Thermal Storage Options Research Articles

Ambient loop district heating and cooling networks with integrated mobility, power and interseasonal storage

This paper describes a heat pump investigation for GreenSCIES (GS), a fifth Generation district heating and cooling (5DHC) network in Islington, London. The paper describes the GreenSCIES concept integrating Mobility, Power and Heat into a Smart Local Energy System (SLES). At the heart of the system is an ultra-low temperature ambient loop network, which permits bi-directional flow within the pipes to allow energy exchange between heating and cooling customers at different times and in different locations, depending on where demand is at any given time. An existing data centre provides the primary source of waste heat for the scheme. Heat pumps in distributed energy centres are utilised to amplify the temperature of the ambient loop to deliver heat in connected buildings. The energy centres integrate heat pumps with building-mounted solar photovoltaic (PV) systems and electric vehicle (EV) charging points. The paper provides an overview of the integrated SLES concept, focussing on the heat pump selection and the short and long-term thermal storage options designed for the scheme. The results show that even the smaller constructible ‘New River’ scheme will save 5,000 tons of CO2e annually. This will tend to 100% as the grid decarbonise further. Therefore, the GS SLES concept applied to urban areas could deliver significant carbon emission savings in the UK and elsewhere. Practical application: Project GreenSCIES, is a detailed design study to develop a Smart, Local Energy System (SLES) for a large community in the London Borough of Islington. Our consortium have developed an innovative SLES concept, centred around a fifth generation district heating and cooling network. The GS ambient loop systems have negligible losses and much greater efficiencies than traditional district heat networks. As recognised by the UK Government’s Heat and Buildings Strategy, ambient loop systems should be considered where large-scale neighbourhood regeneration occurs. The proposed SLES concept applied to wider urban areas could deliver significant carbon emission savings in the UK.

Role of Subsurface Geo-Energy Pilot and Demonstration Sites in Delivering Net Zero

Recent research suggests that the effects of climate change are already tangible, making the requirement for net zero more pressing than ever. New emissions targets have been announced in April 2021 by various governments, including by the United Kingdom, United States, and China, prior to the Conference of the Parties (COP26) in Glasgow. Part of the solution for net zero will be geo-energy technologies in the subsurface, these include: mine water geothermal, aquifer thermal energy storage (ATES), enhanced geothermal systems and other thermal storage options, compressed air energy storage (CAES), and carbon dioxide capture and storage (CCS) including bioenergy CCS (BECCS). Subsurface net zero technologies have been studied by geologists at laboratory scale and with models, but also require testing at greater-than laboratory scale and in representative conditions not reproducible in laboratories and models. Test, pilot and demonstration facilities aid rock characterisation process understanding and up-scaling, and thereby provide a bridge between laboratory testing and computer modelling and full-scale operation. Examples of test sites that have progressed technology development include the Otway International Test Centre (Australia, CCS) and the Äspö Hard Rock Laboratory (Sweden, geological radioactive waste disposal). These sites have provided scale up for key research questions allowing science issues of relevance to regulation, licencing and permitting to be examined at scale in controlled environments. Successful operations at such sites allow research to be seen at first hand to inform the public, regulators, supply chain companies and investors that such technologies can work safely and economically. A Geological Society conference on the “Role of subsurface research labs in delivering net zero” in February 2021 considered the value of test sites and gaps in their capability. Gaps were identified in two areas: 1) test facilities to aid the design of low cost, high resolution, unobtrusive seismic and other monitoring for a seismically noisy urban environment with a sensitive human population, for example for ATES in urban areas; and 2) a dedicated through-fault zone test site to understand fault transmissivity and reactivation. Conference participants also recommended investment and development in test sites, shared facilities and risk, joint strategies, data interoperability and international collaboration.

Heat transfer behavior of elemental sulfur for low temperature thermal energy storage applications

Elemental sulfur provides a low-cost, high-performance thermal storage option for a wide range of applications and over an exceptionally wide range of temperatures (50 °C to over 600 °C). In previous efforts we have shown impressive performance for 200–600 °C, while in this study we examine the low-temperature (50–200 °C) thermal charge and discharge behavior of isochoric sulfur-based storage using a detailed computational model solving for the conjugate heat transfer and solid-liquid phase change dynamics. The model provides excellent agreement with experimental results. We show that sulfur exhibits lower viscosity because of reduction in the chain-length of polymeric sulfur caused by trace amounts of organic substances resulting in attractive charge and discharge performance. The results from the parametric analysis of pipe diameter on the charge and discharge heat transfer characteristics are used to develop a simple, generalized correlation that relates the transient sulfur temperature and liquid fraction evolution as a function of dynamically evolving buoyancy-Fourier number due to the solid-liquid phase change. This solid-liquid buoyancy-Fourier, BFs-l, correlation can be used for effectively designing sulfur-based thermal energy storage systems for transient operation in low temperature applications.

