Energy and the New Reality, Volume 2:
C-Free Energy Supply
Chapter 2: Solar Energy
L. D. Danny Harvey
harvey@geog.utoronto.ca
Publisher: Earthscan, UK
Homepage: www.earthscan.co.uk/?tabid=101808
This material is intended for use in lectures, presentations and as
handouts to students, and is provided in Powerpoint format so as to allow
customization for the individual needs of course instructors. Permission
of the author and publisher is required for any other usage. Please see
www.earthscan.co.uk for contact details.
Framework
• Solar flux density on a plane perpendicular to the sun’s
rays at the mean Earth-Sun distance, Qs, is 1370 W/m2
• The intercepted solar radiation flux (Qs x πRe2) is about
11000 times the 2005 world primary power demand of
15.3 TW
• About 0.8% of the world’s desert area (or 80,700 km2)
covered with 10% efficient modules would be all that is
required to generate the total world electricity
consumption in 2005 of about 18000 TWh
• However, cumulative installation of PV panels to date is
only 25 km2
• The solution is to directly use solar energy where-ever
possible (for passive heating and ventilation, for thermaldriven cooling, and for daylighting), and to use solar
electricity only where electricity really is needed.
This chapter discusses:
• Photovoltaic generation of electricity
• Solar-thermal generation of electricity
• Solar thermal energy for space heating and for
hot water
• Solar thermal energy for air conditioning
• Industrial uses of solar thermal energy
• Direct uses of solar energy for desalination, in
agriculture and for cooking
Chapter 4 (Buildings) of Volume 1 discusses
passive (as opposed to active) uses of solar
energy, with the building itself serving as a
collector of solar energy. These passive uses are
• Passive heating
• Passive ventilation
• Daylighting
Chapter 11 (Community-Integrated Energy
systems with Renewable Energy) of this volume
discusses seasonal underground storage of solar
thermal energy for space heating and for domestic
hot water
Figure 2.1a Stereographic sun path diagram
Source: Computed using
The Solar Tool developed by Square One Research, available through Ecotech (ecotech.com)
Figure 2.1b Stereographic sun path diagram
Source: Computed using
The Solar Tool developed by Square One Research, available through Ecotech (ecotech.com)
Figure 2.1c Stereographic sun path diagram
Source: Computed using
The Solar Tool developed by Square One Research, available through Ecotech (ecotech.com)
Figure 2.1d Stereographic sun path diagram
Source: Computed using
The Solar Tool developed by Square One Research, available through Ecotech (ecotech.com)
Figure 2.2a Solar irradiance, daily variation, clear sky
Figure 2.2b Solar irradiance, daily variation , clear sky
Figure 2.2c Solar irradiance, daily variation, clear sky
Figure 2.2g Solar irradiance, daily variation, clear sky
1200
Horizontal Modules,
21 December
Irradiance (W/m2)
1000
0oN
800
600
30oN
400
60oN
200
0
-12
-6
0
Solar Hour
6
12
Figure 2.2h Solar irradiance, daily variation, clear sky
1200
Irradiance (W/m2)
1000
Module Tilted at
Latitude Angle,
21 Dec
0oN
800
30oN
600
60oN
400
200
0
-12
-6
0
Solar Hour
6
12
Figure 2.2i Solar irradiance, daily variation, clear sky
1200
Sun-Tracking
Modules,
21 Dec
Irradiance (W/m2)
1000
800
0oN
600
30oN
60oN
400
200
0
-12
-6
0
Solar Hour
6
12
Observations on the diurnal variations (Fig 2.2):
• On June 21
- the further north, the longer the day and the less intense the noon
peak
- the differences in irradiance on a panel tilted at the latitude angle
are smaller than on a horizontal panel
- there is almost no difference in the irradiance on a sun-tracking PV
panel within 5 hours of solar noon, but irradiance is less at other times
at high latitudes because of the greater pathlength through the
atmosphere (so more radiation is absorbed by the atmosphere)
• On Dec 21
-- the further north, the shorter the day
– differences are much greater, and sun tracking does not help
much at high latitude (because even when pointed at the sun, the
pathlength through the atmosphere is large)
Figure 2.3a Solar irradiance, annual variation, clear sky
500
Equator
Irradiance (W/m2)
400
300
200
Sun-tracking
Tilt=Latitude-Declination
100
Tilt=Latitude (fixed)
Horizontal
0
J
F
M
A
M
J
J
Month
A
S
O
N
D
Figure 2.3b Solar irradiance, annual variation, clear sky
500
30oN
Irradiance (W/m2)
400
300
200
Sun-tracking
Tilt=Latitude-Declination
100
Tilt=Latitude (fixed)
Horizontal
0
J
F
M
A
M
J
J
Month
A
S
O
N
D
Figure 2.3c Solar irradiance, annual variation, clear sky
600
50oN
Irradiance (W/m2)
500
400
300
200
Sun-tracking
100
Tilt=Latitude-Declination
Tilt=Latitude (fixed)
Horizontal
0
J
F
M
A
M
J
J
Month
A
S
O
N
D
Observations on seasonal variation of diurnal average
irradiance on a PV panel (Fig 2.3)
• If the panel has a fixed tilt equal to the latitude of the site,
the result is greater irradiance in winter and less in
