Power: A new paradigm for energy use in sustainable construction

Ecological Indicators 23 (2012) 109–115

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Ecological Indicators journal homepage: www.elsevier.com/locate/ecolind

Power: A new paradigm for energy use in sustainable construction G. Habert a,∗ , E. Castillo b,c , E. Vincens d , J.C. Morel b a

Université Paris-Est, IFSTTAR, département matériaux, 58 bd Lefebvre, 75732 Paris Cedex 15, France Université de Lyon, Ecole Nationale des Travaux Publics de l’Etat, Département Génie Civil et Bâtiment CNRS FRE 3237, 3 rue Maurice Audin, Vaulx-en-Velin, 69120, France SETRA, Centre de la sécurité des transports et de la route, 46 avenue Aristide Briand B.P. 100, 92225 Bagneux Cedex, France d Université de Lyon, Ecole Centrale de Lyon, LTDS, UMR 5513, 36 Av Guy de Collongue, 69134 Ecully Cedex, France b c

a r t i c l e

i n f o

Article history: Received 16 May 2011 Received in revised form 19 January 2012 Accepted 14 March 2012 Keywords: Embodied energy Power Construction Service life

a b s t r a c t To achieve a sustainable management of resources, political and economic decision-makers need indicators to quantify their technical choice in relation with resource consumption. In this study, a new indicator that reflects the power demand next to energy demand of systems such as buildings is developed. The relevance of the proposed power indicator is tested through two different kinds of systems: retaining walls for civil and agricultural engineering and residential houses. It enables to highlight a close relation between this indicator and the high power energy sources that may exist at different steps of a building’s life cycle. This dependence is presented as a better indicator of sustainability than a traditional energy account as it reflects the ability for the system to rely on flow energies rather than on stock energies. © 2012 Elsevier Ltd. All rights reserved.

1. Introduction About 30–40% of the total natural resources used in industrial countries are exploited by building industries and about 40% of energy use is due to housing (Dixit et al., 2010). This large consumption of resources and energy in the building sector has deep impacts on the environment and new sustainable development issues urge us to take into account these environmental aspects (IPCC, 2007). To achieve such sustainable management, political and economic decision-makers need indicators to quantify their technical choice involving energy consumption issues. Because any decision is made up depending on the discrepancy between the desired state (or goal) and the perceived state of the system at present, both relevant and accurate indicators are required (Meadows, 1998). Energy indicators have been developed after the first oil peak. They have been associated with the first material flow analysis studies and Life Cycle assessment methods developed later on (Klöpffer, 2006). These methods have been widely applied in the building sector (Dimoudi and Tompa, 2008; Pulselli et al., 2008; Asif et al., 2005) and led to worldwide development of energy policies. The current concerns about climate change (IPCC, 2007) and CO2 mitigation have strengthened these energy efficiency policies. For instance, the European Union Directive on Energy Performance of Buildings (EU, 2009) requires from the member states to implement energy efficiency legislations for buildings, including existing

∗ Corresponding author. Tel.: +33 1 40 43 53 26; fax: +33 1 40 43 54 93. E-mail address: [email protected] (G. Habert). 1470-160X/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecolind.2012.03.016

ones with floor areas over 1000 m2 that undergo significant renovations. To handle this new framework, Kesselring and Winter (1994) proposed the concept of a 2000 W society which aims at consuming not more than what corresponds to an average continuous power of 2000 W per capita. By comparison, the energy use is currently around 5000 W per capita in Europe and even tops 10,000 W in the USA. The concept has been then developed further on and used by different authors (Schulz et al., 2008; Pfeiffer et al., 2005; Goldemberg and Johansson, 2004). In these approaches, energy is an equivalent average continuous power over one year. Notwithstanding the relevance and importance of these approaches, they focus on the energy consumption through the use phase, while the buildings are in operation. Although this is an important factor in the overall environmental impact, other aspects such as the construction and the maintenance of the buildings should be considered (Dutil et al., 2010). Historically, the energy used to produce the materials needed for the construction of the buildings, and so called embodied energy, was considered insignificant compared to the energy consumed trough the operational phase (Scheurer et al., 2003; Sartori and Hestnes, 2007; Blengini, 2009; Ortiz et al., 2009; Maddox and Nunn, 2003; Winther and Hestnes, 1999). However, for low energy consumption houses, this is not the case anymore as the energy consumed during the service life is much lower while the embodied energy is higher due to additional construction materials (Wallhagen et al., 2011; Huberman and Pearlmutter, 2008; Sartori and Hestnes, 2007; Thormark, 2002; Chen et al., 2001). For a low energy consumption solar house, the embodied energy requirement is double of that of the classical design while reducing the

