Renewable 1

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Renewable EnergyPart 1

Professor Mohamed A . El-Sharkawi

Renewable Energy

• Solar

• Wind

•

• Small Hydro

• Geothermal

• Tidal

• Biomass

Solar Energy

Solar Power Density

•

: solar power density on earth in kW/m2

pwadt o cos

• o: ext rater rest ra power ens t y . m

• : zenith angle (angle from the outward normal on the earthsurface to the center of the sun)

• dt: direct transmittance of g ases except for water (thefraction of radiant energy that is not absor bed by gases)

• p: is the transmittance of aerosol

• wa: water vapor absorptions of radiation .

Zenith Angle

Center

of Sun

Center of Earth

Solar Energy (Whr/m2/day)


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40%

60%

80%

100%

Density ratio

Daily Solar Power Densi ty

2t t

2

0%

20%

0 2 4 6 8 10 12 14 16 18 20 22 24

Time

22

max

o

e

t:hour of the day using the 24 hr clock

max: the maximum solar power density

t o: time at max (noontime in the equator)

: standard deviation

Solar Efficiency ()

pwadt o cos

0

%705cos pwadt

Example

An area located near the equator has the followingparameters:

%%,%, wadt 29580

Assume that the standard deviation of the solar distribution

function is 3.5hr. Compute the solar power density and

solar efficiency at 3:00 PM.

Solution

2kW/m019500208001353 ..*..)*cos(*

cos

max

pwadt omax

At noon

2532

1215

2 kw/m6930012

2

2

2

.e*.e ).(*

)()t t (

max

o

%.*..)*cos( 74950020800

At 3:00PM

Types of Solar Systems

– Passive Solar System

– ct ve o ar ystem otovo ta c or

Passive Solar System

New supply of cold water Warm water to the house

Lens

Sun rays

water

Cold water

back

to solar

collector

Tank

Collector


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Passive Solar Integrated Solar Combined

Cycle System (ISCCS)

Collector

mirror

Receiver

Integrated Solar Combined Cycle System (ISCCS)

Active Solar Cel l

Photovoltaic PV

SiliconSilicon

Nucleus

Empty

space for

extra

electron

Electrons

Silicon Atom Silicon Crystal

SiliconSilicon

• Silicon is a good insulator

• To make the silicon more conductive

,

added (doping)

– Phosphorus (P), which has 5 electrons in

its outer shell

– Boron (B), which has 3 electrons in its

outer shell


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P-N Material

Electron without

bonding

SI SI SI Extra

space for

SI SI SI

SI

SI SI SI

SI

P

electronSI

SI

SI

SI SI

B

n-type p-type

Lens I

P-Type

Base

N-Type

-

-

Load

Active Solar Cell (PV) Active Solar Cell (PV)

• PV cell is built like a diode out of semiconductor

material.

• Sunlight is composed of photons, or particles of

solar ener Photons are the ener b roducts of .

the nuclear reaction in the sun.

• When photons strike a PV cell, some of the

protons energy is absorbed by the semiconductor

material of the PV cell.

Active Solar Cell (PV) Active Solar Cell (PV)

• With this extra energy, the electron in thesemiconductor material become excited and break off its atom, and eventually begin anelectric current.

• Because PV cells are built like diodes, freeelectrons are forced to flow in only onedirection

– the current is DC.

Glass cover or lens

Antireflective coating

Main Parts of PV

Contacts grid

n-type material

p-type material

Base

Structure of Solar SystemStructure of Solar System

•• PV cell:PV cell: 4X4 inches. The cell can produce

about 1 watt which is enough to run a

calculator.


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•• Panel or Module:Panel or Module: To increase

its energy rating, the PV cells

are connect together in parallel


an ser es.

• Parallel cells increase the

current rating

• Series cells increase the

voltage rating.

•• Array: Array: PV panels connect together in parallel

and series to form a high power system.



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Example

• Estimate the maximum power, current, and voltage ratingsof the panel and array in the figure. Assume that each PVcell produce a maximum power of 2.5 W at the best solarconditions

Solution

• The panel has 9 series cells. Assume thatthe voltage of each cell i s 0.5 V, the total

voltage of the panel is

*

The panel has a total o f 36 cells, the power

of the panel is

.. panel

9036*5.2 panelP W

Total current of panel

205.4

90

panel

panel

panelV

P I A

The array consists of 2 columns of 4 series modules.

The total voltage of the array is

184*5.44* panelarray V V V

Total power of the array is

7208*908* panelarray PP W

4018

720

array

array

array V

P

I A

Computation of PV Energy

40%

60%

80%

100%

2

2

2

2

)(

max

ot t

e

0%

20%

0 2 4 6 8 10 1 2 1 4 1 6 1 8 2 0 2 2 2 4

Time

Solar power density

2)t t ( o

Panel power

Computation of PV Energy

Linear relationship

2t t

Solar power density

22

max panel ePP

2

24

0

22

2

max

)t t (

max panel Pdt eP E

o

Panel Energy

22

max

e

Example

5.12

)12(

max

2

t

e W Pmax 100

Compute the daily energy produced by a PV panel.

