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Performance analysis of a solar photovoltaic operated domestic refrigerator


Applied Energy 86 (2009) 2583–2591

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Applied Energy
journal homepage: www.elsevier.com/locate/apenergy

Performance analysis of a solar photovoltaic operated domestic refrigerator
Anish Modi, Anirban Chaudhuri, Bhavesh Vijay, Jyotirmay Mathur *
Mechanical Engineering Department, Malaviya National Institute of Technology (MNIT), Jaipur 302 017, India

a r t i c l e

i n f o

a b s t r a c t
This paper describes the fabrication, experimentation and simulation stages of converting a 165 l domestic electric refrigerator to a solar powered one. A conventional domestic refrigerator was chosen for this purpose and was redesigned by adding battery bank, inverter and transformer, and powered by solar photovoltaic (SPV) panels. Various performance tests were carried out to study the performance of the system. The coefcient of performance (COP) was observed to decrease with time from morning to afternoon and a maximum COP of 2.102 was observed at 7 AM. Simulations regarding economic feasibility of the system for the climatic conditions of Jaipur city (India) were also carried out using RETScreen 4. It was observed that the system can only be economically viable with carbon trading option taken into account, and an initial subsidy or a reduction in the component costs – mainly SPV panels and battery bank. 2009 Elsevier Ltd. All rights reserved.

Article history: Received 11 September 2008 Received in revised form 16 March 2009 Accepted 28 April 2009 Available online 23 May 2009 Keywords: Solar photovoltaic (SPV) Refrigeration Compression RETScreen Economic simulation

1. Introduction Global warming and general unavailability of important vaccines and medicines in rural and far-ung areas of developing nations due to lack of proper storage options are enough reasons to look into alternative options of technologies for the general dayto-day processes. One such process, the most widely used and generally the most energy consuming, is refrigeration. As per WHO guidelines, the refrigerator used for standard vaccine load shall not exceed the temperature range of 0–8 °C [1]. Reduction of energy consumption for refrigeration cannot be relied solely on the improvement of efciency of current techniques. It is equally important to develop new systems and processes that take into account the variation in cooling demand so as to minimize energy wastage. Considering the fact that the cooling demand increases with the intensity of solar radiation, solar refrigeration has been considered a logical solution [2]. Also, because there are innumerable places in the developing countries where the power supply is still intermittent and irregular, for the storage of vaccines and life saving drugs in such areas, refrigeration systems based on usage of solar energy can be considered to be the optimal solutions. Secondly, the electricity supplied is mainly from conventional fuel based power plants which are the greatest contributors to global warming. The fuels used are also limited in availability. Consequently, researchers and technologists all around the world are actively involved in the development of

* Corresponding author. Tel./fax: +91 141 2529061. E-mail address: jyotirmay.mathur@gmail.com (J. Mathur). 0306-2619/$ - see front matter 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2009.04.037

renewable, non-exhaustible and environment friendly sources of energy, solar energy being one of them. Various solar technologies available with us today can be broadly classied into two parts: solar thermal and solar electric. Out of these, SPV systems from the solar electric family have found widespread application because they are simple, compact and have high power-to weight ratio. Also, the SPV system has no moving parts and in the eld, SPV systems require only modest amount of skilled labour to install and maintain, making them well suited for village power systems. In order to supply the required power, the arrays should be capable of producing sufcient current and voltage to run the applications, and it can be connected in series and in parallel to obtain the desired voltage and current, respectively [3]. Kim and Ferreira [2] have provided with a broad overview of the various technologies available to use solar energy for refrigeration purposes which include the solar electric, thermo-mechanical, sorption and also some newly emerging technologies. They have also compared the potential of these different technologies in delivering competitive sustainable solutions. Enibe [4] has discussed the possibility of using photovoltaic powered vapour compression systems; continuous and intermittent liquid or solid absorption system and adsorption systems for refrigeration purpose in rural or remote locations of developing countries, and concluded that with probable increase in the costs of conventional energy sources, solar cooling technologies are expected to become competitive with the conventional systems in future. Various other researchers have shown the importance of using SPV systems and proper modelling approaches for sustainable development in energy systems. Li et al. [5] have conducted tests

