DESIGN OF PV SYSTEM INTERCONNECTED WITH EU 2-1 INTRODUCTION Photovoltaic, PV, system is a green power source, which can convert sunlight to electricity. It requires no fuel, produces no emissions, and involves no moving parts. There are two modes of PV system operation. Stand-alone PV system with battery storage and PV system connected to electric utility, EU with or without battery storage.

PV system connected to electric utility, EU without BS PV system connected to electric utility, EU with BS

This chapter introduces a proposed computer program for optimum design of a PV system to be interconnected with EU. The proposed computer program has been designed to determine an optimum number of PV modules based on maximum power point, MPPs, by using neural network for the system under study. Many PV module types have been introduced to computer program to choose the best type of PV module. The computer program can completely design the PV system interconnected with EU and determines the optimum operation hour by hour through the year.

Then, it estimates the monthly surplus energy, monthly deficit energy and yearly purchase or selling energy to / or from EU . The decision from the computer program is based on minimum price of the generated kWh from the PV system and maximum power extracted from PV system. Maximum power output from PV system changes when solar radiation and temperature vary. Control is needed for the PV system to track the MPPs. This controller has been designed by neural network approach.

(b) Calculation of radiation on the tilted surfaces: 2-2 METHODOLOGY 2-2-1 Estimation of Hourly Radiation on the Tilted Surfaces Hourly solar radiation incident upon a horizontal surface is available for many locations. However solar radiation data on tilted surfaces are generally not available [77]. The hourly radiation on surface tilted by monthly best tilt angle toward equator estimated using the following method: (a) Computation of the monthly best tilt angle [69], [77]: (b) Calculation of radiation on the tilted surfaces:

2-2-2 Calculation of Average Power for One PV Module The electrical power generated and terminal voltage of PV module depends on solar radiation and ambient temperature. The equivalent electrical circuit describing the solar cells module used in the analysis is shown in Fig. 2-1 [78]. Fig. 2-1 Equivalent Circuit of PV Solar Cells Module.

The mathematical equation describing the I-V characteristics of a PV solar cells module are given by [9], [26], [79]. (2-1) Where; I(t) : The hourly output current, Amp. V(t) : The hourly output voltage, Volt. A : The ideality factor for p-n junction. T(t) : The hourly temperature, Kelvin. KB : The Boltzman's constant in Joules per Kelvin, 1.38*10-23 J/k. q : The charge of the electron in Coulombs, 1.6*10-19C. Io(t) : The hourly reverse saturation current, Amp. This current varies with temperature as follows:

Iph(t). : The hourly generated current of solar cells module Iph(t) : The hourly generated current of solar cells module. This current varies with temperature according to the following equation: Where; Tr : The reference temperature, K. Ego : The band-gap energy of the semiconductor. KI : The short circuit current temperature coefficient. Ior : The saturation current at Tr, Amp. HT(t) : The average hourly radiation on the tilted surface Isc : PV cell short-circuit current at 25o C and 100 W/cm2.

The hourly output of the solar cells module can be calculated by the following equation:

2-2-3 Calculation of Optimum Number of PV Modules The energy balance between the load and the output of PV system must be carried out to compute the optimum number of PV modules, Npv. The output power from PV system must satisfy the load power demand. The hourly generated power, Ppv,out(t), and hourly load power, PLoad(t), are compared with each other. If Ppv,out(t) is larger than the load power demand then there is an hourly surplus power, but if Ppv,out(t) is smaller than the load power demand then there is an hourly deficit power. At any value of Npv, if the summation of hourly surplus power equal to the summation of hourly deficit power then this value of Npv represents the optimum number of PV modules. The following equations have been used to get the optimum number of PV modules.

Then, number of PV module must be decreased by one module and repeating the foregoing process: Then, number PV module must be increased by one module and repeating the foregoing process. Then, Npv is the optimum number of PV modules satisfies the energy balance condition. The value of Npv has been taken as the optimum number of PV modules and can be named ONpv.

2-2-4 Estimation the Number of Subsystems The number of subsystems depends on the inverter rating and efficiency and also size of PV system. To determine the number of subsystems required the following data must be known: Rating and efficiency of the inverter unit. Solar cell data (module data). The optimum number of PV modules that obtained from energy balance process.

