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$: Solar Radiation - ecgllp.com · The electromagnetic spectrum ranges from short wavelength gamma rays and x-rays, to long wavelength radio waves. The solar spe\ൣtrum includes visible$
2012 Jim Dunlop Solar

Chapter 2

Solar Radiation

Terminology & Definitions ● Geometric & Atmospheric Effects ● Solar Power & Energy ●

Measurements & Data

Presenter

Presentation Notes

Solar energy is the fuel that creates and sustains life on earth. The nature and characteristics of the solar radiation resource are of fundamental importance in understanding how solar PV systems are designed and perform. References: Photovoltaic Systems, Chap. 2 National Renewable Energy Laboratory - Renewable Resource Data Center: www.nrel.gov/rredc

2012 Jim Dunlop Solar Solar Radiation: 2 - 2

Overview

Defining basic terminology associated with solar radiation, including solar irradiance (power), solar irradiation (energy) and peak sun hours.

Identifying the instruments used for measuring solar radiation.

Understanding the effects of the earth’s movements and atmospheric conditions on the solar energy received on the earth’s surface.

Locating the sun’s position using sun path diagrams and defining the solar window.

Accessing solar radiation data resources and quantifying the effects of

collector orientation on the amount of solar energy received.

Presenter

Presentation Notes

Reference: Photovoltaic Systems, p. 25


Sun - Earth Relationships

Sun: Diameter: 865,000 miles (1,392,000 km, 109 times earth) Mass: 2 x 1030 kg (330,000 times earth) Density: 1.41 g/cm3

Gravity: 274 m/s2 (28 g) Surface Temperature: 10,000 F (5800 K)

Earth: Diameter: 7,930 miles (12,756 km) Mass: 5.97 x 1024 kg Density: 5.52 kg/cm3

Gravity: 9.81 m/s2 (1 g) Typical Surface Temperature: 68 F (300K) Earth’s Orbit Around Sun: 1 year Earth’s Rotation about its Polar Axis: 1 day

93 million miles, average (1.5 x 108 km)

1 Astronomical Unit (Distance traveled in 8.31 minutes at the Speed of Light)

Presenter

Presentation Notes

A comparison of the physical properties for the sun and earth illustrate the vast differences. Reference: Photovoltaic Systems, p. 26-27


Solar Radiation

Solar radiation is electromagnetic radiation ranging from about 0.25 to 4.5 µm in wavelength, including the near ultraviolet (UV), visible light, and near infrared (IR) radiation.

Common units of measure for electromagnetic radiation wavelengths: 1 Angstrom (Å) = 10-10 meter (m) 1 nanometer (nm) = 10-9 meter 1 micrometer (µm) = 10-6 meter 1 millimeter (mm) = 10-3 meter 1 kilometer (km) = 1000 meters

NASA

Presenter

Presentation Notes

The sun produces immense quantities of electromagnetic radiation. The tiny fraction reaching the earth’s surface amounts to approximately 170 million gigawatts (GW), many thousands of times greater that the electrical power used on earth. Note that the United States has just over 1000 GW of electrical power generation. Reference: Photovoltaic Systems, p. 26-36


Electromagnetic Spectrum

Wavelength (µm)

near infra-red

near ultra-violet

Visible light

0.3 0.5 0.7

Wavelength

Gam

ma

rays

1 Å

10 Å

100

Å

0.1 µm

1 m

m

1 µm

10 µ

m

100 µm

10 m

m

100

mm

1 m

10 m

100

m

103 m

104 m

105 m

X ra

ys

Ultr

avio

let R

adia

tion

Visi

ble

Ligh

t

Infr

ared

Rad

iatio

n

Mic

row

aves

Shor

t Rad

io

Wav

es (F

M/T

V)

AM

Rad

io

Long

Rad

io W

aves

Solar spectrum

0.25 µm 4.5 µm

Presenter

Presentation Notes

The electromagnetic spectrum ranges from short wavelength gamma rays and x-rays, to long wavelength radio waves. The solar spectrum includes visible light and near infrared radiation. Reference: Photovoltaic Systems, p. 30


Solar Irradiance (Solar Power)

Solar irradiance is the sun’s radiant power, represented in units of W/m2 or kW/m2.

The Solar Constant is the average value of solar irradiance outside the earth’s atmosphere, about 1366 W/m2.

Typical peak value is 1000 W/m2 on a terrestrial surface facing the sun on a clear day around solar noon at sea level, and used as a rating condition for PV modules and arrays.

1 m

1 m One

Square Meter

Typical peak value per m2

1000 watts = 1 kilowatt

Presenter

Presentation Notes

Solar irradiance is sun’s radiant power incident on a surface of unit area, commonly expressed in units of kW/m2 or W/m2. The Solar Constant is the value of solar irradiance outside the earth’s atmosphere on a surface facing the sun’s rays, which averages about 1366 W/m2. Due to atmospheric effects, typical peak values of terrestrial solar irradiance are on the order of 1000 W/m2 on surfaces at sea level facing the sun’s rays under clear sky conditions around solar noon. Consequently, 1000 W/m2 is used as a solar irradiance reference condition for rating the peak output for PV modules and arrays. Reference: Photovoltaic Systems, p. 26-29


Solar Irradiance

Time of Day

Sola

r Irr

adia

nce

(W/m

2 )

Sunrise Noon Sunset

For south-facing fixed surfaces, solar power varies over the day, peaking at solar noon.

Presenter

Presentation Notes

For south-facing fixed (non-tracking) surfaces on a clear day, the incident solar irradiance varies over the day in a bell-shaped curve, peaking at solar noon. Reference: Photovoltaic Systems, p. 28


Solar Irradiation (Solar Energy)

Solar irradiation is the sun’s radiant energy incident on a surface of unit area, expressed in units of kWh/m2. Typically expressed on an average daily basis for a given month. Also referred to as solar insolation or peak sun hours.

Solar irradiation (energy) is equal to the average solar irradiance (power) multiplied by time.

Peak sun hours (PSH) is the average daily amount of solar energy received on a surface. PSH are equivalent to: The number of hours that the solar irradiance would be at a peak level of

1 kW/m2. Also the equivalent number of hours per day that a PV array will operate

at peak rated output levels at rated temperature.

