Source of Solar Energy Applications of Solar Energy Introduction to Heat Transfer Introduction to Photovoltaic Solar Thermal Energy Systems Restrictions in Using Solar Energy Examples
Outline
Department of Aeronautics and Astronautics National Cheng Kung University
Prof. Keh-Chin Chang
Solar Thermal Energy
The Sun Between the Sun and the Earth Position of the Sun Solar constant Solar radiation and intensity
Source of Solar Energy
Consist of H, He, O, C, Ne, Fe… Surface temperature: 5,800K Core temperature:13,600,000K
A sphere of intensely hot gaseous matter
The Sun
Source of Solar Energy
equinox
equinox
solstice
Elliptic Orbit
Source of Solar Energy
Between the Sun and the Earth
solstice
Average distance:149.5 million km (1 astronomical unit, AU)
Source of Solar Energy
Between the Sun and the Earth
Zenith angle of the sun: Defined as the angle measured from vertical downward.
Azimuth angle of the sun: Often defined as the angle from due north in a clockwise direction. (sometimes from south)
Source of Solar Energy
Position of the Sun (view from Earth)
Apparent placement of the Sun in the northern hemisphere
Source of Solar Energy
Position of the Sun (view from Earth)
Source of Solar Energy
Solar Constant Entry point into atmosphere Intensity ~ 1350W/m2
Solar Radiation Spectrum
Source of Solar Energy
Amount of incoming solar radiation per unit area incident on a plane perpendicular to the rays.
At a distance of one 1AU from the sun (roughly the mean distance from the Sun to the Earth).
Includes a range of wavelength (not just the visible light).
Solar Constant
Latitude Altitude Atmospheric transparency Solar zenith angle
Source of Solar Energy
Factors affect the Solar intensity
Source of Solar Energy
Solar Radiation Budget (to Earth)
Reserves of energy on Earth Solar energy distribution Advantages of using solar energy Types of applications
67
160755 Gm3 1.57 Mton
Gas Uranium
42
210
152 Gton
Oil
43
660.8 Gton
Available Period (year) Coal
Remaining Reserves
Applications of Solar Energy
Reserves of Energy on Earth
Applications of Solar Energy
Weiss, Werner, I. Bergmann, and G. Faninger. Solar Heat Worldwide–Markets and Contribution to the Energy Supply 2008. International Energy Agency, 2010.
The annual collector yield of Taiwan was 918 GWh (3306 TJ). This corresponds to an oil equivalent of 101,780 tons and an annual avoidance of 322,393 tons of CO2.
Contribution to energy supply and CO2 reduction
The annual collector yield of the world was 109,713 GWh (394,968 TJ). This corresponds to an oil equivalent of 12.4 million tons and an annual avoidance of 39.4 million tons of CO2.
Inexhaustible
No pollution
Application of Solar Energy
Advantages of using Solar Energy
Annual global mean downward solar radiation distribution at the surface
Applications of Solar Energy
Solar Energy Distribution
Energy production prediction
Solar cell
Solar water heater Solar thermal power Solar cooling Solar thermal ventilation
Solar thermal energy
Photovoltaic (PV)
Types of Applications
Application of Solar Energy
Application of Solar Energy
Advantages of using Solar Energy
Heat Transfer in a Solar Collector Heat Transfer Modes Conduction Convection Radiation
qcond,panel
absorbing film
qsun
qemit
Insulator
qcond,insulator
m
qconv,mediu
PanelȐmetalȑ
qconv,air
Mediumflow
Heat Transfer Processes in a Solar Collector
Introduction to Heat Transfer
ݍ௩ǡ : heat loss due to wind ݍ௩ǡௗ௨ : heat transfer to the flow medium throughout tube wall
¾
¾
ݍௗǡ : heat transfer inside the metal panel ݍௗǡ௦௨௧ : heat loss to the insulator from the panel
Conduction
¾
¾
Convection
ݍ௦௨ : solar irradiation ݍ௧ : emitted radiant energy from the panel
thermal conductivity
Fourier’s Law: ݍറ̶ௗ ൌ െ݇ߘܶ
heat flux gradient
area
ݍௗ ൌ ݍറ̶ௗ ή ܣറ
Definition: The transfer of energy from the more energetic to the less energetic particles (atoms or molecules ) of a substance due to interactions between the particles without bulk motion.
