Life cycle analysis of a solar thermal system
with thermochemical storage process
Nur Aini Masruroh, Bo Li, Jiri Klemes*
Department of Process Integration, University of Manchester Institute of Science and Technology, (UMIST),
P.O. Box 88, Manchester M60 1QD, UK
Received 10 February 2004; accepted 4 March 2005
Available online 13 May 2005
Abstract
Solar energy itself is generally considered as environmentally friendly, nevertheless it is still
important to take into consideration the environmental impacts caused by production of thousands of
solar thermal systems. In this work the standard LCA methodology has been extended to analyse the
total environmental impacts of a new more efficient solar thermal system SOLARSTORE during its
whole life cycle. This system is being developed by a 5th Framework EC project. The LCA results
show that to produce 1 GJ energy with SOLARSTORE system will result in global warming
potential of 6.3–10 kg CO2, acidification potential of 46.6–70 g SO2, eutrophication of 2.1–3.1 g
phosphate and photochemical oxidant of 0.99–1.5 g C2H4. The raw material acquisition and
components manufacturing processes contribute 99% to the total environmental impacts. In
comparison with traditional heating systems, SOLARSTORE system provides a considerably better
solution for reduction of negative environmental impacts by using solar energy more efficiently.
q 2005 Elsevier Ltd. All rights reserved.
Keywords: Life cycle analysis; Solar thermal system; Thermochemical storage system
1. Introduction
The use of solar energy is offering a considerable potential to limit the greenhouse
effect. It enables substitution for fossil fuels used for energy generation, and consequently
avoids the atmospheric emissions and other polluting residuals associated with
Renewable Energy 31 (2006) 537–548
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doi:10.1016/j.renene.2005.03.008
* Corresponding author. Tel.: C44 161 306 4389; fax: C44 161 236 7439.
E-mail address: [email protected] (J. Klemes).
N.A. Masruroh et al. / Renewable Energy 31 (2006) 537–548538
conventional, mainly fossil, energy production processes. The major problem is that solar
energy is provided independently of the needs, which leads to a low efficiency of the
installations, covering only 30–60% of heating requirements and domestic hot water. The
majority of thermal storage systems available on the market are based on a hot water tank
(sensible storage) or a phase change material (PCM). These systems need a large area in
the house and are not suited for long life of storage. The storage period needed can be as
long as 5 days and a sensible or latent storage would lead to an important loss of heat
during this period of storage.
SOLARSTORE EU co-funded project is developing a more efficient solar
heating/cooling system based on a pair of salt-water endothermic/exothermic reactions.
Integration of this thermochemical storage process enables to store the solar thermal
energy when heat requirements are lower than heat production and release it when the heat
production cannot cover the requirements. Therefore, it is possible to save the thermal
solar energy, which would be normally lost. The need of auxiliary energy such as
electricity or gas decreases, which is consequently reducing negative environmental
impacts due to the use of conventional energy resources.
Although solar energy itself is considered as ‘green’, it is not always the case for the
processes involved in the use of solar energy. There is always a problem to be answered
when certain equipment is developed for the use of solar energy: is this equipment
environmentally friendly? The production targets for SOLARSTORE system are expected
to be thousand units, which makes it very crucial to assess the environmental impacts
associated with such systems.
A comprehensive appreciation of the environmental impacts associated with the
SOLARSTORE system requires an assessment of the emissions released and the
consumption of energy and materials during its entire life cycle, from raw material
acquisition to waste disposal. Life Cycle Analysis (LCA), which is based on ISO 14040
[1], is an effective tool to make a quantitative assessment of the environmental aspects and
potential impacts associated with a product during its entire life cycle. This ‘cradle to
grave’ (from raw material extraction to waste disposal) approach provides a systematic
way of evaluating the environmental impacts of a product, identifying and quantifying the
emissions and material consumption that affect the environment at all stages during the
entire product life cycle.
2. Objectives and basic specification
2.1. Objectives
The objective is to explore the environmental impacts and raw material consumption
associated with the SOLARSTORE system, by applying the LCA technique. Further,
objective is to find out whether or not SOLARSTORE system could create less negative
environmental impacts, by drawing a comparison of the environmental impacts between
SOLARSTORE system, traditional fossil fuel heating system and traditional solar heating
system.
N.A. Masruroh et al. / Renewable Energy 31 (2006) 537–548 539
2.2. Basic specification of SOLARSTORE system
The SOLARSTORE system consists of two major units that can be treated separately, a
general solar heating unit and a thermochemical storage unit. The general solar heating
unit consists of a solar collector, a backup boiler, heat exchangers, pumps, connections,
valves, and sensors. The thermochemical storage unit consists of reactors, evaporators,
condensers and reactive compounds that are constructed by compressing certain inorganic
salts and certain inert supporting structures together.
