Pumped Thermal Electricity Storage Research Articles

Performance and cost evaluation of an innovative Pumped Thermal Electricity Storage power system

Wind and solar energy have a time dependent nature which is their main disadvantage. To overcome this drawback, energy storage systems need to be set up. High-temperature Pumped Thermal Electricity Storage employing packed bed as storage medium can be an attractive solution. For this reason, in the present paper, firstly, an in-depth literature review on Pumped Thermal Electricity Storage and on storage materials is presented with the aim of assessing the current state of the art. Then, a new Pumped Thermal Electricity Storage configuration is proposed and tested. An electric heater is used to convert electrical energy into thermal energy, a single heat exchanger is installed and air is used as heat transfer fluid. A 1D packed bed model is used to simulate the thermal performance of the hot and cold storage. In the storage model also the pressure drop is taken into account. The plant mathematical model is implemented in Matlab environment while the heat transfer fluid and bed material properties are taken from CoolProp and NIST database, respectively. An energy and cost analysis is performed in order to assess the feasibility of the system. Five types of high storage density material, two bed material shapes and different maximum plant temperature are tested and their influence on the technical and economic characteristics and performance of the plant is assessed.

A novel Pumped Thermal Electricity Storage (PTES) system with thermal integration

Power to heat technologies are becoming more and more important due to the extreme need of energy storage solutions to help manage the mismatch between supply and demand of electric power in grids with a large penetration of intermittent renewable energy systems. Several Electric Energy Storage (EES) technologies have been proposed in the literature and some of them have been built as pilot or commercial plants, with different characteristics in terms of storage capacity, response time and roundtrip efficiency. In this paper, the attention was focused on Pumped Thermal Electricity Storage (PTES), which is a technology that stores electric energy as heat by means of Heat Pumps (HP) and converts it again to power with a Heat Engine (HE). In this study, a hybrid PTES application was studied, which took advantage of a low-grade heat source to boost the electric round-trip efficiency of the system beyond 100%. The main idea was to exploit the heat source to reduce the HP operational temperature difference; this thermal integration boosted the HP COP and thus the electric efficiency of the whole system. A Matlab numerical model was developed, using the thermodynamic properties of the Coolprop data base, and the steady state operation of a PTES system composed by a vapor-compression HP and an Organic Rankine Cycle (ORC) we simulated. Heat source temperature values ranging from 80°C to 110°C and different working fluids were studied. Among the refrigerants, which comply with the latest European environmental legislation, the most promising fluid was R1233zd(E): with such fluid a maximum round trip-efficiency of 1.3 was achieved, when the heat source temperature reaches 110°C and the machinery isentropic efficiencies is 0.8, the heat exchangers pinch points is 5K and the ORC condensation temperature is 35°C.

Performance evaluation and parametric choice criteria of a Brayton pumped thermal electricity storage system

A more realistic thermodynamic model of the pumped thermal electricity storage (PTES) system consisting of a Brayton cycle and a reverse Brayton cycle is proposed, where the internal and external irreversible losses are took into account and several important controlling parameters, e.g., the pressure ratio and heat flows of the two isobaric processes in the Brayton cycle, are introduced. Analytic expressions for the round trip efficiency and power output of the PTES system are derived. The general performance characteristics of the PTES system are revealed. The optimal relationship between the round trip efficiency and the power output is obtained. The influences of some important controlling parameters on the performance characteristics of the PTES system are discussed and the optimally operating regions of these parameters are determined.

Performance optimization and comparison of pumped thermal and pumped cryogenic electricity storage systems

Two generic models, one of a PTES (pumped thermal electricity storage) system and another of a PCES (pumped cryogenic electricity storage) system, are established in which the finite-rate heat transfer and external heat leakage losses are considered and several important parameters connecting the charging and discharging phases are introduced. Analytic expressions for the round trip efficiency and power output of PTES and PCES systems are derived. The influences of some important parameters on the performance characteristics of the PTES and PCES systems are presented, and the optimally operating region of each system is determined. The performances of PTES and PCES systems are compared. The advantages of the PTES system are highlighted. The effects of external heat leakage losses are discussed in detail. Notably, the results reveal that external heat leakage losses must be considered in the performance investigation of the PTES system.

The CHEST (Compressed Heat Energy STorage) concept for facility scale thermo mechanical energy storage

Electric energy storage is considered to become a key element of the future electricity infrastructure. PTES (Pumped thermal electricity storage) represents an emerging thermo mechanical storage technology based on the transformation of low temperature heat by surplus electricity. After transformation, the high enthalpy heat is stored. During the discharge process, this heat is used to drive a thermodynamic cycle generating electricity. This concept allows storage of energy in the multi-MW range for several hours without any specific geographical requirements. Various combinations of thermodynamic cycles and storage types have been suggested for implementation using either low temperature storage (<200 °C) or high temperature storage (>500 °C). In contrast to these PTES concepts, the Compressed Heat Energy STorage (CHEST) concept presented in this paper is based on a medium temperature conventional Rankine cycle combined with a latent heat storage unit according to the current state of the art. This concept attains an efficiency of 70% while the maximum temperature is below 400 °C. The integration of heat provided by low temperature sources during the charging process represents an additional option of the CHEST concept; losses can be compensated, the electric work delivered during the discharge process might even outweigh the work needed during the charging process.

Thermodynamic analysis of pumped thermal electricity storage

The increasing use of renewable energy technologies for electricity generation, many of which have an unpredictably intermittent nature, will inevitably lead to a greater need for electricity storage. Although there are many existing and emerging storage technologies, most have limitations in terms of geographical constraints, high capital cost or low cycle life, and few are of sufficient scale (in terms of both power and storage capacity) for integration at the transmission and distribution levels. This paper is concerned with a relatively new concept which will be referred to here as Pumped Thermal Electricity Storage (PTES), and which may be able to make a significant contribution towards future storage needs. During charge, PTES makes use of a high temperature ratio heat pump to convert electrical energy into thermal energy which is stored as ‘sensible heat’ in two thermal reservoirs, one hot and one cold. When required, the thermal energy is then converted back to electricity by effectively running the heat pump backwards as a heat engine. The paper focuses on thermodynamic aspects of PTES, including energy and power density, and the various sources of irreversibility and their impact on round-trip efficiency. It is shown that, for given compression and expansion efficiencies, the cycle performance is controlled chiefly by the ratio between the highest and lowest temperatures in each reservoir rather than by the cycle pressure ratio. The sensitivity of round-trip efficiency to various loss parameters has been analysed and indicates particular susceptibility to compression and expansion irreversibility.