Presenter

Presentation Notes

Solar irradiation is the sun’s radiant energy incident on a surface of unit area, commonly expressed in units of kWh/m2/day for monthly averages and a given surface orientation. Insolation is also a term used to represent solar irradiation. Solar energy data are used to estimate the performance of buildings and solar energy utilization systems. Reference: Photovoltaic Systems, p. 28-35


Solar Power and Solar Energy

Time of Day

Sola

r Irr

adia

nce

(W/m

2 )

Sunrise Noon Sunset

Solar irradiation (energy) is the area under the solar irradiance (power) curve

Solar irradiance (power)

Presenter

Presentation Notes

Similar to electrical power and energy, solar power and solar energy are related by time. The amount of solar energy received on a surface over a given period of time is equal to the average solar power over the period multiplied by the time. Graphically, solar irradiation (energy) is the area under the solar irradiance (power) curve. Reference: Photovoltaic Systems, p. 33


Peak Sun Hours

Time of Day (hrs)

Sola

r Irr

adia

nce

(W/m

2 )

1000 W/m2

Sunrise Noon Sunset

Peak Sun Hours

Solar Insolation

Solar Irradiance Area of box equals

area under curve

Presenter

Presentation Notes

Peak sun hours (PSH) represents the average daily amount of solar energy received on a surface, and equivalent to the number of hours that the solar irradiance would be at a peak level of 1 kW/m2 to receive the same amount of energy. It is also the equivalent number of hours per day that a PV array will operate at it’s peak rated output levels at rated temperature. Peak Sun Hours = # equivalent hours @ 1 kW/m2 irradiance. Worldwide, the solar energy resource averages around 5 PSH (5 kWh/m2/day) on optimally oriented fixed surfaces facing the sun. Reference: Photovoltaic Systems, p. 33


Solar Power and Energy: Examples

The solar power incident on a surface averages 400 W/m2 for 12 hours. How much solar energy is received? 400 W/m2 x 12 hours = 4800 Wh/m2 = 4.8 kWh/m2 = 4.8 PSH

The amount of solar energy collected on a surface over 8 hours is

4 kWh/m2. What is the average solar power received over this period? 4 kWh/m2 / 8 hours = 0.5 kW/m2 = 500 W/m2

A PV system produces 6 kW AC output at peak sun and average

operating temperatures. How much energy is produced from this system per day if the solar energy received on the array averages 4.5 peak sun hours? 6 kW x 4.5 hours/day = 27 kWh/day

Presenter

Presentation Notes

Average solar power multiplied by time in hours equals solar energy. Solar power defines the instantaneous output of a PV system, while the amount of solar energy accumulated defines the amount of energy produced and the equivalent number of hours that a PV system will operate at its peak output level. Reference: Photovoltaic Systems, p. 28-35


Atmospheric Effects

Approximately 30% of extraterrestrial solar power is absorbed or reflected by the atmosphere before reaching the earth’s surface. Effects vary significantly with altitude, latitude, time of day and year, air

pollutants, weather patterns and wavelength of solar radiation.

Direct beam (normal) radiation is the component of total global solar radiation incident on a surface normal to the sun’s rays, that travels in parallel lines directly from the sun.

Diffuse radiation is the component of the total global solar radiation incident on a surface that is scattered or reflected. May also include ground reflected radiation (albedo).

Total global solar radiation is comprised of the direct, diffuse and

reflected components (albedo).

Presenter

Presentation Notes

Direct beam (normal) radiation is the component of total global solar radiation incident on a surface normal to the sun’s rays, that travels in parallel rays directly from the sun. Diffuse radiation is the component of the total global solar radiation incident on a surface that is scattered or reflected. May also include ground reflected radiation (albedo). Total global solar radiation is comprised of the direct, diffuse and reflected components. Reference: Photovoltaic Systems, p. 30-36


Atmospheric Effects

Parallel rays from sun

Earth’s Surface

Outer Limits of Atmosphere

Direct Radiation

Diffuse Radiation

Atmospheric Absorption, Scattering and Reflections Cloud

Reflections

Solar Constant = 1366 W/m2

Diffuse Radiation

Sun

Reflection

TOTAL GLOBAL SOLAR RADIATION - DIRECT + DIFFUSE

Reflected (Albedo) Radiation

Presenter

Presentation Notes

Approximately 30% of extraterrestrial solar power is absorbed or reflected by the atmosphere before reaching the earth’s surface. Effects vary significantly with altitude, latitude, time of day and year, atmospheric constituents, weather patters and wavelength of solar radiation. Reference: Photovoltaic Systems, p. 30-36


Air Mass

1cos z o

whereAM air mass

zenith angle (deg)zP local pressure (Pa)P sea level pressure (Pa)o

Air mass is calaculated by the following:

PAMP

θ

θ

====

=

Earth

Sun directly overhead (zenith)

Sun at mid-morning or mid-afternoon

Earth’s Surface

Limits of Atmosphere

Air Mass = 0 (AM0)

Air Mass = 1 (AM1.0)

Zenith Angle θz = 48.2 deg

Air Mass = 1.5 (AM1.5)

Horizon

Presenter

Presentation Notes

Air mass (AM) is the relative path length of direct solar radiation through the atmosphere. Air mass affects the amount and spectral content of the solar radiation reaching the earth’s surface, and varies with sun position and altitude (barometric pressure). AM 1.5 defines the spectral irradiance characteristic for the solar radiation source used for testing and rating the electrical performance of PV cells and modules. Reference: Photovoltaic Systems, p. 31-32


Measuring Zenith and Altitude Angles

Sun

Vertical

Horizontal Plane

Length of shadow (l)

Height of stake or ruler (h)

θz

Zenith Angle θz

Zenith Angle: Length of shadow (l) Tan θz = ---------------------------- Height of ruler (h) θz = arctan (l/h)

Altitude Angle

α

Altitude Angle: Height of ruler (h) Tan α = ---------------------------- Length of shadow (l) α = arctan (h/l)

Presenter

Presentation Notes

A simple method to measure altitude and zenith angles using trigonometry. Reference: Photovoltaic Systems, p. 43-45


U.S. Solar Radiation Data

NREL

Presenter

Presentation Notes

In the summer months, most of eastern U.S. averages 5 or more peak sun hours per day on south-facing surfaces tilted at local latitude, while the central and southwestern U.S. averages 6 or more peak sun hours per day. Reference: Photovoltaic Systems, p. 34



NREL

Presenter

Presentation Notes

In the winter months, the effects of latitude, lower sun angles and shorter days result in much less solar energy received at higher latitudes. Reference: Photovoltaic Systems, p. 34



NREL

Presenter

Presentation Notes

On an annual average basis, most of the U.S. receives 4 to 5 peak sun hours per day, with the higher amounts in the southeastern and arid southwestern regions. Reference: Photovoltaic Systems, p. 34


Solar Spectral Irradiance

Spectral Solar Irradiance

0

500

1000

1500

2000

2500

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

Wavelength (µm)

Spec

tral I

rrad

ianc

e (W

m-2

µm

-1)

Extraterrestrial (AM0)

Terrestrial Total Global (AM1.5)

Terrestrial Direct Normal (AM1.5)

Aborbed by CO2 and water vapor

Aborbed by water vapor

Presenter

Presentation Notes

Solar irradiance varies with wavelength. The area under the solar spectral irradiance curve equals total solar irradiance (power). Certain wavelengths, or bands of solar irradiance are absorbed by CO2 and water vapor as the radiation passes through the earth’s atmosphere. Reference: Photovoltaic Systems, p. 35


Solar Radiation Measurements

A pyranometer measures total global solar irradiance (solar power). Measurements over time are integrated to calculate the total solar

irradiation (solar energy) received.

