Abstract: Chile is facing important challenges to develop its energy sector. Estimations demonstrate that in its electricity consumption Chile will grow at an annual rate of 4.6% until 2030, despite ongoing efficiency improvements. To satisfy this demand in a sustainable way, the national energy policy promotes the integration of novel and clean power generation into the national power mix, with special emphasis on concentrated solar power (CSP). The present paper assesses the development of solar-based electricity generation in Chile by CSP, achieved by a Solar Power Tower plant (SPT) using molten salt as heat carrier and store. Such SPTs can be installed at different locations in Chile, and connected to the main national grid. Results show that each SPT plant can generate around 76 GWh(el) of net electricity, when considering solar irradiation as the sole energy source and at a 16% overall efficiency of the SPT process. For operation in a continuous mode, a hybrid configuration with integrated gas backup system increases the generating potential of each SPT to 135 GWh(el). A preliminary Levelized Energy Cost (LEC) calculation provides LEC values between 0.15 and 0.18 $/kWh, as function of the overall process efficiency and estimated investment cost. Chile's solar irradiation favors the implementation of SPT plants. (C) 2013 AIP Publishing LLC.

Abstract: Thermal energy storage (TES) transfers heat to storage media during the charging period, and releases it at a later stage during the discharging step. It can be usefully applied in solar plants, or in industrial processes, such as metallurgical transformations. Sensible, latent and thermo-chemical media store heat in materials which change temperature, phase or chemical composition, respectively. Sensible heat storage is well-documented. Latent heat storage, using phase change materials (PCMs), mainly using liquid solid transition to store latent heat, allows a more compact, efficient and therefore economical system to operate. Thermo-chemical heat storage (TCS) is still at an early stage of laboratory and pilot research despite its attractive application for long term energy storage. The present review will assess previous research, while also adding novel treatments of the subject. TES systems are of growing importance within the energy awareness: TES can reduce the LCOE (levelized cost of electricity) of renewable energy processes, with the temperature of the storage medium being the most important parameter. Sensible heat storage is well-documented in literature and applied at large scale, hence limited in the content of the present review paper. Latent heat storage using PCMs is dealt with, specifically towards high temperature applications, where inorganic substances offer a high potential. Finally, the use of energy storage through reversible chemical reactions (thermo-chemical Storage, TCS) is assessed. Since PCM and TCS storage media need to be contained in a capsule (sphere, tube, sandwich plates) of appropriate materials, potential containment materials are examined. A heat transfer fluid (HTF) is required to convey the heat from capture, to storage and ultimate re-use. Particle suspensions offer a valid alternative to common HTF, and a preliminary assessment confirms the advantages of the upflow bubbling fluidized bed and demonstrates that particulate suspensions enable major savings in investment and operating costs. Novel treatments of the TES subject in the review involve the required encapsulation of the latent and chemical storage media, the novel development of powder circulation loops as heat transfer media, the conductivity enhancement of PCMs, the use of lithium salts, among others. (C) 2015 Elsevier Ltd. All rights reserved.

Abstract: Heat capture and storage is important in both solar energy projects and in the recovery of waste heat from industrial processes. Whereas heat capture will mostly rely on the use of a heat carrier, the high efficiency heat storage needs to combine sensible and latent heat storage with phase change materials (PCMs) to provide a high energy density storage. The present paper briefly reviews energy developments and storage techniques, with special emphasis on thermal energy storage and the use of PCM. It thereafter illustrates first results obtained when encapsulating NaNO3/KNO3-PCM in an AISI 321 tube, as example of a storage application using a multi-tubular exchanger filled with PCM. To increase the effective thermal conductivity of the PCM, 2 inserts i.e. metallic foam and metallic sponge are also tested. Experimental discharging (cooling) rates are interpreted by both solving the unsteady-state conduction equation, and by using Comsol Multiphysics. Predictions and experimental temperature evolutions are in fair agreement, and the effect of the inserts is clearly reflected by the increased effective thermal conductivity of the insert-PCM composite. Application of Comsol to predict the mechanical behavior of the system, when melting and associated expansion increase the internal pressure, demonstrates that the pressure build-up is far below the Young's modulus of the AISI 321 encapsulation and that this shell will not crack (C) 2014 Elsevier Ltd. All rights reserved.