Assessment of Embodied Energy and Carbon Emissions of the Swansea Bay Tidal Lagoon from a Life Cycle Perspective

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Environmental Science, Individual Master Thesis in Environmental Science, 30 credits.

Assessment of Embodied Energy and Carbon Emissions of the Swansea Bay

Tidal Lagoon from a Life Cycle Perspective

Peter Simon 2015

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MID SWEDEN UNIVERSITY

Ecotechnology and Sustainable Building Engineering

Author: Peter Simon, pesi1300@student.miun.se or peter.jc.simon@gmail.com Examiner: Anders Jonsson, anders.jonsson@miun.se

Supervisor: Morgan Fröling, morgan.froling@miun.se

Degree programme: International Master’s Programme in Ecotechnology and Sustainable Development, 120 credits

Main field of study: Environmental Science Semester, year: Spring, 2015

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Abstract

In the pursuit of low-‐‑carbon, renewable energy sources one option with great potential in the UK is tidal energy. Specifically the proposed construction of the Swansea Bay Tidal Lagoon (SBTL) in South Wales has become one such discussed option. With a potential net annual output of 400 GWh and a 120-‐‑

year lifetime the scheme represents a long-‐‑term and large-‐‑scale electricity production option. An assessment of carbon emissions and embodied energy (EE) of the lagoon’s life cycle was carried out. Total lifetime carbon emissions for the SBTL are in the region of 470,000 tCO²e and EE was found to be

around 7,800 TJ. The assessment shows that the SBTL has significantly lower emissions per year than the existing National Grid mix and with emissions of around 0.01 kgCO²e/KWh is significantly lower than the UK emissions target of 0.07 kgCO²e/KWh. Energy payback of the SBTL was found to be in the region of 5.5 years. The use of dredged ballast infill sourced from within the area of the lagoon plays an important role in keeping emissions and energy use low; and is a key consideration when planning future tidal lagoon structures.

[Keywords: Life Cycle Assessment, embodied energy, carbon emissions, tidal energy, tidal lagoon, renewable energy, Swansea Bay]

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Acknowledgements

I would like to thank the following people:

Firstly to all of the lecturers I have had during my time at Mid Sweden

University for developing my skills and understanding, all of which has had a part to play in writing this paper. In particular I would like to thank program coordinator Anders Jonsson for his enthusiasm and encouragement

throughout my two years at MIUN and Morgan Fröling, my thesis

supervisor, for his guidance and assistance with this paper. Without Morgan’s invaluable knowledge of the LCA methodology and report writing in general the quality of this report would not be the same.

Secondly to all of the students I have worked alongside or with throughout my time at MIUN, especially those on the ECOSUD master program who have always helped answer queries and provided support whenever needed, as well as the occasional much needed trip to the pub! A special mention must go to Andreas Willfors who acted as my opponent during the writing of this thesis; his comments, guidance and the time he spent on my paper are much appreciated.

Huge thanks must go to my parents for their constant support; I have no idea how I will ever repay you. And finally to my girlfriend Julia for inspiring me to move to Sweden in the first place and for putting up with me without (too many) complaints!

Pete Simon

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1. Introduction

Electrical energy use and its production represent two of the largest issues facing society; as an awareness of anthropogenic impacts on the environment increases and stocks of fossil fuels diminish our need to find alternative means of power is highlighted. Previously used and existing forms of electricity production have often been both resource inefficient and

environmentally damaging, and countries are setting themselves targets to not only reduce consumption through increased energy efficiency measures but also to reduce their reliance on fossil fuels and finite resources

(Middleton, 2013). As global economic aspirations increase, so will demands for electricity. This has led to the increased interest in renewable energy sources and a demand for new technologies.

In 2011 the UK set itself a target; 15% of its consumed electrical energy must be derived from renewable sources by 2020 (Department of Energy and Climate Change, 2011). In addition the EU has set targets to reduce carbon emissions to “at least 80% below 1990 levels by 2050” (European Climate Foundation, 2010). In 2013 14.9% of the UKs electricity was produced from renewable sources, however in terms of consumed electricity renewables only contributed 5.2%, largely due to energy imports and impracticalities

associated with some renewable energies (producing energy when it is not required). The largest source of generated electrical energy in the UK was coal (36%) followed by gas (27%), nuclear (20%), renewables (15%), and other sources (2%) (Department of Energy and Climate Change, 2014). This

highlights the need for the UK to employ technologies capable of low-‐‑carbon and practical renewable electricity production to meet the set targets and curb anthropogenic climate change. The Swansea Bay Tidal Lagoon, which is the object of study for this thesis, is one such electricity production technology.