3. LCA for SOLARSTORE
3.1. LCA framework
Fig. 1 gives the technical framework for conducting LCA, showing how the basic
components, goal and scope definition, inventory analysis, impact assessment and
inventory assessment, are interrelated.
3.2. System definition and major assumptions
As mentioned in Section 3.1, SOLARSTORE system consists of two major units that
can be treated separately. Therefore, the LCA study can be performed for these two units
separately. Previous LCA study of general solar heating system [2] provided useful
starting point, whilst LCA study of the thermochemical storage system has to be newly
developed.
IMPACT ASSESSMENT
6.Classification
7.Characterisation
8.Valuation
IMPROVEMENT ASSESSMENT
9.Reporting and improvement assessment
GOAL AND SCOPE
DEFINITION
1.Goal and
scope definition
Data analysis
Impacts to be evaluated
Key
LCAFramework
DetailedExecution step
INVENTORY ANALYSIS
2.Constructing the
process flowchart
3.Defining the
system boundaries
4.Collecting the
data
5.Processing the
data
Fig. 1. Technical framework for LCA.
Thermal - Chemical System Conventional Solar Heating System
SOLARSTORE
ReactiveCompounds
Reactor Condenser
Evaporator
ValvePumps
SolarCollector
HeatExchanger
Connections
Boiler Sensors
Salts Binders Steel PlasticsIron Glass AluminiumInsulatingMaterials
Copper
Fig. 2. SOLARSTORE raw material tracing.
N.A. Masruroh et al. / Renewable Energy 31 (2006) 537–548540
Fig. 2 shows the raw materials that are used to construct SOLARSTORE system. The
processes involved include raw material acquisition processes, manufacturing processes of
all components, assembling process of each unit, installation and maintenance processes,
processes of using SOLARSTORE system, disassembling process of each unit, disposal
processes of the components and recycling processes of the materials. The transportation
processes between different sites should also be considered.
The difficulties to obtain the full data set (the SOLARSTORE system is still under
development) and the complexity of this analysis dictate the system definition to be
modified to cope successfully with the task:
1.
The usable lifetime of SOLARSTORE system is expected to be 15 years. SinceSOLARSTORE system is able to store/release solar thermal energy when necessary
without consuming any other energy resources, it can be reasonably assumed that zero
emission would be created by SOLARSTORE system during its usable lifetime.
Therefore, it is reasonable to exclude the use phase of SOLARSTORE system
from LCA as long as SOLARSTORE system is able to cover the full energy
requirement. On the other hand, it is also well considered that the SOLARSTORE
system might be unable to cover certain energy requirement, which implies the
necessity to have a backup boiler. In this case, emissions will be produced by the use of
backup boiler which is based on conventional energy production, i.e. electricity/gas.
These emissions are also taken into consideration when a LCA based comparison of
total environmental impacts is drawn between SOLARSTOER system and other
existing heating systems.
2.
The installation and maintenance processes are excluded from LCA due to lack of data.However, this exclusion does not deteriorate LCA results because experiences show no
significant emissions will be produced during these processes.
N.A. Masruroh et al. / Renewable Energy 31 (2006) 537–548 541
3.
SOLARSTORE system should be disposed off when it loses the ability ofstoring/releasing solar thermal energy, and the reactive compounds and equipments
should be recycled. This should be taken into the consideration when assessing the
environmental impacts. Based on experimental results, the reactive compounds could
be fully recycled without significant production of emissions. The equipment might be
recycled to produce the material with the same quality (primary recycle) or the one with
lower quality (secondary recycle). Although this recycling might be energy intensive
and create significant emissions, this phase is excluded from the system boundary. This
is because firstly only limited information is available for this recycling and secondly, it
is assumed that the emissions produced from the primary recycle process have been
considered in the processes of raw material acquisition and manufacturing.
4.
Railway and road transport are assumed to be major means for transportation anddistribution processes.
Fig. 3 shows the system boundary of this LCA study.
Conventional SolarHeating SystemManufacturing
Solar CollectorBoilerHeat ExchangerPump, ValveSensorConnectionTransportation fromthe resources to themanufacturer
ThermochemicalSystemManufacturing
ReactorEvaporator,CondenserSaltsBinderTransportation
SOLARSTORE System Assembling SiteConventional Solar Heating SystemThermochemical System
Transportation and distribution tothe point of use
Point of useInstallationMaintenance
DisposalSaltsBinder
RecycleEquipmentSaltsBinder
Transportation to the SOLARSTOREassembling site
RM
En
Ems
RM
En
Ems
En Ems
En Ems
En Ems
EmsEms
RMEn
Fig. 3. LCA boundary (RM, Raw Material; En, Energy; EMS, Emissions).