Solution

5.122 2 5.225.12

6275.2*2*1002max P E panel Wh


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Example

A 2 m2 panel of solar cells i s installed i n the Nevada’s

area. The efficiency of the solar panel is 10%.

m / kw.max 012

h.53

1. Compute the electrical power of the panel.

2. Assume the panel is installed on a

geosynchronous satellite. Compute its electrical

power output.

Solution

kW .*. A*Psun 371125685

W .*.PP 1137137110

1.

sun pane

kW .* A*Posun 706221353

W .*.PP sun panel 6270270610

2.

Stand Alone

PV System

e r

Solar array

House

dc current

Charger

Discharger C o n v e r t

Local load Battery

ac current

PV System

without battery

rMeter To utility

Solar

arrayHouse

e n t ac current

C o n v e r t

Local load

d c c u r

Solar System With Battery

•• Battery:Battery: To store the energy whenthe PV power is not f ully uti lized by

the load. – The battery power is later used when the

PV power is less than the demand.

– These batteries are deep cycle types

•• Charger:Charger: To charge the battery by thePV

Solar System With Battery

•• Inverter:Inverter: To invert the dc power of

the battery to the 60Hz power used in

homes.

•• Synchronizer:Synchronizer: Used to connect the

PV system to the power grid.

– DC/AC converter.


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Ideal PV Model: P-N Junction

Cathode (K) Cathode (K)

p

Anode (A) Anode (A)

I

V d


I R

V d

V s+V l

I Forward biased

region

-

V d Reverse biased

region

I o Reverse saturation current


1T

d

V

V

o e I I qkT

V T

I

Forward

biased

region

I o Reverse saturationcurrent

I o: reverse saturation current

V T : thermal voltage

q: elementary charge constant (1.602 10-19 Coulomb)

k : Boltzmann’s constant (1.380 x 10-23 J/K)

T : absolute temperature in Kelvin (K).

V d Reverse biased

region

PV Model

• The current Io makes the upper terminal of the load

positive with respect to the lower terminal

Io

Io

L o a d

V

+

-

• So the diode has a positive voltage on its anode wrt

cathode.

• This is a forward biased voltage which causes a

forward current to flow back into the diode.

• Now we have two currents in the circuit at the same time

1. current coming out of the diode due to the acquired

energy by the PV Is2. current going into the diode due to the positive

polarity across the load Id

PV Model

d

Solar Celld s

I I I

s I d L o= d

I s: the solar current (is a nonlinear variable that changes

with light density (irradiance)

I d : the forward current through the diode.

V d

I s

V d

I d

I o

PV Characteristics

V d

I = I s- I

d

Q I

Q II

Q III Q IV


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PV Power CharacteristicsVI P

d s

d

I I I

V V

I s I d I o

a d

V=V d

Solar Cell

1T

d

V

V

od e I I

1T

d

V

V

od sd e I V I V I V P

PV Power Characteristics

I I sc

I mp

V oc

P

Pmax

V d V mp

PV Power Characteristics

• Main variables

– Short Circuit Current (Isc)

– Open Circuit Voltage ( oc)

– Maximum Power Operating Point (Pmax,

Vmp, Imp)

Short Circuit PV

I s I d =0 I sc=I s

ssc

Open Circuit PV

I s I d =I s V oc

1ln*

1

o

sT oc

V

V

osd

I

I V V

e I I I T oc

Example

• An ideal PV cell with reverse saturation

current of 1nA is operating at 30oC. The

solar current at 30oC is 1A. Com utethe output voltage and output power of

the PV cell when the load draws 0.5A.


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Solution

V10*11.2610*602.1

)15.27330(*10*38.1 319

23

q

T k V T

1V V

os e I I I T

1*1015.0 02611.09

V

e

V523.0*110*5.01ln 9 T V V

W2615.05.0*523.0 I V P

Example

• An ideal solar cell with reversesaturation current of 1nA is operating at

20oC. The solar current at 20oC is 0.8A.

Compute the voltage and current of the

solar cell at the maximum power point.

SolutionVI P

0

I V

I V

V

Pmp

1T V

V

os e I I I

T V V

T

o eV V

/

01/

T mp V V

oT

mp

os e I V

V

I I V

P

At maximum Power

V10*25.2510*602.1

)15.27320(*10*38.1 319

23

q

T k V T

Solution

osV V mp

I

I I e

V

V T mp

/1

o

925.25/ 10*8.025.25

1

mpV mp e

V

mV8479.443mpV

Solution

1T

mp

V

V

osmp e I I I

8479.443

mW948.3357569.0*8479.443*max mpmp I V P

A7569.01108.0 25.259

e I mp

Operating Point of PV

• The operating point of the solar cell depends

on the magnitude of the load resistance R

• The load resistance is the out ut volta e Vdivided by the load current I.

• The intersection of the PV cell characteristic

with the load line is the operating point of the

PV cell.


