Shadow Effect [Compatibility Mode]

7/28/2019 Shadow Effect [Compatibility Mode]

1/39

2011 Underwriters Laboratories Inc.

Shadow affect on PV panels.


2/39

2011 Underwriters Laboratories Inc.

INTRODUCTION

The choice of a proper location is the first and the very essentialstep in solar system design procedure. The modules have to befixed with proper tilt angle and distance to prevent Shadow onthe module for efficient operation.


3/39

Sun

The sun is a gaseous body composed mostly

of hydrogen.

Gravity causes intense pressure and heat at

the core initiating nuclear fusing reactions.

Even when planet Earth is 93 million miles away, we still receivean amazing quantity of usable energy from the sun.

3


4/39

Solar energy in India.

Today, more than 40% of the Indian population, or

approximately 1,25,000 villages, have no access to reliable electricity.

If 1.25% of Indian Land is used to harness Solar energy, It wouldyield 8 million Mega watt.

It is equivalent to 5909 mtoe(million tons of oil equivalent) per year.

4


5/39

Solar Radiation Spectrum

5


6/39

Solar Radiation

Solar irradiance is the intensity of solar power, usually expressed inWatts per square meter [W/m^2]

Since the proportion of input/output holds pretty much linearly forany given PV efficiency, we can very easily evaluate a systemperformance by measuring irradiance and the PV module output.

Solar spectral distribution is important to understanding how the PVmodules respond to it.

Most Silicon based PV devices respond only to visible and the nearinfrared portions of the spectrum.

Thin film modules generally have a narrower response range.

6


7/39

Solar Intensity on Planets.

7


8/39

Solar Radiation

www.cabrillo.edu/.../Chapter%202%20Solar%20Radiation


9/39

Basics of Directions & Angles.

Coordinate systems :

Earth based latitude and longitude.

Observer based azimuth angle and altitude angle.


10/39

Latitude

Latitude lines run east/west but they measure

north or south of the equator (0) splitting the ea rthinto the Northern Hemisphere and SouthernHemisphere.


11/39

Latitude

North Pole

South Pole

Lines of latitude arenumbered from 0at theequator to 90at the North

Pole.

Lines oflatitude arenumbered from 0at the equator to90at the South

Pole.

][

9080

70

60

50

40

20

30

10

90

80

70

60

50

40

20

10

30


12/39

Longitude

The prime meridian is the vertical line that marks the zero degree longitudemeasurement on the globe of Earth.

Lines of longitude are numbered east from the Prime Meridian to the 180

line and west from the Prime Meridian to the 180lin e.

PRIME MERIDIAN

WestLongitude

EastLongitude

180

N

EW

S

North Pole


13/39

True South

In the Northern Hemisphere,stationary PV arrays are orientedsouth to maximize PV output. But

using your compass to find southwill only give you an indication ofmagnetic south, not True South.

.

13

The difference in the orientation is called as magneticdeclination.


14/39

True North

In the Southern Hemisphere,stationary PV arrays are oriented

north to maximize PV output. Butusing your compass to find northwill only give you an indication ofmagnetic north, not True North.

The following link can be used to find the magnetic declination at any place.

http://magnetic-declination.com/

14

Usually the magnetic declination should be either subtracted oradded to your magnetic compass reading to find True North orTrue south. The declination is based on your latitude and

longitude.


15/39

Altitude-Azimuth coordinate system

Based on what an observer sees in the sky.Zenith = point directly above the observer (90o)Nadir = point directly below the observer (-90o) cant be seenHorizon = plane (0o)

Altitude = angle above the horizon to an object (star, sun, etc)(range = 0o to 90o)

Note: lines of azimuthconverge at zenith


16/39

Zenith angle. Zenith is the point in the sky directly overhead a particular location asthe Zenith angle z increases, the sun approaches the horizon.


17/39

Solar Radiation

Tilt angle is the vertical angle between the horizontal and thearray surface

Array orientation is defined by two angles:

www.cabrillo.edu/.../Chapter%202%20Solar%20Radiation


18/39

Altitude and Azimuth angle.

Solar Altitude Angle is the vertical angle between the sun and thehorizon added to the Zenith angle is equal to 90.

Azimuth Angle is the horizontal angle between a reference direction.In the solar industry we call south 180 and this angle will range between

90 (east) and 270 (west).


19/39

Array Azimuth Angle.

Array Azimuth Angle is the horizontal angle between areference direction typically south - and the direction anarray surface faces.


20/39

Solar Declination.

Solar Declination is the angle between the equatorial plane and the ecliptic plane

The solar declination angle varies with the season of the year, and rangesbetween 23.5 and +23.5


21/39

Solstices.

Summer Solstice is atmaximum solar declination(+23.5) and occurs aroundJune 21st Sun is at Zenith at

solar noon at locations 23.5 Nlatitude.Winter Solstice is at minimumsolar declination (-23.5) andoccurs around December 21stAt any location in the NorthernHemisphere, the sun is 47

lower in the sky at noon onwinter solstice than on thesummer solstice Days aresignificantly shorter than nights.