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Fig. 1. Relationship between the covered surface for energy production and the resulting power capacity generated for various renewable power plants. The references of the data are given in the Appendix A.

total energy demand by 50% over a 50 years lifetime (Wallhagen et al., 2011). Blengini and Di Carlo (2010) came to a very similar conclusion when comparing a standard house to its low energy counterpart. Verbeeck and Hens (2010) have performed an analysis of the embodied energy for four types of dwelling in Belgium and show that the additional embodied energy added to improve the energetic performance was recovered in the very short term (<2 yrs). The questions we address in this study are: Does these energy analyses address all the environmental aspects associated with the energy use? Is it coherent to sum energy used for the operation and the construction of buildings? Actually, we consider that for well insulated houses, heating and cooling can be achieved with the use of flow energy while the construction phase is dependent on the stock energy and that this major difference in energy type (flow vs stock) is hidden within current energy analyses. Flow energies are energies such as wind or sun radiation, which means that a certain amount of energy can be used during a certain period of time. In other words, the power is limited but the amount of energy is unlimited with time. This is exactly the opposite for stock energies. Considering fossil fuels which are the main stock energies used, the stock is limited to the amount of fossil fuels that can be extracted, but the power generated only depends on the quantity introduced in the process and is therefore practically unlimited. In Fig. 1, the plant capacity (peak power delivered) of different flow energy plants are plotted against the covered surface area of these plants. A clear trend irrespective of the kind of considered renewable energy is shown (Fig. 1). Therefore, it confirms the fact that with renewable energies, the more capacity is needed, the more surface area for energy production is required. It can be noted that the involved sizes are not negligible. Hence, as the reduction of the use of fossil fuel will probably be associated with an increasing use of renewable energies (Omer, 2008), the principal characteristic of future societies will more probably rely on power restriction, rather than on energy depletion. Fig. 1 illustrates that the maximum power required for a product manufacturing is a much more critical problem than considering the average continuous power needed every day to supply people needs which is the technique used in 2000 W society studies. Indeed, the manufacturing of a product requires a dedicated industrial infrastructure. Then, the question of power consumption and its associated consequences should be addressed by an indicator in energy perspective studies. Furthermore, among the different industrial sectors, the building construction sector is the one that relies most on high power

energy sources since the production of construction materials involves high temperature processes (Werner, 2006). The greatest energy demands are for the steel and cement production where more than 90% of the energy is used in processes involving temperature above 400 ◦ C. (Werner, 2006) and then can not be supplied by heat transfer or heat recovery (Hammond, 2007) which could be produced by renewable energy sources. Only in some marginal cases like the plasterboards production, where processes between 100 ◦ C and 400 ◦ C are generally involved, a cleaner production relying on renewable energies could be proposed for construction materials (Schnitzer et al., 2007). This power question is not addressed by commonly used energy indicators and the majority of energy studies. It has however already been raised by MacKay considering how many surface of United Kingdom would have to be covered by renewable energies in order to supply the power demand (MacKay, 2009). Trainer (2007) also addressed similar considerations on a worldwide scale. He argued that as most of the renewable energies are flow energies, large rates of power require large surfaces which will not always be accepted by the population. As a consequence, this study proposes to introduce a new energy indicator based on power rather than energy itself in order to better reflect sustainable issues. However, the objective is not to show that the previously developed indicators are not adapted but rather that some sustainability points can be hidden or badly addressed. In the first section of the paper a calculation method for the new power indicator is proposed. As an illustration, this indicator is calculated for two case studies: retaining walls for civil and agricultural engineering and residential houses. The results are compared to the ones obtained using classic energy indicators. 2. Materials and method for the design of a power indicator 2.1. Power calculation method As different materials are involved in the construction and the service life of buildings, the specific power for each material is first needed. A detailed study of the different processes leading to the production of a material must be performed in order to identify which process needs the highest power. It is this power that will be considered as it is the one that needs the largest surface to be produced. For instance, within a cement plant, the highest power involved in the cement production is the one needed for the clinkerisation process of the clay–calcareous rock mixture. Then, the power needed for other processes such as grinding clinker is not considered. The power calculation can directly be done if data are available in the literature, or indirectly if one has access for instance to the daily capacity of one plant and to the energy needed to produce one ton of product. In this case, a mean daily power can be calculated by multiplying energy per ton of materials by the amount of ton produced per day. When this value is expressed in J × s−1 , it holds the meaning of a power (W). Once the needed power for each material has been calculated (e.g. cement, iron, plastics and mineral wool), the power needed for a multi-process product can be calculated (e.g. the construction of a house). We propose to design the global power indicator Pg for the system using Eq. (1). Pg =