1.1. Tidal energy UK Potential

The UK is suitably placed to generate large amounts of consistent and predictable energy from the sea; namely from tidal and wave power (Middleton, 2013). Predictions state that as much as 20% of the UKs total electricity demand could be fulfilled by marine energy, with around

30-‐‑50 GW of installed capacity (Middleton, 2013; Department of Energy and Climate Change, 2011). Wave technology is still in a development phase and has not yet become a commercially viable option, however tidal power has been successfully implemented in Europe since the 1960’s. The UK has some of the largest tidal ranges in the world representing a huge potential for renewable energy production; Figure 1 shows the areas of largest tidal range.

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Figure 1. Mean spring tidal range in the UK (Marine Environmental Research, 2015)

One of the key advantages of tidal power is its predictability, a common drawback with many other renewable energy technologies. As tides are driven by relationships between the moon, sun and earth we can predict their time and range with great accuracy (Lewis, Estefan, Huckerby, Musial,

Pontes, & Torres-‐‑Martinez, 2011). This predictability makes tidal energy ideal to form part of a diverse energy network, something the government states is of key importance to the UK (Department of Energy and Climate Change, 2011).

1.2. Tidal energy technologies

There are numerous techniques for the creation of electricity from tidal energy; the most widely used technique so far has been tidal barrages. Tidal barrages act in a similar way to a conventional hydroelectric dam, but instead of preventing water flowing downstream within a river tidal barrages are constructed across estuaries, allowing the tide to flow through them. This allows the upstream estuarine basin to fill, before storing the water for a short period and releasing it once the tide has fallen, electricity can be created on the flood, ebb or both, and there is potential for large scale production (Johansson, Kelly, Reddy, & Williams, 1993). There are a small number of tidal barrages currently in commission (Middleton, 2013) and although these

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have proved successful they have not become more widely used due to environmental and economic concerns (Clery, 2008). As barrages cut off the estuary from normal tidal and river stream interactions there are concerns that this will be detrimental to the estuarine habitat and its species, as well as interfering with the complex salinity and sedimentary balances in estuaries.

Additionally the very high costs of tidal barrage installations can make them unattractive and has prevented their construction in the past (Clery, 2008).

Another method of tidal energy production is in-‐‑stream tidal turbines, which operate much like a submarine wind turbine, and are best suited to areas with a high tidal flow speed (Sea Generation Ltd., 2013). Currently there is only one commercially deployed example of an in-‐‑stream turbine, the SeaGen project in Northern Ireland. Although electricity production is lower than what can be achieved with a tidal barrage so too are the environmental impacts and economic outlay (Sea Generation Ltd., 2013). The UK is the leading expert in in-‐‑stream tidal turbines, and the European Marine Energy Centre (EMEC) has been instrumental in testing different technologies and devices in a bid to help diffusion of the technology.

The technology that this paper focuses on is tidal lagoons; they combine the large-‐‑scale production potential of tidal barrages with the lower

environmental impact of in-‐‑stream turbines. Tidal lagoons operate similarly to tidal barrages, however rather than having a sea wall that spans the entire estuary only a small section of the estuary is cut off, forming a lagoon, which can be flooded and drained with the rising and falling tides (Tidal Lagoon Swansea Bay plc, 2014a). There are currently no tidal energy lagoons anywhere in the world. Environmental impacts are expected to be much lower than with a tidal barrage structure, as only a section of the estuary will be cut off from natural tidal processes. Although there are currently no

examples of tidal energy lagoons the concept is not too complex on a technical level, many aspects of the lagoons technology can be borrowed from existing technologies and construction methods.

1.3. Motivation for study

Increasingly large tidal energy lagoons are discussed for the future, and therefore there is a need for an understanding of the carbon emissions and embodied energy associated with their construction. As there are currently no tidal energy lagoons in use there is also a lack of literature relating directly to their environmental impact from a life cycle perspective; a majority of

academic research available focuses on the direct impact relating to the site and surrounding areas.

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Although there is a lack of existing literature directly related to tidal energy lagoons there are technical and operational similarities with tidal barrages. As a result there are numerous relevant studies. In particular, the formerly

proposed Severn estuary tidal barrage saw a great deal of academic research.

Kelly et al. (2012) carries out an energy and carbon life cycle assessment of the proposed Severn barrage, concluding that the most significant stage of the barrage’s life cycle is the operational phase. This was due to the operation strategy of the barrage; to maximise electricity generation pumping of water upstream of the barrage was employed during the flood tide. Although this led to a net increase in electricity output the pumps were assumed to be powered from the UK National Grid, and therefore this resulted in high emissions and electrical energy use over the 120-‐‑year lifetime of the barrage.

1.4. Purpose and objectives

The purpose of this report is to assess carbon emissions and embodied energy (EE) of the proposed Swansea Bay tidal lagoon from a life cycle perspective.

By considering these factors the low-‐‑carbon and energy efficient

characteristics of a tidal lagoon can be considered and recommendations can be made on how to limit the environmental impact of the construction of such an installation.

