No 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.

An increasing share of the weather-dependent RES generation in the power system leads to the growing importance of flexibility of conventional power plants. They were usually designed for base load operation and it is a challenge to determine the actual long-term cycling costs, which account for an increase in maintenance and overhaul expenditures, increased forced outage rates and shortened life expectancy of the plant and components. In this paper, the overall impact of start up costs is evaluated by formulating and solving price based unit commitment problem (PBUC). The electricity spot market is considered as a measure for remunerating flexibility. This approach is applied to a real-life case study based on the 70 MWe PGE Gorzόw CCGT power plant. Different operation modes are calculated and results are used to derive a mixed integer linear programming (MILP) model to optimize the operation of the plant. The developed mathematical model is implemented in Python within the frame of the PuLP library and solved using GUROBI. Results of the application of the method to a numerical example are presented.