1. Solar Photovoltaic Theory 1-1. Basic principles of PV

1-1.Basic principle of PV Contents 1-1. Basic principles of PV 1-1-1. Mechanism of generation 1-1-2. Various type of PV cell 1-1-3. Installation example 1-1-4. Basic characteristic 1-1-5. Case sturdy

1-1-1. Mechanism of generation The solar cell is composed of a P-type semiconductor and an N-type semiconductor. Solar light hitting the cell produces two types of electrons, negatively and positively charged electrons in the semiconductors. Negatively charged (-) electrons gather around the N-type semiconductor while positively charged (+) electrons gather around the P-type semiconductor. When you connect loads such as a light bulb, electric current flows between the two electrodes. + - Photo Voltaic cell Electrode P-Type Semiconductor N-Type Semiconductor Reflect-Proof Film Solar Energy Load Electric Current I will introduce the principle to begin with. Solar cell, invented in the USA in 1954, is a kind of semiconductor to convert energy of light directly into electricity. Most semiconductor used for solar cell are silicon semiconductors and it is composed of P-type semiconductor and N-type semiconductor. Sunlight hitting the cell produces two types of electrons, negatively charged and positively charged electrons in the semiconductors. Negatively charged electrons gather around N-type semiconductor while positively charged electrons gather around P-type semiconductor. When youconnect loads such as a light bulb or motor, electric current occurs between two electrodes.

1-1-1. Mechanism of generation Direction of current inside PV cell Inside current of PV cell looks like “Reverse direction.” Why? By Solar Energy, current is pumped up from N-pole to P-pole. In generation, current appears reverse. It is the same as for battery. P N Looks like reverse P N ? I will introduce the principle to begin with. Solar cell, invented in the USA in 1954, is a kind of semiconductor to convert energy of light directly into electricity. Most semiconductor used for solar cell are silicon semiconductors and it is composed of P-type semiconductor and N-type semiconductor. Sunlight hitting the cell produces two types of electrons, negatively charged and positively charged electrons in the semiconductors. Negatively charged electrons gather around N-type semiconductor while positively charged electrons gather around P-type semiconductor. When youconnect loads such as a light bulb or motor, electric current occurs between two electrodes. Current appears to be in the reverse direction ?

1-1-1. Mechanism of generation Voltage and Current of PV cell ( I-V Curve ) P N A Short Circuit Voltage on normal operation point 0.5V (in case of Silicon PV) Current depend on - Intensity of insolation - Size of cell (A) High insolation Normal operation point (Maximum Power point) Current(I) Open Circuit P N V Low insolation I will introduce the principle to begin with. Solar cell, invented in the USA in 1954, is a kind of semiconductor to convert energy of light directly into electricity. Most semiconductor used for solar cell are silicon semiconductors and it is composed of P-type semiconductor and N-type semiconductor. Sunlight hitting the cell produces two types of electrons, negatively charged and positively charged electrons in the semiconductors. Negatively charged electrons gather around N-type semiconductor while positively charged electrons gather around P-type semiconductor. When youconnect loads such as a light bulb or motor, electric current occurs between two electrodes. I x V = W (V) Voltage(V) about 0.5V (Silicon)

1-1-1. Mechanism of generation Typical I-V Curve (A) Depend on cell-size 5.55A Standard insolation 1.0 kWh/m2 Depend on Solar insolation 4.95A Depend on type of cell or cell-material ( Si = 0.5V ) Current(I) I will introduce the principle to begin with. Solar cell, invented in the USA in 1954, is a kind of semiconductor to convert energy of light directly into electricity. Most semiconductor used for solar cell are silicon semiconductors and it is composed of P-type semiconductor and N-type semiconductor. Sunlight hitting the cell produces two types of electrons, negatively charged and positively charged electrons in the semiconductors. Negatively charged electrons gather around N-type semiconductor while positively charged electrons gather around P-type semiconductor. When youconnect loads such as a light bulb or motor, electric current occurs between two electrodes. (V) Voltage(V) 0.49 V 0.62 V

1-1-2. Various type of PV cell Types and Conversion Efficiency of Solar Cell Conversion Efficiency of Module Single crystal 10 - 17% Crystalline Poly crystalline 10 - 13% Silicon Semiconductor Non-crystalline Amorphous 7 - 10% Solar Cell Compound Semiconductor Gallium Arsenide (GaAs) 18 - 30% Dye-sensitized Type 7 - 8% Organic Semiconductor Variety of solar cell and conversion efficiency 　There are 2 major types of solar cell: one using silicon semiconductor and one using compound semiconductor. Solar cell using silicon semiconductor is further divided into crystalline and non-crystalline or amorphous semiconductor.The crystalline type silicon semiconductor is widely used for its high conversion rate and reliability track record. The amorphous type semiconductor performs well even under a fluorescent lamp, so, it is used as a source of power for calculators and wrist watches. Compound semiconductor’s conversion rate is very high. But it is difficult to obtain. Organic semiconductor is under development for further reducing cost. Organic Thin Layer Type 2 - 3% Conversion Efficiency = Electric Energy Output Energy of Insolation on cell x 100%

1-1-2. Various type of PV cell Crystal cell (Single crystal and Poly crystalline Silicon) Single crystal Poly crystalline Formed by melting high purity silicon like as Integrated Circuit For mass production, cell is sliced from roughly crystallized ingot.

