Techno-economic assessment of seasonal heat storage in district heating with thermochemical materials

Hydrated salt thermochemical energy storage (TES) is a promising technology for high density energy storage, in principle opening the way for applications in seasonal storage. However, severe limitations are affecting large scale applications, related to their poor thermal and mechanical stability on hydration/dehydration cycling. In this paper, we report the preparation and characterization of composite materials manufactured with a wet impregnation method using strontium bromide hexahydrate (SBH) as a thermochemical storage material, combined with expanded natural graphite (G). In addition to these fully inorganic formulations, an organic polyelectrolyte (PDAC, polydiallyldimethylammonium chloride) was exploited in the structure, with the aim to stabilize the salt, while contributing to the sorption/desorption process. Different formulations were prepared with varying PDAC concentration to study its contribution to material morphology, by electron microscopy and X-ray diffraction, as well as water sorption/desorption properties, by thermogravimetry and differential calorimetry. Furthermore, the SBH/G/PDAC powder mixture was pressed to form tabs that were analyzed in a climatic chamber, which is evidence for an active role of PDAC in the improvement of water sorption, coupled with a significant enhancement of mechanical resistance upon hydration/dehydration cycling. Therefore, the addition of the polyelectrolyte is proposed as an innovative approach in the fabrication of efficient and durable TES devices.

Assessing the potential of seasonal thermal storage for local energy systems: Case study for a neighborhood in Norway

This study focused on the effects of variable renewable electricity (VRE) on full load hours and energy efficiency of fossil-fired power generation in the European Union from 1990-2014. Member states were aggregated into three groups based on the level of VRE penetration. Average full load hours are found to be decreasing since 2006 for all groups. The decrease is most in the group with the highest VRE penetration level with a 53% decline from 2005 to 2014 (while VRE penetration increased from 8% to 25%). For VRE-medium the decrease was 34% from 2007 to 2014 (while VRE increased from 3% to 13%) and for VRE-low 32% (with 1% to 5% VRE penetration increase). Both the financial crisis and the share of VRE show strong correlations with full load hours. Both can explain the developments for VRE-high. For VRE-medium no significant relation with the recession was found and for VRE-low both factors were not significant. For energy efficiency, the commissioning year shows a strong correlation for natural gas and less for coal. Significant impacts are found for average commissioning year and full load hours on the energy efficiency of natural gas-fired power generation but not for coal.

Increased reliance on solar energy conversion technologies will necessarily constitute a major plank of any forward global energy supply strategy. It is possible that solar photovoltaic (PV) technology and concentrating solar thermal (CST) power technology will play roughly equal, but complementary roles by 2050. The ability to increase reliance on CST power technology during this period, however, will be constrained by a number of factors: the large plant sizes dictated by economies of scale, the high associated transmission infrastructure investment cost, and the limitations of current thermal energy storage technologies. Thus, solar technology's main midterm role is seen to be as hybrid solar thermal power plant. The development of low-cost, high-temperature, high-energy density thermal energy storage systems is needed to enable CST plants to be dispatchable and accelerate the deployment of this technology. Thermochemical storage has the best potential to achieve these energy storage requirements and a brief overview of thermochemical energy storage options for CST plants points to high-temperature metal-hydride thermochemical heat energy storage systems. Hydrogen storage systems offer the highest energy storage capacity per volume and are therefore the most likely candidates for achieving the goal of fully dispatchable CST plants. A number of high-temperature metal-hydride thermochemical solar energy storage systems have been proposed and a small number of these systems are currently being investigated and developed. A key component of this work is matching the thermochemical metal-hydride system with a suitable “low-temperature” hydrogen storage material to produce systems that are self-regulating. A summary of the development status of these systems suggests that, despite the technical challenges associated with high-temperature thermochemical energy storage systems, their potential advantages are now seeing development occurring. Although in the early stages, their commercialisation could be fast tracked.

