Life Cycle Analysis of a Solar Tower Thermal Power Plant

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.

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

Thermo-Economic Optimisation of Solar Tower Thermal Power Plants

James Spelling

Amidst a backdrop of rapidly increasing world-wide electricity demand, solar thermal power generation shows great potential for supplying the electricity needs of numerous countries in the Sun-belt regions of the world. In these regions, the absence of significant biomass, hydrological or geothermal reserves makes solar thermal power the most promising solution for meeting that most fundamental of demands: energy. Amidst the different options available for harnessing the Sun’s power, solar thermal technologies have been shown capable of producing electricity at the most economically viable rates [32]. However, all currently existing solar thermal power plants have been based around the use of Rankine, or steam turbine, cycles which are limited in the efficiencies they can achieve. In order to make better use of the Sun’s energy, higher efficiency cycles should be used. With their high concentration ratios, solar thermal power tower systems are amongst the best options for making use of the Sun’s potential. As the energy delivery temperature of central receiver systems is higher, they harness the solar radiation at a higher exergy level [4]. This higher temperature also opens the road to the use of more advanced thermodynamic cycles. Hybrid fossil-fuel – solar systems are also imaginable [13], as the energy delivery temperature is compatible with standard gas turbine cycles. Hybrid systems can help mitigate the requirements of thermal energy storage, as well as reducing the perceived risk when investing in new solar technology, which stimulates research and development, as well as providing employment. Recent developments in the field of high temperature volumetric receivers [10] along with rock- based packed-bed storage systems have opened up an interesting possibility. High temperature receivers allow the use of higher-efficiency combined-cycle setups, whereas packed-bed units offer the possibility of cheap storage. Larger storage volumes allow pure-solar systems to extend their power production into the night, making hybrid options less attractive. This is compounded by the common practice of guaranteeing a preferred tariff for electricity sales from pure-solar sources With this in mind, a complete dynamic model of a power plant based on the pure-solar concept has been elaborated. The performance of the setup is evaluated over a range of days, using solar insolation profiles obtained from satellite data. In order to examine different design options and their impact on the performance of the power plant, a multi-objective, thermo-economic optimisation of both the power plant superstructure and operating conditions was performed using the new, dynamic models. By means of an evolutionary algorithm [17], a family of Pareto-optimal points were obtained, representing the trade-off between increased power plant efficiency, and lower levelised energy costs. Through use of optimisation, it was shown that exergetic efficiencies in the region of 21-27% can be achieved, for relatively low power outputs of between 3 and 11 MWe. These configurations correspond with levelised electricity costs in the region of 14-21 UScts/kWhe. In most regions, the use of solar power is encouraged by the guarantee of a preferential tariff for electricity sales from renewable sources. Sale of electricity at a price of around 24 UScts/kWhe [32] should therefore be imaginable, ensuring the economic viability of solar thermal power tower systems. It can be concluded that, when properly designed, solar thermal power plants based on combined cycles are both economically and thermodynamically promising. By raising the efficiency of the plant, the size of the solar collector field is diminished, increasing the otherwise low energy densities of solar power systems. By reducing the levelised electricity costs, solar thermal power plants become more economically viable, accelerating their construction and thus, hopefully, reducing our dependence on fossil-fuels.

2009

Assessment of Solar Thermal Power Technologies

James Spelling

In the present climate of growing awareness about the dangers of global climate change, the development of new renewable energy technologies is primordial in the efforts to reduce emissions of carbon dioxide and other greenhouse gases. Rapid increases in the price of oil and worries about the stability and security of the extraction of fossil fuels have lead to renewed interest in the development of local energy sources, thereby reducing dependence on foreign fuel sources. Amid the plethora of option available, one of the more promising solutions is the increased use of solar power. Two main contrasting technologies exist for the conversion of the Sun’s energy into useful work, namely photovoltaic cells and solar thermal systems. The development of photovoltaic power has shown massive growth in recent years despite high costs, due mainly to the modular nature of the cells which allow their installation by private citizens, coupled with a number of government incentives. Development of solar thermal power generation has however been reasonably limited until recently, with the only continually operated commercial plants being the Luz SEGS I-IX plants at Kramer Junction in the United Sates. Solar thermal power generation shows great potential for supplying the base electricity needs of numerous countries in the sun-belt regions, stretching from the tropics to the Mediterranean. This has lead to a recent renewal in the development of such systems, notably with the construction of the PS10 central receiver plant in Spain. The Spanish government plans to bring the total solar generation capacity to a total of 300 MW by 2013. In other countries around the world, interest is growing in solar thermal power, with increased government and private spending fuelling research and innovation. Most solar thermal conversion technologies are still at the experimental stage, and no single technology has yet to impose its dominance. Different countries and research groups hold different solutions dear, but if solar thermal power is to become a fully mature electricity generating technology, the best of these diverse solutions must be combined in order to achieve optimal performance of the power plants.

2008

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

Aurélie Kuenlin

2011

Thermo-Economic Optimisation of Solar Tower Thermal Power Plants

James Spelling

2009

Assessment of Solar Thermal Power Technologies

James Spelling

2008