Irradiance measurements are used in the field to translate the actual output of PV array and systems to a reference condition and verify performance with expectations.

Small inexpensive meters using calibrated PV cells as sensors are available from $150 and up. A small PV module with calibrated short-circuit current can also be used to

approximate solar radiation levels.

Presenter

Presentation Notes

Reference: Photovoltaic Systems, p. 36-38


Precision Spectral Pyranometer (PSP)

A pyranometer measures

broadband global solar radiation (direct and diffuse) with a thermopile.

Used for precision laboratory measurements and weather stations.

Dual glass domes improve low incidence angle and thermal accuracy.

$$$$

NREL, Steve Wilcox

Presenter

Presentation Notes

A pyranometer measures total global solar radiation. References: The Eppley Laboratory, Inc.: www.eppleylab.com Photovoltaic Systems, p. 36-38


Normal Incidence Pyrheliometer (NIP)

A pyrheliometer measures the

direct normal component of total global solar radiation.

Instrument must always track the sun.

Sensor is located at the back of a long tube with a field of view of 5.7° - the width of the solar disk.

$$$$$ NREL/Tom Stoffer

Presenter

Presentation Notes

A pyrheliometer measures direct beam radiation. References: The Eppley Laboratory, Inc.: www.eppleylab.com Photovoltaic Systems, p. 36-38


Photovoltaic Reference Cell

A reference cell is a small PV

device used to measure solar irradiance.

Calibrated current output is proportional to solar irradiance.

Used for measuring solar

radiation for PV cell or module performance in indoor simulators.

PV Measurements, Inc.

Presenter

Presentation Notes

A reference cell is a small PV device used to measure solar irradiance. The output current is proportional to solar irradiance, and calibrated to the standard solar spectrum. Reference cells are mainly used for indoor solar simulator measurements and packaged using the same glass and cells as the devices under test. They are not accurate for low incidence angles, nor are they designed for typical field use or permanent outdoor installations. However, a small PV module or cell can be used to measure solar irradiance by calibrating its short-circuit current output with a calibrated pyranometer. References: PV Measurements, Inc.: www.pvmeasurements.com Photovoltaic Systems, p. 36-38


LI-COR LI200 Pyranometer

Silicon pyranometers use a

calibrated PV device to measure solar radiation.

Meter sets instrument calibration, averages and integrates solar irradiance.

Ideal for field use and long-term system performance monitoring.

$$$

Presenter

Presentation Notes

Silicon pyranometers use a small PV device to measure solar radiation. Current output is converted to voltage through a calibrated cable and resistor, with output typically 5-10 mV at 1 kW/m2, or through a special meter that allows the instrument calibration to be entered. References: LI-COR Environmental: www.licor.com/env Photovoltaic Systems, p. 36-38


Daystar Solar Meter

Handheld solar meters use a

small PV cell to measure solar irradiance.

Careful alignment with plane of array required for accurate measurements.

Low cost, good for basic field measurements.

$$$

Presenter

Presentation Notes

Handheld solar meters use a small PV device to measure short-circuit current, and are calibrated to display an output in units of W/m2. Suggested Exercise: Measure solar irradiance on different surfaces and examine the effects of varying incidence angle, shading and cloud cover. References: Daystar, Inc: www.zianet.com/daystar Photovoltaic Systems, p. 36-38


Seaward Solar Solar Survey 100/200R

Measures and records solar irradiance, ambient and PV module temperatures, array orientation and tilt angles.

200R features wireless connectivity with the PV150 Solar Installation tester, built-in data logger and USB interface.

See: www.seawardsolar.com

Presenter

Presentation Notes

References: Seaward Group, LLC: www.seawardsolar.com

http://www.seawardsolar.com/


Sun-Earth Geometric Relationships

Two major motions of the earth affect the solar radiation received

on a surface at any location: The rotation of the earth about its polar axis defines a day. The orbit of the earth around the sun defines a year.

The amount of solar radiation received at any location on earth

depends on the time of day and year, the local latitude, and the orientation of the surface. Also significantly affected by weather conditions.

Presenter

Presentation Notes

The earth’s movements and changing angles between a surface on earth and the sun’s rays affect the amount of solar radiation received at any time of the day or year. Reference: Photovoltaic Systems, p. 38-48


Earth’s Orbit

The ecliptic plane is the earth’s orbital plane around the sun.

The equatorial plane is the plane containing the earth’s equator and extending outward into space.

The earth’s annual orbit around the sun is slightly elliptical. Perihelion is the earth’s closest approach to the sun in its orbit, which is

about 90 million miles and occurs around January 3. Aphelion is the earth’s furthest distance to the sun in its orbit, which is

about 96 million miles and occurs around July 4.

One Astronomical Unit (AU) is the average sun-earth distance, which is approximately 93 million miles.

Presenter

Presentation Notes

The earth’s slightly elliptical orbit around the sun results in a faster orbit around the perihelion, and more rapid day-to-day changes in sun position before and after the winter solstice. Reference: Photovoltaic Systems, p. 38-40


Earth’s Orbit Around the Sun

Autumnal Equinox: September 22 / 23

Declination = 0°

Ecliptic P lane

Sun

Perihelion: January 2-5 Aphelion: July 3-7 96 million miles

(1.017 AU) 90 million miles

(0.983 AU)

Summer Solstice: June 20 / 21

Declination = +23.5°

Vernal Equinox: March 20 / 21 Declination = 0°

Winter Solstice: December 21 / 22 Declination = ( -23.5°)

Presenter

Presentation Notes

The earth’s closest approach to the sun occurs in the winter in the northern hemisphere, and contributes to more extreme summers and winters in the southern hemisphere at similar latitudes and elevations. However, the earth’s distance from the sun does not account for the changing seasons. Reference: Photovoltaic Systems, p. 38-40


Earth’s Polar Axis Tilt

The earth’s polar rotational axis is tilted at a constant 23.5° angle with respect to the ecliptic plane.