The main objectives are as follows:

• Develop understanding of embodied energy and carbon emissions from material production, material transport, construction and operation life cycle stages of the Swansea Bay Tidal Lagoon, and identify which are most significant

• Identify which materials represent the largest carbon emissions and embodied energy

• Benchmark against current electrical energy mix in the UK

1.5. Life cycle assessment

When considering technologies or systems from an environmental

perspective it is important to consider what impacts they will have over their entire operational life. Use of the Life Cycle Assessment (LCA) methodology allows inclusion of environmental impacts of the life cycle phases of raw material extraction, material manufacture, construction, operation and disposal to be taken into account (Bauman & Tillman, 2004). This “cradle to grave” approach helps to identify the overall impact of a product, for example

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a product may have a very low impact during its use phase, making it seem desirable, but its production or disposal may be dramatically different. This study uses an LCA approach to assess the environmental impact of a tidal lagoon power installation in the UK. As of yet there are limited examples of LCA studies on large-‐‑scale tidal energy production.

In 1997 the International Organization for Standardization developed a standard for LCA (ISO 14040, 1997), and the methodology is followed in this study.

1.6. Swansea Bay Tidal Lagoon

1.6.1. Overview

The focus of this study will be on one case study in particular; the proposed Swansea Bay Tidal Lagoon (SBTL) in Swansea, Wales, which if completed would be the first tidal energy lagoon in the world (Tidal Lagoon Swansea Bay plc, 2014a). The project will comprise of a 9.5km sea wall, which will enclose 11.5km² of the bay (see Figure 2); the sea wall will house 16 turbines, which will allow water to pass through both on the rising and falling tide.

This bi-‐‑directional flow will allow the lagoon to create electricity for 14 hours a day, and with an installed capacity of 240MW and a net annual output of 400GWh for an expected lifetime of 120 years (Tidal Lagoon Swansea Bay plc, 2014a). Tidal Lagoon Swansea Bay plc., the company planning to construct the SBTL, are using this project as a gateway to construct a number of increasingly larger tidal energy lagoons in the UK in the future.

1.6.2. Location

The position of Swansea Bay at the entrance to the Severn Estuary, an area that has long been linked with tidal energy projects (Kelly, McManus, &

Hammond, 2012), makes it an interesting situation for a tidal energy lagoon.

The tidal range can be as much as 10.5m which, combined with the gently sloping sea bed, (allowing simple seawall production with minimal materials) and proximity to a large population make it a promising site for a commercial tidal energy.

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Figure 2. Map of proposed SBTL (adapted from Tidal Lagoon Swansea Bay plc. (2014a)), the seawall can be seen, as well as the turbine house situated at the South Western edge of the lagoon.

1.6.3. Design

The design of the lagoons seawall and its construction will be similar to a standard UK breakwater. Figure 3 shows a diagram of a typical cross section of the seawall; the main bulk of the seawall will consist of dredged material, which is enclosed within synthetic geotubes filled with the same dredged material. On top of this foundation granite rock armour will be laid in varying dimensions, with a greater amount positioned on the seaward side of the wall to offer protection from wave activity. Finally a concrete top will be added to provide a road and walkway for access. The dimensions and design of the seawall will change slightly depending on where the most significant protection is required (Tidal Lagoon Swansea Bay plc, 2014a).

Figure 3. Cross-section of typical section of lagoon seawall (Tidal Lagoon Swansea Bay plc, 2014a) N

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To create electricity the lagoon will include a turbine house, containing up to 16 turbines and 8 sluice gates; although the turbines allow generation during both filling and draining of the lagoon the sluice gates allow quick

equalisation of the water level during the rising tide (Tidal Lagoon Swansea Bay plc, 2014a). A final turbine design has not yet been decided upon

however it is likely that it will be based on a 7m bi-‐‑directional bulb turbine.

The turbine house itself will be constructed with reinforced concrete and will be placed at the southwest edge of the lagoon, as seen in Figure 2.

This study will focus on the SBTL and assess the carbon emissions and embodied energy of the 120-‐‑year lifetime of the project.

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2. Goal and scope

The following chapter will outline the scope and boundaries of the study, and detail the methodological considerations that were applied throughout.

2.1. Function of study and functional unit

This study will focus on the potential production of electrical energy from the SBTL. Only the direct output of electrical energy is considered. The functional unit for most results in this study will be one SBTL for a 120-‐‑year lifetime, in addition, for some purposes results will be directly related to electrical energy output from the lagoon; in these instances KWh will be used.

2.2. Impact assessment categories

This study uses two impact categories, carbon emissions and embodied energy. These have been selected as they represent two of the key

considerations when assessing future electrical energy technologies and in addition a majority of the existing literature regarding tidal installations focus solely on these categories.

2.2.1. Carbon Emissions

The first impact category is carbon emissions, which will be highlighted by collecting data regarding carbon equivalent emissions.

Carbon emissions are an important characteristic to consider when discussing future electrical energy solutions as they are one of the key drivers of global warming. Much focus has been placed on renewable energies playing a significant role in future energy mixes; however renewable energy does not necessarily mean low-‐‑carbon. As renewable energies often have low carbon emissions during their operational phase it is important to understand emissions from their whole life cycle.