Conduction
e
d
¾
¾
Three heat transfer modes in a solar collector: c Radiation
Heat transfer modes
௩
௦
: convective heat transfer coefficient
௩
Newton’s cooling/heating law:
Convection
ஶ
Knowledge of convective heat transfer needs to know both fluid mechanics and heat transfer
Definition: Heat transfer between a fluid in motion and a boundary surface
Convection
emissivity
̶ݍௗ ൌ ߝߪܶ ସ ǡ Ͳ
൏ߝͳ
Stefan-Boltzmann constant
or
reflectivity
Gഐ Gഀ Gഓ ͳൌ ൌ G G G
G = Gఘ Gఈ Gఛ
Reflection (Gఘ )
Absorption (Gఈ )
Irradiation (G)
absorptivity
transmitivity
Transmission (Gఛ )
Emission (E=ߝߪܶ ସ )
Example: Glass (transparent material)
For real case:
T: absolute temperature
Stefan-Boltzmann Law: for a blackbody (ideal case) ݍௗ ൌ ̶ݍௗ ൈ ܣൌ ሺߪܶ ସ ሻܣ
Definition: Energy is emitted by matter via electromagnetic waves with the wavelengths ranging between the long-wave fringe ultraviolet (UV, 10-1m) and far infrared (IR, 103m).
(Thermal) Radiation
c)
b)
Ͳߠ
ߨ ʹ
Ͳ ߶ ൏ ʹߨ
blackbody
ഏ
ଶగ
ഏ
௦ ఏ ௦ ఏௗఏௗథ
ൌ
ߝ ܶ ൌ
ܧఒǡ ߣǡ ܶ ݀ߣ
ஶ
ߝఒ ߣǡ ܶ ܧఒǡ ߣǡ ܶ ݀ߣ
ஶ
మഏ
బ
ഏ
ாഊǡ್ ሺఒǡ்ሻ
ஶ ͳ න ߝ ሺߣǡ ܶሻܧఒǡ ߣǡ ܶ ݀ߣ ൌ ߪܶ ସ ఒ
=ߨܫఒǡ (T)
బమ ఌഊǡഇ ூഊǡ್ ௦ ఏ ௦ ఏௗఏௗథ
ൌ మ ߝఒǡఏ ሺߣǡ ߠǡ ߶ǡ ܶሻ ܿ߶݀ߠ݀ ߠ ݊݅ݏ ߠ ݏ గ
ଵ
ഏ మഏ మ బ బ ூഊǡ್
బమ ூഊǡ ௦ ఏ ௦ ఏௗఏௗథ
Total , hemispherical emissivity
ߝఒ ߣǡ ܶ ൌ
బ
మഏ
Monochromatic, hemispherical emissivity
Emissivity
ூഊǡ್ ሺఒǡ்ሻ
ூഊǡ ሺఒǡఏǡథǡ்ሻ
Spherical coordinate
intensity
ߝఒǡఏ ߣǡ ߠǡ ߶ǡ ܶ ൌ
emitted
Defined as the ratio of the radiant energy rate emitting from a blackbody under identical condition a) Monochromatic (or spectral) , directional emissivity
Emissivity
௧
ସ
Looking for high ࢻ while small ࢿ
௦௨
௦௨
ݍ௧
ఒ
ݍ௦௨
Total, hemispherical absorptivity,
c)
For a solar panel (opaque material, ఒ ఒ ,
Monochromatic, hemispherical absorptivity,
b)
ܫ௦௨
)
ఒ
Monochromatic, directional absorptivity, ߙఒǡఏ ሺߣǡ ߠǡ ߶ሻ
a)
Definition: A function of the radiant energy incident on a body that is absorbed by the body
Absorptivity
ሻ
ሻ
ሻ
, ఒ , ఒ ఒ curve moves to higher decreased
ఒ
௪
మ ήఓ
sub-range as T is
ଶగభ ఒఱ ୣ୶୮ మ Τఒ் ିଵ
Plank’s spectral distribution of emissive power
Plank’s Spectral Distribution
Plank’s Spectral Distribution
Source of Solar Energy
0.1
ߣሺߤ݉ሻ
visible light : 0.4-0.7m
ߙఒ ͲǤͻ
3
ߙఒ ൏ ͲǤ1
ఒ
ఒ
As Kirchhoff’s law for a diffuse (i.e., independent of direction) surface
0
1.0
A desired property for a good solar absorptance
Solar Radiation Spectrum
What is photovoltaic Solar cell
Photovoltaic
A method of generating electrical power by converting solar radiation into direct current electricity through some materials (such as semiconductors) that exhibit the photovoltaic effect.