summer compared to a horizontal panel
• 1-axis tracking, whereby the tilt is adjusted each day to
equal the latitude minus solar declination, gives greater
irradiance all year compared to fixed tilt
• 2-axis tracking is substantially better than 1-axis tracking
Figure 2.4a Solar irradiance on windows in June, clear sky
800
700
Radiation (W m-2)
600
South
East
West
500
400
North
300
North
200
100
0
-12
-9
-6
-3
0
3
Time (Hours)
6
9
12
Figure 2.4b Solar irradiance on windows in December,
clear sky
1000
900
South
Irradiance (W/m2)
800
East
700
West
600
500
400
North
300
200
100
0
-12
-9
-6
-3
0
3
Time (Hours)
6
9
12
Figure 2.5 Annual average solar irradiance (W/m2) at
ground level on a horizontal surface
Source: Henderson-Sellers and Robinson (1986, Contemporary Climatology, Longman, Harlow, U.K)
Supplemental Figure: Solar irradiance on a horizontal surface,
kWh/m2/yr
500
700
900
1100 1300 1500 1700 1900 2100 2300 2500
Source: Prepared from data file obtained from the NASA Surface Meteorology and Solar Energy website, power.larc.nasa.gov
Supplemental Figure: Solar irradiance on a surface tilted toward
the equator at an angle equal to the latitude angle, kWh/m2/yr
500
700
900
1100 1300 1500 1700 1900 2100 2300 2500
Source: Prepared from data file obtained from the NASA Surface Meteorology and Solar Energy website, power.larc.nasa.gov
Supplemental Figure: Ratio of annual irradiance on a surface tilted at
the latitude angle to the annual irradiance on a horizontal surface
0.98
1.00
1.05
1.10
1.15
1.20
1.25
Source: Prepared from data files obtained from the NASA Surface Meteorology and Solar Energy website, power.larc.nasa.gov
Two broad ways of making
electricity from solar energy:
• Photovoltaic (PV)
• Solar thermal
PV Electricity
• Electromagnetic radiation (including light) comes
in packets called photons, each with energy hv,
where h=Plank’s constant and v is the frequency
of the radiation
• Electrons in an atom exist in different energy
levels
• A photon can bump an electron to a higher
energy level if the energy of the photon exceeds
the difference in energy from one level to the
next
PV electricity (continued)
• When a solid forms, two outer energy bands are formed,
often separated by a gap in energy level (not a physical
gap)
• The lower energy band is called the valence band, the
upper the conduction band
• In a conductor, electrons occur in both bands and they
overlap
• In an insulator, the valence band is filled and the
conduction band is empty, and the two bands do not
overlap
• In a semi-conductor, electrons occur in both bands and
there is a small gap between the bands
PV electricity (continued)
• Silicon is a semi-conductor with a valence of 4 (4
electrons in the outer shell)
• Two semiconductor layers are used – one layer
(called the n-type layer) is doped with atoms have
an valence of 5 (the extra electron is not taken up in
the crystal lattice and so it is free to move), and the
other layer (called the p-type layer) is doped with
atoms having a valence of 3, so there are empty
electron sites (called holes)
• The juxtaposition of the n- and p layers is called a pn junction.
Figure 2.6 Steps in the generation of electricity in a photovoltaic cell
Source: US EIA (2007, Solar Explained, Photovoltaics and Electricity)
Figure 2.7 Layout of a silicon solar cell
Source: Boyle (2004, Renewable Energy, Power for a Sustainable Future, 65-104, Oxford University Press, Oxford)
Components of a PV system
• Module – consists of many cells wired together
• Support structure
• Inverter – converts DC module output to AC
power at the right voltage and frequency for
transfer to the grid
• Concentrating mirrors or lens for concentrating
PV systems
Types of PV cells
•
•
•
•
•
•
•
Single-crystalline
Multi-crystalline
Thin-film amorphous silicon
Thin-film compound semiconductors
Thin-film multi-crystalline
Nano-crystalline dye-sensitized cells
Plastic cells
Thin-film compound
semiconductors
•
•
•
•
Cadmium telluride (CdTe)
Copper-indium-diselenide (CuInSe2, CIS)
Copper-indium-gallium-diselenide (CIGS)
Gallium arsenide (GaAs)
Table 2.3 Best efficiencies achieved as of 2009
Technology
c-Si
m-Si
a-Si
thin-film Si
CdTe
CIGS
InP
thin-film GaAs
m-GaAs
a-Si/µc -Si
a-Si/a-SiGe/a-SiGe
thin-film GaAs/CIS
GaInP/GaAs
GaInP/GaAs/Ge
GaInP/GaInAs/Ge
Dye-sensitized
Organic
Unconcentrated Sunlight
Concentrated Sunlight
Cell
Module
Cell
Concentration Factor
Single-junction silicon semiconductor
25.0
22.9
27.6
92
20.4
15.5
9.5
16.7
8.2
Single-junction compound semiconductors
16.7
10.9
19.4
13.5
21.8
14
22.1
26.1
28.8
232
18.4
Multi-junction semiconductors
11.7
10.4
25.8
30.3
32.0
40.7
240
41.1
454
Photochemical and Organic
10.4
5.2
Figure 2.8 Trend in efficiency of PV cells and modules
Source: Extended from IEA (2003, Renewables for Power Generation, Status and Prospects,
International Energy Agency, Paris)
Figure 2.9.