2.2.2. Embodied Energy

In addition to carbon emissions, Embodied Energy (EE) will also be assessed.

The EE of an energy technology is important as it gives an insight into the energy efficiency of the product, as well as indicating its energy-‐‑payback

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time. In a majority of cases EE data is estimated according to UK industrial fuel consumption data (Hammond & Jones, 2011).

2.3. System Boundaries

2.3.1. Technical system boundaries

The technical system boundaries are outlined in Figure 4. The included processes are split into four stages, material production, transport,

construction, operation, whereas decommissioning has been excluded from the study. Where possible all materials, structures and processes directly associated with the production of electrical energy from the SBTL are included.

Figure 4. Flow diagram showing the technical system boundaries of the SBTL LCA study. The

decommissioning phase has been excluded from the study.

Excluded processes Included processes

Grid connection

_Other maintenance /operating procedures Construction

Material production

Sea wall Turbine house

Turbines

Transport

Transports

Dredging Turbine

house

Sea wall

Operation

Maintenance -‐‑ turbines

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Not included in this assessment are the impacts associated with production and manufacturing of any external machinery used for either, material production, transports etc. It is assumed that these machines are already manufactured and, as they can be used multiple times for numerous projects should not be associated solely with the SBTL.

There are however some aspects that have been excluded. Firstly, how the SBTL will be connected to the wider electricity grid infrastructure has not yet been decided, and therefore this process will be disregarded; this is expected to have a negligible impact on the overall results. During the operation phase of the SBTL only routine replacement of turbines will be included as this is predictable. All other maintenance relating to the sea wall and other

structures will not be included as it is not known whether or to what extent it will be necessary. It is also likely that a small amount of electrical energy will be drawn from the National Grid during operation to control the technical electricity production functions, however as the details of this are not available, and as it is assumed to be insignificant in relation to the energy produced by the lagoon this has also been excluded.

It is important to note that due to the 120-‐‑year life cycle of the SBTL the decommissioning stage is hard to predict, and therefore will be disregarded.

It is likely that the seawall structure would be left to gradually degrade into the sea in any case (Kelly, McManus, & Hammond, 2012), however it is unclear how other elements of the lagoon will be handled, such as the turbines and sluice gates.

2.3.2. Geographical boundaries

A majority of materials and products used to construct the SBTL will

originate from UK suppliers, where possible local materials and suppliers are intended to be used (sources of material listed in Tidal Lagoon Swansea Bay plc. (2014a) (see Table 2); Tidal Lagoon Swansea Bay plc (2015)). Thus

inventory data for materials production and transports in the UK will be used.

2.3.3. Time boundary

The planned service life of the SBTL is expected to be 120 years. This study assumes that construction and commissioning of the project will start immediately and that the lifetime of the lagoon will not be cut short. Due to planning and funding issues it is conceivable that the project could start in a

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number of years time, which could impact the accuracy of the data used in the Life Cycle Inventory (LCI). Additionally, in the event that the lagoons life was cut short it would have a dramatic influence on this study’s results.

In regards to the operation stage of the lagoon’s life cycle, the turbines are assumed to be replaced twice over 120 years; once in 40 years and again in 80 years. However, the environmental impacts of both sets of replacement turbines are described as if they were produced using present day energy mix, manufacturing processes and equipment.

2.3.4. Data Quality

When compiling data to be used in this study the quality and accuracy is of upmost importance. To ensure consistency, a majority of the inventory data regarding materials has been sourced from the same database, the Inventory of Carbon and Energy (ICE) from Bath University (Hammond & Jones, 2011).

ICE compiles results from wider literature for carbon and energy analyses for many building materials from a UK perspective. In cases where the ICE database indicates a wide variation in data or is missing the relevant

information individual data values have been gathered from peer reviewed literature sources, government reports or large organisations. Whenever this is the case several data sources are considered and compared before use.

The long life expectancy of the SBTL raises numerous issues relating to quality of data used in this study. It can be assumed that the accuracy of data used in this study is likely to decline further into the lagoons lifetime;

although accurate information can be accessed for current processes estimates are increasingly used as time goes on.

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3. Life Cycle Inventory (LCI)

In this study the 120-‐‑year lifetime of the SBTL will be split into four main life cycle stages, material production, transport, construction and operation (see Figure 4); as detailed in section 2.3.1 of this report the decommissioning stage has been disregarded. The different components of these stages and the data that will be used for the results of the study are outlined in the following chapter.

3.1. Material production

The materials and quantities required for construction of the SBTL are shown in Table 1, together with the carbon emissions and EE associated with

material production. Each material in Table 1, and inventory data used to describe its production, is further described in this section. Material

production concerns all bulk materials that will be used for the construction of the SBTL; this study considers all stages of the materials production, from raw material extraction, to processing from a carbon emission and EE

perspective.

