Design and Analysis of a Grid Connected Photovoltaic Power System to Overcome the Energy Crisis in Pakistan

Transcription

1 Design and Analysis of a Grid Connected Photovoltaic Power System to Overcome the Energy Crisis in Pakistan Majid Ali 1 Hafiz Fuad Usman 1 Muhammad Sheraz Siddique 1 Muhammad Fahad Zia @umt.edu.pk Department of Informatics and Systems- School of Science and Technology, University of Management and Technology, Lahore Pakistan Abstract- In this research work analysis and design a scheme of photovoltaic power module to meet the energy demands of Pakistan. The Photovoltaic cells are the devices that are capable of converting photons energy of sunlight to an electrical direct current and voltage. Every country is dependent on energy demand and Pakistan is also under the crises of energy shortage due to which generally and economically, the life of every person is bothered. The best probable way out to this complications is use of static renewable energy resources i.e. solar energy, wind energy biogas etc. Enough amount of different energy has been considered in the literature appraisal. A reasonable and supportable solution to this problem is use of solar energy which is present with an average amount of 5.0 kwh/m2 in Pakistan. To grab the energy crises in Pakistan, solar energy based on Photovoltaic building block is deliberated in this exploration work. According to standard voltage and frequency of Pakistan, a MOSFET based inverter scheme is also designed to reverse this DC to AC. The proposed scheme has been modeled in the MATLAB 7.1 /Simulink software. A structure with energy storage will also be purposed to link Photo Voltaic Power module with utility Grid. This is well-meaningly discussed that PV Power modules have the maximum auspicious and reasonable result of energy crises of Pakistan. So, to meet the energy demand in the present-day condition of severe energy deficiency dominating in the country, solar energy is one of the existing resources in Pakistan which may use as substitute energy resource. Keyword- Utility Grid, Solar Panel, Inverter, Insolation, MPPT, MOSFET I. POWER MODULE PV cells provided the DC Current and Voltage from the conversion of photon energy coming from sunlight. When a photon strikes on the PV Cell, it transfer its energy to the photovoltaic substance or electron which in result pulls out of the binding atom. That free electron starts moving through the metallic contacts which develops the idea of the electricity generation. Comparing solar energy with the total demand of the Earth, the solar energy coming from the sun is more than 6000 times of total demand [1]. The basic PV circuit diagram is shown in fig. 1. Discussing about the constructive part of the Photovoltaic Module, it contains an absorber layer in which incident photos strikes and absorbed effectively and which results in increase of the energy of electrons residing in valence shell. These valence electrons after gaining energy from photons causes the flow which results in the form of Direct Current as shown in fig.1. Solar cell gives the very low voltage (about 0.5 v) [2] which continuously fed at a rate which is directly proportional to the amount of incident light. Further discussing about the PV module, it contains the number of series and parallel connections of solar cells to form a complete solar panel having a higher power (up to kv). This construction of solar panel from arrays and modules is shown in fig.2. Estimated that a clear day has a luminous power of about 1000 W/m 2 [3]. Fig. 01 Solar cell circuit diagram

2 The assembling of solar power module is formed by means of power conditioning units, energy storage devices, protection elements and monitoring devices [5], [6]. Fig. 02 Constracution of array and module form a solar cell II. DEVELOPMENT Semiconductors are very thin layers consisting of p-n junctions made solar cells fabricated [15] Free electrons in the solar cells having p-n junctions move freely in the metallic contacts in order to produce the electric current which depends on the solar insolation. An equivalent electrical model of the PV cell is shown in fig.3. Isc, Vdiode, Iout, Vout, Rseries and Rparallel are short circuit current, diode voltage, load current, series resistance and parallel resistance respectively [18], [16]. The estimated short circuit current is I sc = I λ (1) Where Iλ represents the amount of photon current which is proportional to the incident luminosity. The value of Iλ is calculated by I λ = L L s I λ0 (2) Fig. 03 Equivalent model of Solar cell Where Ls is representing the intensity of the solar of the photon current which is known and L is representing the required photon current solar intensity. [11] I out = I sc I 0 (e α(v out+i out R series ) 1) V out+ I out R series R parallel (3)