During its annual orbit around the sun, the earth's polar axis is never perpendicular to the ecliptic plane, but it is always inclined to it at the same angle, 23.5°.

This results in a constantly varying angle between the earth’s equatorial plane and the ecliptic plane as the earth orbits the sun over a year.

Except at the equinoxes, the earth’s axis is tilted either toward or

away from the sun, causing the change in seasons.

Presenter

Presentation Notes

The earth’s tilt is 23.5°, and does not change. However, the angle between the earth’s equatorial plane and the sun’s rays changes constantly, and is called solar declination. Reference: Photovoltaic Systems, p. 39-43


Solar Declination

Solar declination (δ) is the angle between the earth’s equatorial

plane and the sun’s rays.

Solar declination varies continuously in a sinusoidal fashion over the year due the earth’s nearly circular orbit around the sun.

Solar declination varies from –23.5° to +23.5°, and defines the limits of sun position in the sky relative to any point on earth.

Presenter

Presentation Notes

Solar declination is the constantly changing angle between the earth’s equatorial plane and the sun’s rays, varying between –23.5° to +23.5° in a sinusoidal fashion between the winter and summer solstices, respectively. Those familiar with the principles of AC motors and generators can relate changing solar declination to rotating a coil inside a magnetic field, which produces a sinusoidal voltage waveform. Reference: Photovoltaic Systems, p. 39-43


Solar Declination

Equator

Tropic of Cancer (23.5° N)

Tropic of Capricorn (23.5° S)

Arctic Circle (66.5° N)

Antarctic Circle (66.5° S)

Sun’s Rays

North Pole

23.5 °

Ecliptic Plane

Solar Declination

Presenter

Presentation Notes



Solar Declination

Solar Declination

(30)

(20)

(10)

0

10

20

30

0 15 30 45 60 75 90 105

120

135

150

165

180

195

210

225

240

255

270

285

300

315

330

345

360

Julian Day (1-365)

Sola

r Dec

linat

ion

(deg

)

Autumnal EquinoxSeptember 22

Vernal EquinoxMarch 21

Summer SolsticeJune 21

Winter SolsticeDecember 21

Presenter

Presentation Notes

Solar declination changes constantly over the year in a sinusoidal manner. Reference: Photovoltaic Systems, p. 39-43


The Solstices

The solstices define the points in earth’s orbit around the sun

having maximum and minimum solar declination. The solstices occur when the earth’s axis is inclined at the

greatest angle either toward or away from the sun, and defines the annual range of sun position relative to any point on earth.

The winter solstice occurs on December 21 or 22 when solar declination is at its minimum (-23.5°) and the Northern Hemisphere is tilted away from sun.

The summer solstice occurs on June 21 or 22 when solar declination is at its maximum (23.5°), and the Northern Hemisphere is tilted towards the sun.

Presenter

Presentation Notes

The solstices define the maximum and minimum solar declination, and the annual limits of sun position in the sky at any location. The winter solstice occurs on December 21 or 22 when solar declination is at its minimum (-23.5°) and the Northern Hemisphere tilted away from sun. All points north of the Arctic Circle are in total darkness and the sun is at the zenith (directly overhead) at solar noon on the Tropic of Capricorn. The summer solstice occurs on June 21 or 22 when solar declination is at its maximum (23.5°), Northern Hemisphere tilted towards the sun. All points south of the Antarctic Circle are in total darkness, and the sun is at the zenith (directly overhead) at solar noon at the Tropic of Cancer. At solar noon on the summer solstice at any location, the sun’s altitude is 47° higher in the sky than it is at solar noon on the winter solstice. Reference: Photovoltaic Systems, p. 40


The Equinoxes

The equinoxes define the two points in earth’s orbit around the sun

having zero solar declination.

On the equinoxes, the earth’s axis is neither tilted toward or away from the suns rays, but is perpendicular. The sun rises and sets due east and west, respectively, and days and nights equal

length (12 hours) everywhere on earth. The sun is directly overhead at solar noon on the equator (at zenith).

The vernal equinox occurs on March 20 / 21.

Days become longer than nights in Northern Hemisphere for next six months.

The autumnal equinox occurs on September 22 / 23. Days become shorter than nights in the Northern Hemisphere for next six months.

Presenter

Presentation Notes

The equinoxes occur when solar declination is equal to zero, and the represent the midpoint or average sun position between the winter and summer solstices. On the equinoxes, all points on earth have 12 hour days and nights, the sun rise and sets due east and west, and the sun is directly overhead on the equator at solar noon. Reference: Photovoltaic Systems, p. 40


Winter Solstice

Equator





Sun’s Rays

North Pole

23.5 °

Ecliptic Plane

Presenter

Presentation Notes

Reference: Photovoltaic Systems, p. 40.


Vernal Equinox

Equator




Sun’s Rays

North Pole Titled Backward

Ecliptic Plane

23.5 °

Presenter

Presentation Notes



Summer Solstice

Equator





Sun’s Rays

North Pole

23.5 °

Ecliptic Plane

Presenter

Presentation Notes



Autumnal Equinox

Equator




Sun’s Rays

North Pole Tilted Forward

Ecliptic Plane

23.5 °

Presenter

Presentation Notes



Solar Time

Apparent solar time is based on the interval between daily sun crossings above a local meridian. Apparent solar time can be measured by a sundial.

Mean solar time is based on the average position of the sun assuming the earth rotates and orbits at constant rates.

The equation of time (EOT) is the difference between mean and

apparent solar time. EOT varies annually with apparent time ahead of mean solar time by

about 16.5 min on November 3, or behind by about 14 min on February 12.

Due to changing speed of earth at points in elliptical orbit around sun.

Presenter

Presentation Notes

Solar time is based on the apparent position of the sun to point on earth. Since the earth rotates 360° in a 24 hour day, each hour is approximately equal to the sun traversing 15° of longitude. The equation of time (EOT) is the difference between mean and apparent solar time. The EOT results from two factors: the obliquity of the ecliptic plane, and the eccentricity of the earth's elliptical orbit around the sun. Both cause the earth’s rotational and orbital speed to change slightly over a year. Reference: Photovoltaic Systems, p. 41-43.


Equation of Time

Equation of Time

(20)

(15)

(10)

(5)

0

5

10

15

20

0 15 30 45 60 75 90 105

120

135

150

165

180

195

210

225

240

255

270

285

300

315

330

345

360

Julian Day (1-365)

Equ

atio

n of

Tim

e (m

in) Autumnal Equinox

September 22

Vernal EquinoxMarch 21 Summer Solstice

June 21


Presenter

Presentation Notes



Standard Time and Time Zones

Coordinated Universal Time (UTC) is based on an atomic clock and mean solar time at the Royal Observatory in Greenwich, London, UK. The prime meridian passes through Greenwich and is arbitrarily taken as

0° longitude.

