aie UNIT-I: Behaviour of solar cells-basic struct DS and characteristics: Types - equivalent circuit, modeling of solar cells including the effects of temperature, irradiation and series/shunt resistances on the open-circuit voltage and short-circuit current Solar cell arrays- PV modules-PV generators- shadow effects and bypass diodes- hot spot problem in a PV module and safe operating area.Cont, ® Solar cell T) TYPE of Active Material :~ MONO (SINGLE) CRYSTALLINE The Monocrystalline silicon cell is produced from pure silicon Since the Monocrystalline silicon is pure and defect free, the efficiency of cell will be higher. It us s crystalline Si p-n junctions. Limited by the amount of energy produced by the photons, decreases at higher wavelengths. Radiation with longer wavelengths leads to thermal dissipation and causes the cell to heat up hence reducing efficiency The maximum efficiency has around 23%.TYPE of Active Material :~ MONO (SINGLE) CRYSTALLINE * Siis manufactured to a diameter between 10 tO 15cm, it is cut in wafers of 0.3mm thickness to form a solar cell of 35 A/cm ° Silicon wafer processing technology is most favourable in micro electronic applications ° These types of monojunction, silicon-wafer devices are now commonly referred to as the first- generation (1G) technology, the majority of which is based on a screen printing~based device.Type of Active Material ALL In polycrystalline solar cell, // silicon is used as raw material and polycrystalline silicon was obtained followed by ication ocess. The materials contain various alline sizes. Hence, the efficiency of this type of cell is less than Monocrystalline ‘The advantage of converting, the production of crystalline solar cells from mono silicon to multi-silicon is to decrease the flaws in f metal contamination and crystal structure. Multi-crystalline cell manufacturing is initiated by melting silicon and solidifying it to orient Crystals in a fixed direction producing rectangular ingot of multi-crystalline silicon to be sliced into blocks and finally into thin wafers.Amorphous silicon is obtained by ‘The layer thickness amounts to les the thickness of a than Tym human hair for comparison is 50-100 jum, The efficiency of amorphous cells is much lower than that _ of the other two cell types. They are used mainly in equipment, such calculators, or as facade watches ments. low power and pocket (Thin film) Cont,® Solar c Topic Mono crystalline 189%-20% cell efficiency Less sustainable to produce More expensive 30 years life span crystalline cells 16%-18% cell efficiency More sustainable to produce Less expensive 25 years life span Cont, 5%-10% cell efficiency Most sustainable to produce Least expensive 15-20 years life spanQu »[Binke Qu External Cireuit * AP-N junction in the dark consumes power, as it can be operated in 1* or 8" quadrant Pre-requisites ; 1 ——-| P= +Vasd * Vak Passive Sign Convention + Power Absorbed - Power DeliveredEffect of solar radiation on the I-V curve * Under illumination solar cell can be operated ') | CRE in the fourth quadrant corresponding to ‘during DARKtime delivering power to the external circuit SOURCE (PV cel) » Vat =! * Source (PV cell Ip External ct \cteristics 7a ‘ireuit fester i E> (Gren during DAY time) qv = Current in the illuminated solar cell is negative flows against the conventional direction of a forward diodeSolar Cell model SOURCE (PV cell) —I | mn} Circuit External The I-V relation is given as: I, - dark saturation current , Ip - light generated current. , n - ideality factorSink & Source Representing Source in Quadrant-I t+ Ideal Voltage source * Ideal Current source |. Vake PVCell has both characteristics of constant voltage and constant current source Reduction (slope)of the voltage indicates- stance Reduction (slope) of the current indicates~ 1 1 Qu «GV cell dure Ne) b + Source el derre Des) sosce Presence of series Qu Presence of Shunt resistancePractical PV cell, External Cireuit Ideal Voltage source Ideal Current source Ip = 1g + Igy +1 At Node I Voltage = (V + IRs) Rewriting equation for I, equation becomes V +IRs I= p-ta- (QO a= to lett —1) y= 15 (erm = 1) Va (ots) - (C8) ‘SH T=Ip—ised “Topic | 1 Va V+IR me DINED ri Hy) a GC a But To = xr ( ‘SH Ig = Reverse saturation Current (om Boltzmann's Constant KT ——— temperature Vp = Thermal Voltage = — z 4 —*Hiectron charge = So 11 = Ideality factor which is 2 for silicon K= Constant depends on dimensions of PN junction and Material properties V ¢9=Forbidden band gap energy (it is 1.16 to 1.21v for silicon) m= 1,5 for siliconSolar cell parameters I + V,.