Thesis title: Thermal Energy Storage integration in electrical grids and in energy industries for decarbonization
In the current global context, where it is essential to comply with greenhouse gas emission limits to avoid surpassing the increase in average global temperature, renewable energy sources must replace traditional fossil fuels in the production of both electrical and thermal energy across various sectors, including industry. The inherent unpredictability of renewable energy sources makes it challenging to align energy production with real-time demand. For this reason, the introduction of energy storage systems is crucial, as they play a key role in balancing supply and demand. These systems allow for the storage of excess energy produced during periods of low demand, which can then be released when demand is higher, ensuring a more stable and reliable energy system.
In the various sectors where energy is required, numerous solutions are being proposed for energy storage technology. This doctoral thesis focuses on thermal energy storage systems for steam supply in industrial applications. Specifically, two types of storage systems based on fluidized sand beds will be presented: one charged directly by solar energy and the other by electrical energy. Both systems were designed and patented by Magaldi Power S.p.A. and are named STEM® (Solar Thermo-Electric Magaldi) and MGTES (Magaldi Green Thermal Energy Storage), respectively.
For the STEM® technology, which uses solar energy for charging, two innovative aspects stand out: an advanced algorithm for the integral correction of heliostat (solar tracking mirrors) aiming errors, which improves aiming accuracy and consequently increases the amount of solar energy collected in the fluidized bed; and the use of a biaxial inclinometer for each heliostat, which helps to reduce aiming errors caused by ground misalignments, thus improving system reliability.
For the MGTES technology, which utilizes electric resistances to charge thermally through Joule heating, a study was conducted to identify the most suitable heating system for the fluidized bed of sand particles. Simulations were carried out based on analytical models, comparing resistive elements designed to heat through conduction, convection, and radiation. Following the simulation phase, an experimental testing campaign was conducted to validate the results of the theoretical models, verifying the accuracy of the simulations and the actual performance of the heating systems studied.
To identify the most promising heating method, a qualitative analysis was performed alongside the quantitative assessment, aimed at evaluating critical factors relevant to the industrialization of technology. Key considerations included ease of installation, maintenance requirements, component replaceability, and compatibility of the technology with the storage medium. A SWOT analysis was conducted, encompassing the primary qualitative mentioned factors. The resulting matrices were then structured to systematically evaluate these aspects.
In the proposed scenario, where thermal storage systems are integrated within energy districts, a novel controlled microgrid concept becomes essential. In this framework, both electrical and thermal storage systems require optimal management. An effective Energy Management System (EMS) is critical to the efficient utilization of distributed energy resources. Considering these requirements, research has been initiated to develop an EMS model aimed at optimizing power flows to reduce both energy costs and CO₂ emissions. This topic will form the core of future research efforts.