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Techno-economic analysis of a solar thermoelectric power generator for a rural residential house energy demand.

Introduction

In recent years, accelerated consumption of electricity and with supply of conventional fuel shortfall and poor grid infrastructure in rural areas are reasons to access reliable energy at rural site. The solar energy is expected to be foundation of sustainable energy economy and availability is abundant in developing countries (Zekai Sen; 2000). The thermoelectric power conversion technologies are identified as good aspirant; it is the hot research topic in USA, Japan and European countries. (H. Glosch et al., 1999)

Application of thermoelectric generator for power generation is combining with solar thermal system is attracting the user due to its modular in size, silent in operation and no working fluid. The system can provide electricity in affordable cost to a rural house energy demand, provided a reasonable solar resource site is available. But to provide the assurance that demand can be met during lengthened periods of non availability of solar resource through separate storage or by using fossil fuel to operate it.

The consistency of solar thermoelectric energy system to meet an energy demand can be provided by properly sized solar parabolic dish collector, thermoelectric generator, storage battery and auxiliary source. In most climates, auxiliary energy is needed to provide high reliability and avoid gross over design of the solar system. The value of the solar energy can be obtained by analyzing the savings on conventional grid power and by analyzing the external benefits (Van Wijk et al., 1991). The determination of the external benefits of solar energy can be done by estimating environmental and economic of conventional electricity production from conventional power plant. The environmental charges are damage for the plants, animals, mankind, materials and climate change.

In this paper, techno-economic analysis of standalone solar parabolic dish thermoelectric generator will made to meet electrical energy demand for a rural habitation.

Technology of STEPG System

The STEPG can provide electricity at an acceptably low cost in rural part of developing countries, provided reasonable solar resources available. But to provide the certainty that demand can be met during prolonged periods of non availability of solar radiation, other available energy source can be used to drive thermoelectric generator. The stability of thermoelectric generator has found as 100000 hours under steady state operations. Thermoelectric generator module ( Module :TEP1-12656- 0.6) made of bismuth telluride alloys from Thermonamic (Xiamen) Ltd, China make parameters is used in this analysis. No. of thermocouples presented in module is 127.

Specification of thermoelectric module

Geometry size 56 x 56 x 4.4 mm

Maximum temperature at hot side 280[degrees]C

Maximum temperature at cold side 160[degrees]C

During the thermal cycle load hot side temperature may go up to 380[degrees]C intermittently.

Thermal and electrical performances of module are given for temperature difference of 200[degrees]C (Hot side 230[degrees]C and Cold side 30[degrees]C). It is planned to use ten units of such system.

Heat input 350 Watt

Match load electrical output power 14.7 W

Match load current 3.5 A

Match load voltage 4.2 V

Open circuit voltage 8.2 V

The proposed ten thermoelectric modules are sandwiched in aluminum flat plates where one side of plate act as hot side and other as cold side. The aluminum plate have square in geometry and side of 0.3 m and thickness of 0.002 m. The hot side aluminum plate is coated with matt black paint (non selective absorber) to absorb the concentrated solar radiation. The cold side of aluminum plate is attached with a plate heat exchanger. Water cooled system selected due to its more heat transfer coefficient compared to air and develops maximum temperature difference between hot and cold side of aluminum plates (J.Esarte et al.;2001) for better performance of STEPG. The solar parabolic dish concentrator can be fabricate with an old satellite dish antenna made of aluminum with polished anodized aluminum sheet as reflector fixed on the rib using fitting accessories. The stability of the aluminum sheet depends on it reflectivity and has found as 18 years in the literature 18 years with reduction of 50% reflectivity (Maria Brogren; 2004). The design specification of solar dish concentrator are aperture diameter 2.53 m, rim angle 69[degrees], height of collector at optical axis of dish concentrator is 0.6 m and focal length 0.7m. Thermoelectric generator modules are mounted on the focal point where the concentrated solar radiation striking its hot side.

