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Renewable Energy
Solar Thermal Energy
Gražvydas Kruopys
2012Study semester „Renewable Resources“ Lecturer: Thomas Eickhoff

Table of Content
 Why use solar thermal energy?
 Physics of Solar Thermal Energy
 Solar Collectors
 Solar Thermal Systems
 Storage of Energy
 Economic Efficiency
 Statistical Data
2

Why use solar thermal
energy?
 Solar thermal energy is mostly used because of big
efficiency compared with other renewables.
 It is becoming cheaper than other alternatives.
 Solar thermal energy usage is environmentally
friendly.
3

To use solar thermal energy
are three different ways:
 The first method
collects the energy of
the sun to heat water
or air for direct use in
solar home heating.
http://www.china-solarheater.com/Split-Pressure-Solar-Water-
Heater-System-for-Heating-Freeze-resistant.htm
4

 The second method
is used by large
power utilities to
indirectly create
electricity through
concentrated solar
heat energy.
http://www.pikeresearch.com/tag/concentrating-solar-power
5

 The third method,
known as passive
solar, leverages energy
efficiency and the
design of a building to
regulate the amount of
solar energy it receives
in order to regulate it's
temperature.
http://cactusmusic.ca/systems.htm
6

Physics of Solar Thermal
 The solar constant – S=1360W/m2.
 Portion of light that appears to come straight from the
sun – direct radiation.
 On a clear day, this can approach a power density of
1 kilowatt per square meter (1 kWm-2).
 Practical peak power densities are around 900 –
1000 watts per square meter.
7

Physics of Solar Thermal (I)
The rate of heat energy flow depends on:
 The temperature difference between the two sides.
 The total area available for the flow
 The insulating qualities of the material.
8

Physics of Solar Thermal
(II)
 To understand how heat loss occurs we need to look
at 3 mechanisms are involved in the transmition of
heat:
 Conduction;
 Radiation;
 Convection.
9

Convection
http://www.tangram.co.uk/TI-Polymer-
Plastic&Composite_Windows.html
10

U – Value
 U – Value is defined:
Heat flow through one squire meter = U–Value x
Temperature difference
 The Units in which U – values are expressed are thus
watts per square meter per degree Celsius
(Wm-2 °C-1 ).
The lower U – value, the better the insulation
performance.
11

Solar Collectors
http://www.solarhotwaterworks.com/page28/files/simple-drainback-schematic.jpg 13

Solar Collectors
http://energyinformative.org/wp-content/uploads/2012/04/solar-thermal-collectors.jpg
http://blog.hasslberger.com/img/concentrated-solar-power.jpg
Stationary solar
collectors
Concentrating solar
collectors
14

Stationary Collector Types
 1. Flat plate collectors (FPC);
 2. Evacuated tube collectors (ETC).
 3. Stationary compound parabolic
collectors (CPC);
15

1. Flat plate Collectors (FPC)
http://images.solarcontact.com/images/solar-heating/flat-plate-collector.jpg
http://www.amroofing.net/images/Flat_Plate_Collector.jpg
http://www.trimlinedesigncentre.com/e107_images/Flat_%20Plate_%20Solar_%20Collector.jpg
http://www.acrux.hu/sun/pic/sikkol/sikkoll4.jpg
16

Typical Flat Plate Collector
Scheme:
17

How it works?
http://www.architecture.uwaterloo.ca/faculty_projects/terri/carbon-aia/images/flat-plate-collector.jpg
20

Opperating temperature
Low
temperature
applications
up to 100˚C.
200˚C can be
achieved due to
highly selective
coatings
21

Various types of flat panel
solar collectors:
22

http://www.solarworks.co.uk/wp-content/uploads/2008/01/2007-11-12-131-large.JPG
24
Unglazed solar collectors

2. Evacuated Tube Collectors (ETC)
http://image.made-in-china.com/2f0j00IBFaCdhZwWos/Evacuated-Tube-Solar-Collector-with-Keymark-WKSC-30-.jpg
25

