Thermo-economic optimisation of a tower/trough combination solar power plant

Today a crude oil barrel has five times the prize it had fifteen years ago, moreover, we have increased our global energy consumption by almost 40 percent since then and population growing rates are higher than ever before. In addition, recent tragic events in Fukushima nuclear power plant, Japan, earlier this year, have increased concerns even more about energetic schemes based on nuclear energy. This challenging energetic context requires rapid, economically feasible and reliable progress in the field of renewable energies. We have the great responsibility today of building the energetic scheme of tomorrow. Amongst renewable energies, thermal solar energy has already proven both reliable and competitive with adequate feed-in tariffs and offers some key advantages such as the possibility to store the energy as well as the good controllability of the transformed energy, which entails a great connectivity to the grid. The goal of this project is to perform a thermo-economic analysis and optimization of a solar thermal power plant combining both a tower and parabolic trough power plants and to find out whether or not the combination of these two (with different temperature levels) is advantageous from an energetic or an economic point of view. This idea is fairly innovative and no previous studies have been found on this particular research line. A new, detailed model has been developed for the trough power plant not only for the thermal side but also for the hydraulic and economical side. This model has been then combined with an existing model for the tower power plant. Afterwards, a performance analysis and a multi-objective optimization of the combination have been carried out. Energetic integration, modelling of the power cycles and multi objective optimization all have been performed using LENI tools to analyze and optimize energetic systems such as Energy Technologies and MOO. Trough – tower combination solar power plants present several advantages both from an energetic and economic perspective. Combination power plants feature important efficiency gains compared to either the tower or the trough power plant individually. This efficiency gain comes from the sake of combining both types of power plants, allowing better cycle efficiencies. Efficiency of these combined trough- tower power plants can reach 18.7% (solar to electricity) for certain combinations, with a levelised energy cost of 15 UScts/kWh. Other interesting combinations have been pointed out, for instance, an 80 MW combined power plant, with an efficiency of 16.9% and a levelised energy cost of 8.8 UScts/kWh which is fairly impressive compared to the current solar thermal power plants. Many different interesting combinations can be imagined, each one offering particular advantages. This project confirms that trough – tower combination, when properly integrated, result into more efficient, with a lower levelised energy cost with respect to tower schemes and larger power plants than either tower or trough schemes separately. This new possibility definitely contributes to make solar thermal power an even more promising and interesting technology.