Standard time is based on sun crossing reference meridians or geographical boundaries, generally separated by 15° of longitude. Local standard time is referenced to UTC Eastern Standard Time is UTC-5 hours (UTC-4 during Daylight Savings

Time)

UTC varies from local solar time by as much as +/- 45 min depending on the day of year, whether Daylight Savings Time is in effect, and longitude of the specific location with respect to the reference time zone meridian.

Presenter

Presentation Notes



U.S. Time Zones

Eastern UTC-5

Atlantic UTC-4 Central

UTC-6

Mountain UTC-7

Pacific UTC-8

Alaska UTC-9

Hawaii UTC-10

Samoa UTC-11

Guan UTC+10

UTC with no Daylight Savings Time

NIST/USNO

Presenter

Presentation Notes

U.S. time zones range from the Atlantic Time Zone (UTC-4) in the U.S Virgin Islands to the Chamorro (Guam) Time Zone (UTC+10). References: The Official U.S. Time: www.time.gov Photovoltaic Systems, p. 41-43.


Solar and Standard Time Conversions

( ) 4L local S

L

Example: Determine the local standard time that solar noon occurs on November 3 in Atlanta, GA (33.65 N, 84.43 W) .

The adjustment for longitude is determined by:

t L Lwheret longitude ti

= − ×

=

(84.43 75) 4 37.7

local

S

L

me correction (min)L local longitude (deg)L longitude at standard meridian (deg)

t min = 37:43 mm:ss

==

= − × =

0

12 : 00 : 00 (00 :16 : 30) (00 : 37 : 43) 12 : 21:13

S E L

S

0

E

S

Local standard time of solar noon is determined by:

t t t twheret = local standard time (hh:mm:ss)t = solar time (hh:mm:ss)t = Equation of Time (mm:ss)

t

= − +

= − + = EST

Presenter

Presentation Notes

Suggested Exercise: Calculate the local standard time that solar noon occurs for your location on any give day of the year, and compare the results using the solar time conversion tool on the CD-ROM. Verify using the Solar Pathfinder tool, see Chapter 3. Reference: Photovoltaic Systems, p. 41-43 & CD-ROM


Sunlight on Earth

Near Equinox

Near Summer Solstice

Day Night

NIST/USNO

Day Night

Presenter

Presentation Notes

The portions of the earth that are illuminated by sunlight each day varies over the year. How would the above image change near the winter solstice? Reference: Photovoltaic Systems, p. 41-43.


The Analemma

This Analemma was created by superimposing photographs of the sun taken in the morning at the same clock time, each week of the year, and represents the variation in solar declination and the equation of time over the year.

Analemma

Jan 21

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Vernal EquinoxMarch 21

Summer SolsticeJune 21


FSEC

Presenter

Presentation Notes

The analemma is a plot of solar declination versus the Equation of Time, and represents how fast or slow the sun appears to move with respect to standard time. Reference: Photovoltaic Systems, p. 41-43


Sun Position

The sun’s position in the sky at any moment relative to an observer on earth is defined by two angles.

The solar altitude angle (α) is the angle between the sun’s rays and the horizon.

The solar azimuth angle (θz) is the angle between the horizontal projection of a the sun’s rays and geographic due south.

The zenith angle is the angle between the line to the sun and directly overhead. The zenith and altitude angles are complementary: α + θz = 90°

Presenter

Presentation Notes



Sun Position

North

West South

East

Zenith

Horizontal Plane

Altitude Angle

Azimuth Angle

Zenith Angle

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Presentation Notes



Sun Path Diagrams at the Equinoxes

0° Latitude (Equator): Altitude at Solar Noon = 90°

23.5° N Latitude (Tropic of Cancer): Altitude at Solar Noon = 66.5°

47° N Latitude (Seattle, WA): Altitude at Solar Noon = 43° N

W S

E

Zenith

Presenter

Presentation Notes

At the equinoxes, at every point on earth, the sun rises and sets due east and west, respectively, and days and nights are exactly 12 hours. On the equator, the sun traverses the east-west plane and reaches zenith twice per year at solar noon on the equinoxes. Reference: Photovoltaic Systems, p. 43-45


Sun Path Diagrams at the Summer Solstice

0° Latitude (Equator): Altitude at Solar Noon = 66.5° (Sun in Northern Sky) 23.5° N Latitude (Tropic of Cancer): Altitude at Solar Noon = 90° (Directly Overhead) 47° Latitude (Seattle, WA): Altitude at Solar Noon = 66.5° (Sun in Southern Sky)

N

W S

E

Zenith

Presenter

Presentation Notes

In the northern hemisphere at the summer solstice, the sun rises and sets north of east and west, respectively. Days are increasingly longer than nights at higher latitudes. The sun remains in northern sky all day at latitudes lower than the Tropic of Cancer, and the sun reaches highest altitude of the year at latitudes higher than the Tropic of Cancer. Reference: Photovoltaic Systems, p. 43-45


Sun Path Diagrams at the Winter Solstice

0° Latitude (Equator): Altitude at Solar Noon = 66.5°

23.5° N Latitude (Tropic of Cancer): Altitude at Solar Noon = 43°

47° Latitude (Seattle, WA): Altitude at Solar Noon = 19.5° N

W S

E

Zenith

Presenter

Presentation Notes

In the northern hemisphere at the winter solstice, the sun rises and sets south of east and west, respectively. Nights are increasingly longer than days at higher latitudes, and the sun remains in southern sky all day. The sun reaches lowest altitude of the year at latitudes higher than the Tropic of Cancer. Reference: Photovoltaic Systems, p. 43-45


Sun Position on the Equator

Sun Position for 0o Latitude

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Winter Solstice Summer Solstice Vernal and Autumnal Equinox

Presenter

Presentation Notes

Envision this chart of sun position as a 3-D cylinder – the left axis (180 east) connected to the right axis (180 west). For these charts, the reference for due south is an azimuth angle of 0°. Reference: Photovoltaic Systems, p. 43-45 & CD-ROM


Sun Position for 15°N

Sun Position for 15o N Latitude

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Presentation Notes

Reference: Photovoltaic Systems, p. 43-45 & CD-ROM




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Presenter

Presentation Notes

Note how the maximum solar altitude on the summer solstice at higher latitudes decreases by an amount equal to the difference in latitude. Reference: Photovoltaic Systems, p. 43-45 & CD-ROM




8 AM

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Presenter

Presentation Notes

Note that the sun path for the winter solstice disappears for latitude above the Arctic Circle (sun is always below horizon). Reference: Photovoltaic Systems, p. 43-45 & CD-ROM


The Solar Window

The solar window represents the range of sun paths for a given

latitude between the winter and summer solstices.

