Centrale solaire thermodynamique

Résumé

Une centrale solaire thermodynamique (ou centrale solaire thermique à concentration ou encore héliothermodynamique), en anglais CSP (pour concentrated solar power) est un site industriel qui concentre les rayons du Soleil à l'aide de miroirs afin de chauffer un fluide caloporteur, lequel sert en général à produire de l'électricité. Ce type de centrale permet, en stockant ce fluide dans un réservoir, de prolonger le fonctionnement de la centrale plusieurs heures au-delà du coucher du Soleil. Différents types de centrales sont distingués selon la forme des miroirs (plats ou courbés) et la distribution du fluide caloporteur (ponctuelle ou linéaire). La production des centrales solaires thermodynamiques atteignait en 2020, soit 0,05 % de la production mondiale d'électricité, moins que celle du solaire photovoltaïque. Les principaux pays producteurs sont l'Espagne (36,4 %), les États-Unis (25,0 %), la Chine (12,3 %), l'Afrique du Sud (10,4 %), le Maroc (8,2 %) et Israël (4,7 %). vignet

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Life Cycle Analysis and Thermo-Environomic Optimization of Concentrated Solar Thermal Power Plants

Aurélie Kuenlin

Confronted to resources depletion and the global warming, the humanity has to reduce its fossil fuels dependence. The renewable energy is an interesting option to reach this aim. The most powerful one is the solar energy since in few hours, the Earth receives more energy than the humanity consumes in one year. In order to convert this energy to electricity, the concentrated solar power plants (CSP) are more advantageous than photovoltaics (PV) because of the possibility to store the energy. Indeed, they concentrate with numerous mirrors the sunlight to heat up a ﬂuid which can be stored in a big insulated tank. Then, the heat energy is transferred to a steam which drives a turbine and a generator to produce electricity. Nowadays, this type of power plants has a real potential. The aim of this work is to test and conﬁrm that the CSP engender less environmental impacts than other types of power plants over their entire life cycle including production, operation and end of life. Furthermore, four different technologies of CSP (tower, parabolic trough, Fresnel and dish) are compared in order to ﬁnd the most efﬁcient one for the environment and identify their strong and weak points. Finally, multi-objectives optimizations, which consider economic and thermodynamic aspects, are performed to ﬁnd the optimal conﬁguration for each power plant. In this work, the environmental impacts are calculated by carrying out a life cycle analysis (LCA) with the Impact 2002+ method. It takes into account the damages on resources, climate change, human health and ecosystem quality. According to this study, the results indicate that CSP produce lightly less impacts than PV but much less impacts than fossil fuels energy. The comparisons between the different CSP reveal that the dish technology engenders less damages than other due to its high efﬁciency and less facilities. However, its investment costs are too important to be competitive. From the other hand, Fresnel and parabolic technologies produce too much environmental impacts for lower costs. The weak point of Fresnel is its very low efﬁciency and the disadvantage of parabolic is the use of a speciﬁc synthetic oil which is very harmful for the environment, without speaking of the possible spills. Moreover, the hybridation with natural gas of both technologies reduces their costs but increases considerably the impacts on climate change and resources categories. Finally, the tower technology is the most advantageous CSP regarding the impacts, the electricity production and costs. It does not need hybridation to have low costs and have an important storage capacity to produce electricity during nights and cloudy days. However, the investment is still too important to be more attractive than fossil fuel power plants. Therefore, there are two possibilities: to implement a CO2 tax of around 60$/MWh or to improve CSP technology. For the last option, the steel of the mirrors structure, which is the most harmful material according to LCA results, can be reduced and thus, the impacts and the costs will be lower. It can also be possible to use recycled steel or another material. Another hint is to build CSP in a very sunny regions with a DNI of at least 1750 kWh/m2 /yr with short transmission lines. Finally, it is important to increase as much as possible the efﬁciency of CSP to produce more energy and decrease the environmental impacts too.