What is Photovoltaic
Introduction to Photovoltaic
Sun light of certain wavelengths is able to ionize the atoms in the silicon The internal field produced by the junction separates some of the positive charges ("holes") from the negative charges (electrons). If a circuit is made, power can be produced from the cells under illumination, since the free electrons have to pass through the junction to recombine with the positive holes.
Photovoltaic
How to use solar thermal energy Types of solar collectors Solar water heater Solar thermal power Solar thermal cooling
Solar Thermal Energy Systems
Solar Cell
Solar collector
@ Collectors and working temperature
High temperature
Medium temperature
Low temperature
Solar Thermal Energy
working fluid
thermal energy
Solar Thermal Energy
Types of Solar Collectors
Solar Radiation
Working fluid
Solar Thermal Energy
How to Use Solar Thermal Energy
Solar Thermal Energy
Weiss, Werner, and Matthias Rommel. Process Heat Collectors. Vol. 33, 2008.
Main losses of a basic flat-plate collector during angular operation
Solar Thermal Energy
Use both beam and diffuse solar radiation, do not require tracking of the sun, and are low-maintenance, inexpensive and mechanically simple.
Flat-plate collector
Flat-plate collector
Glazed collector
Flat-plate collector
Flat-plate collector
Solar Thermal Energy
Unglazed collector
Solar Thermal Energy
Solar Thermal Energy
Heat pipe
Sydney tube
Solar Thermal Energy
A collector consists of a row of parallel glass tubes. A vacuum inside every single tube extremely reduces conduction losses and eliminates convection losses.
Evacuated tube collector
Evacuated tube collector
Solar Thermal Energy
Consist of parallel rows of mirrors (reflectors) curved in one dimension to focus the sun’s rays. All parabolic trough plants currently in commercial operation rely on synthetic oil as the fluid that transfers heat from collector pipes to heat exchangers.
Solar Thermal Energy
http://polarsolar.com/blog/?p=171
Parabolic trough collector
Collector efficiency
Concentrate the sun’s rays at a focal point propped above the centre of the dish. The entire apparatus tracks the sun, with the dish and receiver moving in tandem. Most dishes have an independent engine/generator (such as a Stirling machine or a micro-turbine) at the focal point.
Solar Thermal Energy
Simple design of flexibly bent mirrors and fixed receivers requires lower investment costs and facilitates direct steam generation.
Parabolic dish reflector
Approximate the parabolic trough systems but by using long rows of flat or slightly curved mirrors to reflect the sun’s rays onto a downwardfacing linear, fixed receiver.
Solar Thermal Energy
Linear Fresnel reflector
(Mainly using flat plate collector or evacuate tube collector)
Most popular and well developed application of solar thermal energy so far Low temperature applications
Solar Thermal Energy
Heliostat field use hundreds or thousands of small reflectors to concentrate the sun’s rays on a central receiver placed atop a fixed tower.
Solar Water Heater
A heliostat is a device that includes a plane mirror which turns so as to keep reflecting sunlight toward a predetermined target.
Solar Thermal Energy
Heliostat field collector
(Thermosyphon) User
The angle of the collector is roughly equal to the local latitude
Installation tilt angle
Solar Thermal Energy
Heat exchanger
User
User
Solar Thermal Energy
Indirect (close loop)
For northern hemisphere Facing south For southern hemisphere Facing north
Installation direction
Solar Water Heater
Active
Passive
User
Direct (open loop)
Solar Water Heater
Increasing collection area
Direction shifted from south (angle)
Increasing collection area
Solar Thermal Energy
Dormitory hot water Swimming pool Industrial process heating
Large-scale system
Hot water production House warming
Residential hot water system
“Solar Thermal Action Plan for Europe”, ESTIF, 2007
Solar Thermal Energy
Tilt angle of the collector
L=local latitude
Annual heat collection vs. direction/tilt angle (in north hemisphere) Annual heat collection(%)
Solar Water Heater
Solar Water Heater
Annual heat collection(%)
About 50% of the industrial heat demand is located at temperatures up to 250C.
Market potential of industrial process heating
Solar Thermal Energy
In EU, 2/3 of the industrial energy demand consists of heat rather than electrical energy.