As latitudes increase from equator: The solar window is inclined at a closer angle with the southern horizon. Sun path and days are longer during summer; shorter during winter.

For any location, the maximum altitude of the sun at solar noon

varies 47° between the winter and summer solstice.

PV arrays should be oriented toward the unobstructed solar window for maximum solar energy collection.

Presenter

Presentation Notes

The solar window represents the range of sun paths for a given latitude between the winter and summer solstices. Suggested Exercise: Examine the sun path charts for your latitude by using the CD-ROM. Determine the sun’s approximate altitude and azimuth angles for summer and winter solstice at 10 AM solar time. Reference: Photovoltaic Systems, p. 43-45


Solar Window on the Equator Winter Solstice

Equinoxes

Summer Solstice

N

W S

E

Zenith

47°

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Presentation Notes



Solar Window on the Tropic of Cancer (23.5°N)

Winter Solstice

Equinoxes

Summer Solstice

N

W S

E

Zenith

47°

Presenter

Presentation Notes



Solar Window in Seattle, WA (47°N)

Winter Solstice

Equinoxes

Summer Solstice

N

W S

E

Zenith

47°

Presenter

Presentation Notes



Collector Orientation

The orientation of PV arrays and other solar collectors is defined

by two angles with respect to the earth’s surface.

The collector azimuth angle represents the angle between due geographic south and direction the collector faces.

The collector tilt angle represents the angle the array surface

makes with the horizontal plane.

The solar incidence angle represents the angle between the sun’s rays and the normal (perpendicular) to a collector surface.

Presenter

Presentation Notes

The collector azimuth angle is the angle between due south and the horizontal projection of the normal to the collector surface (direction the collector faces). See magnetic declination (Chapter 3) for the differences between the magnetic and true geographic north pole. Reference: Photovoltaic Systems, p. 45-47


Array Orientation

West - 270°

North - 0°

Zenith

Collector Azimuth

Angle

Collector Tilt Angle

Surface Normal

Surface Direction

Solar Incidence

Angle

Horizontal Plane

East - 90°

South - 180°

Presenter

Presentation Notes

The orientation of PV arrays and other solar collectors is defined by two angles. The collector azimuth angle is the angle between due south and direction a collector faces. The collector tilt angle is the angle the collector surface makes with the horizontal plane. Reference: Photovoltaic Systems, p. 45-47


Optimal Collector Orientation

Maximum annual solar energy is received on a fixed surface that

faces due south, and is tilted from the horizontal at an angle slightly less than local latitude.

Fall and winter performance is enhanced by tilting collectors at angles

greater than latitude. Spring and summertime performance is enhanced by tilting collectors at

angles lower than latitude.

For the central and southern U.S., latitude-tilt surfaces with azimuth orientations of ± 45 degrees from due south and with tilt angles ± 15 of local latitude will generally receive 95 % or more of the annual solar energy received on optimally-tilted south-facing surfaces.

Presenter

Presentation Notes

Maximum annual solar energy is received on a surface that faces due south, and is tilted from the horizontal at an angle slightly less than local latitude. This is due to longer days and sun paths during summer months at higher latitudes. Where feasible, PV arrays may be tilted at higher angles to maximize winter performance for wintertime peak loads, and conversely, tilted at angles lower than latitude for summertime peak loads. However, the annual solar energy received varies little with small changes in the collector azimuth and tilt angles. Changing the tilt angle affects the seasonal distribution of solar energy received and wind loading. Changing the azimuth angle affect the daily distribution of solar energy received. Reference: Photovoltaic Systems, p. 46-50


Predicted Insolation on South-Facing Tilted Surfaces

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Effect of Collector Tilt Angle on Solar Energy Received

Orlando, FL

Presenter

Presentation Notes

Fixed PV arrays are installed facing close to due south and tilted from horizontal at an angle close to the local latitude to maximize annual solar energy gain. Higher tilt angles optimize fall and winter performance, while lower tilt angles optimize spring and summer performance. Higher latitudes experience greater variations seasonal variation in solar irradiation. Reference: Photovoltaic Systems, p. 46-50


Effects of Collector Tilt and Azimuth on Annual Solar Energy Received

270 240 210 180 150 120 900

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95-10090-9585-9080-8575-8070-75

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95-10090-9585-9080-8575-8070-75

Miami, FL Boston, MA

Presenter

Presentation Notes

Optimal energy performance of PV arrays is achieved by facing the array due south in the northern hemisphere. Surfaces with azimuth orientations of +/- 45 degrees from due south and tilted within 15 degrees of the local latitude will generally receive 95 percent of solar energy as optimally-tilted south-facing fixed surfaces. The reduction in solar energy received for off-azimuth orientations increases with increasing tilt angles and at higher latitudes. Reference: Photovoltaic Systems, p. 46-50


Solar Radiation Resource Data

Available from National Renewable Energy Laboratory (NREL) -

Renewable Resource Data Center (RReDC): http://www.nrel.gov/rredc/

Includes extensive collection of renewable energy data, maps,

and tools for using biomass, geothermal, solar, and wind resources.

Solar resource data is used for sizing and estimating the performance of solar energy utilization systems.

Presenter

Presentation Notes

Solar radiation resource data are available from the National Renewable Energy Laboratory website and on the CD-ROM. Reference: Photovoltaic Systems, p. 46-53 & CD-ROM

http://www.nrel.gov/rredc/


National Solar Radiation Database

NSRDB 1961-1990 30 years of solar radiation and

meteorological data from 239 NWS sites in the U.S.

TMY2 hourly data files

NSRDB 1991-2005 Update Contains solar and meteorological

data for 1,454 sites. TMY3 hourly data files

NREL

Presenter

Presentation Notes

The National Solar Radiation Database includes data for over 1400 sites in the U.S. and its territories. Typical Meteorological Year (TMY) data files contain hourly data representative of selected months and years from the database, and used in simulation programs. Reference: Photovoltaic Systems, p. 46-53 & CD-ROM


Solar Radiation Data Tables

Standard format spreadsheets provide minimum and maximum data for each month and annual averages for:

Total global solar radiation for fixed south-facing flat-plate collectors tilted

at angles of 0°, Lat-15°, Lat, Lat+15° and 90°.

Total global solar radiation for single-axis, north-south tracking flat-plate collectors at tilt angles of 0°, Lat-15°, Lat and Lat+15°.

Total global solar radiation for dual-axis tracking flat-plate collectors.

Direct beam radiation for concentrating collectors.

