Abstract
Improvement of flexibility is one of the key challenges for the transformation of the Polish Power System aiming at a high share of renewable energy in electricity generation. Flexible and dispatchable power plants will contribute to this ongoing transformation process as they compensate for fluctuations in electricity generation from renewable energy sources such as wind and photovoltaics. In this context, CAES storage tanks are currently the only alternative to storage facilities using pumped-storage hydroelectricity due to the possibility of obtaining the appropriate energy capacity of the storage facility. However, a relative disadvantage of these plants is the heat loss caused by the cooling of the air after compression. The basic elements of the CAES warehouse are: an air compression station, a compressed air reservoir that is also a storage facility (in the existing solutions, these are underground caverns), an expansion station with combustion chambers and gas turbines, and a generator. A key aspect of CAES is the optimal configuration of the thermodynamic cycle. In this paper, the situation of cooperation between the current conventional power plants and wind farms is first analysed, and then, based on thermodynamic models, the process of storing thermal and electrical energy in the CAES system coupled with heat recovery after the gas turbine is analysed. A solution with a ground heat exchanger was also proposed, as the soil, due to its properties, may serve as a thermal energy storage. The paper also analyzes the discharge of the heat storage based on CFD approaches. The ground can be charged during the cooling down of the compressed air. On the other hand, thermal energy was recovered when water flowing to the heat customers was heated. On the basis of non-stationary calculations, the heat stream received from the underground thermal energy storage was estimated.
Highlights
Due to the development of renewable energy, the variability of operation of conventional units will be one of the most noticeable consequences of the transformation of the Polish Power System (PSE, Polskie Sieci Elektroenergetyczne SA) [1], and this involves one of the most important aspects of PSE, namely its stability
It should be remembered that the activities of the UN significantly affect the global energy policy of most countries or even regions of the world, and in particular the policy of the European Union. It is in the framework of climate and energy policy that the EU has defined three key objectives until 2030: 1. a reduction of at least 40% in greenhouse gas emissions, 2. ensure at least a 27% share of energy from renewable sources in total energy consumption, Precisely these targets were adopted by the European Council of 23-24 October 2014 [2]
Assuming thermodynamic parameters as for the existing installations, both for the gas turbine and for the compressor, the calculations were carried out with the assumption of a generator capacity of 30 MWe. The efficiency of this system according to equation (10) amounted to ηηCCCCCCCC =0.52, which is a satisfactory value given the volatility of renewable energy sources such as wind and photovoltaics
Summary
Due to the development of renewable energy, the variability of operation of conventional units will be one of the most noticeable consequences of the transformation of the Polish Power System (PSE, Polskie Sieci Elektroenergetyczne SA) [1], and this involves one of the most important aspects of PSE, namely its stability. This single case of wind farm capacity reduction is obviously not too much of a challenge for the Transmission System Operator (TSO) (in the absence of emergency situations, e.g. sudden failure of a large unit in the system or failure of several units) Such a power loss (frequency drop in the system) can be quickly replenished by launching several hydropower units in pumped-storage power plants for generation operation mode, using the possibility of increasing capacity on cross-border connections in the direction of import, as well as by forcing the opening of regulatory valves in individual conventional generating units, which results in adjusting generation to the load and restoring balance [7]. We present a diagram and model for CFM (Computational Flow Mechanics) analyses, while the third section is an introduction to thermal-FSI analyses and contains the first step, which in this case is the analysis of heat exchange in the ground
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