Thermal energy storage is a key technology to increase the global energy share of renewables-by matching energy availability and demand-and to improve the fuel economy of energy systems-by recovery and reutilization of waste heat. In particular, the negligible heat losses of sorption technologies during the storing period make them ideal for applications where long-term storage is required. Current technologies are typically based on the sorption of vapor sorbates on solid sorbents, requiring cumbersome reactors and components operating at below ambient pressure. In this work, we report the experimental characterization of working pairs made of various liquid sorbates (distilled water, ethanol and their mixture) and a 13X zeolite sorbent at ambient pressure. The sorbent hydration by liquid sorbates shows lower heat storage performance than vapor hydration; yet, it provides similar heat storage density to that obtainable by latent heat storage (40-50 kWh/m 3) at comparable costs, robustness and simplicity of the system, while gaining the long-term storage capabilities of sorption-based technologies. As a representative application example of long-term storage, we verify the feasibility of a sorption heat storage system with liquid sorbate, which could be used to improve the cold-start of stand-by generators driven by internal combustion engines. This example shows that liquid hydration may be adopted as a simple and low-cost alternative to more efficient-yet more expensive-techniques for long-term energy storage.

Pumped hydro storage (PHS) is one of the more suitable energy storage technologies to provide bulk storage of intermittent renewable energy sources (RES) such as wind. Since the main limiting factors to the expansion of this mature technology are environmental and financial concerns, the use of an existing reservoir can help mitigate both types of impacts. In addition, the high number of reservoirs for municipal and irrigation supply in many areas of the world makes the idea of using PHS as a relatively diffuse, open-market, technology for RES management attractive. These arguments in favor of PHS must, however, be convincing for investors and regulators from an economic standpoint. To this end, this paper presents a methodological tool to screen the feasibility of a PHS facility around an existing reservoir based on the principles of cost-benefit analysis, calibrated with data from Sicily, Italy. Each potential plant is characterized by two locational and two plant-specific parameters. Costs and benefits are assessed through a simulation model of the storage-release process on an hourly basis. Costs include both investment, and operation and maintenance expenditures, while the benefits considered include the opportunity cost of the current energy mix substituted by the stored energy, and the avoided CO 2 emissions. The evaluation exercise is carried out parametrically, i.e., looking at a large number of combinations of the four parameters, in order to explore a wide range of possible plant configurations and to identify optimal ones under different locational conditions. A sensitivity analysis performed on models' parameters points out the sensitivity of results to benefit, rather than cost-related, input parameters, such as the efficiency of the generating and pumping system and the opportunity cost of energy.2 of 18 peak/off-peak, working mode [8][9][10][11][12]. Considering construction of a new plant therefore requires a thorough assessment of their techno-economic feasibility based on the specific supply-demand conditions at the appropriate timescale (typically one hour or less).The major drawback of PHS as storage technology lies in the long construction times and environmental concerns [13]. Although there is a growing interest in smart, sustainable solutions, envisaging small PHS plants [14] especially for small islands and isolated grids [15][16][17][18], PHS plant construction is a major technical and financial effort. The full development of a PHS project takes approximately 15 years from time of inception to commissioning. Retrofitting of existing hydropower schemes with PHS has a lower environmental impact and is often seen as a more benign solution, as the receiving environment has already been modified and is regulated by the existence of the hydropower plant. Where hydropower reservoirs do not exist or are not adequately developed, an intermediate solution can be to use the storage capacities of existing water reservoirs for water supply. In fact, many reservoirs, especially those for irrigation,...

Sustainable use of water resources requires a modern approach for complex water systems management based on system's modeling, as unsung operation alternatives may only be devised and tested through a model. The now available IT computing tools enable setting the traditional modelling methodologies for planning and operation of such systems in a new framework. The present work deals with the development of decision support models for optimizing the operation of complex water supply systems with multiple uses and focuses on the validation of the optimization model of the regional water supply systems managed by an Italian water utility. The software used is Aquator, a state-of-the-art commercial tool for generic water resources system simulation and operational optimization. The paper shows and comments the results of the validation of the model and uses them to draw some general principles for the validation of such kind of models: in fact, operational optimization models are conceived for the enhancement of systems management and performance. Consequently, while on the one side model output is expected to reflect the actual state of the system, on the other it can point out significant management enhancements.