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to study the thermal and visual properties; energy performance and nancial issues of semi-transparent photovoltaic and generating electricity so as to cut down the electric lighting and cooling energy requirements to benet the environment, energy and economic aspects. They have observed a simple monetary pay-back of around 15 years and a good amount of reduction in greenhouse gases emissions. Kannan et al. [6] have emphasized on the modelling approaches needed for meeting the target of reduction in carbon-dioxide emissions and have performed MARKAL modelling of the UK residential sector under long-term decarbonisation scenarios. Kattakayam et al. presented the electrical characteristics of a 100 W AC operated domestic refrigerator using R-12 powered by a eld of SPV panels, a battery bank and an inverter. A minimum current region was observed in the mains voltage range of 180– 190 V and at the inverter voltage range of 210–230 V. The refrigerator was then started on a high voltage (about 230–250 V) with the inverter mode to complete the transient quickly so that the thermal overload relay of the compressor does not trip. A 25–30% saving in energy consumption without sacricing the temperature proles inside the refrigerator was made possible with this scheme [7]. With an uninterrupted supply refrigeration unit powered by a eld of SPV panels backed up by a petrol run generator, they observed no difference in the cool-down and warm-up of the cabinet, whether operated with mains or the inverter, and at the same time, the increase in the cycle time in the inverter operation resulted in considerable energy saving making a back up of 3.7 days possible with the battery bank [8]. Tests were performed by Kattakayam et al. to develop the cool down, warm up, steady state and ice making characteristics of the fridge and to calculate the COP, and the inuence of opening the door of the refrigerator on its thermal performance when powered by an inverter [9]. They also presented the characterization of a lead acid battery system as a component of the above system, and the calculation method for the battery bank capacity [10]. Kaplanis et al. [11] describe the design and development stages to convert a domestic refrigerator to a solar powered one where they elaborate the various factors affecting the sizing of the system, the procedure of sizing and the various modications made to decrease the heat losses. Cherif et al. [12] presented the performances, the simulation responses and the dynamic behaviour of a PV refrigeration plant using latent storage where they use a new storage strategy of stand alone PV plants which substitutes the battery storage with thermal, eutectic, latent or a hydraulic storage. Systems using same principle have also been tested for cold storage of potatoes by Eltawil et al. [3], and milk cooling by De Blas et al. [13]. Khelfaoui et al. [14] performed simulation of the thermal part of the system using SIMULINK for the application of the system for preservation of perishable products in the isolated sanitary center. Bakos et al. [15] have performed and presented the techno-economic assessment of an autonomous PV/diesel hybrid system installed in a bungalow for its use as low-cost electrication option at a tourist resort in Greece. They have used RETScreen as their nancial analysis tool and have presented its results for the case study of the system installed at Elounda, Greece in this paper. In this study, an already existing refrigerator has been extended to work using solar photovoltaic power. On successfully recording the performance through various tests and physically recording the SPV panel capacity and battery bank capacity; economic analysis has been carried out using RETScreen-4 software to nd the conditions under which such system would be technically as well as nancially feasible. This study is performed to evaluate the possibility of using old refrigerators for specic rural applications in areas where there is ample availability of solar energy so as to develop an independent system which is both environment-friendly

and free from the dependency on usage of grid electricity and fossil fuels.

