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World Renewable Energy Congress 2011 – Sweden Climate Change Issues (CC)
8-11 May 2011, Linköping, Sweden
Environmental Impacts of Solar Thermal Systems with Life Cycle
Assessment
Alexis de Laborderie
1*
, Clément Puech
1
, Nadine Adra
1
, Isabelle Blanc
2
, Didier
Beloin-Saint-
Pierre
2
, Pierryves Padey
2
, Jérôme Payet
3
, Marion Sie
3
, Philippe Jacquin
4
1
Transénergie, Ecully, France
2
MINES ParisTech, Sophia Antipolis, France
3
Cycleco, Ambérieu, France
4
PHK Consultants, Ecully, France
* Corresponding author. Tel: +33 472860407, Fax: +33 472860400, E-mail: a.delaborderie@transenergie.eu
Abstract: Solar thermal systems are an ecological way of providing domestic hot water. They are experiencing a
rapid growth since the beginning of the last decade. This study characterizes the environmental performances of
such installations with a life-cycle approach. The methodology is based on the application of the international
standards of Life Cycle Assessment. Two types of systems are presented. Firstly a temperate-climate system,
with solar thermal collectors and a backup energy as heat sources. Secondly, a tropical system, with
thermosiphonic solar thermal system and no backup energy. For temperate-climate systems, two alternatives are
presented: the first one with gas backup energy, and the second one with electric backup energy. These two
scenarios are compared to two conventional scenarios providing the same service, but without solar thermal
systems. Life cycle inventories are based on manufacturer data combined with additional calculations and
assumptions. The fabrication of the components for temperate-climate systems has a minor influence on overall
impacts. The environmental impacts are mostly explained by the additional energy consumed and therefore
depend on the type of energy backup that is used. The study shows that the energy pay-back time of solar
systems is lower than 2 years considering gas or electric energy when compared to 100% gas or electric systems.
Keywords: Environmental impact, LCA, Solar thermal systems
1. Introduction
Solar thermal systems have encountered a high interest over the last ten years in many
locations worldwide [1,2]. Indeed, it is a robust, efficient and simple technology to implement
for individual households: solar thermal relies on well known process and materials. Its
capacity in reducing energy load for domestic hot water (DHW) is significant in locations
with high irradiation level.
Some studies have been carried out on thermosiphon solar water heaters in different countries
[3-6] but none was focused on solar thermal systems with auxiliary energy source. This study
is focused on this second type of installation since they often are preferred for Northern-
European countries (collector and storage with integrated backup).
The main purpose of the work is to characterize the environmental impacts of solar domestic
hot water systems, or solar water heaters (SWH), integrating auxiliary heating (electric or gas
heaters). Furthermore, this study also aims at identifying the most discriminating parameters
to support implementation solutions. These systems’ performances are analyzed as case-
studies both for temperate climates (typically in France) and for tropical climates (typically in
the Caribbean).
Life Cycle Assessment (LCA) methodology is used for this environmental evaluation.
Among several LCA impact indicators, this study focuses on primary energy consumption,
global warming potential, effect on ecosystem quality and human health issues. Greenhouse
gas emissions (expressed in CO
2
equivalent) and non-renewable energy consumption are
considered here as key LCA outputs.
hal-00668172, version 1 - 9 Feb 2012
Author manuscript, published in "World Renewable Energy Congress - Sweden, Linköping : Sweden (2011)"
DOI : 10.3384/ecp110573678
World Renewable Energy Congress 2011 – Sweden Climate Change Issues (CC)
8-11 May 2011, Linköping, Sweden
Environmental performances of the different SWH with gas-backup, electrical-backup or no
backup (for tropical zone’s systems) are compared with standard hot water systems without
any solar contribution.
2. Methodology
This Life Cycle Assessment (LCA) study was performed in compliance with the ISO
standards 14040 and 14044 [7,8].
2.1. Scope of the study
This study has been carried out on individual solar thermal
systems applied in the case of temperate and tropical climates.
For temperate locations, four systems have been studied,
namely two traditional systems without solar systems
considering only electricity or gas heater, and two systems
with solar system and integrated backup energy (electricity
backup see Fig. 1 or gas backup). Due to the irregular solar
irradiation all over the year, this kind of solar thermal system
requires a backup system to reach the target temperature.