Minimum-cost district heat production systems of different sizes under different environmental and social cost scenarios

Following the ambitious EU plan in cutting the greenhouse emission and replacing conventional heat sources through the presence of renewable energy share inside efficient district heating fields, seasonal storage coupled with district heating plants can have a viable contribution to this goal. However, the performance uncertainty combined with the inadequate assessment regarding the financial potential and the greenhouse emission reduction associated with the deployment of those innovate district heating systems represents a great challenge for sufficiently apply it. Our work tends to explore the prospects for wide-scale deployment of the seasonal storage in the residential sector in the German market. The proposed methodology framework correspondingly based on a multi-objective approach which is applied to optimize the cost against an aggregated environmental metric throughout the life cycle of the proposed system in comparison to their relative conventional heating systems. In this context, the proposed methodology framework is applied to Berlin as a representative for the central European climate zone with consideration for the seasonal and short-term storage systems and their relatively load profiles. The environmental improvement associated with the solar district heating system (SDHS) coupled with seasonal storage in the central European climate zone is heavily weighed enough in decision making for proposing SDHS as a sustainable solution replacing the conventional heat sources. Furthermore, the proposed methodology framework successes in eliminating the yearly system variation. Thus, the yearly solar fraction never goes down below than 97.8% in the investigated climate zone. Overall this study can assist in approving the feasibility of the SDHS with the goal of establishing a more sustainable energy infrastructure in Germany.

The energy mix of Baden-Wurttemberg – one of the most wooded regions of Germany – could be diversified through the optimal valorisation of the existing free potentials of wood resources. Circa 17 PJ of forest residues and landscape wood raw material grow annually over the territory of this federal state. For this reason, an optimisation of the corresponding value chain for power purposes is accomplished in order to identify the most cost-efficient utilisation pathways. Firstly, each unexploited potential of wood resources for up to ten different types of wood chips is estimated at district level. Next, the stages of felling, extraction, debranching, moving and chipping of wood resources are modelled into four specific logistic chains on the basis of the size of forest ownership, the steepness of slope and the variety of tree. Moreover, specific unit costs based on different cost allocation procedures are assigned to the ten identified types of chipped wood resources. Besides the modelling of the transport sector, an array of all feasible technologies for conversion of wood resources into bio-based power are compared to each other in terms of costs. A singular conclusion is drawn according to which, for each particular capacity under the same operation conditions, gasification is more cost-efficient than combustion – except for co-firing. Hence, the fluidised bed gasification coupled to a gas engine or a combined cycle as well as the direct co-firing of wood resources at a 10% co-fire rate are preselected for the intended analysis on account of their higher cost-effectiveness. Lastly, a new MILP model called BioESyMO (Bioenergy System Model for Operation Optimisation) is created for the optimisation of the value chain of wood resources. This optimising tool includes a unique mathematical constraint aiming at assuring profitability of investments within each utilisation pathway. A scenario-based analysis is first developed for remunerations modelled with a high enough value above the breakeven point. Thereby, a combined heat and power cogeneration process consisting of a fluidised bed gasifier coupled to a gas engine of 20 MWe renders electricity production costs of 10.1-13.8 €cent/kWhe for an annual amount of 7,500 full load hours. The co-firing option for the existing coal-fired power plants with bio-based capacities up to 84.3 MWe generates lower electricity production costs of 6.6-11.7 €cent/kWhe, when the facilities are yearly operated for 3,000 full load hours. If a fluidised bed gasifier is connected to a combined cycle of 210/340 MWe (7,500 full load hours per year), this technology turns out to be the most cost-efficient with electricity production costs in the order of 5.6-7.1 €cent/kWhe. These costs ranges can be reduced by progressively decreasing remunerations below each resulting breakeven point. As for the option of co-firing, cheaper bioenergy configurations arise on the basis of cheaper wood resources that enable lower production costs of up to 5.6 €cent/kWhe for 4,000 hours per year at full load. In conclusion, the low incremental capital costs of co-firing as well as the high efficiencies of fluidised bed gasification-based combined cycles together with the valorisation of the more economical deciduous fractions of wood resources might reduce electricity production costs to a rather low range between 4.5 and 9.5 €cent/kWhe. Leveraging such cost reductions, the introduction of appropriate energy policy instruments for the promotion of carbon-neutral baseload power generation is strongly recommended in view of restrictions induced by Germany’s nuclear and coal phase-outs. Although the quality of the results of this study is mainly conditioned by uncertainty and the high spatial aggregation level of the spatial unit, the implemented methodology as well as the performed optimisation analysis represents an interesting breakthrough that may contribute to the initiated energy transition in Baden-Wurttemberg and the whole of Germany.