— open circuit voltage, oL se~ Short circuit current, + P,,~ maximum power point * Tay Vm ~ current and voltage 1. Ve at maximum power point + FF— fill factor Usual I-V plot of solar cell~ Current is shown on positive y axis +1) efficiency +R, ~ series resistance + Ry, — shunt resistanceThe open-circuit voltage, V.., is the maximum voltage available from a solar cell, and this occurs at zero current. VIR V+IR op it) Step: 2 0=Ip—igle wr — 1} - (Y2et0As) Rsu Yoo Step:3 = Ip —Ip lev — 1}L (22) ‘ ‘ Resfy- cE A gg tine LIE At Open circuit V =Voc,I = 0 Repositioning the Variables Rsu > Voc Ip + Io SUV Me oamotcintm re ercmeuccyae ten} Voc = V7 In Th, to the amount of forward bias on the Helis SAD Vee is logarithmically related to incident power (Ip) solar cell junction due to illumination.[agg At short circuit V = 0,1 = Isc ott scRs 2 Isc =ip—iole wr — 1} — (tests The PV-Cell: Short circuit Current VaiRs V+ IRs — ib= (Es Rsu * The short-circuit current is the through the solar cell when the volt: the solar cell is zero (i.e., when the s current 2 across ell +The short-circuit current is due to the generation and collection of light-generated carriers.Power vs Voltage curve + Power out of a solar cell increases with voltage, reaches a maximum (P,,) and then decreases again. P,, is the Peak (maxium) Power operating point is the maximum current corresponding to peak power F = Vn, is the maximum voltage corresponding to peak powerFILL FACTOR (FF) * The FF is defined as the ratio of the maximum power from the actual solar cell to the maximum power from a ideal ‘solar cell Max power fromreal cell FF omidealcell ‘Max power | * Graphically, the FF is a measure of the "squareness" of the solar ce!Efficiency is defined as the ratio of energy output from the solar cell to y= Mav. Coll Power : Incident light Intensity P,P, on)x(Area of the panel) (L) = 1Kw/m*2 in m2 Efficiency in terms of Lae =o. = Meet =D PTA in Fin cell module < T)cell + Efficiency of a cell also depends on the solar spectrum, and the fe ature of the solar cell.As Radiation Increases Short Circuit current increases Linearly with constant resistance 1000 W/m'2 750 W/10*2, sc = Ip 500 W/m*2 Open circuit voltage increases Logarithmically with constant temperature Voc = Wr w( 250 W/m’ Te +Io\ | To Vo Moc Voe LLY plot of solar cell ~ (Variations in Radiation)(@taximum power point) Po 1000 W/m"'2 300 W/m"'2 Vv Voe LV & P-Vplotof solar cell - (Variations in Radiation) As Radiation Increases Short Circuit current increases Linearly with constant res Ic = Ip tance Open circuit voltage increases Logarithmically with constant temperature Voc = Wr w( Te +Io\ | To Power increases with RadiationVoce, Ve aire @25% LV plotof solar cell— (Variations in Temperature) Short Circuit current increases as temperature increases 0.1% per Kelvin As temperature increases photon current increa reduces and this allows more v Band gap energy id anee electrons into conduction by Open circuit voltage decreases as temperature increases dVoc/dT = -2.1 mv/kelvin Voc = nVr In (2) But lo< + ‘The basic building block for PV applications is a MODULE|) module e © Atypi + Modules can be wired in series to increase volt a ii i et al module has 36 cells in series ent + Arrays are made up of some combination of series and parallel modules to increase power produces + 86cellsin series 12V output produces + 72cellsin series 24V output A PV module, sometimes called a panel, is a grouping of cells. Generally Panel can be used to describe a solar-electric