Renewable Energy Sources Solar Energy

Solar Energy The output of sun is 2.8×1023KW The energy reaching the earth is 1.5×1018KW Solar energy is lost because of following reasons Scattering, Absorption, Cloud cover, Reflection, Climate etc.. Insolation is a quantity indicating the amount of incident solar power on a unit surface, commonly expressed in units of kW/m2

SE…. At the earth’s outer atmosphere, the solar insolation on a 1 m2 surface oriented normal to the sun’s rays is called SOLAR CONSTANT and its value is 1.37 kW/m2 Due to atmospheric effects, the peak solar insolation incident on a terrestrial surface oriented normal to the sun at noon on a clear day is on the order of 1 kW/m2. A solar insolation level of 1 kW/m2 is often called PEAK SUN

SE… Solar PV captures the energy in visible region Solar thermal captures energy in infrared region

SE… Irradiance is an amount of solar energy received on a unit surface expressed in units of kWh/m2 Solar irradiance is essentially the solar insolation (power) integrated with respect to time The worldwide average daily value of solar irradiance on optimally oriented surfaces is approximately 5 kWh/m2 or 5 PSH

SE… The important terminology one needs to know to understand the heat transfer mechanism is the following a) Radiation b) Conduction c) Convection d) Mass transport

Solar Thermal Power Plant The two main types of solar thermal power plants are 1. Concentrating Solar Power (CSP) plants. 2. Solar Chimneys 3. Stationary concentrating collectors or Flat type Concentrating Solar Power (CSP) plants Generally use reflectors to concentrate sunlight into a heat absorber Produce electric power by converting the sun's energy into high-temperature heat using various mirror configurations

CSP Types Parabolic Trough Systems Power Tower Systems Parabolic Dish Systems

Flat Solar Collectors

Solar Water Heater

Solar Air Heater

Solar Water Distillation

Solar Photovoltaic Power

Solar PV Cell Edmond discovered the solar cell photovoltaic effect in 1839. Fxitz fabricated the first thin film solar cell. The Bell labs Chopin fabricated solar cell with 6%. Solar cells are used as power backup in Vanguard-1 satellite. It converts solar energy into electrical power directly.

S PV C…. A solar cell is like a diode. The energy of a photon should be greater than the band gap of the diode to generate hole pair. The semiconductor used for photon- absorption have band gap energy such that the maximum percentage of solar spectrum is efficiently absorbed. This addition of excess majority charge carriers to the respective regions and diffuse away from the junction region as their concentration near the junction has increased. Thus , an illuminated PN junction becomes a photovoltaic cell with a positive terminal on p side.

PN-Diode ? Crystalline silicon that has been doped with phosphorus in suchway that the doped material possesses a surplus of free electrons. It is called n type semiconductor Crystalline Silicon + Boron = P type semiconductor->Absence of electrons are called holes The PN junction creates space charge region-recombination- diffusion current Forward bias, depletion region become narrow and flow charges is called drift current

Solar PV Cell… It consists of a very thick p-type crystal covered by a thin n-type layer exposed to the sun light The energy available in a photon is E=1.24/ƛ For every strike of photon, there is generation of electron hole pair Each PV cell is rated 0.5 V to 0.7 V and current is 30 mA/cm2 PV Modules are formed as a panel

Solar PV Cell.. Based on manufacturing, the PV cells are classified as Mono crystalline: efficiency of 12-14 %. This are now predominantly available in market Poly crystalline: efficiency of 12% Amorphous: efficiency of 6-8% Life of crystalline cells are 25 years but amorphous cells’ life is 5 years

Solar PV Cell…. Solar Cell are formed like constant voltage source or constant current source

Normal operation point (Maximum Power point) PV Cell… 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 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. Low insolation I x V = W (V) Voltage(V) about 0.5V (Silicon)

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% 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. Dye-sensitized Type 7 - 8% Organic Semiconductor Organic Thin Layer Type 2 - 3% Conversion Efficiency = Electric Energy Output Energy of Insolation on cell x 100%

Type of PV cell Hierarchy of PV Array Module,Panel Cell 10 - 50 kW 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)

Maximum Power Point Tracker In order to receive maximum power, the load adjust itself the accordingly to track the maximum power point. Generally, MPPT is an adaptation of dc-dc switching voltage regulator A buck boost scheme is commonly used with voltage and current sensors tied into a feedback loop using a controller to vary the switching times

Buck Boost Converter The buck–boost converter is a type of DC-to-DC converter that has an output voltage magnitude that is either greater than or less than the input voltage magnitude Two different topologies are called buck–boost converter. Both of them can produce a range of output voltages, from an output voltage much larger (in absolute magnitude) than the input voltage, down to almost zero

BBC…. A buck (step-down) converter combined with a boost (step-up) converter

BBC…

BBC…. The basic principle of the buck–boost converter is fairly simple (see figure 2): while in the On-state, the input voltage source is directly connected to the inductor (L). This results in accumulating energy in L. In this stage, the capacitor supplies energy to the output load. while in the Off-state, the inductor is connected to the output load and capacitor, so energy is transferred from L to C and R. Compared to the buck and boost converters, the characteristics of the buck–boost converter are mainly: polarity of the output voltage is opposite to that of the input; the output voltage can vary continuously from 0 to  (for an ideal converter). The output voltage ranges for a buck and a boost converter are respectively  to 0 and  to .

BBC… There are three possible strategies for operation of an MPPT By monitoring dyanamic and static impedances Dynamic impedance = Static impedance By Monitoring Power output dP/dV=0 By fixing the voltage as a fraction of output voltage Operating voltage of array=Open circuit voltage constant (k)*Open circuit voltage

Solar PV Systems Classifications Central Power Station Systems Distributed Systems Stand alone systems Grid Interactive systems Small System for consumer applications

References http://www.daviddarling.info/encyclopedia/F/AE_flat_plate_solar_thermal_collector.html http://rimstar.org/renewnrg/window_covering_solar_air_heater_furnace/how_solar_air_heater_works.jpg www.globalelectricity.org/.../Solar_PV.../1-1Basic%20Principle%20of%2... https://en.wikipedia.org/wiki/Buck%E2%80%93boost_converter