collector

respectively [12]



Figure 3 Photographic picture for evacuated tube.

3. THE CALCULATION

3.1. Calculation of amount of change energy obtained with the difference

in the temperature of the heat transfer fluid within the evacuated tube

In order to calculate the amount of change in the produced energy by the solar thermal

collector for the total area of 1 m2 and with solar radiation of 1000 w/m

2, ambient

temperature (25C), heat transfer coefficient (0.0089 w/m2k), and heat transfer

coefficient in term of temperature (0.001 w/m2k), and using equation (9) with helping

of the MATLAB program, the results would be shown in figure (4):

Figure 4 The Graph shown the change amount of the resulted energy from the evacuated tube

collector of area (1m2) with the change of temperature average of heat transfer fluid.

0 50 100 150 200 250 300250

300

350

400

450

500

550

600

Difference of mean collector fluid and ambient temperature C

Colle

cto

r outp

ut

[w/m

2]

G=1000 w/m2

y = - 0.001*x2 - 0.89*x + 5.9e+002



3.2. Calculation of the amount of change energy obtained with change of

radiation intensity and with the change the difference in temperature of

the heat transfer fluid.

After getting the amount of change in the resulted energy from the assumed solar

collector of a total aperture area (1m2) with the change average of temperature

difference for the heat transfer fluid with solar radiation (1000W/m2) under same

conditions of aperture, ambient temperature, thermal conductivity coefficient, and

thermal conductivity in terms of temperature but with solar radiation intensity from

100 W/m2-900W/m

2 as shown in figure (5).

Figure 5 Graph illustrated changing amount of change energy obtained with change

of radiation intensity from 100W/m2-900W/m

2 and with the change the difference in

temperature of the heat transfer fluid.

4. Calculation of Hybrid System Efficiency

Through this study and from the resulted thermal energy by the solar thermal

collector under the ambient temperature 25C, radiation intensity 1000 W/m2 and

change in heat transfer fluid temperature, the thermal efficiency of the collector can

be calculated ,also the electrical efficiency for the (TEG) can be calculated by the

equation (9), so the result can be shown in tables(1,2,3,4,5,6,7,8)with ZT figure of

merit (0.5, 1,1.5,2,2.5,3,3.5,4)respectively .



Table 1 Show the result of the electrical and thermal energy when the intensity is 1000W/m2,

temperature 25ᵒC and figure of merit 0.5


temperature25C, and figure of merit1.0

Total

efficiency

Total output

energy

Electrical

Efficiency

Thermal

efficiency

Thermal

Energy

Medium

Temp.

Temp.

Difference

0.590 590 0 0.590 590 52 0

0.586 586.7316 0400.0 0.567 265 20 52

0.562 562.2765 040022 0.543 2.0 52 20

0.533 533.6991 040050 0.517 517 000 52

0.505 505.1899 040500 0.491 .00 052 000

0.474 474.9917 040520 0.463 463 020 052

0.444 444.1556 04050. 0.434 .0. 052 020

0.411 411.5839 040500 0.403 403 500 052

0.379 379.2540 040002 0.372 055 552 500

0.345 345.1020 040000 0.339 339 520 552

0.310 310.0935 040065 0.305 002 552 520

0.273 273.1964 040026 0.269 269 000 552

Total

efficiency

Total output

energy

Electrical

Efficiency

Thermal

efficiency

Thermal

Energy

Medium

Temp.

Temp.

Difference

0.590 590 0 0.590 590 52 0

0.601 601.587 0.061 0.567 265 20 52

0.577 577.209 0.063 0.543 2.0 52 20

0.546 546.469 0.057 0.517 517 000 52

0.517 516.532 0.052 0.491 .00 052 000

0.485 484.761 0.047 0.463 463 020 052

0.452 452.228 0.042 0.434 .0. 052 020

0.419 418.717 0.039 0.403 403 500 052

0.385 385.020 0.035 0.372 055 552 500

0.350 350.187 0.033 0.339 339 520 552

0.314 314.150 0.030 0.305 002 552 520

0.277 276.532 0.028 0.269 269 000 552




temperature25C, and figure of merit 1.5

Total

efficiency

Total output

energy

Electrical

Efficiency

Thermal

efficiency

Thermal

Energy

Medium

Temp.

Temp.