module, a solar hot water collector.i, Cell-1 = In series Current is same In series Voltages are additive Vr=Voit Varo e of Module by Calculate the terminal Volt taking cell voltage as 0.6V ? Atypical module his 36 cls connected in series* For Ideality the Rsh and Rs is removed form the equivalent circuit and the ideal cells are connected in series Tn hy , { LV Plotof Combined Cell-1 & Cell-2 Ven I | - P, : \el v, [yrccccccccsccc ccc eer ae 5 ate~ Load Line; 1/R1 Operating point v The operating point of any power system is the intersection of the source line and the load line. If the PV source having the I-V and P-V characteristics supplying power to a resistive load., Let R= R1, it will operate at point A1 If Ris varied slope of load Line varied If the load resistance increases to., R= R2 , the operating point moves to A2 If Ris Very high(nfinity) then slope is Zer0; Then load line is on X-axis If R= Zero, then load line move to vertical i.e. on Y-axisbaaNos al ical Solar Cell * Non- Ideality occurs due to 1. in a Module 2. Effect of Shadowing a) Partial shadowing of a cell in an open circuited, series string of cells b)Complete shadowing of one cell in a short circuited, series string of cells.1. Cell Mismatch in a Module * When two cells with mismatched characteristics are connected in series and load is applied, both cells are bound to carry same current. ¢ At a particular operating point, while one cell may be operating at peak power, the other may not. Thus peak power of the combination is always Jess than the sum of individual peak power of each cell. ° which has lower fill factor * To reduce mismatch losses, modules are fabricated from cells belonging to same batch2. Effect of Shadowing a) Partial shadowing of a cell in an open circuited, series string of cells *When a cell is partially shadowed, the inatiowedl portion will not 7 e any but the remaining portion will remain active and produce power.* The generated voltage by illuminated portion will forward bias the parallel rectifier corresponding to shadowed portion . ¢ If shadowed area is relatively small, the large circulating current through it will result in excessive heating of the shadowed portion. The phenomenon is known as hot spot effect * Hotspot effect completely damage the module for prolonged partial shadowing.2. Effect of Shadowing b) P) Complete shadowing, of a cell in an short circuited, series + When a cell is complete t will not produce any power ring of cells shadowed, the shadowed portion + The voltages produced by the illuminated cells add up and appears as reverse bias voltage across the shadowed cell. V; + As long as peak inverse voltage (PIV) of the shadowed cell is more than the bias, no current will flow. + If, however, the PIV is less than total reverse voltage appearing across the shadowed cell, current will flow through the string, dissipating large power in the shadowed = cell, leading to possible damage of the moduleIn this eon Cell 2 acta colt 2° ¥, x2Vg wt / Rdecreasesi.e., load current increases and a point reaches where Cefl-1;(V,,) terminal voltage is positive and Cell-2;(Vi2) is Zero and further variation in the load (R) causes the Cell-2 to developa reverse series connected circuit current under reverse polarity case of Cell-2 otential ,cue to the virtue of being a me current will flow through the both cells. It is observed that there is no drastic increase inotf Cellet & Cell-2 LV Plot of Series Combined Non Identical Cells Load line ;1/R At 1; the Terminal voltage (V,) of string is the sum of the Cell-1;(V,y) and Cell-2:(V3p) voltages, which are positive At 2; Rdecreasesi.e.,load current increases and a point reaches where Cell- (V1) is Positive and Cell-2;(V;.) is Zero. At8; Further decrease in R; makes Cell-1:(Vz,) is positive and Cell-2;(Vqa) is Negative Cell-2 acts as Sink. At 4; R=0;Voltage generated by of Cell-1;(Vpy) is equal to the reverse voltage generated by Cell-2:(Vp2) But (Vz) is Z eroPV cell2 ting like a sink, therefore its polarity is rever and therefore it is replaced