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.