2-2-6 Design of Neural Network for MPPs [87-91] This item discuses the structure and training of a neural network, NN, to track the MPPs of PV array. The MPPs can be obtained by controlling the switching scheme of the DC/DC boost converter. This can be done by using NN. The Back Propagation, BP, learning algorithm is applied to NN consisting of processing elements with activation functions.

2-2-7 Calculation of Energy Cost Figure, ECF The major concern in the design of an electric power system that utilizes renewable energy sources is the accurate selection of system components that can economically satisfy the load demand. The system's components are found subject to: 1- Minimize the cost of electricity production($/kWh) 2- Ensure that the load is served according to a certain reliability criteria. 3- Minimize the power purchased from the grid [66].

The energy cost figure, ECF, of PV system is determined by dividing the summation of the total yearly expenses of PV system by the expected yearly energy generated, Ey. The following equations are used to determine the ECF [62, 69]. Energy cost figure, ECF, $/kWh =(TLACPV)/Total expected yearly energy generated.

2-3 APPLICATIONS AND RESULTS 2-3-1 Design of PV System A new proposed computer program has been designed depended on the above methodology for calculating optimum design of PV system. The flowchart of this program is shown in Fig. 2-7.

The input data of this program is: 1- Hourly radiation, kW/m2. 2- Characteristics of each PV module type. 3-Site latitude, Degrees. 4- Hourly load demand, kW.

Fig. 2-8 The Radiation on Horizontal Surfaces of Zafarâna Site

Table (2-2) Characteristics of the Different PV Solar Cells Module ASE-300-DGF/17 [94] BP MSX 120 [93] BP MSX 64 [93] BP MSX 80 [93] M55 [40],[92] Solar cells type Item 1.892*1.28 0.99*1.11 1.11*0.50 1.461*0.50 1.29*0.33 Dimensions, m 2.4278 1.104 0.55471 0.7309 m2 0.425 m2 Area, m2 285W 120 W 64 W 80 W 55 W Nominal Peak Power (Pmax) 17.0 V 33.7 V 17.5 V 16.8 V 17.4 V Voltage at Pmax , (Vmp) 16.8 A 3.56 A 3.66 A 4.75 A 3.15 A Current at Pmax , (Imp) 20.0 V 42.1V 21.3 V 21.0 V 21.7 V Open circuit voltage at Pmax , (Voc) 18.4 A 3.87 A 4 A 5.17 A 3.45 A short circuit current at Pmax , (Isc)

Fig. 2-9 Daily Load Curve for January, April, July and October.

The outputs of this program are: 1- Optimum number of each PV module type. The first output of the proposed computer program are the optimum total number of PV modules to feed the whole load demand, number of modules per string, and finally number of inverter units. The inverter has an input voltage 6005% Vdc, efficiency 95% at unity power factor and rating 500 kW. Table (2-3) revels the construction of the designed PV system under sizing different selected types of solar cells module.

Table (2-3) The Construction of the Designed PV system Under Using Different Selected Types of Solar Cells Module ASE-300 DGF/17 BP MSX 120 BP MSX 64 BP MSX 80 M55 Solar cells Item 1692094 1889799 1784731 1893782.0 1611238.0 Module Active Area, m2 696960 1711815 3202920 2582118 3787611 Total Number of Modules 32 17 31 33 Number of series Modules/string 55 245 252 189 293 Number of parallel string /subsystem 1760 4165 7812 6237 9083 Number of Modules /subsystem 396 411 410 414 417 Number of inverter unit

2- Cost of kWh generated, $/kWh. The second output of the proposed computer program is Energy Cost Figure, ECF, for each of solar cells module type. The ECF are displayed in Table (2-5) and Fig. 2-10. From Table (2-5) and Fig. 2-10 it can be seen that the solar cells module type of ASE-300 DGF/17 represents the most economical one for Zafarâna site. The price of kWh ( ECF) produced form PV system which used ASE-300 DGF/17 PV module type is 0.08499 $/kWh. Table (2-5) ECF for each Selected Module Type ASE-300 DGF/17 BP MSX 120 BP MSX 64 80 M55 Module Type 0.08499 0.08791 0.08772 0.08841 0.08915 ECF, (2005) $/kWh 0.045074 0.046625 0.04652 0.04689 0.04728 ECF, (2010) $/kWh

Fig. 2-10 ECF for each Selected Module Type for the year 2005.

Fig. 2-12 The Total Energy Generated and Energy Demand for each Month.