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Solar Cell

I s I d

I L o a d

V=V d

Operating Point of PV

I R1

R2

R1


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Effect of Irradiance

1

P

2

1T 3 T 1

3

V oc V

T 3

T 2 Load line

1 2

Effect of Temperature T

T 1P

T

T 1>T 2>T 3

V

T 3

PV Module (Series

Connection)

I I Vs

Is2Id2 V2

L o a d

Is=Is1=Is2 L o a d

V=Vd1+Vd2

PV Module (Parallel

Connection)

I I V1 a d

Is2Id2 V2

L o a d Is=Is1+Is2

L o= d1= d2

Example

• An ideal PV module is composed of 50

solar cells connected in series. At 20oC,

the solar current of each cell is 1A andthe reverse saturation current is 10nA.

Draw the I-V and I-P characteristics of

the module.


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Solution

mV25.2510*602.1

)15.27320(*10*38.119

23

q

T k V T

1*101 02525.08V

V V

od ee I I T

1*101 02525.08cellV

d scell e I I I

cellcellcell I V P

cellule V nV *mod

cellule PnP *mod 0

5

10

15

20

0 5 10 15 20 25

Module Voltage

M o d u l e C u r r e n t a n d P o w e r

Current

Power

Losses of PV Cell

• Irradiance Losses

• Electrical Losses

Irradiance Losses

1. Due to the reflection of the solar radiation at

the top of the PV cell.

2. The light has photons with wide range of

ener levels – Some don’t have enough energy to excite the

electrons.

– Others have too much energy that is hard to

capture by the electrons.

• These two scenarios account for the loss of

about 70 percent of the solar energy

Losses of PV Cell

(Electrical Losses)

• The resistances of the collector traces at the

top of the cell.

• The resistance of the wires connecting cell to

load.

• The resistance of the semiconductor crystal

Real PV Model

• To account for the electrical losses only

Solar

Cell

Rs

Is IdI

L o a dV

VdRp

Ip

I

Rs : Resistance of wires and traces

R p : internal resistance of the cell

Effic iency of PV Cell

A

I V

P

P sd

s

seirradiance

*

power Sun

yelectricittoconverted powerSun

sd se

out

e I V

I V

P

P

*

*

yelectricittoconverted powerSun

celltheof powerOutput

A

I V

P

P

P

P

P

P

s

out

se

out

s

seeirradiance

*


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Example

• A 100 cm2 solar cell is operating at 30oC

where the output current is 1A, the load

voltage is 0.4V and the saturation current of

e o e s n . e ser es res s ance o e

cell is 10 m and the parallel resistance is1k. At a give time, the solar power density is200W/m2. Compute the irradiance efficiency

and the overall efficiency.

Solution

V10*1.2610*602.1

)15.27330(*10*38.1 319

23

q

T k V T

V41.001.0*14.0 sd IRV V

mA64.61*101 0261.041.0

9

ee I I T d

V

V

od

mA41.01000

41.0

p

d p

R

V I

A00705.100041.000664.01 pd s I I I I

205.001.0*200

00705.1*41.0*

A

I V sd irradiance

Solution

mW168.101000*10*41.001.0*0.1 23222 p pslosse R I R I P

975.0010168.00.1*4.0

0.1*4.0

losselosseout

out

se

out

ePVI

VI

PP

P

P

P

... eirradiance

Conclusion

Most of the losses are irradiance

Assessment of PV Systems

$5.0

$4.0

$5.0

$6.0

h

$1.5

$0.3$0.4$0.6

$0.0

$1.0

$2.0

$3.0

1970 1980 1990 2000 2010

Year

$ / k W

Solar Power and the

Environment

• 6kW from a photovoltaic system

instead of a thermal power plant can

reduce annual ollution b – 3 lbs. of NOx (Nitrogen Oxides),

– 10 lbs. of SO2 (Sulfur Dioxide), and

– 10530 lbs. of CO2 (Carbon Dioxide).


• Consumer products (calculators, watches,

battery chargers, light controls, and flashlights)

are the most common applications

• Lar er PV s stems are extensivel used in space applications (such as satellites)

• In higher power applications, three factors

determine the applicability of the PV systems1. the cost and the payback period of the system

2. the accessibility to a power grid

3. the individual inclination to invest in environmentally

friendly technologies.


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• In remote areas without access to power

grids, the PV system is often the first choiceamong the available alternatives.

• ,

systems worldwide had the capacity of more

than 900 GWh annually – this PV energy is enough for about 70,000 homes

in the USA, or about 4 million homes in developing

countries.


• To manufacture the solar cells, arsenic and

silicon compounds are used – Arsenic is odorless and flavorless semi-metallic

chemical that is highly toxic

– Silicon, by itself, is not toxic. However, when additives

are added to make the PV semiconductor material, the

compound can be extremely toxic.

– Since water is used in the manufacturing process, the

runoff could cause these material to reach local

streams

– Should a PV array catch fire, these chemicals can be

released into the environment.


• Solar power density can be intermittent due to

weather conditions

• PVs are limited exclusively to daytime use

• For hi h ower PV s stems the arra s s read

over a large area.

• The PV systems are considered by some to be

visually intrusive

• The efficiency of the solar panel is still low, making

the system expensive and large

• Solar systems require continuous cleaning of theirsurfaces

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