3.1.1. Bulk Material Quantities

Table 1, column 2, shows estimated quantities of bulk material needed for construction of the SBTL. Material quantities were sourced and are listed in Tidal Lagoon Swansea Bay plc. (2014a).

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Table 1. Summary of material quantities (Tidal Lagoon Swansea Bay plc, 2014a), and chosen factors to describe specific carbon emissions and EE further described in sections 3.3.1-3.3.11.

Material Quantity

(t) Carbon emissions

(kgCO²e/t) EE (MJ/t) Rock Armour

(Section 3.1.2) 2,790,000 20

(Crishna, Goodsir, Banfill, & Baker, 2010)

1,300 (Crishna,

Goodsir, Banfill, &

Baker, 2010;

University of Tennessee, 2008) Dredged Ballast

Infill

(Section 3.1.3)

15,200,000 4.95

(Aumonier, Hartlin, & Peirce, 2010)

24.5 (Kemp, 2008)

Cement

(Section 3.1.4) 80,000 740

(Hammond &

Jones, 2011)

4,500 (Hammond &

Jones, 2011) Sand

(Section 3.1.5) 165,000 4.95

(Aumonier, Hartlin, & Peirce, 2010)

24.5 (Kemp, 2008)

Aggregate (Section 3.1.6)

250,000 5.2

(Hammond &

Jones, 2011)

80 (Hammond &

Jones, 2011) Steel Reinforcement

(Section 3.1.7) 38,000 1,400

(Hammond &

Jones, 2011)

17,400 (Hammond &

Jones, 2011) Steel Sheet Pilings

(Section 3.1.8) 1,100

1,540

(Hammond &

Jones, 2011)

22,600 (Hammond &

Jones, 2011) Turbines

(Section 3.1.9) 9,000 6,150

(Hammond &

Jones, 2011)

56,700 (Hammond &

Jones, 2011) Water

(Section 3.1.10) 35,000 0.4

(Water UK, 2011)

200 (Hammond &

Jones, 2011)

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3.1.2. Rock Armour

Rock armour will be used along the entire length of the lagoon wall (not including the turbine house), it consists of large blocks of roughly broken granite and is positioned on the outside of the wall where it absorbs wave energy. This rock armour will be of varying sizes, from 0.3 to 10 tonnes, with smaller sized rocks placed beneath the larger (Tidal Lagoon Swansea Bay plc, 2014a).

Data concerning the carbon emissions associated with granite acquisition is highly variable (Hammond & Jones, 2011), with values ranging from 6 to 781 kgCO²/tonne (Broekens, Escarameia, Cantelmo, & Woolhouse, 2011).

However it is likely that this great range is largely due to the processing of granite for different uses, and the fact that a majority of studies focus on dimension stone for building and interior uses. Results from a study by Crishna et al. (2010) indicate that granite has carbon emissions of

92.91 kgCO²e/tonne but that a majority of this is due to processing; extraction of granite is responsible for around 22% of this total, therefore around 20 kgCO²e/tonne. Although indications are that if the granite is sourced as a by-‐‑

product of aggregate extraction, it could be assumed that its CO² emissions are the same as that for aggregate extraction (Broekens, Escarameia,

Cantelmo, & Woolhouse, 2011). In this case values could be considerably lower, as low as 5 kgCO²/tonne. However as indicated in Tidal Lagoon Swansea Bay plc (2014a) the quarry that will be used for rock armour will be reopened especially for the project, indicating that any granite extracted will not be a by-‐‑product of aggregate extraction. Therefore for this study a value of 20 kgCO²e/tonne will be used.

In regards to the EE associated with granite extraction there are still widely variable results and a lack of studies that aim to divide the EE between extraction and processing. Hammond and Jones (2011) indicate EE could be as high as 11,000 MJ/t, but does not differentiate between extraction and processing. A study by the University of Tennessee (2008) indicates that granite production in the USA is predicted to have EE of 5,900 MJ/t.

Assuming that EE will be similar for granite produced in the UK and inline with the carbon emissions results from Crishna et al (2010) it could be assumed that the material extraction only represents around 22% of this value, or around 1,300 MJ/t. Therefore EE of 1,300 MJ/t will be used for granite rock armour in this study.

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3.1.3. Dredged Ballast Infill

A majority of the lagoon wall will consist of sediment dredged from the lagoon bed itself. This sediment will be used for the central part of the wall, and will be enclosed within synthetic geotubes, which will also be filled with dredged sediment (Tidal Lagoon Swansea Bay plc, 2014a). It is assumed that the sediment will not need to be further treated or cleaned, however in the case of the sediments being found to be contaminated, further processing of the sediment will be required.

The Crowne Estate has published data regarding the carbon emissions and EE for dredging in the UK (Aumonier, Hartlin, & Peirce, 2010). The total carbon emissions for a short haul dredger are 6.41 kgCO²e/tonne of dredged material making landfall (Aumonier, Hartlin, & Peirce, 2010). It is important to note that dredged material used for SBTL will not need to make landfall, it will be deposited straight from the boat to form the lagoon wall, so all emissions and energy use regarding wharfs and on land processes can be disregarded.