Structure of the
GaInP/GaInAs/Ge
multi-junction
Cell
Source: Kinsey et al (2009, Progress in Photovoltaics: Research and Applications 16, 503-508)
Compound semi-conductors
• Have several pn junctions, each with a different
band gap
• Junctions are placed in the order of decreasing
band gap, starting from the top
• Efficiency is limited by that fact that
• - if the photon energy is less than that of the
band gap, nothing happens and the photon
passes right through
• - if the photon energy is greater than that of the
band gap, the excess energy is wasted (turned
into heat)
Figure 2.10 Organic Semiconductors
Source: Rand et al (2007, Progress in Photovoltaics: Research and Applications 15, 659–676)
Figure 2.11 Dye-sensitized Solar Cell
Source: McConnell (2002, Renewable and Sustainable Energy Reviews 6, 271–295,
http://www.sciencedirect.com/science/journal/13640321)
Factors affecting module efficiency
• Solar irradiance – efficiency peaks at around
500 W/m2 for non-concentrating cells
• Temperature – efficiency decreases with
increasing temperature, more so for c-Si and
CIGS, less for a-Si and CdTe
• Dust – can reduce output by 3-6% in desert
areas
Figure 2.12a Module efficiency vs solar irradiance,
theoretical calculations
Source: Topic et al (2007, Progress in Photovoltaics: Research and Applications 15, 19–26)
Figure 2.12b Module efficiency vs solar irradiance,
measurements
Source: Mondol et al (2007, Progress in Photovoltaics: Research and Applications 15, 353–368)
System efficiency is the product of
• Module efficiency
• Inverter efficiency
• MPP-tracking efficiency
Figure 2.13a Inverter & MPP Efficiency, calculated
Figure 2.13b Inverter & MPP Efficiency, measured
Source: Mondol et al (2007, Progress in Photovoltaics: Research and Applications 15, 353–368)
Figure 2.14 Current-voltage combinations (MPP) giving
the maximum power production for different
solar irradiances on the module
Source: Hastings and Mørck (2000, Solar Air Systems: A Design Handbook. James & James, London)
Figure 2.15 MPP-tracking efficiency
100
MPP Tracking Efficiency (%)
90
80
Morning
70
Afternoon
60
50
40
30
20
10
0
0
20
40
60
80
100
Load (%)
Source: Abella and Chenlo (2004, Renewable Energy World, vol 7, no 2, pp132–146 )
The net effect of all the losses is represented by
the performance ratio: the ratio of actual kWh of
generated AC electricity to kWh of DC electricity
produced by the module
Recent values have averaged around 75-80%
Building-Integrated PV (BiPV)
Figure 2.16 PV mounted onto a sloping roof
Source: Prasad and Snow (2005, Designing with Solar Power: A Sourcebook for Building Integrated
Photovoltaics, Earthscan/James & James, London)
Figure 2.17 PV integrated into a sloping roof
Source: Omer et al (2003, Renewable Energy 28, 1387-1399, http://www.sciencedirect.com/science/journal/09601481)
Figure 2.18a BiPV on single-family house in Finland
Source: Hestnes (1999, Solar Energy 67, 181–187, http://www.sciencedirect.com/science/journal/0038092X)
Figure 2.18b BiPV on a single-family house in Maine
Source: Hestnes (1999, Solar Energy 67, 181–187, http://www.sciencedirect.com/science/journal/0038092X)
Supplemental figure: BiPV on multi-unit housing
somewhere in Europe
Figure 2.19 PV modules (attached to insulation)
on a horizontal flat roof
Source: www.powerlight.com
Figure 2.21 BiPV (opaque elements) on the
Condé Nast building in New York
Source: Eiffert and Kiss (2000, Building-Integrated Photovoltaic Designs for Commercial and Institutional Structures:
A Sourcebook for Architects, National Renewable Energy Laboratory, Golden, Colorado)
Figure 2.22 PV modules servings as shading louvres on
the Netherlands Energy Research Foundation building
Source: Photographs by Marcel von Kerckhoven, BEAR Architecten (www.bear.nl)
Supplemental figure PV modules as vertical shading louvres
on the SBIC East head office building in Tokyo
Source: Shinkenchiku-Sha and www.oja-services.nl/iea-pvps/cases jpn_02.htm
Figure 2.23 PV modules providing partial shading in the
atrium of the Brundtland Centre (Denmark, left)
and Kowa Elementary School (Tokyo, right)
Source: Shinkenchiku-Sha
Source: Henrik Sorensen, Esbensen Consulting
Supplemental figure: Amersfoort project,
The Netherlands
Table 2.4: Potential electricity production from BiPV
Potential BiPV
Area (km2)
Potential Solar
Electricity (TWh/yr)
Source: Gutschner and Task 7 Members (2001, Potential for Building-Integrated Photovoltaics,
www.iea-pvps.org)
Parking lots in the US:
• Area of 1.9 million ha (19000 km2, or 137.8 km x
137.8 km)
• PV covering all parking lots at 180 W/m2 and
15% efficiency would generate
~ 4500 TWh/yr
• Total US electricity demand is
~ 4200 TWh/yr
Concentrating PV
• More sunlight on the expensive solar cell (by up
to a factor of 500), using less expensive mirrors
or lens
• Cell efficiencies are greater under concentrated
sunlight, compounding the benefit of greater
solar irradiance
• Works only with direct irradiance (not diffuse)
• Requires 1- or 2-axis sun tracking
• Passive or active heat removal required
Figure 2.24 Concentrating PV using a Fresnel lens
Source: www.ENTECHSolar.com
Figure 2.25 Entech concentrating PV
Source: www.ENTECHSolar.com
Figure 2.26 Amonix concentrating PV
Source: www.amonix.com
Figure 2.27 Flatcon point focus concentrating PV
Source: Peharz and Dimroth (2005, Progress in Photovoltaics: Research and Applications 13, 627–634)
Figure 2.28b Growth in installed PV power, 2004-2014
Installed Capacity (GWp-AC)
180
160
Rest of World
USA
China
Japan
Rest of Europe
Italy
Spain
Germany
140
120
100
80
60
40
20
0
2004
2006
2008
Year
Source: EPIA Market Update reports and IEA-PVPS Trends reports
2010
2012
2014
Figure 2.28a Growth in annual PV production
Installation Rate (GWp-AC/yr)
40
35
30
25
Rest of World
USA
China
Japan
Rest of Europe
Italy
Spain
Germany
20
15
10
5
0
2004
2006
2008
2010
Year
Source: EPIA Market Update reports and IEA-PVPS Trends reports
2012
2014
Source: G. Masson, 2012. PV Market Status, A New Ecosystem for Electric Utilities
Cost of PV electricity
• Module cost per kW peak output
= (module cost per m2 )/ (ηm Ip)
where Ip is the assumed maximum irradiance (1000
W/m2) and η m is the module efficiency (sunlight to DC).
This cost is cost per peak kW of DC electricity output.