Synthesis and Characterization of Thermochemical Storage Material Combining Porous Zeolite and Inorganic Salts

ABSTRACTThermal energy storage has the potential to decarbonize the heating sector, facilitating the use of renewable energy sources, in particular solar thermal energy. In this paper we present a study on thermochemical storage material composed of inorganic salts hosted in the porous matrix of zeolite 13X; we prepared a series of composites containing different amounts of inorganic salts – MgCl2, MgSO4 by impregnation method and we characterized them by multiple experimental techniques: energy storage and adsorption/desorption rates were assessed using simultaneous thermal analysis by coupling thermogravimetric and differential scanning calorimetry, microstructure, and composition were assessed through scanning electron microscopy and energy-dispersive X-ray spectroscopy. Finally, thermal conductivity was measured by laser flash analysis. With our composite material, we achieved an energy density of 400 kJ/kg across the temperature range 30–150°C and a 35% increase in thermal conductivity by adding 1% of multiwall carbon nanotubes. These features make the material an interesting option for thermal storage in buildings. We attribute the behavior of the material to the combination of large zeolite-specific area coupled with the heat of water sorption/hydration of MgCl2, MgSO4.

Review of control strategies for improving the energy flexibility provided by heat pump systems in buildings

The present work constitutes a review of the existing literature on supervisory control for improving the energy flexibility provided by heat pumps in buildings. A distinction was drawn between rule-based controls (RBC) and model predictive controls (MPC), given the clear differences in their concept and complexity. For both kinds, the different objectives claimed by these strategies have been reviewed, as well as the control inputs, disturbances and constraints. Notably in MPC, the monetary objective (reduction of the energy costs) has been the most utilized in the literature, therefore the authors advocate for the further study of other objectives related to energy flexibility. Further than the control strategies themselves, the different thermal storage options (necessary to activate the flexibility) have also been reviewed, the built-in thermal mass seeming more cost-effective than water buffer tanks in this regard. Based on these conclusions, recommendations for further research topics are drawn.

Geothermal Heat Pump Plant Performance in a Nearly Zero-energy Building

On the behalf of reaching EU directive 2010/31/EU energy performance targets and fulfilling nearly zero-energy energy buildings (nZEB) requirements by the end of 2020, utilization of renewable energy sources becomes important. Renewable solar and ground energy can be efficiently utilized by a hybrid geothermal heat pump with a solar thermal storage, which is expected to yield high seasonal coefficient of performance (SCOP) making it attractive to consider in nZEB design. This numerical study investigates the impact of various ground heat exchangers and thermal storage options along with their possible combinations on heat pump plant heating/cooling performance in the design of commercial hall-type nZEB located in cold climate of Hämeenlinna, Finland. Components applied in a numerical study were energy piles, vertical boreholes (heat wells), solar collector and/or exhaust air heat as a thermal storage source. A whole year dynamic simulations were performed in IDA-ICE simulation environment, where detailed custom ground-source heat pump (GSHP) plants were modelled. Results revealed GSHP plant to be favorable heat source option in nZEB design. Application of thermal storage enabled to reduce energy piles field by more than two times. Proposed exhaust air thermal storage option performed highly efficient in comparison to solar thermal storage.

Wind energy integration via residential appliances

In this paper cold and thermal storage options via wind energy surplus are examined aiming to enable higher wind integration. A case study in Greece with an installed wind farm (WF) was investigated reviewing the possibilities for higher renewables integration using thermostatically controlled loads (TCLs), analysing thermal and cold storage possibilities according to the needs of the local municipalities. The basic aim is to describe the idea of an aggregated system with a number of residential freezers, in order the wind power to be stored in the residential cold stores aiming at maximizing the benefit to the grid, utility or cold store owner avoiding at the same time wind curtailment. In addition, for thermal storage, by calculating thermal losses of the building, ventilation losses and adding up internal thermal gains of the building the space heating needs can be calculated.