Therefore data for only the vessels can be used, which includes transit, loading, dredging and discharge, this value is given as 4.95 kgCO²e/tonne (Aumonier, Hartlin, & Peirce, 2010).

Dredgers use Marine Gas Oil (MGO) for fuel, which has an embodied energy of 49MJ/kg (Alternative Fuels Data Center, 2015), and a typical short haul dredger uses 0.5kg MGO/tonne of dredged material (Kemp, 2008), giving an energy consumption of 24.5MJ/tonne of dredged sediment.

3.1.4. Cement

Cement will be used to make concrete for both the turbine house and also for the top of the lagoon wall as an access path and road. It is not specified what kind of cement will be used so average UK cement data for embodied carbon and embodied energy from the ICE database are used. For carbon emissions a value of 740 kgCO²e/tonne is used and for EE 4,500MJ/tonne is used

(Hammond & Jones, 2011).

3.1.5. Sand

To make the concrete a combination of sand and aggregate will be used. The sand will be sourced from within Swansea Bay by dredging; from both within the lagoon and elsewhere in the area. As with the dredged ballast infill from section 3.1.2 the data found by the Crowne Estate will be applied, carbon

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emissions are 4.95 kgCO²e/tonne (Aumonier, Hartlin, & Peirce, 2010) and EE will be 24.5 MJ/tonne (Kemp, 2008).

3.1.6. Aggregate

Aggregate used for concrete production will use standard UK data for quarried aggregate from the ICE database, with carbon emissions of 5.2 kgCO²e/tonne and EE of 83 MJ/tonne (Hammond & Jones, 2011).

3.1.7. Steel reinforcement

Certain areas of the concrete constructions will require steel reinforcements, especially the turbine house, for this, data for bar and rod steel were acquired from the ICE database. Therefore carbon emissions of 1,400 kgCO²e/tonne and an EE of 17,400 MJ/tonne (Hammond & Jones, 2011) will be used.

3.1.8. Steel sheet pilings

Steel sheet pilings will be used along sections of the coastline to protect from wave erosion. The ICE database suggests carbon emissions for UK galvanised sheet steel with average recycled content as 1,540 kgCO²e/tonne and EE as 22,600 MJ/tonne (Hammond & Jones, 2011).

3.1.9. Turbines

Detailed information regarding the materials needed in the turbines is not available and in SBTL’s preliminary material requirement assessment steel is the only listed material for turbine construction (Tidal Lagoon Swansea Bay plc, 2014a). It is presumed that the turbines will require high quality stainless steel; the ICE database provides data for average stainless steel, with carbon emissions of 6,150 kgCO²/tonne and EE of 56,700 MJ/tonne (Hammond &

Jones, 2011).

3.1.10. Water

Water will be used for the preparation of concrete, and will be sourced from the mains water supply. The ICE database contains information regarding the EE of mains water, but not carbon emissions. EE was given at an average of 0.2 MJ/kg (Hammond & Jones, 2011), which can be converted as 200

MJ/tonne. In a report published by Water UK, the governing body of the UK

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water industry, the carbon emissions associated with mains water supply in Wales was given as 400 kgCO²e/million litres or 0.4 kgCO²e/tonne (Water UK, 2011). It is important to note that both the carbon emissions and EE values here include the effects of distribution throughout the mains water network.

3.1.11. Geotubes

Geotubes have been excluded from this study, as the quantity required is not available in the SBTL reports and data regarding the environmental impact of their production is inconclusive; however their exclusion is expected to have a negligible impact on the results.

The SBTL will use geotubes in the lagoon wall; the geotubes are a tube made of woven synthetic material (often known as a geotextile or geosynthetic), which can be filled with dredged sediment. The synthetic tube holds the material in place but can let water migrate through its membrane, reducing the risk of damage by wave activity but maintaining moisture in the enclosed sediment. They have become widely used in coastal protection constructions;

however there is very limited information regarding their carbon emissions and EE. Stucki et al. (2011) discusses the carbon emissions of four different geosynthetics intended for various applications. The material most similar to the geotubes used in the SBTL was a retaining filter layer, with carbon

emissions of 3.2 kgCO²e/kg of geotextile (Stucki, Busser, Itten, Frischknecht, &

Wallbaum, 2011). However it is likely that the geotubes used in this case will still be markedly different to those from the Stucki study, and therefore this value cannot be included in this study. Likewise there is no available

information relating to the EE of geotubes, this highlights an area where future research is required, especially as the use of geotubes is becoming increasingly widespread in coastal construction. Stucki et al. (2011) and Bruce and Chick (2009) both indicate that in relation to the overall construction, geotubes will have a negligible impact on the end results. Geotubes also allow the use of less bulk materials overall in comparison to a traditional rubble mound structure, so although their direct emissions are not included their impact on the rest of the structure is inherent.

