EXPERIMENTAL WORK AT LABORATORY SCALE:
The CHEST system is formed by a high temperature heat pump (HTHP), a high temperature thermal energy storage (HT-TES) and an ORC unit. Electricity is consumed by the HTHP and the produced heat is stored in the HT-TES, to be used later on by the ORC unit and produce electricity. In addition, a novel heat engine (based on isobaric expansion (IE)) has been developed in order to increase cycle efficiency if integrated into the system.
The HTHP, HT-TES, heat engine and ORC prototypes were designed, manufactured and individually characterized at responsible partners’ laboratory:
• A 10kWe HTHP that uses an environmentally friendly refrigerant (R1233zd(E)) able to operate at high evaporating temperatures (70ºC to 95ºC) and high condensing temperatures (approximately 146ºC) has been built and tested. Measured COP values ranging from 3 to almost 7 were achieved.
• A novel design of a HT-TES system based on PCM has been developed and prototype built (melting temperature of the selected PCM is 133ºC). The system is formed by a latent heat storage unit (LT-TES) of 2,1 m3 and a sensible heat storage unit (SH-TES) of 2 m3.
• A novel ORC prototype has been built, commissioned and tested, including an over 10 kWe nominal power piston expander with a built-in novel variable valve timing mechanism. Experimental results demonstrate the advantageous implementation of the real time control of the expander inlet valve timing to increase the efficiency of the prototype.
• A novel isobaric expansion heat-engine pump prototype has been successfully built, commissioned and tested. Experimental results demonstrate the great potential of IE engines as a technology for conversion of heat to mechanical energy, particularly in low temperature applications.
In the last stage of the project the individual prototypes have been integrated into the whole CHEST prototype and tests were carried out both as full and as partial cycles to investigate the system performance. The results show that the theoretical concept of Compressed Heat Energy Storage for Energy from Renewable sources (CHESTER) works successfully at a laboratory scale. Based on the experimental results, estimations for large scale CHEST systems have been made, concluding that roundtrip efficiencies in the range of 68% would be attainable based on the current prototypes and identified optimizations.
THEORETICAL WORK TO ADVANCE ON THE CHEST CONCEPT:
One of the objectives of the CHESTER project is to establish the theoretical basis for the upscaling and optimization of the CHEST system. After five years of research in the CHESTER project with plenty of results from experiments, market potential and business model opportunity studies, the consortium has drawn the major conclusions and established a roadmap to outline the current and future potential applications of the Compressed Heat Energy Storage (CHEST) system.
An interesting business case study was found for an Eco-Industrial Park in Denmark. This kind of application, which combines the storage of both heat and electricity, makes the best use of the CHEST concep and engages several revenue streams, resulting in a positive business model already at MW scale, with a return on investment within 5 to 6 years for the analyzed boundary conditions.
The CHESTER consortium has also analysed the determining factors for obtaining a good economy with the use of the CHEST system, and identified the following:
• Effort needs to be made to reduce the investment cost of the Latent Heat Thermal Energy Storage (LHTES)
• Favourable taxation on electricity
• High load and long operating hours of the system
• Excess of electricity and/or heat availability/mutualised (sector coupling)
A general conclusion of the techno-economic studies is that the CHEST system is well suited for sector coupling and is likely to fit into the energy systems of the future, where renewables have a higher penetration into the energy system (both heat and electricity production).