2. System description For the study, an old domestic refrigerator (165 l capacity) with the condenser tubes at the back and the compressor placed at the bottom is used. The refrigerant used in the system is R-134a, the eco-friendly refrigerant most commonly used nowadays. The refrigerator cabinet is divided into three zones – the freezer cabinet (top), the crisper tray (middle) and the lower compartment (bottom). The compressor is placed below the condenser tubes and is visible from the back side of the refrigerator. The rated power of the compressor is 110 W and it runs on 50 Hz electricity. The acceptable voltage range for the compressor is 160–250 V. The rated running current is 0.95 A. The thermostat used in the system has markings from 0 to 9 on its control knob: 0 for switching off, and 1–9 for setting up the cutoff temperature at 2 °C to 18 °C in the freezer compartment respectively. The thermostat also had a defrost switch. Four 35 Wp SPV panels were used to convert the solar energy into electrical energy. The specications [16] of the SPV panels are mentioned in Appendix A. The panels are arranged in the following manner: a set of two panels in series – in parallel with – another set of two panels in series. The purpose of this arrangement was to have sufcient potential difference across the 24 V battery bank so that it gets properly charged. One panel could only give a maximum potential of 21 V (open-circuit), hence two panels in series. A similar set was added in parallel to have sufcient charging current. The panels were kept at 45° angle from the horizontal, facing south direction. To provide back-up in the times of no or low solar intensity, a battery bank is used. It consists of two 12 V–135 A h lead-acid batteries connected in series. The battery bank is connected to the compressor via the inverter-transformer system which is used to convert the DC current from the SPV system or the battery bank to AC current at required frequency and voltage to run the compressor. A charge controller, having six terminals – one positive–negative terminal pair for connection to SPV panels, one for battery bank and one for load, and a battery protection circuit are also used to regulate the ow of charge and to protect the battery bank from getting overcharged or getting deep discharged. The SPV panels and the battery bank are connected to the charge controller, but the load is directly connected to the battery terminals. This is to protect the charge controller from getting burnt because of the high initial current during the compressor start-up. The charge controller also helps in stepping down the high voltage from the SPV panel to an appropriate value for charging the battery bank. The need for a separate battery protection circuit arose from the fact that the load was directly taken from the battery bank and hence the charge controller could not protect the battery bank from getting deep-discharged. This circuit had two sub-circuits: the battery overcharging protection sub-circuit or the over-voltage (OV) sub-circuit, and the battery deep-discharging protection circuit or the under-voltage (UV) sub-circuit. Both the sub-circuits take the battery terminal voltage as their cut-off reference and their values for cut-off can be independently set. These values are currently set at 23.5 V for UV protection and 28 V for OV protection. The rst sub-circuit consists of a DC relay that cuts off the charging circuit at the preset voltage to prevent the battery bank from getting overcharged. This is connected in series in the charging circuit of the system, i.e. the SPV panel–battery bank circuit. The second sub-circuit consists of an AC relay which is

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SPV Panel Array 4 x 35 W

Inverter Plate

Transformer

Battery OV Protection Sub-circuit

Thermostat

Charge Controller

Battery UV Protection Sub-circuit

Refrigerator Compressor Battery Bank

(a)

Fig. 1. (a) Block diagram of the system. The dark and the dashed lines represent DC and AC ow, respectively. (b) Schematic representation showing the major components of the refrigerator used in the study.

connected in series in the discharging circuit of the system, i.e. between the transformer and the compressor. This is used to cut-off the supply from the battery bank in case the battery bank’s terminal voltage dips to the preset value to protect it from getting deepdischarged. Along with these sub-circuits, a reset button is also present in the circuit so that once any of the circuits are cut off; they do not get restarted because of the uctuation of the reference terminal voltage between the in-circuit and the open-circuit voltage, i.e., once a circuit is cut-off, it can only be switched on by the user by pressing the reset button to return to the normal operating state so as to protect the battery bank from getting damaged. Wires of different cross-sectional areas were used in the system at different places. Ten mm2 wires were used to connect the load to

SPV 1

SPV 2

SPV 3

SPV 4

Fig. 2. Schematic showing arrangement of solar panels.

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the battery because of the high initial current of nearly 45 A DC from the battery. Similarly, for reducing the losses in wires connecting the SPV panel and the charge controller, 1.5 mm2 wires were used. The increase in the diameter is only limited by the economics of the system. Fig. 1a shows the block diagram for arrangement of the complete system, Fig. 1b shows the refrigerator schematic with location of the major components and Fig. 2 illustrates the arrangement of the SPV panels.

7. No external heating or cooling was provided for the system during experimentation.

4. Observations and analysis The following plots of the various observed and calculated parameters give us an idea about the technical performance of the system.