 m i i

mtot

Pi

(1)

where mi is the mass of material i involved in the production/construction of a product having a total mass mtot and Pi is the maximum power needed for the production/construction of material i. Note that the global power indicator Pg does not hold a true physical meaning. Actually by analogy with electricity, the

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Table 1 Mean power of different equipments (a) calculated, (b) from bibliography. (a)

Energy (MJ/t)

European cement kiln Blast furnace

3600 12,726

Daily production (t)

Mean power (MW)

Ref.

4000 4107

167 605

Bastier (2000) and JCR (2000) Classen et al. (2007)

(b)

Unit

Energy (MJ/Unit)

Mean power (MW)

Ref.

Loader (Caterpilar 950 F) Dragueline Jaw crusher (38–156 m3 /h capacity) Spring cone crusher (PYD1750) Diesel generator (10 kVA) Truck (20 t) Concrete pump truck (40–45 m3 /h) Ready mix plant Crawler excavator (0.6 m3 )

h h h h h t km m3 m3 h

657.4 484.4 475.5 576.5 85.9 1.03 6.19 99 260

18.3 × 10−2 13.5 × 10−2 13.2 × 10−2 16.0 × 10−2 2.4 × 10−2 2.1 × 10−2 6.8 × 10−2. 10.0 × 10−2. 7.2 × 10−2

Martaud (2008) Martaud (2008) Martaud (2008) Martaud (2008) Kawai et al. (2005) Kawai et al. (2005) Kawai et al. (2005) Chen, 2009; Couvrot (2011) FNTP (2010)

power needed should be the sum of all the individual power processes (P). In this new indicator, the individual power processes are weighted by their mass contribution to the global product. As a result, for two products A and B, if Pg A is higher than Pg B, it implies that product B involves less amount of materials depending on high power processes than product A. 2.2. Power calculation for the production of construction materials A detailed study of the different processes involved in the production of different construction materials has been performed leading to the calculation of the required power in each case. Table 1 gathers these data. It is composed of the energy either needed to produce one ton of material (Table 1a) or consumed during one action of a specific equipment (Table 1b). Once these energies are collected, it is possible to calculate a mean power for each process. If one knows the energy per hour, the mean power involves just a unit change. For materials in Table 1a, the energy needed for the production is divided by a typical plant capacity. For processes that involve cubic meter of concrete or km (Table 1b), the power is not calculated but deduced from the literature. The data collected in Table 1 clearly show that the highest power processes are those associated with the kilns for cement and steel. Table 2 gathers the maximum power needed in the production process of each material used for the building construction. For the aggregates production, the highest power of the processes presented in Table 1b has been used. 3. Case studies In order to illustrate and evaluate the relevance of the proposed power indicator, this section presents the methodology of related

Table 2 Energy and power for the production of materials used in this study.

