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The potential energy of compressed air represents a multi-application source of power. Historically employed to drive certain manufacturing or transportation systems, it became a source of vehicle propulsion in the late 19th century. During the second half of the 20th century, significant efforts were directed towards harnessing pressurized air for the storage of electrical energy. Today's systems, which are based on storing the air at a high pressure, are usually recognized as compressed air energy storage (CAES) installations. This paper aims to provide an overview of different technologies that take advantage of the energy accumulated in the compressed air. Particular attention is paid to the CAES installations that are working as electrical energy storage systems (EESs). These systems, developed originally as large capacity (>100 MWe) and fuel-based installations, may soon become fully scalable, highly efficient, and fuel-free electrical energy storage systems. To present this opportunity, a thorough review encompassing previous and up-to-date advancements in their development was carried out. In particular, CAES concepts, such as diabatic (D-CAES), adiabatic (A-CAES), and isothermal (I-CAES), are described in detail. This review also provides the detailed characteristics of the crucial elements of these configurations, including compressors, expanders, air storage chambers, and thermal storage tanks. Knowledge of these components and their role allows us to understand the main challenges behind the further development of the mentioned CAES setups. Apart from the CAES systems that are designed as EES systems, this paper describes other prospective technologies that utilize the energy of pressurized air. Accordingly, compressed air cars and their key elements are explained in detail. Moreover, the technology renowned as wave-driven compressed air energy storage (W-CAES) is described as well, indicating that the utilization of pressurized air represents a viable option for converting ocean energy into electrical power. [ABSTRACT FROM AUTHOR]

Nowadays, almost 30% of total energy consumption (130 EJ) is consumed for the operation of buildings, mainly by space heating/cooling and ventilation systems, hot water preparation systems, lighting, and other domestic appliances. To improve the energy efficiency of buildings, several countries are promoting the use of renewable energy. The most promising systems include active and passive solar installations. In passive systems, the solar energy is collected, stored, reflected, or distributed by the roof ponds, natural convective loops, and the most popular direct gain walls and thermal storage walls (known as Trombe walls). This paper reviews the experimental and numerical studies devoted to the different solutions of Trombe walls, including solar chimneys integrated on the vertical walls, classic Trombe walls, Trombe walls with incorporated phase change materials, and photovoltaic Trombe walls. The actual state of the art is presented in the context of reducing energy consumption and enhancing thermal comfort. Most of the analyzed studies showed that the application of thermal storage walls allowed achieving these goals, led to lower emissions of greenhouse gases, and improved living standards. Nevertheless, there is a need for more detailed feasibility studies, including cost and environmental indicators. [ABSTRACT FROM AUTHOR]

Passive solutions in buildings have recently been rediscovered because they allow the rational use of solar radiation, which promotes energy savings. Thermal energy gained from the sun may be stored in the form of sensible heat in accumulative solid materials in a building envelope. This paper proposes an innovative solar air heater that captures and accumulates solar energy during the day and releases it during the night. The analyzed system is based on inexpensive ceramic modules, which can be used to construct thermal storage walls or solar chimneys in modern buildings. Both configurations have been tested experimentally and by a numerical model in ArCADia BIM software. Experiments have been carried out in laboratory conditions using a specially developed prototype. Among other parameters, power transferred from the solar air heater to the ventilation air in different conditions has been analyzed. When airflow was set to 150 m3/h, the maximum power observed under stable working conditions was approx. 355.0 W when the developed solar air heater operated as the solar chimney, and approx. 165.0 W when it operated as the solar thermal wall. When airflow was set to 200 m3/h, the maximum power was approx. 385.0 W. Experimental results have been used to calculate the efficiency of the solar air heater in real conditions. The total efficiency in the case of the solar chimney was estimated as 0.25, while in the case of the thermal wall it was estimated as 0.78, which resulted in an annual reduction in energy usage at a level of 190.7 kWh and 556.1 kWh, respectively (4.8 and 14.0%). In practice, these values can be significantly higher due to the possibility of increasing the length and shape of the accumulation heat exchanger. [ABSTRACT FROM AUTHOR]