STEPG is supported steel pipe support in cement concrete on a roof top of Department of Mechanical Engineering building, National Institute of Technology, Trichirappalli, India (Latitude 10.36[degrees]N and Longitude 78.43[degrees]E). The structure contains stepper motor to track the dish for hour angle variation of sun and declination position of sun adjusted by manually using screw mechanism to make axis of parabolic dish concentrator always parallel to solar radiation for getting maximum solar concentration ratio. The STEPG setup can observe the operating parameters solar irradiation, wind speed, hot side and cold side of thermoelectric generator and ambient temperature.

The schematic diagram of STEPG is shown Fig. 1. The solar radiation is the input to the system. The hot side of thermoelectric modules are positioned its focal point and normal to optical axis of dish.

[FIGURE 1 OMITTED]

The block diagram of STEPG is shown in Fig. 2. The concentrated solar radiation flux absorbed at receiver is [Q.sub.S] after reflection and misalignment losses. The receiver is delivering [Q.sub.H] to the hot side of thermoelectric generator after convection and radiation losses in receiver to activate it. The heat rejected by circulating water in plate heat exchanger [Q.sub.L]. The output power from the thermoelectric generator is [P.sub.O] and electrical load is connected via battery and inverter after some storage losses under realistic condition. Under real condition by considering the irreversibility of process and system it is

[Q.sub.S]>[Q.sub.H]>[Q.sub.L] and [P.sub.o]>[P.sub.L] (1)

[FIGURE 2 OMITTED]

Economic Assessment

Any equipment becomes attractive if it becomes economically viable. Research and development helps to improve its economic performance. The cost of any energy conversion equipment includes all the hardware items and involvement of labour in installing the equipment plus the operating expenses. Factors which need to be taken into account include interest on money borrowed, property and taxes, resale value of equipment, maintenance, insurance, fuel and other operating expenses (John A. Duffie & WA. Beckman 1991; Kreider JF et al. 1989). The standalone solar saving is difference between the cost of grid energy saved and maintenance cost for solar system.

The simple techno-economic model can be used for preliminary evaluation of the technical and financial viability of any standalone energy system and it shown in Fig.3. (RET screen. 2000)

[FIGURE 3 OMITTED]

Energy analysis: The basic information concerning annual average solar radiation, wind speed and ambient temperature and the system technical details to be known. Also the local electric utility, such as the demanded peak electrical load and annual energy consumption in order to estimate the amount of energy coming from grid supply that the energy system will be able replace.

Cost analysis: A detailed cost analysis is performed taking into account the initial costs and annual costs involved in the proposed energy project. Initial cost includes feasibility study, design and development, installation and training. The annual cost includes maintenance cost and interest on loan

Financial analysis: This analysis to be made with energy balance, financial parameters, project cost and savings and financial feasibility ad yearly cash flow.

The following financial terms are generally used in an economic assessment of any project: Internal Rate-of-Return (IRR), Net Present Value (NPV), Pay-Back Period (PBP)

The internal rate-of-return (IRR) represents the true interest yield provided by the project over its life. It is also referred to as the return-on-investment (ROI) or the time-adjusted rate-of-return. It is calculated by finding the discount rate that causes the net present value of the project to be equal to zero. If the IRR of the project is equal to or greater than the required rate-of-return of the investor, then the project will likely be considered acceptable. If it is less, then the project is typically rejected.

Under the net present value (NPV) method, the present value of all cash inflows is compared against the present value of all cash outflows associated with the investment project. The difference between the present values of these cash flows, called the NPV, determines whether or not the project is generally an acceptable investment. Positive NPV values are an indicator of a potentially feasible project.

The Pay Back Period (PBP) represents the length of time that it takes for an investment project to get back its own initial cost, out of the cash receipts it generates. This index is great importance to private owners or smaller firms that may be cash poor. The Net Present Value of solar system can calculate from the following expression (S.P.Sukatame; 1999)

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

The income tax rate and subsidy rate are not included in this analysis.