Fired brick Cement Steel Aggregates General timber Stone a

Fossil cumulative energy demand (MJ/t)a

Maximum power needed in production process (MW)

Ref

3.0 × 103 4.7 × 103 24.4 × 103 1.0 × 102 8.5 × 103 3.0 × 102

1 167 605 18.3 × 10−2 18.3 × 10−2 18.3 × 10−2

Fornoceramica This study This study This study This studyb This study

All data come from ICE v1.6 (Hammond and Jones, 2008). It is considered that for general timber power of materials will not be different from those used for aggregates. b

power calculation for two different structures: retaining walls and residential houses.

3.1. Retaining walls The motivation for the choice of retaining wall’s study relies on the simplicity of the construction phase where the sensitiveness and the limits of the new indicator can be evaluated more easily than for complete buildings.

3.1.1. Description of the system The three types of retaining walls that have been studied are associated to three different technologies: a dry stone retaining wall, a gabion retaining wall and a reinforced concrete (cantilever) wall. The three structures are presented in Fig. 2. In the dry-stone retaining wall, if one knows the nature of the soil and the stone, the dimensions of the wall is obtained by a limit equilibrium approach or a yield design method (Colas et al., 2010a,b; Colas et al., 2008; Villemus et al., 2007). The dry stone retaining wall considered herein is a 3 m height wall, which is the most common height found in the European heritage (Fig. 2a). This involves a stone volume for 1 m wall length equal to 3.11 m3 , that is to say 8228.25 kg. However as the walls are, most of the time, rebuilt on the basis of older ones, there is a possible re-use of stones already present on site. One considers that 30% of the stones are generally re-used (Bruno Durand, ABPS, dry stone retaining wall contractor, personal communication, 2009) which induces only 5759 kg of stones resulting from quarries. The gabions walls involved in this study are electro welded wire mesh gabions, with square mesh or rectangular which allows a very good rigidity (Fig. 2b). Moreover, they are easily recoverable and steel can then be recycled. The fill materials for the gabions are big aggregate materials with the highest possible density and frost-resistance, but crushed concrete can also be employed. For a better basket fill, the largest stone dimension is generally limited to 250 mm. The baskets are often installed in their final place on site, then filled and closed, which provides more efficiency than if they would have been assembled in plant. The quantity of stones required to build a retaining wall with gabions is similar to the one required for dry-stone retaining wall, except that 100% of the used stones generally comes from quarries. The information related to steel quantity involved in gabion technology can be found in Table 3. For cantilever walls the stability is ensured by the rigidity of the wall itself but also by friction between the wall and the basement if the bearing capacity of the soil foundation is correct (Fig. 2c). The wall is then as thin as possible with steel reinforcement in order to resist to the bending moment. This type of walls is very common

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G. Habert et al. / Ecological Indicators 23 (2012) 109–115 Table 4 Equipment required for the construction of retaining walls of 3 m high (From Alava et al., 2009). Concrete Excavation works Crawler excavator

h

Materials transport Concrete Cement (by 9t truck) Steel (by 28 t truck) Aggregates (by 28 t truck)

km km km km

Construction works Man-made Crawler excavator Diesel generator (10 kVA) Ready mix plant Agitator truck (4.5 m3 ) Concrete pump truck (40–45 m3 /h)