2011

Chargement

Life Cycle Analysis of a Solar Tower Thermal Power Plant

Aurélie Kuenlin

In this present work, a life cycle assessment is realized on Solar Two, a test project of a solar tower thermal power plant. The aim of this study is to quantify the impacts on the environment associated with all the stages from cradle-to-grave (production, use and end of life). The ﬁrst step is to deﬁne the scope of the study: objectives, function, functional unit and system limit. Secondly, an inventory of all material, processes and energy required for the system will be made to determine relevant energy and material inputs and environmental releases which represent all the substances emitted into air, soil and water for the entire life cycle. Finally, the last two steps are the impacts analyze, which evaluates the potential impacts associated with inputs and releases, and the interpretation. The most interesting result of this analyze shows that 80% of ecological impacts are due to the steel production used to build the heliostats. Furthermore, the impact of the transmission network, material transport, potassium nitrate and mirrors are not negligible despite that their role is smaller than the steel. The variation of the steel impact is analyzed for diﬀerent solar power plants which have a optimized cost for a speciﬁc thermal power. The result shows that the steel impact decreases with the increase of the thermal power. Moreover, comparing two identical thermal power, the most expensive plant is the most ecological. Finally, the Solar Two impact was compared with other types of power plants. Coal, natural gas and nuclear power plant have, as expected, more negative eﬀect on the environment. Concerning the renewable energy, wind and hydro power plant emit around 10% less impact on the four damages categories. Only the photovoltaic impacts are similar to Solar Two with a equivalent eﬃciency. Further improvements of this LCA could now carry out. For example, the amount of steel used in the heliostats should be technically reduced or substituted by recycled steel or a material with less impact. The storage, the tower and the mirror number should also be optimized to minimize the damages on the environment. A thermo-environomic optimization is also required to ﬁnd the perfect future competitive solar tower thermal power plant.

2010

Chargement

The possibility of combining both the advantages of a solar tower thermal power plant and of a solar parabolic trough power plant could be interesting from an energetic point of view as well from an economic point of view. The preliminary study of this combination feasibility is the goal of this project. The study of the project viability consist first of all on the modeling of the trough system, the energy balance of the parabolic troughs will be established at first. Secondly, and choosing a perfect solar day simulating a day when the solar radiation is rather stable, with no cloudy periods along the day, the power available from the trough plant can be calculated. Once we have estimated the power that we can introduce into the cycle of the tower plant, the main issue consists on how and where it is better to use this energy in the cycle. Several possibilities seem to be interesting a priori, however a more detailed study of each one is to be done in order to get to the most economic and efficient layout. The work related to the tower thermal power plant will be done taking as starting point the master thesis of James Spelling, who did an incredible work in this field and whose work will be a valuable help to continue the research on the proposed concept in this project of combining two plants, tower and trough. The main advantage of the tower design compared to the parabolic trough design is the higher temperature. As it will be explained further, thermal energy at higher temperature can be converted more efficiently, the exergy efficiency is better. In terms of storage, the high temperature results in a cheaper and a more efficient storage system. Nevertheless, the set up of the field of heliostats is more complex than the set up of the parabolic trough lines even though the area for a trough plant must be previously flattened. The lower temperature level that entails an inconvenient itself for a parabolic trough power plant may become an advantage when combining both types of concentrating solar power plants. If the results are positive enough that it seems interesting to combine both types of power plants, another step forward will be done towards the use of the sun energy as a renewable source thus making it a more interesting choice for power generation. Sun potential has already shown as an important technology not only at the present time but also in the future. Commercial solar plants have already achieved levelized energy costs around 12-15 UScts/kWh, and the potential for cost reduction is expected to follow this trend even further, to costs as low as 5 UScts/kWh. In addition the taxes imposed for the non-green power should make even more interesting the use of concentrating solar power plants. The requirements of high beam normal radiation lead to a limited amount of suitable places where the implantation of this technology is possible. However many places exist on Earth where the conditions are perfectly adapted, we talk about regions such as United States (the country with more carbon dioxide emissions in the world), some regions in Mexico, North Africa, India, Australia, northeastern Brazil and some locations around the Mediterranean, especially in the south of Spain. The challenge is therefore set for a change in our energy production scheme.

2010

Chargement