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

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• 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

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• Solar PV captures the energy in visible region• Solar thermal captures energy in infrared region

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• 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

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• 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

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PV Cell…

• Voltage and Current of PV cell ( I-V Curve )

(V)

(A)

Voltage(V)

Curr

ent(

I)P

N

A

Short Circuit

Open Circuit

P

N

V

about 0.5V (Silicon)

High insolation

•Voltage on normal operation point0.5V (in case of Silicon PV)

•Current depend on- Intensity of insolation- Size of cell

•Voltage on normal operation point0.5V (in case of Silicon PV)

•Current depend on- Intensity of insolation- Size of cell

Low insolation

Normal operation point(Maximum Power point)

I x V = W

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CrystallineCrystalline

Non-crystallineNon-crystalline

Single crystalSingle crystal

Poly crystallinePoly crystalline

AmorphousAmorphous

Gallium Arsenide (GaAs)Gallium Arsenide (GaAs)

Conversion Efficiency of Module

Conversion Efficiency of Module

10 - 17%10 - 17%

10 - 13%10 - 13%

7 - 10%7 - 10%

18 - 30%18 - 30%

Conversion Efficiency =Electric Energy Output

Energy of Insolation on cellx 100%

Dye-sensitized TypeDye-sensitized Type

Organic Thin Layer TypeOrganic Thin Layer Type

7 - 8%7 - 8%

2 - 3%2 - 3%

Type of PV cell

• Types and Conversion Efficiency of Solar Cell

Silicon SemiconductorSilicon Semiconductor

CompoundSemiconductorCompoundSemiconductor

Solar CellSolar Cell

OrganicSemiconductorOrganicSemiconductor

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Type of PV cell• Hierarchy of PV

2 – 3 W

100 - 200 W

10 - 50 kW

Cell

Array

Module,Panel

Volt Ampere Watt SizeCell 0.5V 5-6A 2-3W about 10cmModule 20-30V 5-6A 100-200W about 1mArray 200-300V 50A-200A 10-50kW about 30m

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

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• A buck (step-down) converter combined with a boost (step-up) converter

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• 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 .

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• 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