Industrial demand-side flexibility is essential for power systems with high shares of variable renewables, yet static grid fees and full load hours incentives can suppress flexible electrification by penalizing peaks and rewarding uniform consumption. This paper introduces an open, extensible, regulation-aware optimization platform that integrates market and emission data with a mixed-integer scheduling model of a bi-valent industrial dryer capable of using electricity and gas. The platform is demonstrated through a representative use case from the energy intensive paper manufacturing sector operating under the current reduced static grid fee pursuant. Because the reduction is contingent on meeting a minimum full load hours threshold, the scope for exploiting the bivalent flexibility potential remains limited. As an alternative, a proposed dynamic grid fee regime featuring time-varying low- and high grid fee windows is evaluated. Any reduction of power consumption from the grid during the high grid fee window does not count against meeting the full load hours threshold. With dynamic fees, the optimization concentrates electric operation within low grid fee windows, increasing electrified heat, reducing emissions, and maintaining competitive costs. Notably, during summer months, these windows align well with periods of lower grid carbon intensity, reinforcing cost–emission co-benefits. However, this alignment deteriorates in winter due to higher variability in renewable generation patterns and constrained window timing, limiting incentive effectiveness. The findings demonstrate that tariff parameterization materially shapes realizable industrial flexibility and that regulation-aware optimization can translate latent technical potential into sustained, temporally targeted electrification aligned with system conditions. The platform enables reproducible, policy-relevant scenario analysis and can aid plant operators for scheduling flexible assets and tariff designers in testing tariff parameters against realistic operational responses.

Production costs for synthetic methane in 2030 and 2050 of an optimized Power-to-Gas plant with intermediate hydrogen storage

Local or district heating by natural gas: Which is better from energetic, environmental and economic point of views?

Corrosion evaluation and prevention of reactor materials to contain thermochemical material for thermal energy storage

Demand response has been studied in district heating connected buildings since the rollout of smart, communicating devices has made it cost-effective to control buildings’ energy consumption externally. This research investigates optimal demand response control strategies from the district heating operator perspective. Based on earlier simulations on the building level, different case algorithms were simulated on a typical district heating system. The results show that even in the best case, heat production costs can be decreased by only 0.7%. However, by implementing hot water thermal storage in the system, demand response can become more profitable, resulting in 1.4% cost savings. It is concluded that the hot water storage tank can balance district heating peak loads for longer periods of time, which enhances the ability to use demand response strategies on a larger share of the building stock.

In recent times, the thermochemical energy storage (TCES) method is gaining prominence due to its high energy storage density and minimal heat losses compared to the conventional thermal energy storage (TES) methods. This paper presents the cyclability behavior of selected zeolites for the TCES applications. The zeolites were subjected to sequential desorption and adsorption processes for five times using a differential thermogravimetric analyzer (DTG-60H). To investigate their suitability for the commonly available sources of thermal energy (e.g. solar energy, industrial waste heat), the samples were heated up to 150°C. These zeolites were also tested on Brunauer–Emmet–Teller (BET) analyzer for total surface areas and pore volumes, thus to read their sorption behavior. A field emission scanning electron microscope (FESEM) equipped with an energy dispersive X-ray (EDX) analyzer was used to examine the surface morphology and elemental composition of zeolite sorbents before and after the multi-cycle test run. The changes in the mass of a material during a process, either desorption or adsorption, were notably almost the same across the cycles tested, which confirms the cyclability of the materials tested. Amongst the tested materials, Zeolite-NaY and Zeolite-HY exhibited relatively better process enthalpies owing to their active water adsorption capacities. Of the six materials tested, Zeolite-NaY has offered better results and its enthalpies range from 287.5 J g−1 to 348.5 J g−1 for the desorption and from 81 J g−1 to 292.1 J g−1 for the adsorption. A mass gain was noticed for each of the tested materials as they undergo the cooling process, thus affecting water vapor adsorption capacity negatively.

Techno-economic competitiveness of 50 MW concentrating solar power plants for electricity generation under Kuwait climatic conditions

This paper presents a comprehensive and state-of-the-art review on thermochemical energy storage (ES) technologies using thermochemical materials (TCMs) for building applications. Thermochemical storage devices (materials, open and closed sorption as well as chemical heat pump) enhance the energy efficiency of systems and sustainability of buildings by reducing the mismatch between supply and demand. Thermal ES (TES) systems using TCMs are particularly attractive and provide a high ES density at a constant temperature. Technical and economical questions will need to be answered for all possibilities, which warrant more development and large-scale demonstration of TES in future. Copyright , Oxford University Press.