• Electricity cost ($/kWh) =
(CRF+INS)*(1+ID)*CapCost/(8760 * CF * ηbos)
where CRF and INS are the cost recovery and insurance
factors, ID is an indirect factor, CapCost is the total
capital cost ($/kWp-DC), CF = Ia/Ip ,ηbos is the balance-of
system efficiency, and Ia is the mean annual irradiance
Component and installed costs
(as of 2010)
• Modules: ~ $400/m2, or $4000/kW-DC if the
efficiency is 10%
• Inverters: ~ $300-600/kW-DC (less for larger
systems)
• Total installed cost: ~ $6000-9000/kW-AC
Costs of alternative cladding materials:
•
•
•
•
Stainless steel:
~ $250-350/m2
Glass-wall systems: ~ $500-750/m2
Rough stone:
~ ≥ $750/m2
Polished stone:
~ $2000-2500/m2
Projection of future costs
• Extrapolation using the progress ratio concept
• Engineering-based bottom-up analysis
(Recall from the wind chapter: The progress ratio is the factor
by which the cost is multiplied for each successive doubling
in cumulative global production. It gives a good fit to the
change in cost over time for a very wide range of technologies,
although of course the progress ratio value varies from
technology to technology, but is usually 0.8-0.9)
Figure 2.29 Price of Photovoltaic Module
Price of PV modules (US$/Wp)
100
10
1
0.1
1
10
100
1000
10000
Cumulative global PV module shipments in MWp
Source: van Sark et al (2008, Progress in Photovoltaics: Research and Applications 16, 441-453)
Results of bottom-up analyses:
• A “bottom-up analysis” involves an item-by-item
consideration of everything that affects cost, and
how each could change over time or with
economies of scale.
• Projected near-term (2015) module costs of
$1/Wp for both c-Si and a-Si, installed costs of
$3/Wp or less with 1 GWp/yr manufacturing
facilities
What actually happened?
0.0
Source: Clean Energy Canada (2015)
Nov 2014
May 2014
Nov 2013
May 2013
Nov 2012
May 2012
Nov 2011
May 2011
Nov 2010
May 2010
Nov 2009
May 2009
Module Cost (2014 USD/Wp)
Trend in average PV module costs in the US
3.5
3.0
2.5
2.0
1.5
1.0
0.5
Installed cost of residential PV systems in Germany and
the US (and the common module+inverter cost)
Source: Seel et al. (2014, Energy Policy 69:216-226)
Cost of electricity from systems installed at the end of 2012 in Los
Angeles, in Los Angeles if they had German costs, and in German
cities (which have much less solar radiation). Electricity costs with Los
Angeles solar radiation and German installed-costs would be about 8
cents/kWh without any subsidy.
Source: Seel et al. (2014, Energy Policy 69:216-226)
Costs of signing up a residential PV customer
in the US and Germany
Source: Seel et al. (2014, Energy Policy 69:216-226)
Person-hours spend installing a PV system in the USA and
Germany (left) and in doing various paperwork (right)
Source: Seel et al. (2014, Energy Policy 69:216-226)
Figure 2.30 Triple-junction a-Si on laminated roofing
Source: Hegedus (2006, Progress in Photovoltaics: Research and Applications 14, 393–411)
Resource constraints on thin-film PV
• CIGS will be limited by the indium supply
• CdTe will be limited by the tellurium supply
• The constraints involve both the absolute supply
of In or Te, and the rate at which it can be
supplied
• In and Te are supplied as a byproduct of mining
copper, zinc, and bauxite
In the absence of concentrating PV,
• CdTe, CIGS, and a-Si:Ge together are unlikely
to be able to provide more than 1 TW peak
power (compared to 4.3 TW global electricity
generating capacity and 15.3 TW average global
primary power demand in 2005)
• Dye-sensitized cells (which require ruthenium)
could provide 6 TWp
• Near 100% recycling of rare elements would be
required for long-term sustainability
Solar Thermal Generation
of Electricity
• Mirrors are used to concentrate sunlight either
onto a line focus or a point focus
• Steam is generated, and then used in a steam
turbine
• In some cases, concentrated solar energy heats
a storage medium (such as molten salt), so
electricity can be generated 24 hours per day
using stored heat at night
• Best in desert or semi-desert regions, as only
direct-beam solar radiation can be used
The radiation available for use by concentrating solar thermal
power (CSTP) systems is referred to as the ‘direct normal’
radiation – the annual value is the irradiance on a surface that is
always at 90o to the sun’s rays
As only the direct beam radiation can be used, the peak
irradiance that can be used by CSTP is typically about 850
W/m2, compared to 1000 W/m2 for PV systems
Thus, peak power capacity for CSTP is given assuming a direct
beam irradiance of 850 W/m2 rather than 1000 W/m2
The annual capacity factor is equal to the annual average direct
normal irradiance (in W/m2) divided by 850 W/m2 (in the same
way that the annual capacity factor for PV is given by the annual
average irradiance on the module divided by 1000 W/m2)
Supplemental Figure: Annual direct normal irradiance, kWh/m2/yr
500
700
900
1100 1300 1500 1700 1900 2100 2300 2500
Source: Prepared from data files obtained from the NASA Surface Meteorology and Solar Energy website, power.larc.nasa.gov
Supplemental Figure: Ratio of annual direct normal
irradiance to annual total irradiance on a horizontal surface
0.6
0.8
0.9
1.0
1.1
1.2
1.3
1.4
Source: Prepared from data files obtained from the NASA Surface Meteorology and Solar Energy website, power.larc.nasa.gov
Types of Solar Thermal Systems:
• Parabolic trough
• Parabolic dish (Stirling engine)
• Central tower
Figure 2.34a Parabolic trough schematic