Difference

0.590 590 0 0.590 590 52 0

0.612 612.927 0.081 0.567 265 20 52

0.589 589.155 0.085 0.543 2.0 52 20

0.557 557.326 0.078 0.517 517 000 52

0.525 525.370 0.070 0.491 .00 052 000

0.492 492.632 0.064 0.463 463 020 052

0.459 459.172 0.058 0.434 .0. 052 020

0.424 424.359 0.053 0.403 403 500 052

0.390 390.228 0.049 0.372 055 552 500

0.354 354.255 0.045 0.339 339 520 552

0.317 317.810 0.042 0.305 002 552 520

0.279 279.491 0.039 0.269 269 000 552



Total

efficiency

Total output

energy

Electrical

Efficiency

Thermal

efficiency

Thermal

Energy

Medium

Temp.

Temp.

Difference

0.590 590 0 0.590 590 52 0

0.662 622.6227 040000 0.567 265 20 52

0.598 598.9833 040000 0.543 2.0 52 20

0.566 566.5286 040020 0.517 517 000 52

0.533 533.7170 040050 0.491 .00 052 000

0.499 499.5307 040500 0.463 463 020 052

0.465 465.2046 040500 0.434 .0. 052 020

0.429 429.5174 040620 0.403 403 500 052

0.394 394.5432 040606 0.372 055 552 500

0.358 358.0518 040265 0.339 339 520 552

0.320 320.9515 040250 0.305 002 552 520

0.282 282.1541 040.00 0.269 269 000 552







Total

efficiency

Total output

energy

Electrical

Efficiency

Thermal

efficiency

Thermal

Energy

Medium

Temp.

Temp.

Difference

0.590 590 0 0.590 590 52 0

0.630 630.7875 040052 0.567 265 20 52

0.607 607.7256 040005 0.543 2.0 52 20

0.574 574.4904 02111. 0.517 517 000 52

0.540 540.7874 04000. 0.491 .00 052 000

0.505 505.6886 040055 0.463 463 020 052

0.470 470.4994 0400.0 0.434 .0. 052 020

0.434 434.1116 040555 0.403 403 500 052

0.398 398.4846 040505 0.372 055 552 500

0.361 361.3740 040660 0.339 339 520 552

0.323 323.7575 040602 0.305 002 552 520

0.284 284.4675 040252 0.269 269 000 552

Total

efficiency

Total output

energy

Electrical

Efficiency

Thermal

efficiency

Thermal

Energy

Medium

Temp.

Temp.

Difference

0.590 590 0 0.590 590 52 0

0.637 637.8750 040520 0.567 265 20 52

0.615 615.3819 040000 0.543 2.0 52 20

0.581 581.6250 040520 0.517 517 000 52

0.547 547.1213 0400.0 0.491 .00 052 000

0.511 511.2446 0400.5 0.463 463 020 052

0.475 475.3168 040025 0.434 .0. 052 020

0.438 438.2625 040052 0.403 403 500 052

0.402 402.0576 040000 0.372 055 552 500

0.364 364.4250 040520 0.339 339 520 552

0.326 326.3195 040600 0.305 002 552 520

0.286 286.6195 040622 0.269 560 000 552




temperature25C, and figure of merit 3.



Total

efficiency

Total output

energy

Electrical

Efficiency

Thermal

efficiency

Thermal

Energy

Medium

Temp.

Temp.

Difference

0.590 590 0 0.590 590 52 0

0.649 649.7253 040.20 0.567 265 20 52

0.628 628.4682 04025. 0.543 2.0 52 20

0.593 593.8779 040.05 0.517 517 000 52

0.558 558.1197 040065 0.491 .00 052 000

0.520 520.9213 040520 0.463 463 020 052

0.483 483.7798 0400.5 0.434 .0. 052 020

0.445 445.5971 040025 0.403 403 500 052

0.408 408.3816 040050 0.372 055 552 500

0.369 369.8151 040000 0.339 339 520 552

0.230 230.8945 0400.0 0.305 002 552 520

0.290 290.4124 040506 0.269 269 000 552

From the data in tables the maximum electrical efficiency at different values of

figure of merit and at average of heat transfer fluid temperature equal to 75ᵒC, as

illustrated in figure (6), and The maximum total efficiency at different values of figure

of merit and at average of heat transfer fluid temperature equal to 50ᵒC this is explain

in figure (7).

