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The scarcity of energy and water resources and rising temperatures due to climate change has set the focus on improving the energy efficiency of power plant thermodynamic cycles to adapt to higher heat sink temperatures and use fewer resources for energy production. In this work, a review of power production thermodynamic cycles is presented: from Brayton to Rankine and combined cycles, alongside particular cycles such as Organic Rankine Cycles, Kalina, Goswami or the more recently developed Hygroscopic Cycle. The efficiency of these cycles and their possible improvements are considered, as well as their environmental impact. Costs associated with existing power plants found in the literature have also been included in the study. The main existing facilities for each cycle type are assessed, and the most sustainable options in terms of resource consumption (fuel, water, etc.) and future perspectives to ensure both their energy efficiency and sustainability are identified.

A kind of energy storage proceeding from renewable sources is presented. It has been studied the storage, in the form of Compressed Air Energy Storage Systems (CAES) or Liquefied Air Energy Storage Systems (LAES) of the renewable electricity that, at the time it is generated, it is not delivered to the network because of technical or economic reasons, or saturation. The possibility of using an artificial storage system allows the installation not to be conditioned by the availability of a natural reservoir. This article focuses on the use of artificial storage systems, mainly for small power wind farms (about 30 kW), so storage systems will alternatively be called CAES or SCAES and LAES or SLAES (S from “small”) CAES systems advantages and disadvantages of each different thermodynamic cycle are studied. One of CAES systems higher limitations is the huge volume needed to store air mass enough. Instead of storing gaseous phase air, much more energy density can be accumulated by storing air in liquid phase (LAES). LAES system functioning is similar to CAES one. Liquid air is produced in an air liquefying plant when there is an excess of energy or it is not interesting to drop it into the network Some LAES systems advantages are storage volume reduction for the same energy density and the possibility of storing at about atmospheric pressure.

This article focuses on the advantages found by incorporating Hygroscopic Cycle Technology into the 12.5-MWe “Vetejar” biomass power plant operating in the province of Cordoba (Spain) since 1996. The power plant required upgrades to increase its availability, net electrical performance and to extend the service life span of refrigeration equipment. The incorporation of the new Hygroscopic Cycle Technology has allowed not only to alleviate the shortcomings of the power station in a simple way, but also to make the most of the existing equipment, despite the adverse environmental conditions. The scarcity of water in the area is one of the greatest difficulties the plant has met since its start-up. It significantly diminishes the operation hours of the plant, reducing the electrical power generated, electrical performance and availability. The incorporation of this novel technology to the existing plant has allowed the cooling temperature to increase by 13 °C while maintaining the same condensing pressure. As a result, significant net increase in electrical efficiency, reduction of auto-consumption and cut down on annual cooling water consumption were obtained.

The Hygroscopic cycle is a novel proprietary power cycle characterized by working with hygroscopic compounds which optimize the condensation of the turbine output steam in a steam absorber. This technology can be incorporated in any power plant that uses a Rankine cycle, obtaining higher electrical efficiency without limiting the cold sink temperature and without cooling water consumption. The novelty of this article is that Hygroscopic cycle is experimentally investigated in a test power plant with high concentrations of lithium bromide solution in water in the cooling reflux to analyze the effect on condensing temperature, condensing pressure, power output and efficiency. Mass concentration of lithium bromide in the cooling reflux stream ranges from 45 to 65%. The increase in salt concentration at the cooling reflux stream allows the condensing temperatures to be significantly increased by more than 15 °C in a Hygroscopic cycle with respect to a Rankine cycle. Results also show that it is possible to decrease the turbine outlet condensing pressures for the same condensing temperature. Thereby, as mass concentration of lithium bromide is increased the gross electric power output increases with reference to a Rankine cycle for the same condensing temperature. The minimum increments in net electric power output and electrical efficiency are 7.6% and 2.6% respectively.

Power output of power plant is substantially reduced when cooling is conducted at high ambient temperatures. The problem is also intensified at locations with water scarcity. Hygroscopic cycle is a novel technology that improves Rankine cycle and solve those problems in an effective way. Hygroscopic Cycle Technology works with hygroscopic compounds that increase the cooling temperature for each output pressure of the steam turbine and uses dry coolers for refrigeration. As a result, much better cooling conditions are obtained and water consumption is avoided. Higher electrical performance is obtained without the limitation of high ambient temperatures. In this paper, Hygroscopic Cycle is experimentally studied. Results have been obtained in a test plant with a live steam generation capacity of 110 kg/h. This article shows cooling temperatures increase obtained for high mass concentrations from 45 to 65% of lithium bromide solution in water at the cooling reflux stream. The increase of the saline concentration in the cooling reflux significantly increase the cooling temperatures by more than 15 °C in a Hygroscopic cycle with respect to a Rankine cycle, for the same condensing pressure. Consequently, it reduces the electrical power required by the chosen cooling system, as well as to save all the cooling water consumption needed for cooling towers in other installations. Hygroscopic Cycle with high concentrations is able to increase up to 17.41% the net electrical power output respect to Rankine cycle.