ES368 Renewable Energy Systems Part B: Solar Energy

Brett Martinson Office F334 Office hours Monday 12:00 – 13:00 Office hours Wednesday 12:00 – 13:00 Phone

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 2 nd 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 systems Wiley, (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 pages The International Solar Energy Society Centre for the Analysis and Dissemination of Demonstrated Energy Technologies (CADDET) Dti’s solar grants

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

B1.1Nature of the solar resource The sun The source of all power on the earth radiates at about 5,777º K (Blackbody equivalent)

B1.1Nature of the solar resource Spectral power distribution of the sun

B1.1Nature of the solar resource Irradiance 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 ( G sc )and is equivalent to 1353, 1367 or 1373 W/m 2 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

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

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

G on = Irradiance G sc = Solar constant n = day number (number of days since 1st January) Note: cosine is for degrees

B1.3Nature of the solar resource Earth is tilted 

On the winter solstice (December 21) –The north pole has its maximum angle of inclination away from the sun –Everywhere above  N ( ) is in darkness for 24 hours, Everywhere above  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

B1.3Nature of the solar resource Solar geometry Beam radiation  

B1.3Nature of the solar resource Solar 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 B1.3Nature of the solar resource Solar geometry: Declination

B1.3Nature of the solar resource Solar geometry: Hour angle Rotation  Beam radiation

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 B1.3Nature of the solar resource Solar geometry: Hour angle

AST = Apparent solar time LCT = Local clock time TZ = Time zone L = Longitude (west = + ve ) EQT = Equation of time B1.3Nature of the solar resource Solar geometry: Hour angle

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 B1.3Nature of the solar resource Solar geometry: Equation of time

EQT = Equation of time n =day number B1.3Nature of the solar resource Solar geometry: Equation of time Where

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

B1.3Nature of the solar resource Solar geometry: Sun angles ss Beam radiation Horizontal zz  

B1.3Nature of the solar resource Solar geometry: Sun angles zz ss ss N South E W Zenith

B1.3Nature of the solar resource Solar geometry: Sun angles  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 B1.3Nature of the solar resource Solar geometry: Sun angles Note:  &  should be the same sign

 s =Sunset angle  =Declination =Latitude Note: Day length is in hours B1.3Nature of the solar resource Solar geometry: Sun angles: Sunset angle and day length

B1.3Nature of the solar resource Solar geometry: Collector angles  ( - )  Normal Beam radiation Horizontal 

B1.3Nature of the solar resource Solar geometry: Collector angles zz  ss ss   N South E W Zenith

B1.3Nature of the solar resource Solar geometry: Collector angles  = 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

B1.3Nature of the solar resource Solar geometry: Collector angles = 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 B1.3Nature of the solar resource Solar geometry: Collector angles Northern Hemisphere Southern Hemisphere

B5.1System design Irradiance: 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

B5.1System design Irradiance on a horizontal surface G b = Beam Irradiance normal to the earth’s surface (W/m 2 ) G b,n = Beam Irradiance (W/m 2 )  z = Zenith angle

G b,t = Beam Irradiance normal to a tilted surface (W/m 2 ) G b,n = Beam Irradiance (W/m 2 ) = Angle of incidence B5.5System design Tilt: Beam radiation