Source: Greenpeace (2005, Wind Force 12: A Blueprint to Achieve 12% of the World’s
Electricity from Wind Power by 2020, Global Wind Energy Council, www.gwec.org)
Figure 2.34b Central receiver schematic
Source: Greenpeace (2005, Wind Force 12: A Blueprint to Achieve 12% of the World’s
Electricity from Wind Power by 2020, Global Wind Energy Council, www.gwec.org)
Figure 2.34c Parabolic dish schematic
Source: Greenpeace (2005, Wind Force 12: A Blueprint to Achieve 12% of the World’s
Electricity from Wind Power by 2020, Global Wind Energy Council, www.gwec.org)
Figure 2.35a Parabolic Trough Thermal Electricity,
Kramer Junction, California
Figure 2.35b Parabolic Trough Thermal Electricity,
Kramer Junction, California
Figure 2.35c Close-up of parabolic trough
Growth in global CSTP capacity, 2006-2014
Source: Compiled from various REN21 Update reports
Distribution of CSTP capacity at the end of 2014
UAE
2.3%
India
5.2%
US
37.6%
Source: REN21 2015 Update
Algeria
0.6%
Egypt Morocco
0.5%
0.5%
Other
0.6%
Spain
52.9%
The latest parabolic trough
systems either
• Directly heat the water that will be used in the
steam turbine, or
• Directly heat water that in turn is circulated
through a hot tank of molten salts (40% K-nitrate
and 60% Na-nitrate), with the molten salts
storing heat and in turn heating the steam that is
used in a steam turbine, as illustrated in the
following diagram
Figure 2.36 AndaSol-1 Schematic
Source : Translated from Aringhoff (2002, Proyectos Andasol, Plantas Termosolares de 50 MW’,
Presentation at the IEA Solar Paces 62nd Exco Meetings Host Country Day )
Molten salt storage tanks at Andasol-1, Spain
Source: Garvin Heath (2009, LCA of Parabolic Trough CSP….), www.nrel.gov/docs/fy09osti/46875.pdf
With thermal storage,
• Electricity can be generated 24 hours per day
• The capacity factor (average output over peak
output) can reach 85%
Figure 2.37 Parabolic trough capacity factor
0.9
0.8
Solar Field Size
(Solar Multiple)
Annual Caqpacity Factor
0.7
1.0
0.6
1.5
2.0
0.5
2.5
0.4
3.0
3.5
0.3
4.0
5.0
0.2
0.1
0.0
0
2
4
6
8
10
12
14
16
18
20
Thermal Energy Storage (Hours)
Source : Price et al (2007, Proceedings of Energy Sustainability 2007, 27-30 June, Long Beach, California)
Table 2.14 Characteristics of existing and possible future parabolictrough systems
Source: EC (2007, Concentrating Solar Power, from Research to Implementation,
www.solarpaces.org) and Solúcar
Figure 2.38 Integrated Solar Combined-Cycle
(ISCC) powerplant
Source: Greenpeace (2005, Wind Force 12: A Blueprint to Achieve 12% of the World’s
Electricity from Wind Power by 2020, Global Wind Energy Council, www.gwec.org)
Figure 2.39 Parabolic dish/Stirling engine
for generation of electricity
Source: US CSP (2002) Status of Major Project Opportunities, presentation at the 2002 Berlin Solar Paces CSP Conference
Figure 2.40 Stirling Receiver
Source: Mancini et al (2003, Journal of Solar Energy Engineering 125, 135–151)
Figure 2.41 Energy flow in 4 different parabolic
dish/Stirling engine systems
Figure 2.42 Central tower solar thermal
powerplant in California
Source: US CSP (2002) Status of Major Project Opportunities, presentation at the 2002 Berlin Solar Paces CSP Conference
Figure 2.43 Solar Thermal Seasonal variation in the production of
solar-thermal electricity in Egypt, Spain, and Germany
120
Monthly Electricity Yield (%)
100
El Kharga
Madrid
80
Freiburg
60
40
20
0
Jan
Feb Mar
Apr
May Jun
Jul
Aug Sep
Oct
Nov Dec
Source: GAC (2006, Trans-Mediterranean Interconnection for Concentrating Solar Power, Final Report,
www.dlr.de/tt/trans-csp )
US DOE target for cost of CSTP established in 2010
for 2020 as part of the “SunShot” programme
Source:
http://energy.gov/eere/sunshot/downloads/2014-sunshot-initiative-concentrating-solar-power-subprogram-overview
US CSTP projects online in 2013-2014
Source:
http://energy.gov/eere/sunshot/downloads/2014-sunshot-initiative-concentrating-solar-power-subprogram-overview
Progress toward 2020 cost goals
Source:
http://energy.gov/eere/sunshot/downloads/2014-sunshot-initiative-concentrating-solar-power-subprogram-overview
Pilot projects in China
• 2 central tower projects, July 2013 start,
-a 1-MW powerplant, $5900/kW cap cost, $0.40/kWh, ___electricity cost
-a 50-MW powerplant, $3000/kW , $0.19/kWh
• 1 parabolic trough project, 50 MW at $4620/kW,
$0.27/kWh
• 1 parabolic dish project, 1 MW at $6505/kW, $0.43/kWh
• Costs expected to fall in half by 2020
Source: Zhu et al. (2015, Energy 89:65-74)
Figure 2.44 Projected cost of heliostats (accounting at present for half the
cost of central-tower systems) vs production rate (starting from present
costs and production)
300
Price (USD/m2)
250
200
150
100
50
0
100
1000
10000
100000
Production Rate (units/yr)
Source: IEA (2003, Renewables for Power Generation, Status and Prospects, International Energy Agency, Paris)
Overall projections for CSTP
(applicable to all 3 types)
•
•
•
•
$2000-3000/kW capital cost
5-8 cents/kWh electricity cost
25% capacity factor without thermal storage
13-15% overall conversion efficiency, sunlight on collectors to AC
electricity output
• Saudi Arabia had been planning to install 5 GW of CSTP
(roughly doubling current global capacity), which would have
driven costs down, but this is on hold due to the self-induced
collapse of oil prices (and hence, in the country’s oil revenue)
• Planned projects in Tunisia and Egypt are also on hold because
of unrest in the region
• Spain has pulled back for budgetary reasons
• For now, its seems that the US and China will be driving the