Total

efficiency

Total output

energy

Electrical

Efficiency

Thermal

efficiency

Thermal

Energy

Medium

Temp.

Temp.

Difference

0.590 590 0 0.590 590 52 0

0.644 644.1120 040060 0.567 265 20 52

0.622 622.2780 040.60 0.543 2.0 52 20

0.588 588.0358 04005. 0.517 517 000 52

0.552 552.8660 040560 0.491 .00 052 000

0.516 516.2913 040020 0.463 463 020 052

0.479 479.7436 04002. 0.434 .0. 052 020

0.442 442.0507 040060 0.403 403 500 052

0.405 405.3312 040006 0.372 055 552 500

0.367 367.2387 040000 0.339 339 520 552

0.328 328.6985 040555 0.305 002 552 520

0.288 288.5832 040550 0.269 269 000 552



Figure 6 Graph represents the increasing amount the maximum electrical

efficiency at different values of figure of merit and at average of heat transfer fluid

temperature equal to 75C.

Figure 7 Graph represent amount of maximum total efficiency at different values

of figure of merit and at average of heat transfer fluid temperature equal to 50ᵒC.

6. CONCLUSION

After studying the basic of the evacuated tube and thermoelectric generator working

and after the knowledge of efficiency of energy conversion for each one under

defined measurement conditions to produce these types of energy generator (the

evacuated tube convert the solar energy to thermal, and the thermoelectric generator

convert the thermal energy to electricity)it was conclude the following:

Within the considering measurement conditions the amount of energy and

temperature must be matched within the production range of the electrical power for

the thermoelectric generator. It was noted that from the specifications of the

0 0.5 1 1.5 2 2.5 3 3.5 40

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

ZT

maxim

um

ele

ctr

ical eff

icie

ncy

y = - 0.0062*x2 + 0.063*x + 0.0035

data 1

quadratic

R square = 0.99

0.5 1 1.5 2 2.5 3 3.5 4

0.58

0.59

0.6

0.61

0.62

0.63

0.64

0.65

0.66

0.67

ZT

maxim

um

tota

l eff

icie

ncy



thermoelectric generator and the solar collector get near in terms of operating age and

environmental friendly. The highest electrical efficiency when the averages of heat

transfer fluid temperature equal to 75C. The highest total efficiency when the

averages of heat transfer fluid temperature equal to 50C. It was shown that electrical

power generated from this hybrid collector is enough electrical power to turn the heat

transfer fluid, so that no need to use the external electric source.

REFERENCES

[1] Soteris A. Kalogirou, 2004, Solar thermal collectors and applications,

Progress in Energy and Combustion Science, 30, pp. 231–295

[2] N.S.Sathawane, Dr. P.V.Walke, 2014, A review on solar thermoelectric

cogenerator with evacuated tube solar collector, IJARSE, 3, pp. 36-41

[3] Jarman T. Jarman1, Essam E. Khalil, Elsayed Khalaf, 2013, Energy Analyses

of Thermoelectric Renewable Energy Sources "Open Journal of Energy

Efficiency, 2, pp.143-153.

[4] M. L. Olsen, E. L. Warren, P. A. Parilla, E. S. Toberer, 2014, A high-

temperature, high-efficiency solar thermoelectric generator Prototype, Energy

Procedia ,49, pp. 1460 – 1469

[5] Lauryn L. Baranowski,a G. Jeffrey Snyder, 2012, Concentrated solar

thermoelectric generators, Energy Environ. Sci., 5, pp. 9055–9067

[6] M.Eswaramoorthy, S.Shanmugam, AR.Veerappan,2013, Experimental Study

on Solar Parabolic Dish Thermoelectric Generator, International Journal of

Energy Engineering (IJEE) Jun., 3, PP. 62-66

[7] Babu.Uppalapati, Design and Anlysis of Modified Hybrid Solar System

Using Nano Fluids. International Journal of Design and Manufacturing

Technology, 6(2), 2015, pp. 14-18.

[8] Mahendra Pratap Singh and Dr. Anil Kumar Sharma, Eyes Detection Using

Morphological Image Processing Through Matlab. International Journal of

Advanced Research in Engineering and Technology, 4(7), 2013, pp. 139-146.

[9] Maria Theresa de Leon, Harold Chong, and Michael Kraft, 2012, Design and

Modeling of SOI-based solar thermoelectric generators, Procedia

Engineering, 47, pp. 76 – 79.