es368 renewable energy systems part b: solar energy

ES368 Renewable Energy Systems Part B: Solar Energy

Brett Martinson

Office F334

Office hours Monday 12:00 – 13:00Office hours Wednesday 12:00 – 13:00

Phone 22339

E-mail [email protected]

Objectives

• understand the nature of the solar resource

• appreciate the performance and limitations of solar conversion technologies

• undertake simple system design for solar energy conversion systems.

Syllabus

1. Nature of the solar energy resource

2. Flat Plate Collectors

3. System types

4. Storage

5. System performance prediction

6. Concentrating collectors

7. Other applications of solar thermal

8. Photovoltaics

Books

Duffie and Beckman (1991) Solar engineering of thermal processes 2nd Ed.,Wiley, (TJ 810.D8)

Reddy (1987), The design and sizing of active solar thermal systems,Clarendon, (TJ 810.R3)

Lunde (1980) Solar thermal engineering: space heating and hot water systemsWiley, (TH 7413.L8),

Roberts (1991), Solar electricity: a practical guide to designing and installing small photovoltaic systems,Prentice Hall, (TK 2960.R6)

Web resources

Course site

www2.warwick.ac.uk/fac/sci/eng/staff/dbm/es368/

US Department of Energy solar pageswww.eere.energy.gov/solar

The International Solar Energy Society www.ises.org

Centre for the Analysis and Dissemination of Demonstrated Energy Technologies (CADDET)www.caddet-ee.org/

Dti’s solar grants www.solargrants.org.uk/

http://www2.warwick.ac.uk/fac/sci/eng/staff/dbm/es337/

http://www.eere.energy.gov/solar

http://www.ises.org/

http://www.caddet-ee.org/

http://www.solargrants.org.uk/

Assessment

• Exam (80%)– 3 ½ of 7 questions (choose five)

• Assessed work (20%)– Set in week 14– Due Week 19– Worth 1.5 CATS ( 15 hours work)

Some solar things

Thermo-siphon hot water cisterns

The thermo siphon uses the heat of the water to circulate the water by convection so no pump is necessary

Evacuated tube collector

Evacuated tube collector on a roof in Germany

Parabolic trough collectors in the USA

Power tower at CESA in Spain

Solar furnace in France

Solar Chimney in Spain

Solar roof in the USA

Solar challenge

Part B1: Nature of the solar resource

B1.1 Nature of the solar resourceThe sun

The source of all power on the earthradiates at about 5,777º K

(Blackbody equivalent)

B1.1 Nature of the solar resourceSpectral power distribution of the sun

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

Wavelength (m-1)

Spectral power distribution of 6000K blackbody

Actual Spectral power distribution of the sun

Energ

y d

istr

ibuti

on (

kW

/m2/

m)

B1.1 Nature of the solar resourceIrradiance

• The amount of the suns energy that reaches the earth (before entering the atmosphere)

• The average value of irradiance per year is called the solar constant (Gsc)and is equivalent to 1353, 1367 or 1373 W/m2 depending on who you believe

• 1353 (1.5%) from Thekaekara (1976) – derived from measurements at very high atmosphere and used by NASA

• 1367 (1%) Adopted by the World Radiation Centre

• 1373 (1-2%) from Frohlich (1978) - derived from satellite data

B1.2 Nature of the solar resourceEarth’s orbit ain’t circular

B1.2 Nature of the solar resourceEarth’s orbit: Variation in radiation

1,300

1,350

1,400

1,450

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Irra

dia

nc

e (

W/m

2 )

B1.2 Nature of the solar resourceEarth’s orbit: Variation in radiation

Gon = Irradiance

Gsc = Solar constant

n = day number (number of days since 1st January)

Note: cosine is for degrees

3601 0.033cos

365on sc

nG G

B1.3 Nature of the solar resource

Earth is tilted 23.45


Earth is tilted 23.45

• On the winter solstice (December 21)– The north pole has its maximum angle of inclination

away from the sun

– Everywhere above 66.55 N (90-23.45) is in darkness for 24 hours, Everywhere above 66.55 S is in sunlight for 24 hours

– the sun passes directly overhead over the tropic of Capricorn (23.45 S)

• On the equinox (March 22 & September 22)– Both poles are equidistant– the day is exactly 12 hours long – the sun passes directly overhead over the equator– The sun tracks a straight line across the sky