Results and Discussion

The typical rural residential energy demand was considered with the following assumption to develop STEPG Specifications with available solar radiation data at site. The electrical appliance operated only in night time between times 6 P.M. to 10 P.M. on each day in year. The operating hours CFL capacity of 14 W in two numbers for four hour per day, Radio/TV capacity of 70 W is two hour day, A ceiling fan capacity of 20 W is 4 hours. It requires 580 W-h electricity per day. The annual energy demand for a house is mentioned in Table I. The thermoelectric generator conversion efficiency of 5% and conversion efficiency of solar dish concentrator is 70% are considered for this analysis. Annual average solar radiation at site of installation is considered as 5.5kWh/[m.sup.2] day. The solar dish concentrator surface area estimated as 5.2 [m.sup.2]. Two lead acid batteries of 24 V DC and 75 Ah nominal capacities are used for electricity storage and their efficiency is 90%. The capacity of battery is selected for three days backup

The available solar radiation at the proposed site is estimated from taken from report (M.Eswaramoorthy and S. Shanmugam; 2009), the estimated useful annual electrical energy production from STEPG is given in Table. II.

The solar energy system provides an annual energy output of 321 kWh, which is 100% of the total annual energy demand for two rural dwelling energy demand of 248 kWh.

The purchase cost of the dish concentrator from the scrap yard was INR5000/- and the cost of the reformation and conditioning process was INR2000/- were taken as local market rate and it vary from place to place. This process was necessary in order to bring the dish back to its initial shape and thus to achieve good optical properties and high stiffness. Initially the process involved stretching of the deformed areas of the dish and then careful scrapping and conditioning of the entire surface in order to ensure the successful attachment of anodized polished aluminum sheet of its cost around INR 1150/[m.sup.2], which is fairly cheap compared to the cost of other candidate materials such as glass mirror. The total cost estimate of the proposed system is shown in Table III. It ascertained that the cost of dish concentrator exceeds to INR 3076/[m.sup.2] (51 Euro/[m.sup.2]) which is very low compared to other point focus collector presented in the literature that reach up to 153 Euro/[m.sup.2] (N.D.Kausika and K.S.Reddy, 2000) and 86 Euro/[m.sup.2] (I. Palavras and G.C. Bakos,2006). The proposed standalone STEPG should meet the energy demands of rural house. The capital investment of INR70000/and the supply from conventional grid of 30 km away from the load, which is provided by state electric supply, is estimated at about INR30/kWh after taking into consideration distribution and loss parameters.

The cost of delivered electricity from the grid supply to various remote areas, located in a distance range of 5-25 km was found to vary from INR 230/ kWh to INR23/kWh [(M.R. Nouni et.al 2009) depending on peak electrical load and load factor. The higher energy delivery cost delivery is considered to evaluate payback period to show it potentiality to practice by user and to reduce the grid dependence.

[FIGURE 5 OMITTED]

To study its economic viability of present system made for financial scenarios of owner covers INR30000/- and Loan amount INR40000/- with interest of 5%, the delivered energy cost INR230 per kWh it increment rate of 2% and maintenance cost of INR 6000/- per year and its annual increment rate of 2% chosen to find its ROI factor using the equation no 2. The results were shown in Fig.3 in the form of chart. It shows the variation of the IIR and years. The higher the true interest provided by the investment over its life and the shorter the time that it takes for the owner to recoup the initial investment

In the financial analysis, it has been found the payback period of the system based on cost of energy delivered is one year and one month. This system will attract the government policy developer to provide such system in the rural part of India where electricity accessible is not feasible from the grid supply.

Conclusion

The standalone STPEG of technical and financial analysis is made based on available solar radiation data, designed specification of system and cost of delivered energy to site from the grid supply. The fabrication of solar dish from old dish antenna and polished aluminum sheet is considered here to reduce the overall cost collector. It is found that from the technical analysis based on annual data, the designed system is generates 321 kWh electricity with 147W capacity of thermoelectricity generator in 5.2 square meter aperture area of dish concentrator. The payback period for the system has found 1 year and 1 month based on cost of energy delivered at rural site. IRR Rate at 4% net present value becomes at 18 years. This paper will hope for energy researcher community to develop such technologies for helping the lives of rural people and saves their nations energy economy.
Nomenclatures

E- Annual energy generated by standalone solar system
[c.sub.e]- Unit cost of energy delivered by the grid to site
[i.sub.e]- Rate of increment of delivered energy cost
[i.sub.l]- Rate of interest for loan
[i.sub.m]- Rate of increment of maintenance cost
d- Market discount rate
[C.sub.l]- loan amount
[C.sub.i]- Initial down payment
[C.sub.m]- Annual maintenance cost


References

[1] H. Xi, L. Luo, Gilles Fraisse "Development and applications of solar based thermoelectric technologies" Renewable and Sustainable Energy Reviews, (2007) 11: 923-936.