Evacuated Tube Collectors (ETC)
Evacuated collectors consist of a heat pipe
inside a vacuum-sealed tube.
Good performance at high temperatures.
Collectors can operate at higher temperatures
than FPC.
Eefficiency is higher at low incidence angles
than FPC.
26

ETC schemes:
http://www.daviddarling.info/images/evacuated-tube_collector.gif
27
Source: IORDANOU, 2009
2. Heat pipe tubes1. Direct flow tubes

3. Stationary compound
parabolic collectors (CPC);
http://www.psa.es/webeng/instalaciones/images/quimica_madrid_3.jpg
http://andyschroder.com/images/EvacuatedTubes/100_1739.JPG
29

Schematic diagram of a
compound parabolic collector
30

 These collectors are more useful as linear or trough-
type concentrators.
http://ars.els-cdn.com/content/image/1-s2.0-S0926337301003150-gr2.gif
31

 Evacuated tubes with CPC-reflectors are also
commercialized by several manufacturers.
http://www.evergreenenergy.ie/images/CPC_S_03.jpg
32

Effieciency Curves
 A comparison of the efficiency of various collectors at
irradiation levels of 500 and 1000 W/m2
33

Effieciency Curves
 Final selection of a collector should be made only
after energy analyses of the complete system:
34

Thermosyphon Systems
(passive)
http://images.cpbay.com/uploadfile/comimg/big/400L-Direct-Plug-Solar-Water-Heating-Thermosyphon-System-76423.jpg
http://www.solarhotwaterquotes.com.au/images/thermosiphon2.jpg
36

Thermosyphon Systems
http://www.solarbook.ie/images/suntreksolar.gif
37

Direct circulation System
(active)
38

Indirect Water Heating Systems
(active)
40

Solar Pool Heating System
http://www.purasol.co.cr/wp-content/uploads/TVSW-5-21-10-4.jpg
42

Extremely simple.
Usually unglazed colectors are used.
Typically, the collector will be about half the
area of the pool it self.
The best result are achieved with pools that do not
have other forms of heating and are consequently at
relatively low temperatures (under 20˚C)
43
Solar Pool Heating System

Shcematic Diagram
http://www.inyopools.com/Images/solar_plumbing_inground.jpg
44

Storage of Heat
Water heating
 38% of heat is absorbed by the oceans, 9% by the
continents and 24% by the atmosphere.
 Water is a good heat carrier!
 Specific heat of water - 4.187 kJ/kgK
45

Storage of Heat (I)
There are two types of space heating:
 Using water as fluid;
 Using air as fluid.
46

Economic Efficiency
 Solar thermal energy costs between 19-35 cents per
KWh in US (2004).
47
http://large.stanford.edu/courses/2010/ph240/danowitz2/

 In Lithuania solar thermal energy costs – 3-14 euro
cents per kWh (2008).
 Solar thermal systems are rated in kWth (thermal
kW).
48

Solar energy payback time
 The average of payback time is 5-9 years.
 Used for only hot water – 5-7 years;
 Used for hot water and house heating – 7-9 years;
 Used for hot water, house heating and pool heating –
5-6 years;
 Solar thermal system’s lifetime – about 20-25 years.
50

The Feed-in Tariff (FIT)
Government subsidize until 30% of solar thermal
system cost.
51
http://www.theuglycow.net/wp-content/uploads/2010/05/Euro-money.jpg

Statistical Data
http://2.bp.blogspot.com/-DI6bhkm65Gg/TtUlOuP8M6I/AAAAAAAAACo/hRaJMcejGKI/s1600/NASA_Map_WorldSolarEnergyPotential_LowRes.jpg
52