costs down through learning-by-doing
Solar Thermal Energy For
Heating and for Domestic Hot
Water
Figure 2.45 Types of collectors for heating
and domestic hot water
Source: Everett (2004, Renewable Energy, Power for a Sustainable Future, 17-64, Oxford University Press, Oxford)
Figure 2.46 Installation of flat-plate solar thermal collectors
Source: www.socool-inc.com
Figure 2.47a Integration of solar thermal collectors
into the building facade
Source: Sonnenkraft, Austria
Figure 2.47b Integration of solar thermal collectors
into the building roof
Source: Sonnenkraft, Austria
Supplemental figure:
Evacuated-tube solar thermal collectors
Source: Posters from the AIRCONTEC Trade Fair, Germany, April 2002,
available from www.iea-shc-task25.org
Supplemental figure: Evacuated-tube solar thermal
collectors
Source: Posters from the AIRCONTEC Trade Fair, Germany, April 2002,
available from www.iea-shc-task25.org
Figure 2.48 Integrated passive evacuated-tube
collector and storage tank in China
Source: Morrison et al (2004, Solar Energy 76, 135-140, http://www.sciencedirect.com/science/journal/0038092X)
Figure 2.49 Compound parabolic-trough solar-thermal
collector by Solargenix
Source: Gee et al (2003, 2003 International Solar Energy Conference, Kohala Coast, Hawaii, USA,
15-18 March 2003, 295-300)
Efficiency of solar thermal collectors:
• This is the ratio of heat energy supplied to solar
energy incident on the collector
• Heat is lost as the collector heats up
• Thus, the key to high efficiency is to supply lots
of heat at a relatively low temperature, through a
combination of low inlet water temperature and
high flow rate
• To do this, the end use applications must be
able to make use of heat at relatively low
temperature
For space heating, this requires being able to use heat as it
is generated in a radiant floor heating system, which in turn
requires high thermal mass exposed to the inside (so that
the building does not overheat) and a high-performance
envelope (so that the building stays warm after sunset
without having to store solar heat in a hot water tank)
For domestic hot water, this requires use of a thermallystratified hot-water tank, with cold water from the bottom of
the tank fed to the solar collector and hot water for use
drawn from the top of the collector
Phase-change materials (which store heat without a further
increase in temperature) can also be used. Materials with
melting points around 60-70oC would be ideal for domestic
hot water applications.
Figure 2.50 Efficiency of solar thermal collectors
1.0
0.9
Evacuated-tube
0.8
5-cm
Encapsulated
TIM
Efficiency
0.7
0.6
0.5
0.4
0.3
0.2
Single-glazed
0.1
Double-glazed
0.0
0
0.04
0.08
(T i-Ta)/I
0.12
As seen in the previous slide, the efficiency of all
collectors drops as the inlet temperature to air
temperature increases. Domestic hot water might
need to be at 70 C while air temperature is at 10C;
with 1000 W/m2 solar irradiance, (Ti-Ta)/I = 0.06,
giving an efficiency range of 30-50%. For space
water, water at 40 C could be sufficient in a very
well insulated house, giving (Ta-Ti)/I = 0.03 and an
efficiency range of 0.55-0.65
Costs in Europe
• Solar-air collectors, 200-400 euros/m2
• Flat-plate or CPC collectors, 200-500 euros/m2
• Evacuated-tube collectors, 450-1200 euros/m2
Storage system costs are extra
Table 2.17 Illustrative costs of solar thermal energy
Table 2.16: Countries with 1 million m2 or more of solar thermal
collectors in 2007.
Country
Australia
Austria
Brazil
China
France + Terr
Germany
Greece
India
Israel
Italy
Japan
Spain
Switzerland
Taiwan
Turkey
USA
Total
Total Capacity
(GWth)
Water Collectors
Unglazed
Glazed
Evacuated
4070
608
97
105
750
24
26
3
212
27,639
35,820
25.1
1660
2950
3587
10,400
1417
7784
3566
2150
4936
874
6825
1164
433
1137
10,150
1898
66,272
46.4
Air Collectors
Unglazed
Glazed
23
43
0.35
103,740
33
864
6.8
17
103
127
46
25
118
578
105,885
74.1
434
13
838
0.09
1409
0.99
230
282
0.12
Source: Weiss et al (2009, Solar Heat Worldwide, www.iea-shc.org)
Total
5753
3601
3685
114,140
1554
9398
3573
2167
4961
1002
7399
1213
1509
1255
10,150
30,346
209,669
146.8
Total
Added in
2007
782
290
573
21,140
323
970
283
257
72
249
183
265
78
135
700
1276
28,440
19.8
Figure 2.51 Growth in the worldwide area of
solar thermal collectors
Installed Area (millions m2)
600
500
400
300
Rest of World
Australia
Brazil
Japan
Germany
Turkey
US
China
200
100
0
1999
2001
2003
2005
2007
Year
2009
2011
2013
The thermal power capacity at the end of 2013 was 373 GW
Figure 2.52a Top ten countries in terms of total solar
thermal collector area, end of 2007
China
US
Evacuated tube
Glazed
Unglazed
Air
Turkey
Germany
Japan
Australia
Israel
Brazil
Austria
India
0
20
40
60
80
2
Collector Area (millions m )
100
120
Figure 2.52b Top ten countries in terms of solar
thermal collector area per capita, end of 2007
Cyprus
Israel
Austria
Greece
Evacuated-tube + Glazed
Barbados
Unglazed
Australia
Jordon
Turkey
Germany
US
China
0
100
200
300
400
500
600
2
Collector Area (m per 1000 inhabitants)
700
System-level interactions with solar
domestic hot water
• Normally, some back-up hot water heating system is
needed with solar thermal systems
• When solar thermal energy is used, the back-up
system on average runs at lower efficiency than if it is
the sole source of hot water (efficiency can drop from
85% to 45% if solar provides 80% of the required hot
water)
• Thus, the net savings in energy is less than the
fraction of the hot-water load met with solar energy