h h h m3 m3 km m3

0.33 15 150 500 25

Gabion 0.33

500 25

Dry stone 0.33

25 30

2 2 2.5 37.5 2.5

and can be calculated using the classical structural mechanics theory. 3.1.2. Energy and power associated to retaining walls The materials used for the three types of walls are indicated in Table 3 and the equipments involved in the process of construction are presented in Table 4. The data involved in this table come from expert advice (Alava et al., 2009). The energy and power data used in this process are presented in Tables 1 and 2. Table 5 allows comparing the power indicator (Pg ) to the embodied energy indicator (cumulative energy demand, total-CED) and also to the sum of the power (P) used during the construction. One can note that in Table 5, Pg is the most sensitive indicator distinguishing the three technologies. Using P, the values obtained for gabion and concrete walls are rather close. Actually if concrete value is set to 100%, then gabion P is equal to 78% instead of 53% found with Pg . If CED is used, then the values obtained for gabion and dry stone walls are closer than with Pg (Table 5). Indeed, when the embodied energy of the concrete wall is set to 100%, the gabion and dry stone walls have an embodied energy of respectively 27% and 8% of the concrete wall’s embodied energy. When a similar comparison is performed on the basis of Pg , the relative values are equal to 53% and 0.04% for gabion and dry stone wall respectively. Therefore, the new indicator Pg enhances the differences between a structure where no power intensive materials are involved (dry stone wall) and a structure where power intensive material such as steel is used, even in small quantities (gabion walls). Therefore this study of 3 very different civil engineering systems shows that Pg is able to make the clearest distinctions compared to their indicators. The sum of power (P) indicator, which holds a physical value, makes a lower distinction between a concrete wall and a gabion wall and the embodied energy indicator (CED) makes a lower distinction between a stone wall and a gabion wall. Fig. 2. Three different technologies for a retaining wall, (a), a dry stone solution, (b) a gabion technology, (c) a reinforced concrete technology (cantilever wall).

Table 3 materials used to build the three different walls of 3 m high (From Alava et al., 2009). Concrete Excavation Cement Steel Aggregate/stone

m3 kg kg kg

7 672 240 4680

Gabion

Dry stone

7

7

40 8228

5759

3.2. Residential houses The case of residential houses consisting in a series of small residential buildings in Southern France has already been studied in a previous paper (Morel et al., 2001). An illustration of these buildings is given in Fig. 3. The house is a one-storey building with a ground surface of 40 m2 . When possible, a sustainable approach has guided each phase of the construction: for example the materials were generally resourced on site. Around 90% of the mortar used for the stone masonry was made with an inorganic subsoil layer extracted from the site of construction. In addition to the site bedrock material, stone (dolomite limestone) for the masonry work was obtained from a local quarry. This house is

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Table 5 Embodied energy (total-CED), power sum (P) and proposed power indicator (Pg ) calculated for the three different walls.

Energy indicator, Total-CED (MJ) Power sum, P (MW) Power indicator, Pg (MW)

Concrete

Gabion

Dry stone

10.26 × 103 (100%) 7.72 × 102 (100%) 3.97 × 102 (100%)

28.02 × 102 (27%) 6.05 × 102 (78%) 2.10 × 102 (53%)

8.10 × 102 (8%) 3.19 × 10−1 (0.04%) 1.72 × 10−1 (0.04%)

4. Discussion 4.1. Operating phase vs building phase

Fig. 3. Picture of the studied residential buildings. Stone masonry house in Southern France (constructed in year 2000).

then compared to a concrete house with a same size. More details about the construction can be found in Morel et al. (2001) but some information about the materials used for the construction of the building are shown in Table 6. The energy needed during the 50 year service life of the house has been given by the user and estimated at 4.55 kWh/yr. No maintenance of the house has been considered. The results are presented in Fig. 4. The energy indicator (Fig. 4a) confirms results from previous studies (Sartori and Hestnes, 2007) that show that for conventionally built dwellings, the energy used for the operation phase constitutes in most cases more than 80% of the total energy consumed in a house life cycle. For passive houses, this value is lower but still reaches up to 50% of the total energy consumed (Sartori and Hestnes, 2007). Concerning the power indicator (Fig. 4b), the pattern is completely different. As the operation phase needs very low power to meet the needs of a single house, the building phase is then the critical phase for power evaluation. Furthermore, as steel and cement production require high power processes, the power indicator provides a clear distinction between the stone house and the concrete house. Finally one can note that even if the house built with local materials needs far less power, it still requires around 70 MW, which is difficult to produce with renewable energies. Actually, the main solar plant project in Europe has a power capacity of 20 MW (PS20 solar power tower, Sanlucar la Mayor, Spain: Appendix A).