• On the summer solstice (June 22)– The reverse of the winter solstice

B1.3 Nature of the solar resourceSolar geometry

Beamradiation

B1.3 Nature of the solar resourceSolar geometry

= Latitude

= Declination – the between the earth’s axis of rotation and the surface of a cylinder through the earth’s orbit

= Declination

n = day number (number of days since 1st January)

Note: cosine is for degrees

B1.3 Nature of the solar resourceSolar geometry: Declination

28423.45sin 360

365

n


Solar geometry: Hour angle

Rotation

Beamradiation

• The angular displacement of the sun east or west of the local meridian due to the rotation of the earth

• Denoted by ()

• 15 per hour – noon is zero, so morning negative, afternoon positive

• Depends on Apparent Solar Time

B1.3 Nature of the solar resourceSolar geometry: Hour angle

AST = Apparent solar time

LCT = Local clock time

TZ = Time zone

L = Longitude (west = +ve)

EQT = Equation of time

B1.3 Nature of the solar resourceSolar geometry: Hour angle

15 60

L EQTAST LCT TZ

• Sunrise and sunset are asymmetrical– the plane of the Earth's equator is inclined

to the plane of the Earth's orbit around the Sun

– the orbit of the Earth around the Sun is an ellipse and not a circle

B1.3 Nature of the solar resourceSolar geometry: Equation of time


-20

-15

-10

-5

0

5

10

15

20

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Equ

atio

n of

tim

e (m

in)

EQT = Equation of time

n = day number


Where

0.000075 0.001868cos 0.032077sin229.2

0.014615cos2 0.04089sin 2

B BEQT

B B

3601

365B n

B1.3 Nature of the solar resourceSolar geometry: Equation of time: Analemma

http://www.analemma.com

B1.3 Nature of the solar resourceSolar geometry: Sun angles

s

Beam

radiation

Horizontalz


z

s

s

N

South E

W

Zenith


z = Zenith angle – the angle between the vertical (zenith) and the line of the sun

s = Solar attitude angle – the angle between the horizontal and the line to the sun

s = Solar azimuth angle – the angle of the projection of beam radiation on the horizontal plane (with zero due south, east negative and west positive)

Z = Zenith Angle

= Latitude

= Declination

= Hour angle

s = Solar azimuth angle

s = Solar attitude angle


cos cos cos cos sin sinz

sin cos cos sin sincos

cosss

Note: & should be the same sign

s = Sunset angle

= Declination

= Latitude

Note:

Day length is in hours

B1.3 Nature of the solar resourceSolar geometry: Sun angles: Sunset angle and day length

cos tan tans

12Day length cos tan tan

15

B1.3 Nature of the solar resourceSolar geometry: Collector angles

( - )

Normal

Beam

radiation

Horizontal


z

s

s

N

SouthE

W

Zenith


= Slope – the angle between the plane of the collector and the horizontal

= Surface azimuth angle – the deviation of the projection on a horizontal plane of the normal to the collector from the local meridian (with zero due south, east negative and west positive)

= Angle of incidence – the angle between the beam radiation on the collector and the normal


cos cos sin sin sin

cos cos sin cos

sin cos

s s

s s

s

cos sin sin cos cos sin cos

cos cos cos cos sin sin cos

cos sin sin sin

= Angle of incidence

s = Solar attitude angle

= Surface azimuth angle

s = Solar azimuth angle

= Collector slope

= Declination

= Latitude

= Hour angle

Sun angles

Earth angles

ss = Sunset angle

= Declination

= Latitude

= Collector slope


cos tan tanss

Northern Hemisphere

cos tan tanss

Southern Hemisphere

B5.1 System designIrradiance: Variables

• Latitude at the point of observation

• Orientation of the surface in relation to the sun

• Day of the year

• Hour of the day

• Atmospheric conditions

B5.1 System designIrradiance on a horizontal surface

, cosb b n zG G

,b nG

bG

Gb = Beam Irradiance normal to the earth’s surface (W/m2)Gb,n = Beam Irradiance (W/m2)z = Zenith angle

,b TG,b nG

, , cosb t b nG G Gb,t = Beam Irradiance normal to a tilted surface (W/m2)Gb,n = Beam Irradiance (W/m2) = Angle of incidence

B5.5 System designTilt: Beam radiation

, ,,

,

cos cos

cos cosb t b n

b tb b n z z

G GR

G G

,b nG,b tG

bG

,b nG

B5.5 System designTilt: Beam radiation

es368 renewable energy systems part b: solar energy

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