(when 80% of the load is met with solar, the savings
could be 80% of that, or 64%)
• If the backup system is a modulating condensing
heater, there will not be an efficiency loss at part load
Solar Thermal Energy For
Air Conditioning and
Dehumidification
• Absorption chillers
• Solid desiccant systems
• Liquid desiccant systems
From Chapter 4 of Volume 1: Desiccant cooling systems
require heat in order to regenerate the desiccant. The
desiccant dehumidifies the supply air, making it sufficient
dry that cooling of the supply air through evaporation of
water is feasible with producing air that is too humid
Heat
Exchanger
Evaporative
Cooler
D
E
Optional Evaporative
Cooler
C
Desiccant
Wheel
F
G
H
Heat
Input
B
A
Temperature-mixing ratio trajectories with desiccant
dehumidification and evaporative cooling
H
60
40
20
10
6
30
3
26
H'
24
22
20
18
16
F
E
G
14
A
12
D
10
8
6
B
C
4
2
0
5
10
15
20
25
30
35
40
45
50
55
60
65
o
Dry Bulb Temperature (C)
70
75
80
85
90
0
95 100
Mixing Ratio (grams moisture per kilogram dry air)
28
The effectiveness of any cooling system is
represented by its Coefficient of Performance
(COP), which is the ratio of cooling provided to
energy input
• For conventional electric cooling systems, the COP
ranges from 2.0 (low-end room air conditioners) to
7.0 (in large central systems with cooling towers)
• For absorption chillers, the COP is ~0.6 using 90°C
heat and ~ 1.2 using 120°C heat as the energy
input
• For solid desiccants, the COP is ~ 0.5 using 80°C
heat
• For liquid desiccants, the COP is ~ 0.75 using
75°C heat
System considerations with solar air conditioning
with absorption chillers:
• If fossil fuels are used to produce heat for absorption
chillers as a backup when there is not adequate solar
heat, the inefficiency of the absorption chiller compared
to an electric chiller offsets some of the benefit of moving
from an electric chiller to an absorption chiller using solar
energy part of the time
• The low COP of the absorption chiller compared to an
electric chillers means that more heat in total needs to
be removed by the cooling tower, so the electricity use
by auxiliary equipment (fans, motors, pumps) is larger,
and this offsets some of the benefit of switching from
electricity to solar heat for the core cooling function
Figure 2.53 COP vs Driving Temperature for
thermally-driven cooling equipment
1.4
Absorption double-effect
1.2
Steam jet
1.0
Liquid
desiccant
Absorption H 2O/LiBr
COP
0.8
Absorption NH3/H2O
0.6
0.4
Solid desiccant
Absorption diffusion NH 3/H2O
Absorption
0.2
0.0
50
70
90
110
130
Driving temperature (oC)
Source: Balaras et al (2007, Renewable and Sustainable Energy Reviews 11, 299–314,
http://www.sciencedirect.com/science/journal/13640321)
150
170
Costs
• 1000 to 8000 euros per kW of cooling capacity
for solar thermal systems
• 100 euros/kW for large conventional cooling
systems
• The cost of solar systems is dominated by the
cost of the collectors, so if collector costs come
down, or the collectors are used for heating in
the winter (so that only part of the collector cost
need be ascribed to cooling), then the cooling
cost will be smaller
Solar cogeneration
• Mount a PV module over a solar thermal
collector, so that both electricity and useful heat
are collected
• By removing heat from the back of the module,
the PV electrical efficiency increases
• However, the thermal collection efficiency will
not be as large as for a dedicated solar thermal
collector, and there might be an extra glazing
over the PV panel, which reduces the production
of electricity by absorbing some solar radiation
Figure 2.54 Cost vs solar collector area for
solar-thermal air conditioning
9000
Initial Cost (Euros/kW)
8000
7000
Absorption
6000
Solid
desiccant
5000
Absorption NH3/H2O
4000
Liquid desiccant
3000
2000
Absorption H2O/LiBr
1000
0
0.0
2.0
4.0
6.0
Specific Collector Area (m 2/kW)
Source: Balaras et al (2007, Renewable and Sustainable Energy Reviews 11, 299–314,
http://www.sciencedirect.com/science/journal/13640321)
8.0
10.0
Figure 2.55 Cost of saved primary energy versus
the magnitude of the savings
Cost of Saved Primary Energy (eurocents/kWh)
25
Absorption, heat backup
Absorption, electric backup
20
Adsorption, heat backup
Adsorption, electric backup
15
10
5
0
25
30
35
40
45
Primary Energy Savings (%)
50
55
Figure 2.56 Proposed hybrid electric-thermal cooling
using parabolic solar collectors
Solar input
100 kW
Parabolic
solar
collector
collector = 0.8
80 kW
thermal
turbine = 0.42
1.0 -
turbine
33.6 kW
electricity
Electric
chiller
COP = 3 - 4
100.8 - 134.4 kW
cooling
- losses
= 0.48
38.4 kW
thermal
Waste heat
Absorption
chiller
COP = 1.35
51.8 kW
cooling
Figure 2.57: Cross-section of a PV/T solar collector
Source: Charalambous et al (2007, Applied Thermal Engineering 27, 275–286,
http://www.sciencedirect.com/science/journal/13594311)
Industrial uses of Solar Energy
• Low temperature (60-260oC)
Food processing – often at 80-120oC
Textiles
Some chemical and plastics processes
• High temperature (900-2400 K, readily achieved
with solar furnaces) reduction of metal ores
Other uses of solar energy:
• Desalination of seawater
• Fixation of nitrogen
• Solar cooling of greenhouses (with desiccants
and evaporation)
• Crop drying
• Cooking
Desalination Options:
• Solar electricity to power reverse osmosis
desalination (80 MJ solar/m3)
• Solar heat to power multi-stage flash
desalination (600 MJ solar/m3)
• Extraction from night air with desiccants,
regeneration of desiccant with solar heat