N.A. Masruroh et al. / Renewable Energy 31 (2006) 537–548542
3.3. Environmental impacts to be considered
Generally the environmental impacts to be considered include the resource depletion,
human health and ecological consequences [3]. In this work, for consideration of data
availability and complexity of the study, only four generally considered impacts, i.e.
global warming potential (CO2 equivalent), acidification (SO2 equivalent), eutrophication
(phosphate equivalent) and photochemical oxidant (C2H4 equivalent) are evaluated.
3.4. Functional unit
The SOLARSTORE system is developed to improve the efficiency of traditional solar
heating system. The size of hardware equipment and the amount of the reactive compounds
are directed by the potential of energy savings that can be achieved by SOLARSTORE
system. The functional unit in this study is 1 GJ energy provided by SOLARSTORE system.
Considering the other expected results of the project, reduction to negative
environmental impacts, such a functional unit makes it easier to compare the emissions
released by SOLARSTORE during its life cycle with the emissions released by a
traditional solar heating system or fossil fuel based heating system.
3.5. LCA results
In this LCA study are six options for selection of appropriate salt/binder combinations,
three situations in which different energy requirements are to be fulfilled by using
SOLARSTORE system, and two possible market places. Thirty-six LCA case studies, as
shown in Table 1, have been carried out to support to select appropriate reactive
compounds for different situations and different market places.
Figs. 4–7 gives the results of four case studies: (MP1, ER 1, SB A, CO I), (MP2, ER 1,
SB A, CO I), (MP1, ER 1, SB A, CO II) and (MP2, ER 1, SB A, CO II). The phase-based
breakdowns of the four environmental impacts are shown, respectively. The phases in
these figures are as follows:
Tab
Cas
SB
SB
SB
MP
Phase 1: Raw material acquisition and components manufacturing.
Phase 2: Transportation of raw materials to manufacturing site.
le 1
e studies that are carried out
MP 1 MP 2
ER 1 ER 2 ER 3 ER 1 ER 2 ER 3
A CO I # # # # # #
CO II # # # # # #B CO I # # # # # #
CO II # # # # # #
C CO I # # # # # #
CO II # # # # # #
, market place; ER, energy requirement; SB, salt/binder combination; CO, composition.
0
0.005
0.01
0.015
0.02
0.025
0.03
Phase 3
CO I CO II
Phase 1 (×103)
Phase 4.1
Phase 2
Phase 4.2
Fig. 4. Global warming potential (kg CO2/GJ).
N.A. Masruroh et al. / Renewable Energy 31 (2006) 537–548 543
Phase 3: Transportation of units from manufacturing site to assembling site.
Phase 4.1: Transportation of SOLARSTORE product to consumers (France).
Phase 4.2: Transportation of SOLARSTORE product to consumers (Spain).
The LCA results show that the environmental impacts caused by producing 1 GJ energy
with use of SOLARSTORE system are: global warming potential impact of 6.3–10 kg
Phase 3
CO I CO II
Phase 1 (×103)
Phase 4.1
Phase 2
Phase 4.2
0.00E+00
2.00E-05
4.00E-05
6.00E-05
8.00E-05
1.00E-04
1.20E-04
Fig. 5. Acidification (kg SO2/GJ).
Phase 3
CO I CO II
Phase 1 (×103)
Phase 4.1
Phase 2
Phase 4.2
0.00E+00
1.00E-06
2.00E-06
3.00E-06
4.00E-06
5.00E-06
6.00E-06
7.00E-06
8.00E-06
9.00E-06
Fig. 6. Eutrophication (kg phosphate/GJ).
Phase 3
CO I CO II
Phase 1 (×103)
Phase 4.1
Phase 2
Phase 4.2
0.00E+00
5.00E-05
1.00E-04
1.50E-04
2.00E-04
2.50E-04
Fig. 7. Photochemical oxidant (kg C2H4/GJ).
N.A. Masruroh et al. / Renewable Energy 31 (2006) 537–548544
N.A. Masruroh et al. / Renewable Energy 31 (2006) 537–548 545
CO2, acidification potential of 46.6–70 g SO2, eutrophication of 2.1–3.1 g phosphate, and
photochemical oxidant of 0.99–2.2 g C2H4. It is also shown that the major part of
emissions comes from the raw material acquisition and component manufacturing phase
(around 99%).