Meteorological data.

Presenter

Presentation Notes

Standard solar radiation data tables for selected cities give several key sets of data for different fixed and tracking surfaces. The major limitation of the data tables is that they only provide data for south-facing fixed surfaces. Other tools, such as PVWATTS can be used to predict the solar energy received on fixed-tilt surfaces facing directions other than due south. Reference: Photovoltaic Systems, p. 46-53 & CD-ROM



City: DAYTONA BEACH State: FLWBAN No: 12834Lat(N): 29.18Long(W): 81.05Elev(m): 12Pres(mb): 1017Stn Type: PrimarySOLAR RADIATION FOR FLAT-PLATE COLLECTORS FACING SOUTH AT A FIXED-TILT (kWh/m2/day), Percentage Uncertainty = 9Tilt(deg) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year0 Average 3.1 3.9 5.0 6.2 6.4 6.1 6.0 5.7 4.9 4.2 3.4 2.9 4.8 Minimum 2.7 3.2 4.2 5.6 5.3 5.4 5.5 4.8 4.3 3.5 2.9 2.4 4.6 Maximum 3.7 4.4 5.5 6.8 7.0 7.0 6.6 6.3 5.5 4.8 3.7 3.3 5.1Lat - 15 Average 3.8 4.5 5.5 6.4 6.4 6.0 5.9 5.8 5.2 4.7 4.1 3.6 5.2 Minimum 3.2 3.7 4.5 5.8 5.3 5.3 5.4 4.8 4.5 3.8 3.4 2.8 4.8 Maximum 4.6 5.2 6.1 7.1 7.0 6.8 6.4 6.5 6.0 5.5 4.6 4.1 5.5Lat Average 4.3 4.9 5.7 6.3 6.0 5.5 5.5 5.6 5.3 5.0 4.6 4.1 5.2 Minimum 3.6 4.0 4.6 5.7 5.0 4.9 5.1 4.6 4.5 4.0 3.8 3.1 4.9 Maximum 5.4 5.8 6.3 7.0 6.6 6.3 6.0 6.3 6.1 5.9 5.2 4.9 5.7Lat + 15 Average 4.6 5.1 5.6 5.9 5.4 4.8 4.9 5.1 5.1 5.1 4.8 4.4 5.1 Minimum 3.8 4.1 4.5 5.3 4.5 4.3 4.5 4.2 4.3 4.0 3.9 3.3 4.7 Maximum 5.8 6.0 6.3 6.5 5.8 5.5 5.3 5.7 5.9 6.0 5.6 5.3 5.590 Average 3.9 3.8 3.6 2.9 2.1 1.8 1.9 2.4 3.0 3.6 4.0 3.9 3.1 Minimum 3.1 3.1 2.9 2.7 2.0 1.6 1.8 2.0 2.5 2.7 3.1 2.8 2.8 Maximum 5.1 4.7 4.0 3.1 2.2 1.9 2.0 2.6 3.4 4.3 4.7 4.7 3.3

NREL

Presenter

Presentation Notes

This section of the solar radiation data tables gives the total global solar radiation for fixed south-facing flat-plate collectors tilted at angles of 0°, Lat-15°, Lat, Lat+15° and 90°. Suggested Exercise: Obtain the solar radiation data tables for a site close to your location from the CD-ROM. Compare the average daily solar energy received in the months of June and December for a latitude–15° and latitude+15° fixed surfaces. Reference: Photovoltaic Systems, p. 46-53 & CD-ROM


Sun-Tracking Arrays

North

South

West

East

Vertical-Axis Tracking

Optional seasonal adjustment

Two-Axis Tracking East-West Tracking

Optional seasonal adjustment

Presenter

Presentation Notes

Sun-tracking arrays use mounting structures that automatically and continually move the array surface array to follow the sun position throughout the day. Sun-tracking arrays are characterized by their tracking mode and whether they track the sun on one axis or two axes. Most single axis trackers are designed to move the array surface east to west on a north-south tracking axis that is tilted from the horizontal. Sun tracking arrays can receive up to 20-30% more solar radiation than fixed south-facing arrays. Single-axis trackers do not point exactly to the sun at all times, but can receive 20% or more solar radiation than received on south-facing fixed-tilt surfaces. Marginal gains in solar energy received are achieved in going from single to two-axis tracking. Point-focus concentrating PV modules and arrays require two-axis sun-tracking to capture the direct beam solar radiation component. Reference: Photovoltaic Systems, p. 266-267



City: DAYTONA BEACH State: FLWBAN No: 12834Lat(N): 29.18Long(W): 81.05Elev(m): 12Pres(mb): 1017Stn Type: Primary

SOLAR RADIATION FOR 1-AXIS TRACKING FLAT-PLATE COLLECTORS WITH A NORTH-SOUTH AXIS (kWh/m2/day), Percentage Uncertainty = 9Axis Tilt Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year0 Average 4.3 5.2 6.6 8.1 8.2 7.5 7.4 7.1 6.2 5.5 4.6 3.9 6.2 Minimum 3.5 4.2 5.2 7.1 6.3 6.5 6.6 5.8 5.0 4.2 3.8 3.0 5.7 Maximum 5.4 6.2 7.6 9.5 9.2 8.9 8.3 8.3 7.3 6.6 5.3 4.7 6.8Lat - 15 Average 4.8 5.7 7.0 8.3 8.2 7.4 7.4 7.2 6.5 5.9 5.1 4.4 6.5 Minimum 3.8 4.6 5.5 7.3 6.3 6.4 6.5 5.9 5.2 4.5 4.1 3.3 6.0 Maximum 6.1 6.8 8.0 9.7 9.2 8.8 8.2 8.4 7.6 7.1 5.9 5.4 7.1Lat Average 5.2 6.0 7.2 8.3 7.9 7.1 7.1 7.0 6.5 6.1 5.5 4.9 6.6 Minimum 4.1 4.8 5.6 7.2 6.1 6.1 6.2 5.8 5.2 4.6 4.4 3.6 6.0 Maximum 6.7 7.3 8.3 9.7 8.9 8.4 7.9 8.3 7.7 7.4 6.4 5.9 7.2Lat + 15 Average 5.4 6.1 7.1 8.0 7.4 6.6 6.6 6.7 6.4 6.2 5.7 5.1 6.4 Minimum 4.3 4.9 5.5 6.9 5.7 5.7 5.8 5.5 5.0 4.6 4.5 3.7 5.9 Maximum 7.0 7.4 8.2 9.3 8.4 7.8 7.4 7.9 7.5 7.5 6.7 6.3 7.1SOLAR RADIATION FOR 2-AXIS TRACKING FLAT-PLATE COLLECTORS (kWh/m2/day), Percentage Uncertainty = 9Tracker Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year2-Axis Average 5.5 6.1 7.2 8.4 8.2 7.5 7.5 7.2 6.5 6.2 5.7 5.2 6.8 Minimum 4.3 4.9 5.6 7.3 6.3 6.5 6.6 5.9 5.2 4.6 4.5 3.7 6.2 Maximum 7.1 7.5 8.3 9.8 9.3 9.0 8.4 8.4 7.7 7.5 6.8 6.4 7.5