3. Performance tests Experimentation was carried out to analyse the performance of the fabricated system by measuring various related parameters under different operating conditions. Trends of all the parameters were then studied through their respective plots. 3.1. Experiments performed The following three experiments were performed: 1. Normal running of the refrigerator was observed under extreme conditions as the temperature inside the room reached around 42 °C due to hot atmospheric conditions. This experiment was performed with the solar panels connected to the system and current drawn from the panels consumed by the load (battery/compressor). 2. Pull down and steady state tests at ideal ambient conditions were performed. This time, only the battery bank was used to run the refrigerator. This was done to check the refrigerator performance in better ambient conditions as well as the battery bank’s back-up capacity. 3. Warm-up test was performed on the refrigerator. The refrigerator was switched off and allowed to reach near-ambient conditions while the observations were taken. 4. Other performance tests have not been carried out due to absence of standard test set-up for conducting energy performance test. However, the three tests conducted cover variety of situations to which the solar refrigerator is likely to face. Hence, results are sufcient enough for highlighting the usefulness of the development.
820

Solar Radiation Sin Curve Trendline

Solar Intensity (W/sq mt)

800 780 760 740 720 700 680 11:00 11:20 11:40 12:00 12:20 12:40 13:00 820 13:00

Time
Fig. 3. Variation in intensity of solar radiation with time.

Current From SPV Panels Current From Charge Controller

3.9

Current (A)

3.8 3.7 3.6 3.5 3.4 11:00 11:20 11:40 12:00 12:20 780 12:40 800

3.2. Experimental conditions The conditions maintained during the course of all the tests are specied below: 1. The refrigerator and other equipments were kept in a room with all sides made of PVC sheets and other insulating materials. All the walls of the room except the bottom were exposed to sun from the outside. 2. The solar panels were kept at a place where there was no shade throughout the day, at an angle of 45° to the horizontal facing south direction. 3. The thermostat position was set at no. 2, i.e., the freezer temperature goes till 4 °C before the compressor is automatically cut-off by the thermostat. 4. The panels were always kept dust free to take advantage of maximum possible solar insolation that can be gathered by the panels. 5. No external load was kept inside the refrigerator during the experimentation. 6. The door of the refrigerator was kept closed while the tests were being performed.

Time
Fig. 4. Variation of charging current with time.

Current From SPV Panels Current From Charge Controller

3.9 3.8

Current (A)

3.7 3.6 3.5 3.4 720

740

760

Solar Intensity (W/sq mt)
Fig. 5. Variation of charging current with intensity of solar radiation.

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4.1. Normal running test with power from both SPV and battery bank The values of solar radiation intensity when plotted against time in Fig. 3 closely follow a sine curve. This is in accordance with the accepted fact that during a day variation of solar radiation intensity with time is a sinusoidal function.

1.2

Current (A)

1 0.8 0.6 0.4 0.2 0 11:00 11:20 11:40 12:00 12:20 12:40 13:00

Time
Fig. 6. Variation of compressor running current (AC) with time.

Voltage on Charge Controller - SPV Terminal Voltage on Charge Controller - Battery Terminal Battery TerminalVoltage (Cut-off Ref.)

26

25

24

Fig. 4 above shows the drop in the value of charging current in the charge controller. It can be observed that the current curves follow the solar intensity curve very closely. Fig. 5 helps us in relating the charging DC current to the system with the solar radiation intensity available. This graph shows an increasing trend for the current with the solar radiation. The drop in current in the charge controller is more or less equal to 0.08 A at all times. The continuous gap between the two curves denotes the constant energy loss in the charge controller. A similar gap can be observed in Figs. 3, 4 and 7. The maximum value of the charging current attained from the SPV panels during the study period is 3.87 A at 813 W/m2 of solar radiation. From Fig. 6, it is observed that the running current to the compressor is almost constant nearing 0.9 A. However, the starting current went up to as high as 3.68 A. Thus, however, the running current is very less as compared to the starting current, the system wires and components need to be designed as per the starting parameter values, thereby increasing the initial cost. As can be observed from Fig. 8, all the refrigerator temperatures are going down continuously which means that there was no cutoff of the compressor during this test. This occurred because the refrigerator was operating in a very high ambient temperature causing the evaporator temperature never actually reaching the set cut-off point which was 4 °C at the thermostat position 2. Because there was no tripping of the compressor, the compressor worked continuously for two hours in this test which raised the compressor body maximum temperature to 89.9 °C which is very high as compared to its general operational value (Fig. 9). Fig. 10 shows that the refrigerating effect is almost constant for a particular amount of work input which itself is approximately constant in value throughout the test. This is because of using a constant rpm compressor. It is conrmed from Fig. 11 that the COP of the system goes down as the system approaches the hottest time of the day. This is in accordance with the ndings of Eltawil et al. [3]. 4.2. Pull down test and normal running test with power from battery bank only Fig. 12 shows that the compressor tripped three times during this test. This time because of the better ambient operating conditions, the compressor performed as its normal behaviour of on–off cycle.