The new power indicator proposed in this work enables the evaluation of the system adaptation capacity when stock energies will become scarce while flow energies will remain abundant. Moreover, this new indicator allows identifying the kind of construction materials and building methods that induce very high power dependence. Hence it shows that power intensive materials used to increase insulation or thermal inertia should not always be used when the saved energy during the operating phase would be provided by flow energies such as in low energy buildings. For instance, concrete is proposed as a material that can be used to achieve significant energy savings (Damtoft et al., 2008) since case studies show that the thermal mass of concrete decreases the energy consumption of the buildings in order to produce low energy buildings (Öberg and Damtoft, 2008; Cembureau, 2006). A similar study of a residential building (Utama and Gheewala, 2009) demonstrated that a double wall (made with fired brick + plaster) was more energy efficient over a 40 years period than a single wall. Nevertheless, the initial embodied energy of typical double wall and single wall envelopes for high-rise residential buildings is 79.5 GJ/m2 and 76.3 GJ/m2 , respectively. This small difference in embodied energy is overwhelmed by the expected energy savings; the energy consumption dropping from 480 GJ/m2 to 283 GJ/m2 . However it has been shown in the present study that providing low power energies for the operating phase or high power energies for the materials used during the construction phase do not have the same meaning in term of sustainability. Then, sustainability may not be related to the notion of “light buildings” (defined as buildings with good insulation and no thermal mass) or “heavy buildings” (good insulation and thermal mass) as Öberg and

Table 6 Materials used for the construction of residential buildings in Southern France using two different building technologies (from Morel et al., 2001).

Cement (t) Aggregates (t) Stone (t) Timber (t) Steel (t) Baked brick (t)

Stone masonry with soil mortar

Concrete

7 0 120 5.25 0.21 0

20 20 0 2 10

Fig. 4. Energy (a) and power (b) involved in the construction and service life duration of two building technologies for residential buildings in Southern France: stone masonry with soil mortar and reinforced concrete. In Fig. 4b, the impact of both operating phase and materials production are plotted; however, cement and steel are the only one that can be seen. Other processes are negligible.

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Damtoft proposed (Öberg and Damtoft, 2008). It must involve the type of materials which are used to provide the necessary thermal mass. With the present indicator, it is possible to highlight the difference which exists between a heavy house where thermal mass is provided by rammed earth or dry stone (low power materials) and the same heavy house where the mass is provided by concrete (high power material). It is also possible to compare heavy low energy house made with fired brick (power of 1 MW) and cement (power of 150 MW) (Table 4). With current energy indicators, it would not have been possible to make such a difference since in that case, the operating phase controls the final energy needs, even for low energy buildings.

Consequently, it induces a clearer cleavage between construction materials that can be used. Therefore, this indicator support a new paradigm for energy used in construction sector even if further research is needed to strengthen the methodology. In particular further work must be undertaken to increase the power database for all the industrial processes involved in the construction sector. Acknowledgement This work is part of the national project PEDRA n◦ 10 MGC S 017 devoted to the study of “dry stone constructions”. The authors would like to acknowledge the French Ministry of Ecology (MEDDTL) for its financial support to this project.

4.2. House scale vs national scale Appendix A. The scale of the present study is limited to a single house. However, if a larger scale is considered, for example the scale of a whole country, the pattern would be completely different. If France is taken as an example, there are around 25 millions of residential housings that will need energy at the same time especially during winter time. On the contrary, there are around 30 cement plants that are running 24 h a day (SFIC, 2010). In that context, during winter, when 30 cement plants using 150 MW are compared to 25 × 106 residential housings using at least 2000 W for heating, the power demand is actually controlled at 90% by house heating. Consequently, in a national context, the construction phase is no longer the most critical phase with respect to the peak capacity, but the operating phase. Then, one could argue that the power indicator developed herein will become pertinent when more and more passive houses will be built. Actually, if all houses were consuming 180 W, the power for all the houses would be similar to the power needed for the 30 cement plants. This indicator is therefore useful in order to orient long term energy policies; even if, in the short term, the insulation improvement is the most efficient action able to reduce the environmental impact of construction. 4.3. Boundaries and perspectives The boundaries of the system as defined in Life Cycle Analysis are not well constrained in this study. So far, only the last process involved in the production of building materials has been used to calculate the power demand. For instance, concerning cement, the power needed to run a cement plant has been used, but the other background processes such as petrol extraction and refinement processes have not been considered in the power indicator. This is different from common energy indicators such as the cumulative energy demand that include these energy consumptions in the calculation. Therefore, both indicators do not use the same system boundaries for their calculation In order to solve this problem and use the same system boundaries for all indicators, it is necessary to increase the database of power needed for all the industrial processes involved in the construction sector and also to all the related processes such as petrol production. 5. Conclusion This article focused on a new indicator related to energy consumption able to be used in sustainability approaches in the building and construction sector. This new indicator for energy is based on power calculation. This method has been applied to two different kinds of systems: retaining walls and houses. For retaining walls, the indicator clearly allowed differentiating three common technological solutions. For houses, the new power indicator allowed highlighting the dependence of construction materials to high power energy sources during the operation phase.