Installed Capacity
Worldwide
 The solar thermal collector capacity in operation
worldwide equaled 127.8 GWth corresponding to
182.5 million m2 at the end of the year 2006.
 102.1 GWth for by flat-plate and evacuated tube
collectors;
 24.5 GWth for unglazed plastic collectors;
 Installed air collector capacity was 1.2 GWth.
53

Total installed capacity of
solar water collectors:
Top 10 Countries
55

Installed Capacity in Europe
 By the end of 2007, the solar thermal collector
capacity (flat-plate and evacuated tube collectors) in
operation in Europe equaled 15.3 GWth
corresponding to 21.9 million square metres.
 In this context it is remarkable that 70% (10.9 GWth)
of this collector area was installed in just three
countries: Austria, Germany and Greece.
56

Installed Capacity in Germany
 The solar thermal market for glazed flat-plate and evacuated
tube collectors in Germany is well established, and has
experienced a constan growth since 2002.
 The German market is one of the main drivers of the overall
European solar thermal market.
 It is stimulated to a great extent by subsidies and other political
support mechanisms.
 With reference to the total capacity in operation of flat-plate and
evacuated tube collectors installed at the end of the year 2006
in Germany was 5,6 GWth.
57

Solar Thermal Development
in Europe
58

Solar Thermal Market in
the Reference Countries
 The solar thermal markets in the reference countries
are very different. Germany, Denmark and Austria
have well established markets, the Spanish market
has quickly developed in recent years, and while
Poland has a relatively small market, but it has a
significant potential.
 In absolute terms, Germany leads in the number of
installations Germany loses it‘s dominance however
when the installed capacity is calculated per
inhabitant.
59

New Installations per year:
60

World Market Leaders:
 With reference to the total capacity in operation of
flat-plate and evacuated tube collectors installed at
the end of the year 2006: China (65.1 GWth), Turkey
(6.6 GWth), Germany (5.6 GWth), Japan (4.7 GWth)
and Israel (3.4 GWth) are the leading countries.
 They are followed by Greece (2.3 GWth), Brazil (2.2
GWth), Austria (1.9 GWth), the USA (1.6 GWth) and
Australia (1.1 GWth).
 As can be seen from these figures, China is by far
the largest market, representing 64% of the world
market of flat-plate and evacuated tube collectors.
62

References:
 Sorensen, Bent. „Renewable Energy: Its physics, engineering, environmental impacts,
economics and planing“. Third Edition. Burlington: Elsevier Academic Press, 2004.
 Boyle, Godfrey. „Renewable Energy: Power for Sustainable Future“. Second Edition.
Oxford: Oxford University Press, 2004.
 Kalagirou, Soteris. „Solar Thermal Collectors and Applications“. Nicosia: Higher Technical
Institute, 2004.
 AEE - Institute for Sustainable Technologie. „Potential of Solar Thermal in Europe“.
Bruxelles: Renewable Energy House, 2008.
 IORDANOU, GRIGORIOS. „Flat-Plate Solar Collectors for Water Heating with Improved
Heat Transfer for Application in Climatic Conditions of the Mediterranean Region“. Durham,
Durham University, 2009.
 http://www.b-es.org/sustainability/solar-thermal-guidance/
 http://www.solarbook.ie/solar_panel_types.html
 http://agrobasis.com/2012/01/price-per-kwh-of-solar-generated-electricity-to-drop-in-the-
next-years/
 http://www.solarbuzz.com/facts-and-figures/retail-price-environment/module-prices
 http://www.estif.org/fileadmin/estif/content/esttp/downloads/SRA/ESTTP_SRA.pdf
 http://www.b-es.org/sustainability/solar-thermal-guidance/
 http://www.solarbuzz.com/going-solar/using/economic-payback
 http://www.ekokarta.lt/uploads/failai/Atsinaujinanti_energija_Saules_energija.pdf
 http://large.stanford.edu/courses/2010/ph240/danowitz2/
 http://www.solarserver.com/knowledge/lexicon/e/energy-payback-period.html
63

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