Voltage (V)

23 11:00 11:10 11:20 11:30 11:40 11:50 12:00 12:10 12:20 12:30 12:40 12:50 13:00

Time
Fig. 7. Variation of voltages at various terminals with time.

Freezer Temp. Crisper Temp. Compartment Temp. Ambient Temp.

Ambient Temp. Compressor Body Maximum Temp.

50

90

Temperature (C)

Temperature (C)

40 30 20 10 0 11:00 11:20 11:40 12:00 12:20 12:40 13:00

80 70 60 50 40 30 11:00 11:20 11:40 12:00 12:20 12:40 13:00

Time
Fig. 8. Variation of temperatures at different places with time as compared to the ambient temperature.

Time
Fig. 9. Variation of compressor body maximum temperature with time as compared to the ambient temperature.

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Figs. 13 and 14 both show a similar trend as Fig. 12. In Fig. 13, the voltage across the battery terminals is observed to rise during the cut-off period as the in-circuit battery terminal voltage during discharge cycle is always lesser than the battery terminal voltage when the battery circuit is cut-off.

120 100 80 60 40 20 0 11:00 11:20 11:40 12:00

RE WI

Time
Fig. 10. Variation of refrigerating effect (RE) and work input (WI) with time.

Similarly, in Fig. 14, the temperatures are observed to fall when the compressor is running, and rise during the cut-off period. The compressor body temperature is an important parameter towards knowing the performance characteristics of the refrigerator because the higher it is, the higher will be the temperature of the refrigerant leaving the compressor and entering the condenser, the higher will be the absolute temperature of the refrigerant at condenser outlet (assuming the temperature drop in the condenser to be almost consistent), the higher will be the overall temperatures at all the places in the refrigeration circuit which will ultimately result in much lesser refrigerating effect. Here, the compressor body gets time to cool down during the cut-off of the compressor as shown in Fig. 15 enhancing the overall performance of the system. Fig. 16. A maximum COP of 2.102 and pull down time of 40 min were observed for the system during this test. This time too the values of COP keep on decreasing as we approach the noon. The zero values of COP in Fig. 17 denote the cut-off of the compressor where both RE and WI assume zero values. At these points, the COP cannot be dened, hence represented by zero in the plot.

RE & WI (kJ / Kg)

12:20

12:40

13:00

1.8 1.7 1.6 1.5 1.4 11:00 11:20 11:40 12:00 12:20 12:40 13:00

07:00

07:20

07:40

08:00

08:20

08:40

09:00

09:20

09:40
09:40 10:00

Time
Fig. 11. Variation of coefcient of performance (COP) with time.

Time
Fig. 14. Variation of various refrigerators temperatures with time as compared to the ambient temperature.

1.2 1 0.8 0.6 0.4 0.2 0 07:00 07:20 07:40 08:00 08:20 08:40 09:00 09:20 09:40 10:00

Current (A)

Ambient Temp. Compressor Body Maximum Temp.

80

Fig. 12. Variation of compressor running current (AC) with time.

Temperature (C)

Time

60

40

25

Voltage (V)

20

24 23 22 07:00 07:20 07:40 08:00 08:20 08:40 09:00 09:20 09:40 10:00
0 07:00 07:20 07:40 08:00 08:20 08:40 09:00 09:20

Time
Fig. 13. Variation of battery terminal voltage (cut-off reference) with time.

Time
Fig. 15. Variation of compressor body maximum temperature with time as compared to the ambient temperature.

10:00

40 35 30 25 20 15 10 5 0 -5 -10

Freezer Temp. Crisper Temp. Compartment Temp. Ambient Temp.

Temperature (C)

COP

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140

RE WI

Ambient Temp. Compressor Body Maximum Temp.