3 Here α is the temperature dependent constant which can be calculated by α = q kt = = T T (4) Where q is representing the amount of charge on the electron and k is the Boltzmann s constant with having temperature T in the Kelvin [12]. We cannot ignore the losses of the PV cell so we have to model our PV cell in terms of the minimum internal and leakage losses from the parallel resistance which normally in the range of 200 to 300 ohms. Similarly there is also a resistance between photon current and load connected which can be modeled as series resistance normally in the range of 0.05 to 0.10 ohms [10], [8] Estimated cell has the open circuit voltage (I out = 0) is represented as V oc = 1 ln α (I sc V oc + 1) (5) I 0 I 0 R parallel V And oc 0 so, I 0 R parallel V oc = 1 α ln (I sc I 0 + 1) (6) From using above equations the characteristics of V out I out can plotted easily which are shown in fig. 4. A. MAXIMUM POWER POINT Fig. 04 VI characteristics of PV cell For the maximum power delivering to the load there will become a point where the product of Voltage,V out and current, I out is maximum which describes the maximum power delivering point to the load. As it is our first priority that we can achieve maximum power from the sun insolation [5]. B. MAXIMUM POWER POINT TRACKERS To get the maximum efficiency there is maximum power point tracking device which is used to operate the PV module to the point where there is a maximum power is achieved all the time [9]. This point is highlighted and shown in fig.5. This is not completely the mechanical system which indicates the direction of the sun. This is basically an electronic system which operates the module of the photovoltaic in the direction or at the points where there is a maximum power can be produced.

4 C. IMPACT OF TEMPERATURE To analyze the temperature effect on the PV module we should take into account the radiant intensity and also the temperature of the cell [14]. The equations shown above tells that naturally the PV system has a nonlinear I-V and P-V characteristics which varies due to the radiant energy and cell temperature. As α is the function of temperature so, α 1 T Fig. 05 Maximum Power Point Temperature impact on the I-V characteristics of solar cell is shown in figure 6. Fig. 06 Impact of variable Temperature on PV cell

5 Varying temperature impact on the P-V power is shown in figure 7. Fig. 07 Impact of variable Temperature on power and voltage of PV cell D. IMPACT OF INSOLATION Solar insolation is directly proportional to the short circuit current I sc which depicts that the plot curves of PV current-voltage for different solar intensity values can be drawn easily. These characteristics are shown in fig. 8. III. GRID CONNECTED AND AUTONOMOUS SYSTEMS A. GRID CONNECTED There is a system shown in figure in which grid and load are connected directly to the supply. Power Conditioning Unit (PCU) is used to convert the DC to AC which is connected to grid connected PV power module for uninterrupted power and also supply power to both the load and the grid which is shown in fig. 9. To fulfill the demand all the time it is necessary to adopt a good scheme. For this purpose we should take into account the condition when PV produces the less energy than the total demand of the load, the Power Conditioning Unit plays its role to draw the auxiliary power from the grid connected. In that case the power demand can be easily fulfilled. Similarly, looking at the second condition when PV module supplies more power than the required demand then there should be a system which sent back this excess power to the grid and on the other hand the electricity meter should never be moves back. Fig. 08 Impact of variable sunlight on voltage and power of PV cell

6 The structure to design such requirement is very simple because the energy storage is not required most of the times but sometimes it may be integrated with the grid if outage is observed. The design should have the ability to operate the PCU which is built in MPPT at the most efficient point on the i v curves when there will be a change in environmental conditions. Fig. 09 Grid connected system B. AUTONOMOUS SYSTEMS The scheme in which the load connected to system do not utilize the energy from the utility grid is known to be autonomous system. So where there is a distributed generation, there should be the system available all the time to store the energy and provide it for such period of time when the source of the system is not available to provide the demand. This scheme is shown in fig. 09. C. POWER CONDITIONING UNIT The device that is connected to the utility grid network for the purpose to recover or get back the importance of power which is supplied to load is known to be a Power Conditioning Unit (PCU). There are many types of abnormalities and parameters available which disturbs the supply power. So, to overcome this problem we mainly use the PCU to resolve the problems which are caused due to sudden voltage drops, reactive power, low power factor, transients in the system, surges of the current etc. PCU may have voltage regulators to regulate the voltages, filters, relays etc. It is especially manufactured depending upon the supply at the input and the ctual conditions. IV. INVERTER DESIGN Investors are specially purpose designed to use for the conversion of a DC source supply to an AC source supply of high voltage, similar to power that would be offered at an electrical barrier opening. To run the AC power, we used the invertors in many applications where low level DC voltage sources such as batteries, fuel cells and solar panels are there. To convert this DC to AC we use invertors there. The implementation of this invertor scheme design is shown in fig. 10. There are two steps for converting any time the DC power to an AC power.