Solar Thermal Energy
Industrial process heating
Solar Water Heater
Solar Water Heater
Solar thermal power
Solar Thermal Energy
Electrical power is generated when the concentrated light is converted to heat and, then, drives a heat engine (usually a steam turbine) which is connected to an electrical power generator.
Solar Thermal Energy
(by means of sun-tracking, concentrated solar collectors)
High temperature applications
Direct means : photovoltaics (PV), Indirect means : concentrated solar power (CSP).
Conversion of sunlight into electricity
Solar Thermal Power
Solar Thermal Power
Solar Thermal Energy
Combination of storage and hybridisation in a solar thermal plant
Solar Thermal Energy
Technology roadmap concentrating solar power, IEA, 2010.
Types of solar thermal power plant
Solar Thermal Power
Solar Thermal Power
Kimberlina solar thermal energy plant (LFR) (Bakersfield, CA), 2008.
Solar Thermal Power
PS10 and PS20 solar power tower (HFC) (Seville, Spain). 2007 and 2009
Solar Thermal Power
Solar Thermal Energy
Solar Thermal Energy
Andasol solar power station (PTC) (Granada, Spain), 2009
Solar Thermal Energy
Solar Thermal Energy
Puertollano solar power station (PTC) (Ciudad real, Spain), 2009
Solar Thermal Power
Calasparra solar power plant (LFR) (Murcia, Spain) 2009.
Solar Thermal Power
Solar thermal ventilation
International Journal of Refrigeration 3I(2008) 3-15
Solar Thermal Energy
Use solar thermal collectors to provide thermal energy for Solar thermal cooling driving a thermally driven chiller
Passive cooling
Use PV panel to generate electricity for driving a conventional air conditioner
Solar Thermal Energy
Active cooling
Solar Thermal Cooling
Solar (Thermal) Cooling
Solar Thermal Energy
Chiller
Cooling distribution
Cooling tower
Use solar thermal collectors to provide thermal energy for driving thermally driven chillers.
Active cooling
Heat source
Solar Thermal Cooling
2
Solar Thermal Energy
Solar cooling benefits from a better time match between supply and demand of cooling load
1 "Renewable Energy Essentials: Solar Heating and Cooling," International Energy Agency, 2009. 2 B.W. Koldehoff and D. Görisried, "Solar Thermal & Solar Cooling in Germany," Management.
Solar Thermal Cooling
Absorption coolingƐLiBr+H2O Adsorption coolingƐsilica gel+H2O DEC, Desiccant Evaporative Cooling
Basic type of solar thermal chiller
:H
evaporator
4&
expansion valve
condenser
COPelect=QC/We
low pressure vapor
compressor
high pressure vapor
4/
Conventional compression cooling
4D
Solar Thermal Energy
Open cycle
Closed cycle
Solar Thermal Energy
4/
evaporator
4&
expansion valve
condenser
COPthermal=QC/Qg COPelect=QC/We
low pressure vapor
absorption
(switch)
:H
high pressure vapor
desorption
4J
Adsorption/absorption cooling
Solar Thermal Cooling
Solar Thermal Cooling
Solar Thermal Energy
Solar Thermal Energy
"Solar Assisted Cooling – State of the Art –,“ESTIF, 2006.
Solar Thermal Cooling
Henning, H. “Solar assisted air conditioning of buildings – an overview.” Applied Thermal Engineering 27, no. 10 (July 2007): 1734-1749.
COPthermal of different type of chiller
Solar Thermal Cooling
Solar Thermal Energy
Solar Thermal Energy
D. Mugnier, "Refrigeration Workshop Market analysis Market actors Systems costs Politics : incentives & lobbying Conclusion Introduction," 28.04.2010 – Workshop Århus, Denmark ABSORPTION, 2010.
Solar Thermal Cooling
A. Napolitano, "Review on existing solar assisted heating and cooling installations," 28.04.2010 – Workshop Århus, Denmark ABSORPTION, 2010.
Solar Thermal Cooling
Solar Thermal Energy
Solar Thermal Energy
A way of improving the natural ventilation of buildings by using convection of air heated by passive solar energy. Direct gain warms air inside the chimney causing it to rise out the top and drawing air in from the bottom.
Passive Cooling (solar ventilation, solar chimney)
Solar Thermal Cooling
D. Mugnier, "Refrigeration Workshop Market analysis Market actors Systems costs Politics : incentives & lobbying Conclusion Introduction," 28.04.2010 – Workshop Århus, Denmark ABSORPTION, 2010.