For tropical climates, one thermosiphonic solar system
(without backup energy) has been analyzed (Fig. 2).
To study both temperate and tropical systems, two
climatologically average located places have been determined,
namely Lyon (continental France) for temperate climate and
Le Lamentin (Martinique, overseas France) for tropical
climate.
The solar systems configuration and backup energy uses are
different according to the climatic conditions. Therefore, two
different Functional Units have been defined:
The temperate climate Functional Unit: Production of DHW for a four-person household,
(assessed to be 140 litres of 60°C) in temperate climate and 20 years of life expectancy.
The tropical climate Functional Unit: Production of DHW for a four-person household,
(assessed to be 200 litres of 50°C) in tropical climate and 20 years of life expectancy.
Given that tropical-type SWH does not include backup energy, the target temperature (50°C)
is an indicator required to calculate solar energy but it does not represent the real outlet water
temperature.
Corresponding irradiation levels and electricity mixes have been considered.
2.2. Inventory
2.2.1. Inventory building strategy and sources
Many hypotheses are necessary to evaluate the life cycle environmental impacts of DHW
production. These hypothesis have been defined with the expertise of the consulting and
Fig. 1. Sketch-plan of
temperate-type solar water
heaters (electric backup)
Fig. 2. Sketch-plan of
tropical-type solar water
heaters
hal-00668172, version 1 - 9 Feb 2012
World Renewable Energy Congress 2011 – Sweden Climate Change Issues (CC)
8-11 May 2011, Linköping, Sweden
engineering partner
1
as well as technical data collected from public industrial actors. Thus, the
different systems’ component has been determined and sized. On the second hand, inventories
for the electricity mix have been determined for the temperate-climate system.
For this study, the ecoinvent 2.0 LCI database [9] was used. Ecoinvent 2.0 contains
international industrial life cycle inventory data on a various range of activities (energy
supply, resource extraction, transport services,…). However, most of the SWH components
are not defined exactly in the existing database. Thus, it has been necessary to modify or
create new processes. When components’ inventories were available in the database they were
assessed in order to determine the validity of this inventory regarding the components’ origin
and main characteristics (materials used, manufacturing process and weight). When
necessary, some inventories were modified by applying a weight or size ratio. Some
inventories have also been completed by specific technical data collected within this project.
When no inventory was available for a component, a new inventory has been built by the
project team to estimate the required data.
As for the construction of the inventory, the composition of each component comes from
different sources, which are described in Table 1.
Table 1. Data collection for infrastructures in scenarios
Component
Sources
Solar panel
Ecoinvent modified (to match with the surface defined for the scenarios)
Water Pump
Ecoinvent modified (estimates, from the mass of material)
Expansion Vessel
Ecoinvent (slightly oversized compared to usual design, but minor impact)
Hot water tank
Ecoinvent modified (from a 2000 l tank)
Solar regulation
Rough estimate (from the mass of the material, mostly electronics)
Mounting support
Datasheets from manufacturers, completed by estimates when necessary
Plumbing
Experience and estimates from the consulting and engineering partner
Electrical backup
Ecoinvent (slightly oversized, but minor impact)
Gas backup
Ecoinvent modified (to exclude the impacts related to domestic heating)
2.2.2. System boundaries
The system boundaries are
described in Fig. 3. They include the
solar panels manufacturing (panels,
mounting systems), water tanks,
internal heat exchanger, pipes,
hydraulic components (pumps,
valves, expansion vessel),
regulation, cabling and solar fluid.
In addition, they also include the use
phase (backup energy consumption
for temperate-climate SWH) and the
recycling of components.
1
Transénergie, http://www.transenergie.eu
Fig. 3. Scheme of system boundaries
hal-00668172, version 1 - 9 Feb 2012
World Renewable Energy Congress 2011 – Sweden Climate Change Issues (CC)
8-11 May 2011, Linköping, Sweden
2.2.3. Scenarios
Table 2 describes the four scenarios (scenarios 1-4) built for this study used for temperate
climate systems. Scenario 5, standing as a reference for other scenarios results, comes from
the ecoinvent 2.0 database.
