Initial situation, motivation and research question

The transition to renewable and sustainable energy systems poses a significant challenge globally, particularly in Europe, where ambitious goals have been set to increase the share of renewable energies in the energy mix. To successfully integrate a high proportion of variable renewable energies, ways must be found to balance supply and demand, with storage technologies playing a crucial role. The economically motivated selection of grid electricity at low hourly rates and its thermal utilization in the NEW Ice Storage concept also includes the future utilization of wind power peaks. The increasing prevalence of air-to-water heat pumps motivates the search for ways to operate them in a grid-friendly manner during lower outdoor temperatures.

The following research questions arise:

• How can an ice storage system improve the efficiency of heat pumps and become more efficient and cheaper?
• How can an ice storage absorber be designed to make rapid freezing and defrosting processes possible?
• What optimized surface coatings can the ice storage absorber be coated with?
• What options do additional integrated phase change materials (PCM) offer?
• How can an ice storage absorber be designed to make the dimensions as compact as possible?
• Can costs and CO2 emissions be saved by the price-controlled operation of a heat pump ice storage system, and how can the integration of heat pump ice storage systems contribute to minimizing the curtailment of renewable energies in the Austrian energy system by 2050?

Project contents and objectives

• The project contents and extended objectives are as follows:
• Extensive utilization of existing components, technologies, and construction methods
• Possibility of expanding conventional heat pump concepts
• Reduction in volume and space requirements of ice storage systems
• Consequently reducing costs compared to conventional ice stores of the same heat output
• Price-controlled optimization of heat demand and resulting grid electricity demand when operating a heat pump ice storage system

Methodical procedure

For the feasibility of the NEW Ice Storage Concept, the best available components and devices are identified and missing "connecting pieces" are shown based on existing research results. Based on this, the functional configuration of the new system is presented, and a realistic assessment of efficiency improvements is made. Economic analyses include the investigation of load shifting effects using a dynamic optimization model of the electricity market. A bottom-up energy model is developed, followed by the analysis of dynamic energy scenarios to investigate optimised integration of renewable energies and storage capacities. In addition, electricity costs of a single-family household are analysed based on weather data and dynamic electricity prices, with and without ice storage.

Results and conclusions

The implementation of the NEW Ice Storage Concept shows promising possibilities for the efficient utilization of existing components and technologies. It enables the expansion of conventional heat pump systems, reduces volume and space requirements, and lowers costs compared to conventional ice stores of the same performance. The separation of heat and electricity demand during times of high electricity demand enables flexibility, especially during cold winter nights or periods of low wind.

The development of the NEW ice storage includes bivalent operating modes, vertical metallic heat exchanger plates, electrically heated coatings, thermal decoupling upwards and coupling with CO2 geothermal pipes downwards, as well as the integration of PCM capsules to increase the heat storage capacity. The system is regenerated using both external air absorbers and direct electricity, which can be achieved using favourable hourly tariffs during wind power peaks.

A complex simulation is required to capture thermal effects and make accurate dimensioning. This currently makes a more concrete dimensioning and, above all, the calculation of the necessary depth of the CO2 geothermal pipe not possible. Therefore, a cost calculation and the dynamic simulation of the integration of the NEW Ice Storage Concept into building energy systems and building district systems are currently not feasible.

Simulations of the future energy system show positive effects on the energy system by reducing the use of fossil power plants and avoiding unused surplus electricity. Despite promising aspects, the investment costs for conventional heat pump ice storage systems, based on cost research, are higher due to additional acquisition costs than when using the heat pump alone, even with dynamic optimization based on electricity prices. The future of such systems depends on factors such as energy costs and CO2 prices. An increase in the CO2 price could enable higher cost savings. The study shows that consumer involvement at the household level is possible and can lead to energy savings. Therefore, a dynamic and market-based framework is essential to motivate consumers.

Outlook

Further development of the concept by testing a prototype would be useful and desirable. For the necessary recording and simulation of the complex thermal processes and the selection of suitable additional project partners, it makes sense to wait for the results of research projects underway around the world.

Project management

Schöberl & Pöll GmbH

Project or cooperation partners

TU-Vienna - Institute for Energy Systems and Electrical Drives (ESEA), Energy Economics Group (EEG)

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