1. Solar Photovoltaics

2. Phenomenal Price Reduction of Solar Photovoltaics

3. Phenomenal growth of installation of Solar Photovoltaics

4. Mainly Due to massive production of SPV in China

5. Basic Features of Solar pV  pV systems have no fuel requirement in remote areas diesel or kerosene fuel supplies are erratic and often very expensive. The recurrent costs of operating and maintaining pV systems are small.  pV systems are modular – A solar array is composed of individual pV moduels so each system can be sized to meet the particular demand.

6.  pV systems can be used to improve quality of life - for example the provision of lighting in a rural school allows evening educational or community activities. Refrigeration at a health centre improves effectiveness of immunization programmes.  pV Systems are highly reliable – the reliability of pV systems are significantly higher that of diesel or any similar generators

7.  pV Systems are easy to maintain – Operation and routing maintenance requirements are simple.  pV modules have long life – There is little degradation in performance of over 15 yrs.  pV systems provide national economic benefits – Reliance on imported fuel such as coal and oil is reduced.

8.  pV systems are environmentally begin – There is no harmful pollution through the use of a pV system.  Pv systems are economically viable – On a life cycle cost basis and taking into consideration the higher reliability of PV many small scale applications can be more economically powered by PV than with diesel systems or some other small systems.

9. Applications of Photovoltaics  RURAL ELECTRIFICATION(EITHER GRID CONNECTED OR OFF GRID)  SOLAR HOME SYSTEMS (SHS)  WATER PUMPING AND TREATMENT SYSTEMS  HEALTH CARE SYSTEMS  COMMUNICATIONS  MID SEA BUOYS  CATHODIC PROTECTION

10. 10 grid ) Solar cell capacity: 3.4kW Wind Power capacity: 1.8kW Inverter capacity: 5kVA Stationary power station (Off grid or mini grid)

11. 11 Stationary power station (Grid connected ) Site:Funafuti Tuvalu Installation:Feb. in 2008 Capacity:40kW Purpose:Grid connected power supply for fuel conservation and CO2 reduction.

12. Solar array Controller Light Storage battery

13. 13 Roof top of school,community-center building. (For education and emergency power)

14. 14 Roof top of residence ( Grid connected ) Most popular installation style in Japan. (Almost 85% PV in Japan ) Owner can sell excess power to power utility.

15. 15 Distant and independent power supply ( Off grid ) Relay station on top of mountain Advertising sign beside highway

16. 16 Solar Home Systems in remote locations Mountain lodge ( Off grid ) 1.2kW system Inverter and controller

20. Technical Comparison of off grid energy System

21. Off Grid Systems – Diesel Generators Advantages  Widespread Operating and maintenance experience  Moderate capital cost  Easy to install  Can be a combined power supply for additional uses Disadvantages  Creates noise and fume pollution  Requires a reliable fuel supply  High running costs  High maint. Costs  Low operating efficiency

22. Automotive Battery Recharging Advantages  Low capital cost  Easy to install  Batteries locally available Disadvantages  Relies on transportation to charging centres  High charging fees often apply  Short battery life times

23. Photo – Voltaics  High reliability  Low maintenance requirements  Low running costs  Suited to most locations  Long life expectancy for main components  Involves the introduction of a new and poorly understood technology  High capital cost  Not physically robust so vulnerable to damage  Specialized batteries not widely available

24. Micro Hydro Systems  Uses simple engineering principles hence widely accepted technology  Locally available skills only required for most applications  Robust machinery used  Most village level and local technicians can do maintenance  Relatively high capital cost  Generation depends on availability of water  Control gear may require sophisticated components  Conflicting water users may hinder total potential unlisation

25. Solar PV is a very good substitute for Kerosene lighting !

26. Solar Phtovoltaic Technology Semi Conductor Physics The equivalent circuit of a solar cell The maximum power point of a cell The significance of the parallel resistor The significance of the series resistor The current and voltage relationship of a cell Solar Cell, Module and Arrays Series Connection and Parallel Connections

27. Solar Phtovoltaic Technology Cont… Standard testing procedure of a module. Effects of Temperature on the produced power. Effects of shading and how to avoid ill effects of shading in a module and in an array. – the significance of a by-pass diode. The purpose of a Blocking Diode and its many usages. Designing of Solar PV Systems. Grid Connected Solar Systems

31. Semi-conductor Physics In an intrinsic semi-conductor valance band has four electrons and hence only very few electrons can escape to conduction band. E G = Energy gap energy required for an electron to jump from the valance band to conduction band ~ 0.5 eV to 2.5 eV.