with a resistor. + While sinking PV cell acts like a resistor and it becomes hot, it can be avoided by bypassing it by putting a diodeaeross it Lets cut-in voltage of diode is less than PV cell2 The moment PV cell2 reverses the diode bypass the cell2 and it has no power dissipation. Now all the powers are positive in the module and PV cell is alone delivering the power to the load during jaded condition and thereby the efficiency is increased by keeping the diode Bypass Diode Cell-2 Cell- ResistorWith bypass diode the power output is still low during shade, but the current from unshaded cell bypass the shaded cell. * The power output is lowered due to shading + Shaded Cell dissipates powerLV Plot of Combined Cells with BYPASS Diode + pu Blues Green __, Series Combined cells with nypasetiode ratingvey, x ff Ty _Hlotforseries combinationot ‘Non-Identical cells with types Diode Tot for series combination of Identical Cells(On comparison * The maximum power of Identical cells is more than the remaining * The maximum power of Non- Identical cells is less than the remaining * The maximum power of Non Identical cells with bypass diode is more than maximum power of Non- Identical cells but less than the maximum power of Identical cellsCircuit Theory ls shaded: Current passes through all No current passes through bypass += One coll shaded: Current bypasses the 24 cell series string and passes through the bypass diode in parallel with that string + One row of clls shaded: Current bypasses three 24-cel s through three byp: + One column of cells shaded: Current bypasses the 24-cell series string and passes through the bypass dade in parallel with that string. + Entire module shaded: Current bypasses all calls and passes through three bypass diodes. 72-cell PV circuit A bypass diode is typically installed in parallel with every 24 cells.“ When the sun shines, as long as the voltage produced by the panel is greater than that of the battery, charging will take place. “ However, in the dark, when no voltage is being produced by the panels, the voltage of the battery would cause a current to flow in the opposite direction through the panels, which can lead to the discharging of battery. Hence a blocking diode is used in series with the panels and battery in reverse biasing. “ Normal p-n junction diodes can be used as blocking diodes. “To select a blocking diode, following parameter should be kept in mind +The maximum current provided by the panels The voltage ratings of the diode “The reverse breakdown voltage of the diode.The blocking diode on shaded module prevents current flow into shaded module from the parallel module. Bypass diodes ke see ote ep ae a = aa 3 ae ey as Ss se a Bypass diodes reduce the impact of mismatch losses from modules connected in series. + Ina panel with various modules blocking diodes are connected in series with each series string of modules, + so if any string fail, the power output of the remaining series strings will not be absorbed by the failed string, + The bypass diodes are installed across each module, so that if one module fails, the output of the remaining modules in a string will bypass the failed modulesPolycrystalline 210W-240W Module Type Peak Power Max Powe Voltage Vm) ‘Max. Power Cunt (np) ‘Open Circuit Vorage(Voe) Short Cet Cree (se) (el ficiency Module Effoency Maximum Stem Voltage Temp, Coeff of se ‘Temp. Coeff. of oc Temp, Coe. of Prax Seis Fuse Rating els Sunction Box Front Glass (cel Encapsulation Bock Frame Dimensions Weight Max Surface Load Capaciy Hal Temperature Range '10240.60P 81D230.60P BLD225-60P BL0220.60P B1021560P BLO2I0OF 240Wp 230 «225% «2202S Wp 210 Wp 3018V2982V29S2V.2934V 2970-2870 3672V 3610V3630V BSB 3550V 3648 50% — T6OD% —1575% 1525 500% 14509 4.6 405% 3a 344% 113% ‘12.82% vc 1000 0065 96K ~0349%/K “047 8k ISA with 3 bypas des toughened saety oes 3.2 mm VA [ethene Ving Acetate) compost fin anodized alunisiam profile 50109250 (as 93 kg tested upto 5,400 Pa IEC 67215 maximum siometer of 25 mm wth inact peed of 23 mea END OF THE UNIT-1