Table 2. Scenarios for temperate climates
Temperate climate Scenarios
Scenario 1
Scenario 2
Scenario 3
Scenario 4
Scenario 5
System
Solar Thermal +
Gas
Solar Thermal
+ Electricity
Gas heater
Electric
heater
Solar Thermal +
Gas
Solar Panels
Flat plate collectors
2
Flat plate collectors
3
Water tank
300 litres
vertical tank
300 litres
vertical tank
400 litres vertical
tank
Backup
system
Individual gas
heater and heat
exchanger
4
Electric
resistance
5
Individual
gas heater
Electric
heater
tank
Individual gas
heater and heat
exchanger
5
Other
components
Mounting system, pipes,
regulation and solar station
Pipes
Mounting system,
pipes, regulation
and solar station
Overall lifetime
energy consumption
205 000 MJ
~330 000 MJ
Solar coverage
50%
None
58,4%
Life expectancy
20 years
25 years
Table 3 describes the scenario built
for this study for tropical SWH
which is based on a thermosiphonic
solar system. Flat plate collectors
inventory is an average of the three
main products that exists on the
Caribbean market.
Table 3. Scenarios for tropical climate systems
Tropical climate Scenarios
System
Thermosiphon
Solar Panels
Flat plate collectors
5
Solar tank
200 l horizontal tank
Other components
Mounting system, pipes
Overall lifetime energy
consumption
147 000 MJ
Life expectancy
20 years
2.3. Payback time indicator
Energy Payback Time (EBPT) has been calculated with the following definition:
production
p
backup
p
nfabricatio
p
avoidedE
EE
EPBT
(1)
2
Collector Area = 4,4 m² with solar panel coefficients : B=0,75 ; K=4,5 W/(m².K)
3
Collector Area = 4 m² with unknown solar panel coefficients
4
Integrated in the upper part of the tank
5
Collector Area = 2 m² with solar panel coefficients : B=0,75 ; K=4,5 W/(m².K)
hal-00668172, version 1 - 9 Feb 2012
World Renewable Energy Congress 2011 – Sweden Climate Change Issues (CC)
8-11 May 2011, Linköping, Sweden
0%
20%
40%
60%
80%
100%
Relative scatter (%)
STS with gas backup (S1)
STS with electric backup
(S2)
Gas only (S3)
Electricity only (S4)
Ecoinvent (STS with gas
backup - S5)
nfabricatio
p
E
: Non-renewable primary energy used for the fabrication of the installation.
backup
p
E
: Non-renewable primary energy used for the backup system.
production
p
avoidedE
: Non-renewable primary energy avoided (thanks to the backup energy used,
in case of electric backup, specific electricity mix of the country avoided where the SWH is
installed.
In the case of electric backup or the comparison with the full electric system, this method of
calculating EPBT gives results only valid for the country where the solar panels are installed.
3. Results and analysis
Results have been calculated according to the impact 2002+ (v2.04) [10] method available in
SimaPro 7.1 PhD and the database ecoinvent 2.0.
3.1. Temperate climate-type systems
3.1.1. Overall environmental impacts
Scenarios are compared among all impact
categories in figure 4. Figures 5 and 6
present the results for the most significant
impact categories with the details of their
origin.
It strikes that the necessary water
auxiliary heating has a strong influence
on the overall impact indicators. In the
case of a SWH with electric backup
(scenario 2), CO
2
equivalent emissions
are significantly cut down compared to a
SWH with gas backup (scenario 1).
However, considering the other three impact categories, SWH with gas backup appears as the
best impact reduction potential option compared to “traditional systems” (scenarios 3 and 4:
respectively gas only or electricity only) as well as SWH with electric backup.
It is important here to point out that the electricity mix chosen here influences thoroughly the
environmental performances of the ST installation, as well as the comparison with the
electricity only scenario. Indeed, according to ecoinvent 2.0, the French electricity mix has
particularly low carbon content: 103g/kWh. Thus, the energy backup’s choice is critical
according to the environmental impact reduction targeted.
3.1.2. Distribution of environmental impacts
The graphs below presents the climate change and non-renewable primary energy impacts.
They show the distribution of the impacts of each scenario for the different main life cycle
components.