4. Comparison with other heating systems
Although SOLARSTORE system could improve the efficiency of traditional solar
heating system, it cannot fulfil the total annual heating requirement in most locations
around Europe. A backup boiler is used to accommodate the rest heat requirement. In this
case the use of conventional energy production, i.e. electricity/gas will produce certain
emissions, which should be taken into consideration. Therefore, there is a need to draw
a comparison of total environmental impacts between SOLARSTORE system and
conventional heating systems. In this study three conventional heating systems are
considered: conventional solar heating system, natural gas based heating system and low
sulphur oil based heating system.
Fig. 8 shows how different heating systems cover certain annual energy requirement,
which indicates a significant reduction in fossil fuel consumption (around 72% in
comparison with fossil fuel based systems) by SOLARSTORE system. Figs 9–11 shows
the annum-based comparison of global warming potential impact, acidification and
eutrophication, respectively. The photochemical oxidant is not given due to the lack of
data for conventional heating systems. The results show that SOLARSTORE system
creates more environmental impacts during its manufacturing processes. In spite of this
Solar energy Fossil fuel Energy
1000
0
2000
3000
4000
5000
6000
7000
SOLARSTORE Conventional SolarHeating System
Natural Gas Low Sulphur HeatingOil
Fig. 8. Energy arrangement to cover certain annual heating requirements (kWh).
SOLARSTORE Conventional SolarHeating System
Natural Gas Low Sulphur HeatingOil
Caused by use offossil fuel
Caused by productionof equipment
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
2600
Fig. 9. Annual global environmental potential impact (kg CO2).
N.A. Masruroh et al. / Renewable Energy 31 (2006) 537–548546
the use of SOLARSTORE system results in a significant reduction of the total
environmental impacts due to the considerable replacement of fossil fuel based energy
with solar energy. Table 2 shows how much emission reduction can be achieved by using
SOLARSTORE system in comparison with other heating systems.
SOLARSTORE Conventional SolarHeating System
Natural Gas Low Sulphur HeatingOil
Caused by use offossil fuel
Caused by productionof equipment
0
1
2
3
4
5
6
Fig. 10. Annual acidification (kg SO2).
SOLARSTORE Conventional SolarHeating System
Natural Gas Low Sulphur HeatingOil
Caused by use offossil fuel
Caused by productionof equipment
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Fig. 11. Annual eutrophication (kg phosphate).
Table 2
Annual reductions in environmental impacts
Heating system GWP (%) Acidification (%) Eutrophication (%)
Conventional solar heating system 42.3–59.6 19.1–23.4 37.1–48.0
Natural gas 46.4–65.4 28.9–30.2 41.6–55.2
Low sulphur heating oil 48.9–67.0 65.2–65.4 49.5–61.2
N.A. Masruroh et al. / Renewable Energy 31 (2006) 537–548 547
5. Conclusion
This work employs LCA technique to study the environmental impacts associated with
a new solar heating/cooling system which is integrated with a thermochemical storage unit
to improve the efficiency of traditional solar heating system. Thirty-six case studies have
been carried out for consideration of different heating requirements, different salt/binder
combinations and different market places. The total environmental impacts to produce
1 GJ energy with the use of this novel system are: global warming potential impacts of
6.3–10 kg CO2, acidification potential of 46.6–70 g SO2, eutrophication of 2.1–3.1 g
phosphate and photochemical oxidant of 0.99–2.2 g C2H4. The raw material acquisition
and components manufacturing processes contribute 99% to the total environmental
impacts during the whole life cycle.
This study also draws a clear comparison of total environmental impacts between
SOLARSTORE system, conventional solar heating system and traditional fossil fuel
based heating system. The results show that the SOLARSTORE system provides a better
solution for reduction of negative environmental impacts by using solar energy, which
encourages further, development and production from the environmental point of view.
N.A. Masruroh et al. / Renewable Energy 31 (2006) 537–548548
Acknowledgements
The financial support from the EC Project ENERGIE NNE5-2000-00385
‘Improvement of the efficiency of solar thermal systems by integration of a
thermochemical storage processes—SOLARSORE’ and a substantial and highly valuable
collaboration from project partners CREED, CLIPSOL, ADAI, CNRS and DALKIA are
gratefully acknowledged. For more information about the project please visit http://www.
cpi.umist.ac.uk/solarstore.
References
[1] Burgess AA, Brennan DJ. Application of life cycle assessment to chemical processes. Chem Eng Sci 2001;
56:2589–604.
[2] Mirasgedis S, Diakoulaki D, Assimacopoulos D. Solar energy and the abatement of atmospheric emissions.
Renewable Energy 1996;7(4):329–38.
[3] Masruroh NA. Life Cycle Analysis of a Solar Thermal System with Thermochemical Storage Process. MSc
Dissertation. Manchester, UK: Department of Process Integration, UMIST; 2002.