3.2. Transports

The main modes of transports for materials in this project are road and sea.

Tidal Lagoon Swansea Bay plc (2014a) discusses the likelihood that railway will be used, however this will require re-‐‑commissioning of a section of disused railway which runs adjacent to the proposed SBTL site. For the case

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of this study it is assumed that this railway will not be used, largely due to the local sources of a majority of the material being transported by land, however if transport distances were to increase re-‐‑commissioning of the railway may be necessary. The main mode of land transport considered in this study will be by heavy goods vehicles. The UK Department for Environment, Food and Rural Affairs (DEFRA) have compiled data regarding fuel conversion factors and direct emissions from numerous transports (Hill, Walker, & Beevor, 2011), this data was used when calculating both transport emissions and energy use (see table 2, two last columns).

3.2.1. Transport types and distances

The sources of construction materials are described in brief in Tidal Lagoon Swansea Bay plc (2014a), where specific locations are not noted, a likely source in close proximity to the construction site is assumed. Table 2 outlines the assumed source locations of each bulk material and the transport method.

Table 2. Material transport information. Carbon emission values are taken from Hill et al. (2011) and EE values from Allen and Browne (2010) for road transport and Lipasto (2009) for sea transport.

Material Assumed

place of origin

Mode of transport

Distance Carbon Emissions (gCO²e/tonne km)

EE

(MJ/tonne km) Rock Armour

(Section 3.1.2) Cornwall,

England Boat 300 km 13.2

0.34

Dredged Ballast

(Section 3.1.3) Swansea bay,

dredged N/A 0 km N/A N/A

Cement

(Section 3.1.4) Aberthaw, S.

Wales Road 60 km 86.7 0.5

Sand

(Section 3.1.5) Swansea bay,

dredged N/A 0 km N/A N/A

Aggregate

(Section 3.1.6) Swansea,

local quarry Road 25 km 86.7 0.5

Steel

Reinforcement (Section 3.1.7)

Port Talbot,

S. Wales Road 15 km 86.7 0.5

Steel Sheet Pilings (Section 3.1.8)

Port Talbot,

S. Wales Boat 10 km 13.2 0.34

Turbines

(Section 3.1.9) Port Talbot,

S. Wales Road 15 km 86.7 0.5

Water

(Section 3.1.10) Mains water N/A 0 km N/A N/A

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3.2.2. Heavy goods vehicles (HGVs)

With respects to HGV use, it is presumed due to the type and quantity of materials being used for the SBTL construction that articulated HGVs greater than 33 tonnes will be used in most instances. Whilst emissions from HGVs vary depending on their laden weight, this study will use the UK average value of 61% laden in tonne kilometres, which give carbon emissions of 86.7 gCO²e/tonne km (Hill, Walker, & Beevor, 2011).

In terms of EE HGVs have an average fuel efficiency of 3.15km/l of fuel (Allen

& Browne, 2010), and diesel oil has an EE of 35.8 MJ/l of fuel, which means HGVs use around 11.4 MJ/km or 0.5 MJ/tonne km.

3.2.3. Sea transport

In addition to road transport many materials will be moved via boat straight to the site. Again data from DEFRAs report by Hill et al. (2011) is used for this study. The average carbon emissions of a general cargo vessel laden to the UK average of 60%, is given as 13.2 gCO²e/tonne km (Hill, Walker, & Beevor, 2011).

In terms of EE an average figure for fuel use for general cargo ships is 0.34 MJ/tonne km (Lipasto, 2009).

3.2.4. Materials without transports

As indicated in Table 2 the dredged ballast infill and sand have no transports associated with them as they are dredged on-‐‑site and any short movements of dredgers are included in the carbon emissions and EE associated with the material production.

As expressed in section 3.1.10 carbon emissions and EE associated with water distribution are included in the material production data from Water UK (2011) and (Hammond & Jones, 2011).In addition, the water required for construction is also assumed to have no transport as it is sourced from the mains water supply.

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3.2.5. Fuel production emissions and energy

When calculating emissions and energy use in regards to transports it is important to consider the indirect influences of fuel production and

distribution. Sheehan et al. (1998) suggest that 0.2 MJ of energy is consumed during the production and distribution of 1 MJ of petroleum diesel. Assuming that the same is true for carbon emissions then fuel production should be responsible for an additional 20% of tailpipe emissions.

3.3. Construction

As the SBTL does not yet have a start date for construction work it is not known precisely what processes will be required for the construction. This combined with the lack of previous research into tidal energy lagoons from energy and carbon perspectives make this life cycle stage problematic and the method employed represents an estimate.

In line with a study by Bruce and Chick (2009) on UK breakwater

construction it is assumed that construction emissions and EE will be within the same order of magnitude as those associated with transports. However numerous methods for construction analysis were considered.

