• Energy Research

Seasonal Thermal Energy Storage (STES) is widely researched for having benefits in that it utilizes excess energy which would be wasted otherwise. The purpose of this study is to analyze energy efficiency of seasonal solar thermal energy system as heating system for greenhouses and compare it with conventional variable air volume (VAV) heating system. Greenhouse was chosen as a simulation model because it requires constant and stable heating through winter season to extend growing season and also because greenhouse can provide enough area to install solar collectors and heat storage tanks. The proposed seasonal solar thermal energy storage system consists of solar thermal collector, fully mixed heat storage tank, and VAV system. Energy simulation was conducted in two steps: heat storing in summer season, and heating in winter season. For greenhouses with area sizing 1600 m2, solar thermal collector of 1250 m2 and heat storage tank of 2000 m3 were designed. TRNSYS 17 and engineering equation solver (EES) were implemented for simulation and calculation of the systems thermal data. Simulation results showed the tank water temperature rising up to optimal temperature (95 oC) before heating season, and STES heating contributed to 55% of total heating load. Consequently, 30% of total heating cost was cut down showing energy efficiency of seasonal solar thermal energy storage system.

This study regards the evaluation of the performance of a thermally stratified tank as an intermediate combi-storage tank for a solar-driven residential thermal system coupled to a seasonal energy storage system. In such applications, the efficient operation of this intermediate tank is crucial to the enhanced exploitation of the harvested solar energy and the minimization of heat losses. In this perspective, the development of a dedicated model in TRNSYS software and its validation with experimental results are investigated. With respect to the simulation model’s discretization, it was found that beyond 60 nodes, the benefits to the model’s accuracy are almost negligible. Comparing the experimental data with the simulation’s results, the predicted temperature profile converges accurately to the measured values under steady-state conditions (threshold stabilization period of 1000 s after charging/discharging has occurred). However, the response of the model deviates considerably under transient conditions due to the lack of detailed inertia modeling of both the tank and the rest of the system components. Conclusively, the developed 1D simulation model is adequate for on- and off-design models where transient phenomena are of reduced importance, whereas for dynamic and semi-dynamic simulations, more detailed models are needed.

Sweden is only utilizing half of the available excess heat. To utilize more of the excess heat a seasonal thermal energy storage could be implemented to store excessed heat from the summer when the demand is lower to the winter when the demand is higher. This can be achieved by an integration of a seasonal thermal energy storage to the district heating system. A seasonal thermal energy storage may also reduce the need of the system’s peak load, which often is economically costly and adversely affect the environment. The purpose of the paper is to investigate the possibility for Skövde Värmeverk to implement a seasonal thermal storage. The paper is performed by a literature collection and calculations are made by software programs. The result shows that it is technically possible to implement a pit thermal energy storage and a borhole thermal energy storage, but no outcome shows a profitability within 20 years. A pit thermal energy storage can replace the system’s peak load up to 79 percent and a borhole thermal energy storage up to 2,8 percent. The most suitable case for Skövde Värmeverk is to install a pit thermal energy storage with a storage capacity of 4 GWh.

Thermochemical heat storage has the potential to store a large amount of thermal energy from renewables and to cope with the seasonal mismatch of energy demand and supply, ideally without energy losses typical of sensible heat storage. However, in order to have a commercially attractive system, research at material, reactor, and ultimately at system level is still required. The aim of this work is to investigate the current state-of-the-art research at prototype- and system-scale, and to estimate the performance of ideal long-term low-temperature thermochemical storage systems in terms of energy densities and storage capacity costs. First, a review on existing systems based on solid/gas reactions is carried out. Especially for open systems, the choice of adsorbents rather than salt hydrates as active materials is prominent due to their enhanced stability. However, high material costs and desorption temperatures, coupled with lower energy densities, decrease their commercial attractiveness. Then, the performance of ideal open thermochemical heat storage systems based on solid/gas reactions are estimated for different active materials among which salt hydrates, an adsorbent, and an ideal composite. The common reference scenario assumes that the seasonal space heating energy of a passive house has to be stored. The results show that the open system based on a composite material, can represent a valid compromise between hydrothermal stability and storage capacity costs. However, it results in a very large system for the assumed reference scenario conditions. The performances of open systems are then compared with the ideal performance of closed solid sorption systems. The results show that closed systems are in general more expensive and less compact for the assumed reactor layouts. Finally, liquid sorption systems from the literature are compared with the open and closed solid sorption systems. The results show that most of the liquid systems are not able to achieve the minimum temperature required by the consumer in the reference scenario. However, a liquid sorption system based on NaOH-H2O can in principle satisfy the consumer needs and result more compact and less expensive than solid sorption systems based on pure adsorbents and certain salt hydrates. Beside research at material- and reactor-scale, integration of thermochemical storage at grid level has to be investigated to assess its techno-economic feasibility based on their performance and interactions with production and consumption technologies.