32. Fermi Level Fermi Level E f is the energy level at which an electron has an equal probability of being either in the valance band or the conduction band Hence in an intrinsic semiconductor Fermi level lies exactly at the mid point of the forbidden zone or the energy gap.

34. Fermi Level in a n type semi conductor Fermi level lies close to conduction band

36. Fermi Level in a p type semi conductor Fermi Level lies close to valance band

38. Compare the Band Gap with the Energy in the Solar Radiation Solar light wave length~ 0.3 μmto2.5μm This corresponds to photon energy range of 0.5 eV to 4.0 eV 1 eV= 1.6x10 -19 J E= hν Where ν=c/λ h= 6.626x10 -34 J-s Plank’s Constant

43. When a n type and p type junction is created in a semiconductor The energy level at each end of the semiconductor and at the junction appears like this:

44. Initially electrons diffuse to p type and holes diffuse to n type at the junction This diffusion creates an electric field that leads to a drift current I e while the movement of holes from p type and electrons from n type creates a current known as the diffusion current I d Due to the electric field at thermal equilibrium I e = I d

45. Behavior under forward bias of a Diode When a diode if forward biased, an electric current flows in the forward direction of the diode i.e. a current pass through the diode from p type to n type in the semiconductor

46. When a Diode if forward biased E decreases Hence I e decreases V b increases I d increases

47. When a Diode if forward biased V b Increases causing I d to increase and E decreases causing I e to decrease hence when a diode is forward biased a current passes through the diode

48. Characteristic curve of a Diode I increases rapidly when a diode is forward biased caused by excitation of electrons across the n-p junction to gain enough energy from the battery to jump to the valance band

49. n-p junction under solar Insolation With the absorption of photon energy from the light more electron – hole pairs are created in the solar cell (n-p junction)

50. What happens when a solar cell exposed to light is connected externally With the solar insolation a current flows from the solar cell depicting I = I L -I d where I L is the current created by excitation of electrons in the junction to flow out of the n side in the external circuit to combine with holes created in the p type thus a current flows in the external circuit from the p side to the n side. Due to this current, a voltage is built up in the external circuit forward biasing the diode hence the ‘drift current flows in the opposite direction of the current created by solar light

51. What Happens When the Solar Cell is Short Circuited Under Short Circuit conditions V=0 hence diffusion current I d becomes zero. Hence the current flowing in the external circuit is the same current produced in the solar cell due to solar light equal to the drift current

52. Characteristic Curve of a solar cell At Short circuit V = 0 hence I = I L At Open Circuit No external current flows hence I e = I d

53. The Equivalent circuit of a solar cell This is the simplified equivalent circuit of a solar cell however the real solar cell should comprise of a series resistance depicting the internal resistance of the cell and the contact resistance and also a parallel resistance depicting the reverse saturation current of the diode.

63. Example

66. A More Accurate Equivalent Circuit for a PV Cell The Parallel Resistor If a single cell in series is shaded no current theoretical should flow in the entire string – however though significant power loss occur in practice a current does in fact flow in the string, suggesting there is a parallel resistor of high magnitude, hence the representation of a parallel resistor in the string. This is known as the leakage resistor. R p

67. The equivalent circuit of a single cell now becomes:

72. V‐I Characteristic of Full Equivalent Circuit

73. Cells Modules and Arrays In a module n Number of cells are connected in series usually n=36 In an Array many modules are connected series and /or parallel to obtain the desired voltage and current.

77. PV Arrays Modules can be connected in series to increase the terminal voltage They also can be connected in parallel to increase the output current

78. In PV Arrays

79. Please also note: There is a reason, however, to prefer the wiring of strings in parallel, If an entire string is removed from service for some reason, the array can still deliver whatever voltage is needed by the load, though the current is diminished, which is not the case when a parallel group of modules is removed.

88. Shading of a cell of a module – The output of a module can drop drastically even if one cell is shaded

89. I-V Characteristics with one cell shaded The output of the module with one cell shaded will be: The cumulative voltage of the un-shaded cells will be: Hence : The Drop in voltage due to shading of one cell therefore will be: Since R p >>R s

95. In PV Arrays bypass Diodes will start conducting when the voltage in the un-shaded cells less than the shaded cells

96. Potovoltaic Arrays with by-pass Diodes to overcome the effects of shading

98. Summary of Lecture We reviewed the generalised equivalent circuit of a solar cell We traced the arrangement of an array from modules and how a module is arranged from a cluster of cells – add in series voltage increases, add in parallel – current increases Standard testing procedure of a module. Maximum Power Point, Fill Factor, Effects of Temperature on the produced power. Effects of shading and how to avoid ill effects of shading in a module and in an array. – the significance of a by- pass diode. The purpose of a Blocking Diode and its many usages.