22/39

Sun path

Sun path refers to the apparent significant seasonal-and-hourlypositional changes of the sun as the Earth rotates, and orbits

around the sun.

Sun path helps us to find,

Azimuth angle and Altitude angle

For particular place at specific

Time of the day.

22


23/39

Steps to find Azimuth angle and Altitude angle.

Step 1: Select the sun path diagram for the site latitude (or nearest latitude).

For Bangalore 1258 North latitude may be selected.Step 2: Find the date curve for December 21.

Step 3: Find the hour line for 9:00 am and mark its intersection with the curve of December 21.

Step 4: Lay a straight-edge from the center of the chart from the observation point) through the marked

hour point to the perimeter circle. Read the Azimuth Angle from the perimeter scale. For this

example () = 127.

Step 5: On he straight line, measure the distance in millimeter between the perimeter circle and themarked point. Each millimeter represents one degree of altitude angle. This distance will be

measured 28.5 mm. This means the altitude of the sun at 9:00 am of December 21 in Bangalore

is () = 28.5.

23

For a certain location, for a certain day and hour, azimuth and altitudeangles may be defined by the following procedure. For this purpose the sun pathdiagram prepared for that location should be used.

Example : Define the position of the sun in Bangalore at 9:00 am of December 21.


24/39

SUN path for Bangalore.

24


25/39

Hourly Sun Path

25


26/39

Annual Sun Path

26


27/39

The main aspect to study are

Tilt of the solar panel.

Shadows of extern elements.

Shadows of own elements.

27


28/39

Edge shadowing.

Shading of one region of a modulecompared to another leads tomismatch is PV modules.

28

Edge shadowing which may happen in PVfield due to dust accumulated on the tilted PVarray. This happens intensively in the bottomedges of the panels causing another type of

reduction of the PV output.

Edge shading is also possible tohappen in field due to the shadows

cast by other PV cells and the tilt, theorientation and the surfacetemperature variation of the PV panel.


29/39

Tilt angles

The optimum tilt angle of the solar panel can be expressed by thefollowing simplified formula:

Tilt = Latitude

Tilt angles below 15 in urban areas may cause system losses dueto pollution and dirt accumulation on the panels.

Local land slope will be logically taken into account, which can helpreducing distance between the panel rows to improve the surfaceprofit.

29


30/39

Another tilt angles table.

30

Jan Feb Mar Apr May Jun

61 69 77 85 93 100

Jul Aug Sep Oct Nov Dec

93 85 77 69 61 54

Winter

54angle

Spring/Autu

mn

77angle

Summer

100angle

BangaloreOptimum Tilt of Solar Panels by Month

Figures shown in degrees from vertical

http://solarelectricityhandbook.com/solar-angle-calculator.html


31/39

Orientation angle

The most favorable orientation is 180 South (North

hemisphere).

For Southern hemisphere 0 North.

An orientation deviation below 20 (East or West) causenegligible system losses.

31


32/39

Distance between panel rows

A basic rule would be to avoid shadows during the 6 8 centralhours of the day, in the day of the year with less radiation.

This implies calculating the angle of the sun (height regarding theline of the horizon) to +/- 3 - 4 hours regarding the solar midday. This

angle will vary depending on the latitude.

The objective is to avoid that the top of the front panel projects ashadow to the lowest part of the panel that is placed behind.

32

SS4

SS5


33/39

Slide 32

SS4

As a rule of thumb it is better to separate the two rows by a distance of 2 * effective height of the structure considering that the land isplant.

If it is sloping in S N direction it depends upon the amount of alope for Indian conditionsSathyanarayan, SRC, 12/11/2012

SS5

Better 6 - 8 hrsSathyanarayan, SRC, 8/2/2012


34/39

Distance between the panels.

D= Sin( + ) * H

Sin

() The variable is the tilt of the panels.

(H) The height of the panel.

() is a function of the latitude of the installation and the optimal sunelevation.

(D) is the distance between the panels.

33


35/39


36/39

Hot-Spot Heating

Hot-spot heating occurs when there is one low current solar cell in astring of at least several high short-circuit current solar cells.

One shaded cell in a string reduces the current through the goodcells, causing the good cells to produce higher voltages that canoften reverse bias the bad cell.

Power gets dissipated in the poor cell.

35


37/39

Hot spot effects

Local overheating, or "hot-spots", leads to destructive effects cellor glass cracking, melting of solder or degradation of the solar cell.

36


38/39

Bypass Diodes

One by pass diode per solar cell is too expensive option.

Amount mismatch depends on the degree of shading.

A partial shading will cause a lower forward bias voltage.

The maximum group size per diode, without causing damage, isabout 15 cells/bypass diode, for silicon cells.

Normally for 36 cell module 2 bypass diodes are used.

37


39/39

THANK YOU.

Documents

Shadow Effect [Compatibility Mode]