This work is partially funded by the Ministerio de Ciencia, Innovación y Universidades de España (RTI2018-093849-B-C31 - MCIU/AEI/FEDER, UE) and the Ministerio de Ciencia, Innovación y Universidades - Agencia Estatal de Investigación (AEI) (RED2018-102431-T). The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2017 SGR 1537). GREiA is a certified agent TECNIO in the category of technology developers from the Government of Catalonia. This work is partially supported by ICREA under the ICREA Academia programme. This project has received funding from the European Union´s Horizon 2020 research and innovation programme under the No 764025 (SWS-Heating). Alicia Crespo would also like to acknowledge the financial support of the FI-SDUR grant from the AGAUR of the Generalitat de Catalunya and Secretaria d’Universitats i Recerca del Departament d’Empresa i Coneixement de la Generalitat de Catalunya.

Sensible Heat Storage is the most common method of thermal energy storage, particularly in the form of hot water tanks. Essentially, sensible heat storage systems work by charging them with heat from a higher temperature source to raise the temperature of the thermal store, and by extracting heat to discharge them. On a larger scale, these sensible heat stores should be designed to store heat long term over seasons, which allow the thermal storage systems to be charged using solar thermal systems to then supply heat over colder periods and can be applied in an array of buildings, including individual dwellings and larger buildings. These seasonal storage systems consist of: Tank Thermal Energy Storage (TTES), Pit Thermal Energy Storage (PTES), Borehole Thermal Energy Storage (BTES) and Aquifer Thermal Energy Storage (ATES). The aim of this report is to provide useful information about the different construction techniques for the mentioned systems in addition to FP7 Einstein Project, where a big information research has already been done, analysing the main characteristics that interfere in the various proceedings. In addition, a general study for the three different CHESS-SETUP pilots is done regarding the availability and constraints of every case to introduce the different technologies. Finally, in order to ensure the correct operation of the installations, some guidance of the different types of maintenance is done as well as maintenance plans for the different elements of the system.

Underground Energy Storage (UES) Program activities during the period from April 1984 through March 1985 are briefly described. Primary activities in seasonal thermal energy storage (STES) involved field testing of high-temperature (>100/sup 0/C (212/sup 0/F)) aquifer thermal energy storage (ATES) at St. Paul, laboratory studies of geochemical issues associated with high-temperatures ATES, monitoring of chill ATES facilities in Tuscaloosa, and STES linked with solar energy collection. The scope of international activities in STES is briefly discussed.

Architecture and The Built Environment ; Architectural Engineering + Technology

The Pacific Northwest Laboratory (PNL) leads the U.S. Department of Energy`s Thermal Energy Storage (TES) Program. The program focuses on developing TES for daily cycling (diurnal storage), annual cycling (seasonal storage), and utility-scale applications [utility thermal energy storage (UTES)]. Several of these storage technologies can be used in a new or an existing power generation facility to increase its efficiency and promote the use of the TES technology within the utility and the industrial sectors. The UTES project has included a study of both heat storage and cool storage systems for different utility-scale applications. The study reported here has shown that an oil/rock diurnal TES system, when integrated with a simple gas turbine cogeneration system, can produce on-peak power for $0.045 to $0.06 /kWh, while supplying a 24-hour process steam load. The molten salt storage system was found to be less suitable for simple as well as combined-cycle cogeneration applications. However, certain advanced TES concepts and storage media could substantially improve the performance and economic benefits. In related study of a chill TES system was evaluated for precooling gas turbine inlet air, which showed that an ice storage system could be used to effectively increase the peak generating capacity of gas turbines when operating in hot ambient conditions.