In each of the five scenarios, transports (of materials to the manufacturing plant, as well as of
the products to the installation location) play a minor role in non-renewable primary energy
consumption. The electricity consumed for the operation of the SWH accounts for a smaller
amount of non-renewable primary energy too. Backup energy consumptions stand by far
(>80-90%) for the most important part of for the climate change and non-renewable primary
Fig. 4. Comparison of the temperate-climate-
type scenarios on the complete lifetime
hal-00668172, version 1 - 9 Feb 2012
World Renewable Energy Congress 2011 – Sweden Climate Change Issues (CC)
8-11 May 2011, Linköping, Sweden
0
200
400
600
800
1000
1200
1400
STS with gas
backup
STS with
electric
backup
EcoInvent
CO2 equivalent emissions (kg)
Pipes
Expansion tank
Ecoinvent hot water tank
Hot water tank (300L)
Solar station
Solar regulation
Solar thermal modules
Truck transport
Train transport
Roof support structure
Heat transfer fluid
0
5000
10000
15000
20000
25000
STS with gas
backup
STS with
electric
backup
EcoInvent
Non-renewable primary energy (MJp)
Pipes
Expansion tank
Ecoinvent hot water tank
Hot water tank (300L)
Solar station
Solar regulation
Solar thermal modules
Truck transport
Train transport
Roof support structure
Heat transfer fluid
0
2
4
6
8
10
12
14
16
18
20
STS with gas
backup
STS with
electric
backup
Gas only
Electricity
only
CO2 equivalent emissions per liter of
domestic hot water (gCO2eq/L)
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
STS with gas
backup
STS with
electric
backup
Gas only
Electricity
only
Gas boiler system + pipes
Solar regulation + pump + pipes
Electricity for the operation of STS
Fabrication of the STS
Gas for water heating
Electricity for water heating
Transport
Electric auxiliary system
Non-renewable primary energy per liter of
domestic hot water (MJp/L)
energy consumption impacts. Components of the solar thermal systems (solar thermal panels,
pumps, solar tank and regulation system) finally make up for a lesser part of overall impacts,
and once produced, consume very little electricity in the operating phase while providing 50%
of DHW energetic demand.
In the case of electric backup, CO
2
equivalent emissions are low because the electricity mix
chosen is mainly based on nuclear energy (France) and has particularly low CO
2
emissions.
On the other hand, the French electricity mix has an important primary energy use (13.6 MJ
of primary energy per kWh, according to ecoinvent 2.0), which is why, in this precise
configuration (scenario 2), electric backup stands for 91% of non-renewable primary energy
(see Fig. 5).
Fig. 5. Distribution of environmental impacts on climate change and non-renewable primary
resources for the first four scenarios for temperate-climate-type SWH
Figure 6 shows the impacts of the fabrication of the solar thermal systems’ components for
the three scenarios with SWH. The results for those three scenarios show the same trend: solar
thermal panels and the hot water tank are the major contributor to the environmental impacts
of the two analyzed impact categories.
Going further into details, it shows that the use of a large amount of steel stands for the most
important part of the impacts of the hot water tank. As for solar thermal panels, it is aluminum
(mainly for the frame) that causes most of the impacts. The major differences between the two
SWH scenarios come from the fitting between the hot water tank and the boiler for the gas
backup (fitting that is not necessary in the case of electric backup, which is integrated in the
hot water tank).
Fig. 6. Detailed environmental impact potential of temperate-climate solar thermal system on climate
change and non-renewable primary resources
hal-00668172, version 1 - 9 Feb 2012
World Renewable Energy Congress 2011 – Sweden Climate Change Issues (CC)
8-11 May 2011, Linköping, Sweden
3.1.3. Comparison with ecoinvent 2.0
Scenario 5 (the ecoinvent scenario) shows significant different results compared to the first
two scenarios. This is due to the water tank used which is 1/3 larger in scenario 5 (400 l
instead of 300 l). Besides, the transports hypotheses are much less favorable in scenario 5
compared to the first two. On the other hand, the supposed solar coverage ratio (SCR) is
noticeably higher in the ecoinvent scenario while the solar thermal panels surface is lower:
respectively 58.5% instead of 50% for the SCR, and 4 m² instead of 4.4 m². A further
examination indicates that the main differences of results between the two sets of scenarios
comes from hypotheses and choice of study parameters (lifetime, SCR, annual energy
demand), and therefore shows the coherence between scenarios 1 (gas backup) and 2
(electrical backup) and the ecoinvent scenario (scenario 5).