1-1-2. Various type of PV cell Surface of PV cell Aluminum Electrode (Silver colored wire) To avoid shading, electrode is very fine. Example of Poly Crystalline PV Anti reflection film (Blue colored film) Front Surface (N-Type side) Back surface is P-type. All back surface is aluminum electrode with full reflection.

1-1-2. Various type of PV cell PV Module (Single crystal, Poly crystalline Silicon) Single crystal Poly crystalline 128W (26.5V , 4.8A) 120W (25.7V , 4.7A) 1200mm 1200mm （3.93ft） (3.93ft) Solar Panels (Single-crystal and Polycrystalline Silicon) 　On the left is a single-crystal silicon solar panel. Single-crystal is formed by melting high purity silicon, then sliced very thinly and processed into solar panel. 　On the right is a polycrystalline silicon solar panel. To reduce the cost of solar panels, metal silicon pure enough to manufacture solar cell is poured into a mold and crystallized. Solar cell consists of many crystalline silicon. Same size 800mm （2.62ft） 800mm (2.62ft) Efficiency is higher Efficiency is lower

1-1-2. Various type of PV cell Hierarchy of PV Volt Ampere Watt Size Cell 0.5V 5-6A 2-3W about 10cm Module 20-30V 5-6A 100-200W about 1m Array 200-300V 50A-200A 10-50kW about 30m Array 10 - 50 kW Module,Panel 100 - 200 W Cell 2 – 3 W 6x9=54 (cells) 100-300 (modules)

1-1-2. Various type of PV cell Roughly size of PV Power Station. How much PV can we install in this conference room? Please remember 1 kw PV need 10 m2 (108 feet2) 10m(33feet) 20m(66feet) Conference Room (We are now) Our room has about 200 m2 (2,178 feet2) We can install about 20 kW PV in this room

1-1-3. Installation example Roof top of residence ( Grid connected ) Owner can sell excess power to power utility. Most popular installation style in Japan. (Almost 85% PV in Japan )

1-1-3. Installation example Roof top of school ,community-center building. (For education and emergency power)

1-1-3. Installation example Distant and independent power supply ( Off grid ) Advertising sign beside highway Relay station on top of mountain

1-1-3. Installation example Mountain lodge ( Off grid ) Inverter and controller 1.2kW system

1-1-3. Installation example Stationary power station (Grid connected ) e8 & PPA project in Tuvalu 30kW array 10kW array Site: Funafuti Tuvalu Installation: Feb. in 2008 Capacity: 40kW Purpose: Grid connected power supply for fuel conservation and CO2 reduction.

1-1-3. Installation example Stationary power station (Off grid or mini grid ) Site: Mongolia Installation: May & June in 1999 Purpose: For lighting, refrigerator and outlet in a hospital. Solar cell capacity: 3.4kW Wind Power capacity: 1.8kW Inverter capacity: 5kVA

1-1-3. Installation example Solar Home System (SHS) Solar array Controller Light Storage battery

1-1-4. Basic Characteristic I / V curve and P-Max control To obtain maximum power, current control (or voltage control) is very important. P N A V P- Max control “Power conditioner” (mentioned later) will adjusts to be most suitable voltage and current automatically. Power curve (V) (A) Voltage(V) Current(I) I x V = W P2 PMAX P1 Vpmax Ipmax I/V curve

1-1-4. Basic Characteristic Estimate obtained power by I / V curve P N A If the load has 0.05 ohm resistance, cross point of resistance character and PV-Character will be following point. Then power is 10x0.5=5 W (V) (A) Voltage(V) Current(I) 12 10 8 6 4 2 0 0.1 0.2 0.3 0.4 0.5 0.6 PV character ( I/V curve ) Resistance character Ohm’s theory

1-1-4. Basic Characteristic I / V curve vs. Insolation intensity P N Mismatch 5A 1A Current is affected largely by change of insolation intensity. Partially shaded serial cell will produce current mismatch. Bypass Diode (V) (A) Current(I) High intensity insolation Low intensity insolation I x V = W 5A 1A P N Bypass Diode 5A 1A 4A

1-1-4. Basic Characteristic Temperature and efficiency When module temperature rises up, efficiency decreases. The module must be cooled by natural ventilation, etc. Module Temperature (deg.C) Efficiency (%) Crystalline cell Amorphous cell 0.25 (%/deg) Typical (25C) Summer time on roof top (65C) 2% down 0.4 – 0.5 (%/deg)

1-1-5. Case sturdy 1.Maximum power control Q : Calculate how much power you can get by following three resistance. ( I / V curve is next page) P N P N P N

1-1-5. Case sturdy 1.Maximum power control Current(I) Voltage(V) I/V curve of current insolation. (V) (A) Voltage(V) Current(I) 12 10 8 6 4 2 0 0.1 0.2 0.3 0.4 0.5 0.6

1-1-5. Case sturdy 2.Temperature vs. Efficiency Q: There is 50 kW Crystalline PV system. If surface temperature rises from 25ºC to 65ºC, How much the capacity will be?