RE & WI (kJ / Kg)

120

80

Temperature (°C)
07:00 07:20 07:40 08:00 08:20 08:40 09:00 09:20 09:40 10:00

100 80 60 40 20 0

60 40 20 0 10:10 10:20 10:30 10:40 10:50 11:00 11:10

Time
Fig. 16. Variation of refrigerating effect (RE) and work input (WI) with time.

Time
Fig. 19. Variation of compressor body maximum temperature with time as compared to the ambient temperature.

2.5 2

COP

1.5 1 0.5 0 07:00 07:20 07:40 08:00 08:20 08:40 09:00 09:20 09:40 10:00

5. Economic simulation using RETScreen For economic simulation of the system developed and experimented, an MS Excel based clean energy project analysis software called RETScreen 4 was used. It allows us to simulate any clean energy project and based on the provided data, compares the base case, i.e., the case of current usage with the proposed case, i.e., the case regarding the future usage of energy [17–18]. In our study the base case is the usage of grid electricity for running the 165 l domestic refrigerator, and the proposed case is to make this refrigerator run completely on solar energy, independent of the grid supply. Following are the different sheets of RETScreen analysis software used in this study: 1. Start sheet: In this sheet, the following inputs are given: the project title and other details about the project, the project location so that the climate data location can be xed, the project type, the technology type, the reference heating value, the analysis type, the currency units, language, and the measurement units. 2. Energy model sheet: In this sheet, the details regarding the base case and the proposed case are provided. In this study, the inputs provided for the base case are: type of energy resource for the base case, cost of consumption, value and type of load. For the proposed case, the inputs provided are: details related to inverter, battery, SPV panels and peak load power system, if any. As output, this sheet provides the annual expenditure for the base case, the percentage of energy saved when shifting to the proposed case, the size of the battery bank and the SPV panel array depending upon the various efciencies and other parameters. 3. Cost analysis sheet: This sheet takes all the inputs regarding the cost of the system: the initial, recurring and the periodic costs. It also allows the user to put the credit gures for the costs that are not paid in cash. 4. Emission analysis sheet: This sheet takes the greenhouse gas (GHG) emission factors, and Transmission and Distribution loss percentage as its input. It also allows inputting any GHG transaction fees for carbon trading. As output, this sheet shows that by opting to go for the proposed system, how many tonnes of GHG can be saved annually. 5. Financial analysis sheet: This sheet allows inputting all the data related to the nancial analysis of the proposed system. This include the ination rate, the fuel escalation rate, the discount rate, the GHG trading rate, initial incentives or grants, and any

Time
Fig. 17. Variation of coefcient of performance (COP) with time. The zero values of COP actually show the switching off of the compressor by the thermostat.

4.3. Warm-up test In Fig. 18, the temperatures inside all the three zones of the refrigerator are observed to stabilize to a common value nearing the ambient temperature. Similarly, from Fig. 19, the compressor body temperature is also observed to reach a value nearing the ambient temperature. The warm-up tests showed that the freezer temperature rose from 4 °C to 28 °C within one hour which suggests that either the insulation need to be improved or the ambient operating conditions be improved.

50

Freezer Temp. Crisper Temp. Compartment Temp. Ambient Temp.

Temperature (C)

40 30 20 10 0 10:10 10:20 10:30 10:40 10:50 11:00 -10 11:10

Time
Fig. 18. Variation of various refrigerators temperatures with time as compared to the ambient temperature.