Levelized Cost of Heat for Linear Fresnel Concentrated Solar Systems

In this paper, a deep investigation upon levelized cost of heat (LCOH) produced by small-scale solar linear concentrating Fresnel collectors (CSLFC) is proposed. Solar industrial process heat applications have temperature requirements from about 60°C to 260°C. CSLFCs can effectively integrate conventional fossil fuel thermal systems. The study is addressed to assess technology cost projection needed to achieve competitive LCOH. So, on the basis of a framework specifically developed for these economic assessments, the best investment scenarios, in terms of industrial application, geographical location and technical design solutions, where to effectively apply the technology of CSLFC, are highlighted.The analysis has been focused on specific cost of several existing CSLFCs associated with declared performances at different operating temperatures. Two main classes of CSLFC with different total efficiency (optical and thermal) corresponding to various design solutions and specific cost were selected. The expected performances in the whole application temperature range have been evaluated through Glayx Tech proprietary simulation code, including optical and thermal unsteady analysis.A huge database coming from full CSLFC simulation varying latitude, yearly DNI, operating fluid, outlet temperature, thermal storage options, has been collected. CLSFC design and performance requirements are the key-choice to achieve competitive LCOH: the use of high efficiency – high cost components is not always rewarding in terms of final LCOH and must be attentively decided basing on site, irradiation, heat quality and LCOH target. In this perspective, CLSFCs are the most promising for industrial small scale heat applications since they show the greatest potential to reduce manufacturing costs.

Advancements in the Field of Direct Steam Generation in Linear Solar Concentrators—A Review

Direct steam generation in parabolic trough or linear Fresnel collectors represents one interesting technological option for concentrating solar electricity production. Today's state of the art characterized by the first commercial plants in operation is a result of more than 20 years of intensive research on this topic. This article provides a review on the key results from research that includes physical effects like heat transfer and pressure drop in horizontal boiler tubes, plant layout considerations, and thermal storage options. An overview on test and demonstration facilities as well as on commercial plants is given, leading to an outlook on the next generation of direct steam generation systems.

Large-scale urban renewable electricity schemes – Integration and interfacing aspects

Large-scale renewable electricity schemes (RES) for urban areas are investigated here with emphasis on RES integration and interfacing with the energy system to limit the outflow of RES electricity outside the city boundaries. Different electricity-to-thermal energy strategies to supply also heating and cooling demands were investigated to enable higher than usual RES shares through converting surplus renewable electricity into thermal energy which often constitute a major part of the end-use energy in a city. Case examples from a southern climate (Shanghai) with distributed PV schemes and a northern city (Helsinki) with off-shore seaside wind power were analyzed. The results from the Shanghai case indicate that when using thermal storage options, 2-folding of the PV capacity from the self-use limit of PV could be possible. With optimal electricity-to-thermal energy strategies and energy management, a 40–65% solar fraction of yearly electricity could be possible. In the Helsinki climate with wind power coinciding with the seasonal load peak, RES may satisfy beyond 30% of all energy and beyond 70% of all electricity demand annually. The size of thermal storage needed in the above cases is between 10 and 100GWh. A higher RES use leads to higher spatial power flows and power variability in the city which requires more sophisticated control strategies and flexible auxiliary power options to handle transmission bottlenecks.

Electric Thermal Storage Option for Nova Scotia Power Customers: A Case Study of a Typical Electrically Heated Nova Scotia House

ABSTRACT Nova Scotia Power (NS Power) offers an incentive to the owners of electrically heated houses in Nova Scotia to switch from conventional electric baseboard heaters to electric thermal storage (ETS) systems and enjoy the rebated time-of-day (TOD) electricity rates. For this study, a statistically representative, electrically heated, existing Nova Scotia house was modeled in the building energy simulation software ESP-r to estimate its peak heating load and hourly heating energy consumption for an entire year. Based on the ESP-r simulation results, the ETS system was sized for the house, and the energy cost saving realized with this system was estimated. It was found that, compared to conventional electric baseboard heating system, the ETS heating system can save 41–48% in the heating cost on an annual basis, yielding a simple-payback (SPB) period for this retrofit of less than eight years.

Optimal Technology Selection and Operation of Commercial-Building Microgrids

The deployment of small ( < 1-2 MW ) clusters of generators, heat and electrical storage, efficiency investments, and combined heat and power (CHP) applications (particularly involving heat-activated cooling) in commercial buildings promises significant benefits but poses many technical and financial challenges, both in system choice and its operation; if successful, such systems may be precursors to widespread microgrid deployment. The presented optimization approach to choosing such systems and their operating schedules uses Berkeley Lab's Distributed Energy Resources Customer Adoption Model (DER-CAM), extended to incorporate electrical and thermal storage options. DER-CAM chooses annual energy bill minimizing systems in a fully technology-neutral manner. An illustrative example for a hypothetical San Francisco hotel is reported. The chosen system includes one large reciprocating engine and an absorption chiller providing an estimated 11% cost savings and 8% carbon emission reductions under idealized circumstances.

Sensible thermal storage in rock beds for space conditioning: a state of the art study

SYNOPSIS This paper presents a state-of-the-art study on sensible thermal storage options. Various thermal models for rockbed storage system are reviewed and relevant studies on the performances of rockbed storage systems are presented. It is found that the rockbed storage system is more suitable for solar space conditioning and the collection/storage option for solar energy applications. Further work on system parameters and a comparative assessment of the rockbed storage sytem should be carried out in this direction.