7 Fig. 10 Inverter Scheme for PV Module The first step is the conversion of the low level voltage of DC power to a high level of DC voltage source. The second step of this conversion is to convert this high voltage level of DC power to an AC (alternating waveform) using the Pulse Width Modulation (PWM). An alternative method of converting the low level DC voltage to high level AC is to first convert it into low level AC power and then we can use the transformer to step up the voltage level to the required voltages. The implementation of this scheme in SIMULINK block diagram is shown in fig. 11 and its results in fig. 12. Similarly the scheme for the implementation of the 3-phase Invertor in Matlab/Simulink tool, and also the block diagram of the three phase invertor in shown in fig. 13a and their results in fig. 13b. Fig. 11 Single Phase Inverter Simulink Block Diagram

8 Fig. 12 Single Phase Inverter Simulation Fig. 13[a] 3-Phase Inverter Simulink Block Diagram

9 Fig. 13[b] 3-Phase Inverter Simulation V. CONCLUSION This is well-meaningly discussed that PV Power modules have the maximum auspicious and reasonable result of energy crises of Pakistan. As Geographical longitudes extent of Pakistan is between E and latitude N and as per approximation and due to which amount of global insolation in Pakistan is very much high. The span of the day show a discrepancy considerably throughout the year with regular daytime of 12:10 hours. The shortest day is 21st December with an approximate 9:55 hours of the daylight and longest day 20th June with 14:20 hours of the daytime. PEPCO, the electric power supply company of Pakistan, illustrates the standard average load demand of a house is about 4-6kW and almost in Pakistan the ordinary daytime is of 12 hours so, with a minimum of 400 watt solar panel having characteristic efficiency factor (about 80%), we can extract satisfactory energy of 3840Wh [400 x 12 x 0.80] for domestic use. VI. REFERENCES [1] Huan-Liang Tsai, Ci-Siang Tu, And Yi-Jie Su "Development Of Generalized Photovoltaic Model Using Matlab/Simulink",Wcecs 2008, October 22-24, 2008, San Francisco, USA [2] Michael E. Ropp, Member, IEEE, And SigifredoGonzalez Development Of A Matlab/Simulink Model Of A Single-Phase Grid-Connected Photovoltaic System, Ieee Transactions On Energy Conversion Renewable And Efficient Electric Power Systems By Gilbert M Masters [3] Martin A. Green,"Photovoltaic Principles", Physica E 14 (2002) [4] S.B. Kjær, J.K. Pedersen, F. Blaabjerg, Power inverter topologies for photovoltaic modules a review, IEEE proc. of the 37th annual industry application conference (IAS 02), vol. 2, pp , [5] S.B. Kjær, F. Blaabjerg, Design optimization of a single phase inverter for photovoltaic applications, IEEE proc. of the 34th power electronics specialists conference (PESC 03), vol. 3, pp , 2003.

10 [6] Y. Xue, L. Chang, S. B. Kjær, J. Bordonau, T. Shimizu, Topologies of singlephase inverters for small distributed power generators: an overview, IEEE trans. On power electronics, vol. 19, no. 5, pp , September [7] R. Teodorescu, M. Liserre and P. Rodríguez, Grid Converters for Photovoltaic and Wind Power Systems, Wiley-IEEE Press, [8] H. Seo, C. Nat, G. H. Kim, S.Y. Kim, N. Kim, H. G. Lee, C. Hwang, M. Park, and I. K. Yu, Power quality control strategy for grid-connected renewable energy sources using PV array and supercapacitor, International Electrical Machines and Systems (ICEMS) Conference, [9] E. Lorenzo, G. Araujo, A. Cuevas, M. Egido, J. Miñano and R. Zilles, Solar electricity: engineering of photovoltaic systems, Progensa, [10] J. Nelson, The Physics of Solar Cells, London: Imperial College press, [11] E. F. Camacho, T. Samad, M. G. Sanz, and I. Hiskens, Control for Renewable Energy and Smart Grids. [12] R. Faranda and S. Leva, Energy comparison of MPPT techniques for PV Systems, WSEAS Trans. on Power Systems, Vol.3, No , pp [13] R. Mallwitz, B. Engel, Solar Power Inverters, CIPS 2010, March, 16-18, 2010, Nuremberg/Germany. [14] P. Chapman, G. Madianos, AC modules and solar power electronics, in Solar Bridge technologies, Rev. 1.0 October 8, [15] M. A. Guerrero, E. Romero, F. Barrero. M.I. Milanes and E. Gonzalez, Overview of Medium Scale Energy Storage Systems, Compatibility and Power Electronics, [16] G. W. Neudeck, PN Junction Diode, 2nd ed., Prentice Hall, ISBN-10: , [17] G. M. Masters, Renewable and Efficient Electric Power Systems, 2004 Wiley-IEEE Press. [18] J.W. Bishop, "Computer Simulation of the Effects of Electrical Mismatches in Photovoltaic Cell Interconnection Circuits," Solar Cells, 25(1988), [19] M. A. Guerrero, E. Romero, F. Barrero. M.I. Milanes and E. Gonzalez, Overview of Medium Scale Energy Storage Systems, Compatibility and Power Electronics, 2009.