• Condensation from humidified air with cool
seawater
Source: Clery (2011, Science 331, 136)
Source: Clery (2011, Science 331, 136)
Dealing with intermittency
• Use rapidly variable fossil backup
• Aggregate geographically-dispersed PV arrays
• Install energy storage (V2G plug-in hybrid cars
in particular) and develop dispatchable loads
• Link diverse renewable energy resources
(especially if the variability of non-solar
resources complements the solar variability)
Figure 2.58a PV Variability
1.0
0.9
100 systems
one system
0.8
P/P Installed
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0
12
24
36
48
60
72
Time (hours)
Source: Wiemken et al (2001, Solar Energy 70, 6, 513–518, http://www.sciencedirect.com/science/journal/0038092X)
Figure 2.58b PV Variability
0.5
Average of 100 systems
Stdev of 1 system
Stdev of 100 systems
Normalised Power
0.4
0.3
0.2
0.1
0.0
0
6
12
18
24
Time (hours)
Source: Wiemken et al (2001, Solar Energy 70, 6, 513–518, http://www.sciencedirect.com/science/journal/0038092X)
Figure 2.59 Decreasing correlation between output of PV
modules with increasing distance between them
1.0
0.8
rij
0.6
0.4
0.2
0.0
0
100
200
300
400
500
600
700
Distance (km)
Source: Wiemken et al (2001, Solar Energy 70, 6, 513–518, http://www.sciencedirect.com/science/journal/0038092X)
Concluding Comments
• The solar energy resource is enormous but diffuse,
so large land areas would be involved in capturing it
• Many of our energy needs involve low-temperature
heat (for space heating and hot water, and for some
industrial processes), and so do not require the
intermediary of expensive solar electricity
• Thus, the first strategy in using solar energy should
be to design buildings to make passive use of solar
energy – for heating, ventilation, and cooling (which
occurs when passive ventilation brings in outside air
that is cooler than the temperature that the building
would reach on its own)
Concluding Comments (continued)
• Two strategies for generating electricity for solar
energy are photovoltaic (PV) and solar-thermal
• PV electricity can be done centrally or on site as
building-integrated PV (BiPV)
• BiPV alone could provide 15-60% of total
electricity needs in various countries
• Solar thermal electricity can be generated 24
hours per day but requires direct-beam solar
radiation – so it is best in desert or semi-arid
regions
Concluding Comments (continued)
• PV cells can use conventional materials (silicon)
or various toxic (As, Cd) or rare (Ge, In, Te, Ru,
Se) elements, with those using rare elements
being most efficient (up to 30%, vs 10-15% for
crystalline silicon-based cells and 6-8% for
amorphous silicon)
• Limits on the availability of the rare materials
represent real constraints on how much
electricity could be supplied with these cells
• The limit can be increased by a factor of 100 or
so using concentrating PV cells, and would no
longer be an issue.
Table 2.21: Summary of methods to produce
electricity from solar energy
PV
Crystalline
silicon (single,
poly)
Thin film
amorphous
silicon
Multi-junction
thin films using
various rare
substances (e.g.
CIS, CdTe)
Nanocrystalline
dye cells
Costs
30-40
cents/kWh in
best locations,
9-13 cents/kWh
for best
projection
Highest cost
Efficiency
10-15%
modules, 20%
eventually
Advantage
Silica is
abundant,
higher
efficiency than
amorphous
5-6% modules,
10% hoped for
Can go on
anything, suited
to continuous
production
25-33% cells,
41% under
concentrated
sunligh
10% cell at
25°C
High efficiency
Efficiency
increases with
temperature,
can be
transparent to
visible radiation
Disadvantage
Material
inputs, greater
embodied
energy
Low efficiency
Uses toxic or
rare elements,
high cost
Requires rare
ruthenium
Table 2.21: Summary of methods to produce
electricity from solar energy
Costs
Concentrating crystalline Si
PV
CIGS
thin-film GaAs
GaInP/GaAs/Ge
Quantum dot
Efficiency
28% @ 92 suns
22% @ 14 suns
29% @ 232
suns
41% @ 454
suns
Advantage
Potentially
lower cost,
stretches rare
elements
Disadvantage
More
complicated,
requires direct
beam solar
radiation
Concentrates
direct and
diffuse
radiation
without
tracking
Still under
development
Table 2.21: Summary of methods to produce
electricity from solar energy
Parabolic
trough
Costs
12-20
cents/kWh
now,
5-10 cents
kWh future
Parabolic dish
10-14000
€/kW,
eventually $23000/kW (8-24
cents/kWh)
Central receiver
18-32
cents/kWh
today
Thermal
Efficiency
15-20%, 4248% CF with
6-hour storage
20-28%
10-15%
Advantage
Large scale, lots
of demo
projects, some
storage
Suitable for
isolated
villages, low
infrastructure
costs, quick
start
Most amenable
to 24-hour
electricity
Disadvantage
Thermal
storage more
difficult than
for other
thermal
methods
Expensive at
present,
limited heat
storage ability
Each mirror
must
individually
track the sun
Concluding comments (continued)
• PV electricity is currently expensive (~ 20-25
cents/kWh in sunny locations, 45-60 cents/kWh
in midlatitude locations) but will likely fall in price
by a factor of 2 or more during the next decade
• This would make BiPV highly competitive with
peak electricity, which can cost 15-30 cents/kWh
(retail price)
• Parabolic-trough concentrating solar-thermal
electricity is already in the 12-20 cents/kWh
range and could drop to as low as 5 cents/kWh
Other active uses of solar energy
•
•
•
•
•
•
Solar air conditioning
Medium-temperature (60-260oC) industrial heat
High-temperature (1000-2500oC) industrial heat
Solar fixation of nitrogen
Crop drying
Cooking