One option available is to convert data from studies relating to the Severn estuary tidal barrage, the most highly regarded of these studies being Roberts (1982). However Roberts’ study and results have limitations, namely the age of the study and the method employed for energy and carbon accounting;

basing estimates off the expected cost of construction activities, the method is not consistent with this study. Kelly et al. (2012) conclude that the

construction stage (including material extraction, processing and transports) of the Severn barrage has carbon emissions in the region of 5 Mt.CO²e or 300,000 tCO²e/km and EE of around 6,000 TJ/km. However the design considered for the Severn estuary is concrete caissons, and the physical dimensions of the sea wall are greatly different to the SBTL, so these figures are only appropriate for benchmarking against.

The physical similarities between the SBTL and a standard rubble mound breakwater allow for the use of a wider data set; there are a number of studies that attempt a quantitative analysis. Bruce and Chick (2009) highlights the complexities associated with the construction phase. Bruce and Chick (2009) assume that due to the types of equipment, and their typical fuel (diesel oil) that construction EE and carbon emissions will be of a similar magnitude to those associated with the transports of the materials themselves. Problems

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with this approach are that this assumption largely relates to the mode and distance of transport.

Bruce and Chick (2009) conclude that construction of a typical rubble mound breakwater would represent 90,000 tCO²/km; this includes the emissions associated with material production and transports. In the case of the SBTL the sea wall will be around 9.5km in length, meaning total construction emissions including materials and transports should be in the region of 855,000 tCO². In terms of EE Bruce and Chick (2009) conclude that embodied energy of construction (including materials and transports) will be 1,500 TJ/km, giving a total for the SBTL of 14,250 TJ. However due to the design and inventory value differences between the example used in Bruce and Chick (2009) and the lagoon in this study these figures cannot be used. In addition, Bruce and Chick (2009) discuss emissions and EE for standard

breakwater constructions which are very rarely on a similar scale to the nearly 10km lagoon wall in this study; it is likely that the scale of the overall

construction would impact the emissions and EE per kilometre.

Therefore this study will use the first assumption by Bruce and Chick (2009);

that construction emissions and EE will be within the same order of magnitude as those associated with total material transports.

3.4. Operation

As outlined in the system boundaries the scheduled replacement of the turbines will be the only considered process during the operation stage. It is assumed that full replacements of the turbines will be required every 40 years, as estimated in Kelly et al. (2012), this means that following the initial construction of the SBTL two further sets of turbines will have to be installed over the following 120 years. Although emissions related to turbine

manufacture are likely to reduce in the future this study will use the same values for replacement turbines as used for the initial construction of the lagoon as detailed in section 3.1.9. In contrast to the tidal barrage considered in Kelly et al. (2012) flood pumping is not expected to be used during

operation of the SBTL.

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4. Results

4.1. Carbon Emissions

The carbon emissions associated with the various life cycle stages of the SBTL are detailed in the following sections.

4.1.1. Overall carbon emissions by life cycle stage

The overall carbon emissions related to different life cycle stages are shown in Figure 5. The life cycle stage with the largest emissions is material production, with a total of around 300,000 tCO²e. The stage with the next highest

emissions is the operation stage with around 110,000 tCO²e followed by transports and construction both with 27,000 tCO²e. The total emissions associated with the SBTL are around 470,000 tCO²e.

Figure 5. Carbon emissions by life cycle stage

0 50,000 100,000 150,000 200,000 250,000 300,000 350,000

Material Production Transport Construction Operation

Emissions (tCO2e)

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Figure 6. Carbon emissions of bulk material production of the SBTL.

4.1.2. Material Production

shows the total carbon emissions associated with the production and

manufacture of each bulk material used in the SBTL. The dredged ballast infill represents the largest contributor to carbon emissions with around 75,000 tCO²e. The second most significant material in terms of carbon emissions is cement; despite being nearly 190 times less mass than the dredged ballast infill it still has carbon equivalent emissions of about 60,000 tonnes.

In relation to the functional unit of one SBTL for 120 years, the total emissions associated with material production are 300,000 tonnes of CO²e.

4.1.3. Material transports

Figure 7 shows the CO²e emissions associated with the transports of materials to the SBTL site. The dredged ballast infill and sand are both dredged from within the area of the lagoon so external transport distances are zero and short distances of transports within sites are already considered in the

inventory data used for material production. The same is true for water; as it is accessed through the mains water system transport emissions are not

applicable, and distribution throughout the mains water system is included in the material production inventory data.

0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000

Tonnes CO2e

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Figure 7. Carbon emissions (fuel production and tail pipe) of material transports to site. Note the

logarithmic scale of the y-axis.

Figure 8. Percentage division of carbon emissions per material between material production and

transport

0 1 10 100 1,000 10,000 100,000

Tonnes of CO2e emissions

Fuel production Emissions

Tailpipe Emissions

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

% of total emissions

Transport Material Production

Assessment of Embodied Energy and Carbon Emissions of the Swansea Bay Tidal Lagoon from a Life Cycle Perspective