Solar Thermal Cooling
The simplest configuration: the solar still. In sophisticated systems, waste heat is minimized by collecting the heat from the condensing water vapor and pre-heating the incoming water source.
Solar Thermal Energy
HDH is based on evaporation of brackish water and consecutive condensation of the generated humid air, mostly at ambient pressure.
Solar humidification-dehumidification (HDH)
Solar Thermal Applications
Solar desalination/distillation
Conventional installation way in Taiwan
Facade integration (roof)
Damage due to typhoon invasion
Conventional installation way in Taiwan
Roof integrated flat-plate collectors on house in Denmark (Source: VELUX)
Damage due to typhoon invasion
Summary, Executive, Werner Weiss, and Peter Biermayr. Potential of Solar Thermal in Europe - Executive Summary, 2009.
Reduction of -40%
Solar Thermal Energy
Contribution of solar thermal to EU heat demand by sector
Facade integration (balcony)
Geographical aspects Financial aspects
Restrictions in Using Solar Energy
Solar radiation has a low energy density relative to other common energy sources
Solar Energy supply is restricted by time and geographical location Easily influenced by weather condition
Unstable energy supply
Low energy density
Geographical Aspects
Restrictions in Using Solar Energy
Restrictions in Using Solar Energy
The capital cost in utilization of solar energy is generally higher than that of traditional ones, especially for PV.
Examples
Most economically competitive technology by now The need of SWH is inversely proportional to local insolation
Solar water heater
Higher cost compared with traditional energy
Financial Aspects
A family with 5 members plans to install a solar water heater which is mainly used for bath. The hot-water temperature required for bath is 50 ʚ, while the annual average temperature of cold water is 23 ʚ. Assuming that each person needs 60 liters of hot water for taking bath a day. How much heat should be provided by the solar water heater to satisfy the family’s demand for bath?
T
temperature difference between hot and cold water
Q Heat Demand M Hot Water Quantity C p specific heat capacity of water
M u C p u 'T
§ · l kcal Q ¨¨ 60 u 5 person ¸¸ u1 u 50qC 23qC © person u day ¹ kg u qC § · kg kcal ¨¨ 60 u 5 person ¸¸ u1 u 50qC 23qC person u day kg u q C © ¹ kcal 8100 day
Q
Answer 1
(Note: water specific heat Cp is assumed to be 1 kcal/kg-к, water density is 1 kg / l. )
Example 1
(Note: 1cal = 4.186J = 4.186 W × s).
Qc
Qc
Heat provided from collector
4
kWh u 1m2 u 0.5 2 m day kJ 3600 s kWh s 2 2 day day kcal 1720 day
7200
H Daily accumulative insolation A Effective collector area Efficiency of solar water heater
Qc
H u A uK
kJ day
1 kcal 4.186 7200 day
A solar water heater is equipped with an effective collect area of 1m2, and the daily cumulative insolation onto the collector is 4 kWh/m2-day in February. If the average efficiency of the solar water heater is 0.5, how many kilo-calories (kcal) of heat can be collected by this solar water heater during a day?
Answer 2
Example 2
The minimum heat demand is 8100 kcal/day, and there is a certain solar panel which can offer a heat supply of 1720 kcal/m2 in a day. With the absence of auxiliary heating device, calculate the required installation area of the solar panel. If the effective arer of this solar panel is 0.8 m2 /piece, how many pieces of solar panel should be installed to collect this heat demand?
1720 kcal
m 2 day
4.764m 2
Effective collector area
A
day
Heat provided from collector per m 2 Qc
8100 kcal
Demand Heat
Q
4.764m 2 | 5.955 6 pieces 0.8m 2
A
A
Q Qc
Answer 3
Example 3
420
(Note: ly = Langley = cal/cm2).
420
kcal u 2 m2 m day
1 1000 2 1 10000
cal u 2 m2 2 cm day
4.186W s (2) 420 1 2 u 2 m2 10000 m day
(1) 420
ly u 2 m2 day
420
1 kW 3600 hr u 2 m2 2 m day
kcal day 4.186 1000 1 10000
4200
9.767
kWh day
From meteorological data, the average daily accumulative insolation in Tainan is 420 ly/day (i.e., langley / day). For a solar collector that faces south with a area of 2 m2 and tilt angle of 0 degree, what is the daily accumulative insolation onto the collector surface? (in kWh and kcal, respectively)
Answer 4
Example 4