NREL

Presenter

Presentation Notes

This section of the solar radiation data tables gives the total global solar radiation for single-axis, north-south tracking flat-plate collectors at tilt angles of 0°, Lat-15°, Lat, Lat+15°, and for two-axis tracking surfaces. Suggested Exercise: Obtain the solar radiation data tables for a site close to your location from the CD-ROM. Compare the average daily annual solar energy received on single and two-axis tracking surfaces with a fixed surface tilted at local latitude. Reference: Photovoltaic Systems, p. 46-53 & CD-ROM



DIRECT BEAM SOLAR RADIATION FOR CONCENTRATING COLLECTORS (kWh/m2/day), Percentage Uncertainty = 8Tracker Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year1-X, E-W Average 3.1 3.3 3.6 4.2 3.9 3.3 3.3 3.1 2.8 3.1 3.2 3.0 3.3Hor Axis Minimum 2.1 2.4 2.4 3.3 2.2 2.4 2.4 2.1 1.7 1.8 2.2 1.8 2.9 Maximum 4.5 4.4 4.6 5.5 4.8 4.6 4.2 4.0 3.6 4.1 4.1 4.1 3.91-X, N-S Average 2.7 3.4 4.4 5.5 5.1 4.3 4.2 4.0 3.5 3.3 3.0 2.5 3.8Hor Axis Minimum 1.9 2.5 2.9 4.3 2.9 3.1 3.2 2.8 2.1 2.0 2.0 1.5 3.3 Maximum 4.0 4.5 5.6 7.3 6.3 5.8 5.3 5.3 4.6 4.5 3.8 3.5 4.51-X, N-S Average 3.5 4.1 4.8 5.6 4.9 4.0 4.0 4.0 3.7 3.9 3.7 3.3 4.1Tilt=Lat Minimum 2.4 3.0 3.2 4.4 2.8 2.9 3.0 2.8 2.2 2.3 2.5 1.9 3.5 Maximum 5.1 5.4 6.1 7.4 6.0 5.4 5.0 5.3 4.8 5.2 4.7 4.6 4.82-X Average 3.7 4.2 4.8 5.7 5.2 4.3 4.3 4.1 3.8 3.9 3.9 3.6 4.3 Minimum 2.6 3.0 3.2 4.4 2.9 3.1 3.2 2.9 2.2 2.3 2.7 2.1 3.7 Maximum 5.4 5.6 6.1 7.6 6.4 5.9 5.3 5.4 4.8 5.3 5.0 4.9 5.0AVERAGE CLIMATIC CONDITIONSElement Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec YearTemp. (deg C) 14.2 15.0 17.9 20.7 23.7 26.3 27.3 27.2 26.3 23.0 18.8 15.6 21.3Daily Min (deg C) 8.3 9.1 12.2 14.8 18.3 21.6 22.5 22.7 22.2 18.4 13.5 9.8 16.1Daily Max (deg C) 20.0 20.8 23.8 26.7 29.2 31.1 32.1 31.7 30.4 27.5 24.2 21.3 26.6Record Lo (deg C) -9.4 -4.4 -3.3 1.7 6.7 11.1 15.6 18.3 11.1 5.0 -2.8 -7.2 -9.4Record Hi (deg C) 30.6 31.7 32.8 35.6 37.8 38.9 38.9 37.8 37.2 35.0 31.7 31.1 38.9HDD,Base= 18.3C 157 114 62 12 0 0 0 0 0 0 46 115 505CDD,Base= 18.3C 28 21 50 83 167 240 279 276 240 147 61 31 1622Rel Hum percent 75 72 71 69 72 77 78 80 79 75 76 76 75Wind Spd. (m/s) 3.8 4.1 4.2 4.1 3.8 3.4 3.2 3.0 3.5 4.0 3.7 3.6 3.7

City: DAYTONA BEACH State: FLWBAN No: 12834Lat(N): 29.18Long(W): 81.05Elev(m): 12Pres(mb): 1017Stn Type: Primary

NREL

Presenter

Presentation Notes

Direct beam solar radiation data is used for sizing and estimating the performance of concentrating solar energy collectors. Note that the direct beam component is usually 65 to 75 percent of the total global radiation received on a dual-axis sun-tracking surface. Reference: Photovoltaic Systems, p. 46-53 & CD-ROM


PVWATTS Performance Calculator

Used to evaluate solar energy

collected and the performance of grid-tied PV systems for any array azimuth and tilt angles.

User selects state and city from map, and enters size of PV system, array orientation and derating factors.

Results give monthly and annual solar energy received and PV system AC energy production.

NREL

Presenter

Presentation Notes

PVWATTS is an online tool produced by the National Renewable Energy Laboratory to estimate the performance of grid-connected PV systems. The user selects a site, size of PV array and orientation. The results factor in system losses for AC output and temperature, and provide estimates of the solar energy received and AC energy production. Suggested Exercise: Run PVWATTS Version 1 online using a site near your location. Enter a 1 kW PV array and use the default system derating parameters, and examine the solar energy received and AC energy production for various array tilt and azimuth angles. References: Photovoltaic Systems, p. 46-53 PVWATTS Website: http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/


PVWATTS Output

NREL

Presenter

Presentation Notes

References: Photovoltaic Systems, p. 46-53 PVWATTS Website: http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/


Summary

The solar radiation received on earth is affected by the earth’s movements and atmospheric conditions.

Solar irradiance (power) is expressed in units of W/m2 or kW/m2, and

measured with a pyranometer. Typical peak values are around 1000 W/m2 on a surface at sea level facing the sun

around solar noon; used as the rating condition for PV modules and arrays.

Solar irradiation (energy) is solar power integrated over time, expressed in units of kWh/m2/day. Solar energy resource data are used in sizing and estimating the performance of

PV systems, and varies location and with collector orientation.

The solar window defines the range of sun paths between the winter and summer solstices for a specific latitude. PV arrays are oriented toward the solar window for maximum energy gain.

Presenter

Presentation Notes



Questions and Discussion

Presenter

Presentation Notes


solar radiation - ecgllp.com · the electromagnetic spectrum ranges from short wavelength gamma...

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