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source of income through the proposed system. As output, this sheet provides the yearly cash ow table and graph which are helpful in calculating the pay-back period. This sheet also gives the value of IRR, NPV, annual life cycle savings, benet–cost ratio and other such parameters. In this study, the simulations were carried out for the climate conditions of Jaipur city (India). Table 1 shows the input parameters for the study, and variations considered for doing the sensitivity analysis. Other major assumptions and input values are: 1. The compressor is assumed to run for 15 h/day, 7 days/week throughout the year. 2. Life of SPV panels is considered as 24 years, same has been taken as project life. Life of the battery bank is considered as 5 years. 3. Battery bank and inverter efciencies are taken to be 80% and 90%, respectively. 4. The ‘system overhaul expense’ includes the overhauling cost of the additional components of the proposed case power system, viz., the inverter plate, transformer, additional wiring, etc. 5. The GHG reduction credit duration is taken as 21 years because it is the maximum duration for which a Clean Development Mechanism (CDM) project is allowed to sell carbon credits as per the current norms. It is assumed that the project gets cleared at all the renewal times. 6. The GHG reduction credit rate is taken as Rs. 750/- per tonne of CO2 and the annual average rate of increase in this rate over the project life is assumed to be 2%. 7. Both the ination rate and the fuel cost escalation rate are taken as 7%. 8. The GHG emission factor is taken as 0.927 for India. 9. Climatic data for Jaipur/Sanganer in India is chosen for the analysis. 10. All monetary calculations are represented in Indian Rupees. 11. Load is kept same for both the base and the proposed cases, equal to the compressor rating. 12. Maximum depth of discharge for the battery bank is assumed to be 65%. 13. The initial cost of the additional components, i.e., the inverter, the transformer, the connecting wires etc. are assumed to be Rs. 2500/-.

On the basis of nancial pay-back period, the results obtained from the simulations can be summarized as: 1. The system is not economically viable without carbon trading option taken into account, and the initial incentive or Government subsidy. 2. The system congurations with 180 A h capacity battery bank are not economically viable as their pay-back periods exceed the project life. 3. The system conguration with the best pay-back period among the simulated cases consists of 140 Wp panel array and 135 A h capacity battery bank with 50% initial subsidy. The pay-back period is 18.2 years for equity pay-back. Also, the pay-back period for this combination remains lesser than the project life only if there is an initial subsidy of at least 15%. 4. The system can be made economically attractive with pay-back period less than 4 years only if the prices of the individual components, esp. SPV panels and the battery bank are reduced; or the Government increases the subsidy on the system to at least 70% for the 140 Wp–135 A h system, and to at least 85% for the 300 Wp–180 A h system.

6. Conclusions It is technically feasible to convert an existing 165 l refrigerator to photovoltaic refrigerator. Under normal operating conditions, the modied refrigerator performed similar to a conventional domestic refrigerator working on grid electricity. The normal running test and pull down test indicate that 140 Wp photovoltaic capacity and two 12 V–135 A h battery bank is the least possible conguration required for this converted system to work properly under normal ambient conditions. However, for a sustainable system, larger PV module capacity or larger battery bank are required which currently make the system economically unviable because of their high initial cost. The RETScreen simulations show that system is not economically viable without the initial nancial incentive or Government subsidy, or an appreciable reduction in the costlier component costs. A minimum initial subsidy of 15% is required to bring the nancial pay-back period of the current system within the assumed project life, i.e., 24 years. Further, to bring the pay-back period to an attractive gure, a subsidy of at least 70% is required. The warm up test indicates that the heat gain through the jacket needs to be reduced by use of more insulation material, for improving technical and nancial performance of SPV refrigerator. The system under test was able to maintain a temperature (in its freezer compartment) as specied by the WHO for vaccine preservation (0–8 °C). Thus, if the system is particularly developed further for vaccine preservation or similar specic purposes, it could prove to be a vital environment-friendly development step.

Table 1 Various input parameters analysed through RETScreen simulations. Parameter Value in base case – – – – – – Lowest value analysed in proposed case 140 Wp Rs. 200/Wp 135 A h Rs. 12,000/10% Rs. 1500/Highest value analysed in proposed case 300 Wp Rs. 200/Wp 185 A h Rs. 15,000/50% Rs. 1500/Other values analysed in proposed case 200 Wp – – – 20%, 30%, 40% –

SPV panels capacity Cost of SPV panels Battery bank capacity Cost of battery bank Initial subsidy System overhaul expense after 13 years Cost of grid electricity

Appendix A Each of the SPV panels used has the following specications: Make and type REIL, mono-crystalline silicon Rated capacity 35 WP Short circuit current (Isc) 2.4 A 21 V Open circuit voltage (Voc) 2.13 A Maximum power current (Imax) 16.4 V Maximum power voltage (Vmax)

Rs. 4/ kW h

Rs. 4/kW h

Rs. 4/kW h



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