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

www.elsevier.com/locate/renene

0960-1481/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.renene.2005.03.008

* Corresponding author. Tel.: C44 161 306 4389; fax: C44 161 236 7439.

E-mail address: j.klemes@umist.ac.uk (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. Since

SOLARSTORE 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 of

storing/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 and

distribution 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.

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