[2] Van Wijk AJM, Turkenburg WC. The value of wind energy. In: Proceedings of 13th BWEA Wind Energy Conference, Swansea, 10-12 April 1991. p. 1-9.

[3] Duffie JA, Beckman WA. Solar engineering of thermal processes. USA: John Wiley & Sons; 1991.

[4] Kreider JF, Hoogendoorn CJ, Kreith F. Solar design: components, systems economics. USA: Hemisphere; 1989.

[5] RETScreen manual. Canada: Energy Diversification Research Laboratory (CEDRL), 2000.

[6] M.R. Nouni , S.C. Mullick , T.C. Kandpal "Providing electricity access to remote areas in India: Niche areas for decentralized electricity supply" Renewable Energy 34 (2009) 430-434

[7] Kaushika ND, Reddy KS. Performance of a low cost solar paraboloidal dish steam generating system. Energy Conv. Manage 2000;41(7):713-26.

[8] Palavras, G.C. Bakos Development of a low-cost dish solar concentrator and its application in zeolite desorption , Renewable Energy 31 (2006) 2422-2431

[9] S.P. Sukatame, Solar Energy Principle and Application of Thermal Energy Storage, 1999 , TataMcgra Hill- Publisher India

[10] H. Glosch, M. Ashauer, U. Pfeiffer , W. Lang "A thermoelectric converter for energy supply "Sensors and Actuators 74 (1999). 246-250

[11] J. Esarte, G. Min, D.M. Rowe "Modeling heat exchangers for thermoelectric generators" Journal of Power Sources 93 (2001) 72-76

[12] M. Eswaramoorthy and S. Shanmugam "A Feasibility study of solar thermoelectric generator" International Conference on Energy and Environment 2009 held at Chandigarh March 2009 by NIT Kurushestra.

[13] Maria Brogren Ph.D Thesis titled on "Optical efficiency of low concentrating solar energy system with parabolic reflectors" "ACTA UNIVERSITY OF UPPSALA, UPPSALA (2005)

[14] www.thermonamic.com

(1) M. Eswaramoorthy and (2) S. Shanmugam

(1) Research Scholar with Department of Mechanical Engineering, National Institute of Technology, Trichirappalli-620015, India E-mail:rmeswar@gmail.com.

(2) Professor of Department of Mechanical Engineering, National Institute of Technology, Trichirappalli-620015,India
Table I: Estimated Annual Energy Consumption.

Electrical appliances          Estimated kWh/year

CFL Lamp                       43.8
Radio/Telivision               29.2
Ceiling Fan                    51.1
Annual Energy Consumption      124.1kWh/year

Table II: Monthly useful Energy Production from STEPG.

Month                       Energy output kWh

January                     23.94
Febrary                     24.77
March                       28.60
April                       28.61
May                         28.81
June                        28.48
July                        28.01
August                      27.97
September                   27.89
October                     26.34
November                    24.32
December                    23.23
Annual Energy Production    321 kWh

Table III: Total cost solar dish concentrator.

Components of proposed solar dish     Value
system                                (INR)

Satellite dish antenna old unused     5000/-
Conditioning and reformation          2000/-
Reflector- polished anodized          6000/-
aluminum sheet
Support and structure material        3000/-
Miscellaneous                         4000/-
The cost of dish concentrator         20000/-
The cost of thermoelectric modules    50000/-
Total cost                            70000/-
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Article Details
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Author:Eswaramoorthy, M.; Shanmugam, S.
Publication:International Journal of Applied Engineering Research
Article Type:Report
Geographic Code:1USA
Date:Oct 1, 2009
Words:2936
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