List of renewable energy plants. The area for the different power systems has been calculated as follow: for hydraulic power, the lake surface has been used, for wind farms the area allocated for the wind farms without considering that other activities could be done at the same place. For solar system the total of the covered surface has been taken without considering the other activities that could be done at the same place (for roofs for instance). Solar systems: *: BE Espagne N◦ 51 – Ambassade de France en Espagne; 2*: Ciemat, Pacsa, Elecnor, Enertron; 3*: Cohen, Gilbert (2006), “Nevada First Solar Electric Generating System” (PDF), IEEE May Technical Meeting, Las Vegas, Nevada: Solargenix Energy, p. 10; 4*: Frier, Scott (1999), “An overview of the Kramer Junction SEGS recent performance” (PDF), Parabolic Trough Workshop, Ontario, California: KJC Operating Company; 5*: Kearney, D. (August 1989). “Solar Electric Generating Stations (SEGS)”. IEEE Power Engineering Review (IEEE) 9 (8): 4–8. doi:10.1109/MPER.1989.4310850; 6*: Price, Hank (2002), “Parabolic trough technology overview” (PDF), Trough Technology – Algeria, NREL, p. 9; 7*: Saint Charle solaire, press announcement, 9 Feb. 2009; 8*: Themis-PV, http://www.themis-pv.com/, available on line december the 9th, 2009; 9*: JMB energie, Midi Libre, 9 dec 2009. 10*: Le Figaro, lundi 21 avril 2011. Wind farms: 1$: http://www.larousse.fr/encyclopedie/article/Ally-Mercoeur%20La %20Ferme%20%E9olienne%20d%27Ally-Mercoeur/11004863; 2$: http://www.haute-marne.equipement-agriculture.gouv.fr/ rubrique.php3?id rubrique=157; 3$: http://www.haute-marne. equipement-agriculture.gouv.fr/rubrique.php3?id rubrique=158; http://www.haute-marne.equipement-agriculture.gouv.fr/ 4$: rubrique.php3? id rubrique=159; 5$: http://www.haute-marne. equipement-agriculture.gouv.fr/rubrique.php3?id rubrique=160; 6$: http://www.ushuaia.com/ushuaia-terre/info-planete/actu-encontinu/energie/0,4826835,00-le-plus-grand-champ-eoliensitue-au-texas-.html 7$: http://tpe.eolienne.gr2.free.fr/finistere 106.htm, 8$: http://www.manicore.com/documentation/eolien. html, 9$: http://www.c-power.be, 10$: http://www.londonarray. com/, 11$: BWEA, 2006. Offshore wind at crossroads (www.bwea.com) Hydraulic power plants: w1: Wikipedia; w2: Technologie barrage; w3: Présentation de l’aménagement hydroélectrique du Pouget et du barrage de Pareloup (Aveyron). 1994. Hydroecologie appliquée, 6, 1–7, w4: Marot L. Le barrage de petit saut agit comme réacteur chimique. Le monde 19 avril 2011. References Alava, C., Augeraud, L., Apavou, S., Bouskela, D., Lenoir, C., Peyrard, M., Vincens, E., 2009. Retaining walls: economic and environmental comparison of different construction technologies (in French). projet d’option, Ecole Centrale de Lyon, 65 pp. Asif, M., Muneer, T., Kelley, R., 2005. Life cycle assessment: a case study of a dwelling home in Scotland. Build. Environ. 42, 1391–1394. Bastier, R., 2000. Cement kiln: clinker workshops (in French), Tech. Ing.

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