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Compressed Heat Energy Storage for Energy from Renewable sources

Periodic Reporting for period 1 - CHESTER (Compressed Heat Energy Storage for Energy from Renewable sources)

Reporting period: 2018-04-01 to 2019-09-30

CHESTER project aims to develop a CHEST (Compressed Heat Energy Storage) system that delivers heat and power on demand, making use of the excess renewable and other excess energy sources available. CHEST is an innovative power-to-heat-to-power energy storage system that is comprised by a HTHP, a thermal storage unit and an ORC. It will be managed by an intelligent energy management, storage and dispatchable supply system that integrated in district heating networks will provide a high-efficient and cost competitive solution. The combination of the CHEST system with Smart District Heating leads to a very flexible and smart renewable energy management system that is able to store electric energy with a round trip efficiency of 100% or even higher, site-independent unlike pumped hydro, cyclically stable unlike batteries, able to convert power into heat, able to convert renewable low temperature heat into power, able to store and deliver independently from each other upon request both, heat and power, cost competitive.

The overall objective of CHESTER is to overcome ground-breaking advancements to ensure a high-efficient and cost-competitive CHEST system. A smart system control strategy will be developed, including the implementation of forecasting models, that allows the system to use the energy in the most cost efficient, technically appropriate and flexible way. It will consider the interaction with the electric grid (supply and demand side), the interaction with the district heating network and the integration of other heat sources. A complete 10 kWel laboratory CHEST system will be built and validated in a relevant environment. Overall TRL will be increased from 3 to 5. The CHEST system, a promising energy storage and management system, will be key towards the achievement of energy objectives and mitigating the energy challenges of the future energy system. Large scale plants (multi-MWrange) at cost- competitive costs (130€/kWh) could reach the market by 2025.
- The assessment of the 7 case studies, with very different frameworks, has been performed to evaluate the characteristics and requirements of each and asses the feasibility/suitability to deploy the CHEST system.

- The individual technologies: High Temperature Heat Pump (HTHP), thermal energy storage (TES) unit, Organic Rankine Cycle (ORC) and the ECT Engine-pump, have been simulated in detail to analyse the requirements of each technology. These simulations have provided the initial design of the individual technologies which follows the configuration that maximises the efficiency of the integrated system but also considers manufacturability, costs and operational requirements.

- The model of CHEST has been integrated into a complete energy framework to understand the system performance in its scenario. This analysis has identifyied the general specifications to comply with a variety of potential case studies.

- A PESTEL analysis of the electricity market for the countries of the case studies has been performed. This study has assessed the suitability to introduce CHEST into the corresponding energy network

- Potential refrigerant/lubricants to be used in the HTHP have been tested. Their interactions, viscosity, influence on temperature and mixing behaviour among others were analysed, to identify the most suitable fluids for the heat pump efficient operation.

The main project results are:

- From the TRNSYS models the most promising 2 demonstrators have been identified (Aalborg and Ispaster). From here the requirements of the overall system and individual technologies have been defined.

- The complete thermodynamic analysis of the individual technologies (HTHP, LH-TES, ORC and ECT´s engine-pump) was performed and the detailed design of each one was accomplished. The main achievements are:

o A preliminary prototype of the HTHP was built and experimentally tested over 12 different operating points. The main purpose of these tests was to fully characterize the high temperature compressor while operating with the refrigerant selected for the project.
o A new concept of HT-TES was defined, which is based on a novel LH-TES that considers a special finned tube arrangement and a SH-TES system based on a two-tank configuration.
o A preliminary ORC prototype was built which will serve to fully characterize the variable volume expander while operating with the project´s selected refrigerant and to gain knowledge of the off-design expander control.
o A scalable low-grade heat driven engine pump prototype was designed and built. Preliminary tests had served to validate the system´s functionality and expected efficiencies, as well as to settle the basis for a straightforward up-scaling of the prototype to the project´s required capacity.

- The platform to monitor the selected 2 case studies has been successfully deployed. It reads, processes and displays the data gathered from the sites. A web infrastructure has been developed that stores, processes and displays the data. https://datuma.aiguasol.coop/db/api/. Additionally, a time series forecasting SW has been implemented which forecasts the electricity price and the heat demand.

- The full-scale CHEST system integrated into the energy framework was modelled in TRNSYS. This model will be the basis used by the SEMS to evaluate system performance and maximize economic potential of the system.

- The main conclusions from the economic assessments and business perspective of CHEST, demonstrate the specific market niche of the CHEST system. The main drawback is its rather high current investment costs. However, the new legislation, lower investment costs achieved through learning curve and large-scale deployment are only to improve the economic feasibility of the CHEST system.
The innovative demonstrator’s main technologies have been pre-tested through the correspondent pre-prototypes developed by the partners. The HTHP, the ORC and the ECT engine have been successfully tested, with important initial outcomes.

- A preliminary prototype of the HTHP was built and experimentally tested over different operating points, to fully characterize the high temperature compressor. From these pre-tests initial positive results have been obtained related to the project goals and progress beyond state of the art:

A modified compressor with advanced cooling system allowing refrigerant outlet temperatures of >150ºC.
The use of alternative refrigerant with low GWP.
The selection of the most appropriate lubricant that ensures the compressor operation and durability.
The design of a dedicated thermodynamic cycle to match the specific requirements of the HT-TES system including a smart control strategy to efficiently operate the HP in a wide range of flow rates.

- The implementation of the forecasting algorithm of the gathered monitored data has been carried out successfully. The implementation of these into control strategies and the SEMS implementation will be carried out in the following period.
- The simulation models developed for each technology have provided the characteristics of the components required (compressor, expansor, heat exchangers, etc.) to fulfil each technology’s operating needs and requirements to fulfil with an integrated CHEST. A thoughtful simulation work has allowed to assume some simplifications in the models and get in deep when required, to finally have a confident and validated model of each technology.