3.1.4. Energy payback time
Energy payback time (cf. its definition in paragraph 1.3) has been studied in order to compare
the energy required for the fabrication of SWH, to the energy avoided thanks to these systems
while providing the same service (cf. functional unit). For the sake of clarity, only SWH with
gas backup (scenario 1) has been compared to “traditional systems” (scenarios 3 and 4).
Energy payback time is 1.5 years when comparing SWH with gas backup to gas only
(scenario 1 to scenario 3), and less than 1 year when comparing SWH with gas backup to
electricity only (scenario 4).
3.2. Tropical-type scenario
3.2.1. Environmental impacts and distribution
As detailed in Table 2, the solar thermal systems studied here as the tropical-type scenario
shows specific differences with the systems used in temperate-climate conditions.
Considering that the impact of gas or electricity consumption makes up the major part of
overall impacts in the previous scenarios, the impacts of this scenario are significantly
different from the previous in terms of distribution.
Fig. 7 shows the distribution of the impacts for
each category. The water tank strikes as the
major contributor to the impacts of the SWH,
between 31% and 60% of each impact.
The other significant contributions are made by
the solar thermal panels (about 20% of the
impacts), the pipes (mostly because of the copper
used), 23% and 31% respectively for human
health and quality of ecosystems. The support
structure accounts for 7% to 11% according to
the impact category.
3.2.2. Energy Payback Time
Payback time of tropical SWH (with no auxiliary energy) ranges between 5 and 6 months.
4. Conclusions, recommendations and perspectives
This study clearly shows that solar thermal systems are a very interesting solution to reduce
the environmental impacts of domestic hot water production.
The impact assessment results for temperate climate systems highlight the backup energy as
the major factor on environmental impacts. However, this study does not end with a clear-cut
Fig. 7. Distribution of environmental
impacts of the tropical-type SWH for
each category of impact
hal-00668172, version 1 - 9 Feb 2012
World Renewable Energy Congress 2011 – Sweden Climate Change Issues (CC)
8-11 May 2011, Linköping, Sweden
environmental hierarchy among the different SWH systems: electricity or gas as a backup
energy. This is mainly due to characteristics of the French electricity mix that has a low CO
2
content but an important primary energy ratio.
For all SWH, regardless of backup energy, solar panels, water tank and pipes emerge as the
key environmental components.
Therefore, considering those results, technical improvement related to the main impacting
components can be realized to lower the environmental impacts of the solar thermal part of
SWH.
This project has been followed by a LCA on larger solar thermal installations to determine
their related environmental impacts and compare with domestic solar systems
6
.
5. Acknowledgments
ADEME (French Environment and Energy Management Agency) is co-financing this project
which brings together different French specialists from the solar thermal industry and LCA
fields.
References
[1] Eurobserv’er, Solar thermal Barometer, SYSTÈMES SOLAIRES - le journal des
énergies renouvelables N° 191, June 2009
[2] Solar Thermal Markets in Europe Trends and Market Statistics 2009, ESTIF, 2010
[3] Soteris Kalogirou, Thermal performance, economic and environmental life cycle analysis
of thermosiphon solar water heaters, Solar Energy 83, 2009, pp. 39–48
[4] Fulvio Ardente, Life cycle assessment of a solar thermal collector: sensitivity analysis,
energy and environmental balances, Renewable Energy 30, 2005, pp. 109–130
[5] Crawford, R. H., Net energy analysis of solar and conventional domestic hot water
systems in Melbourne, Australia, Solar Energy 76, 2004, pp. 159-163
[6] Soteris Kalogirou, Environmental benefits of domestic solar energy systems, Energy
Conversion and Management 45, 2004, pp. 3075-3092
[7] International Standard Organization. ISO 14040. Environmental management – Life
Cycle Assessment – principles and framework. 2006
[8] International Standard Organization. ISO 14044. Environmental management – Life
Cycle Assessment – requirements and guidelines. 2006.
[9] Swiss Center for Life Cycle Inventories. The life cycle inventory data version 2.0.
http://www.ecoinvent.ch. 2008.
[10] O. Jolliet, M. Margni, R. Charles, S. Humbert, J. Payet, G. Rebitzer, R. Rosenbaum.
Impact 2002+: A new life cycle impact assessment methodology, International Journal of
Life Cycle Assessment. 2003. Volume: 8, Issue: 6, Pages: 324-330
6
More information are available on http://www.esthace.eu
hal-00668172, version 1 - 9 Feb 2012
