Advances in Sustainable Energy Planning and Thermal Energy Storage

Dear Colleagues,

The modern energy sector encompasses numerous areas and faces significant challenges, including reducing CO₂ emissions, rejection of fossil fuels, increasing the utilisation of renewable energy sources, and integrating them into various industries.

The aim is to produce energy under the most favourable conditions; that is, easily, safely and cost-effectively. It is especially beneficial to utilise the naturally occurring processes. On the one hand, the more efficiently energy is used, the lower the overall cost. That leads to reduced energy demand, which helps conserve resources and lowers the need for energy production capacities. In practice, we often see a mismatch between the time of the most favourable conditions for energy production and the time when energy is needed. A clear example is the surplus of natural heat in summer and the shortage of it for building heating in winter. On the other hand, how can we maintain coolness from winter until summer to cool the buildings?

The above examples demonstrate the need for thermal energy storage. The operation of an energy accumulation system can be described in three stages. The first stage is the accumulation of energy that is produced or collected under the most favourable conditions—this is essentially the charging phase. The second stage is storage, keeping this energy until it is needed. The duration of this stage is essential. Short-term storage lasts for hours or days. The medium-term period might span weeks or a few months. Lastly, the most complex is long-term energy storage, which can span months, seasons, and even longer periods. In that case, the energy losses increase, and engineering solutions are necessary to mitigate them. Finally, the third stage of the thermal energy storage system is discharge, which refers to the utilisation of accumulated energy.

This Special Issue focuses on thermal energy storage methods and systems.

A specific material medium is used to store heat; that is, a defined volume is filled with the material, and heat exchangers are installed within it. Currently, water-based heat storage systems are the most prevalent. However, the soil can also be used directly or indirectly as a heat storage medium. Soil is inexpensive, easy to prepare, and simple to operate. Our goal is to develop the use of the soil as a medium for heat storage. That includes analysing the storage processes themselves, examining structural characteristics, studying the interaction between buildings and soil, and considering other relevant factors.

Heat generation is planned from renewable energy sources. The most suitable options are solar collectors, photovoltaic panels, and small wind turbines. Research related to integrating these energy sources into building engineering systems, such as the building's heating or cooling systems, is highly desirable. The use of heat and electricity accumulators to balance loads, optimise energy networks, and reduce overloads is also a key issue in modern engineering.

In this Special Issue, original research articles and reviews are welcome. Research areas may include (but are not limited to) the following:

• Building energy efficiency;
• Integration of renewable energy sources into building engineering systems;
• Heat storage systems at small and large scales;
• Integration of energy storage systems into energy networks;
• Overloads in electricity and district heating networks;
• Thermal and electrical accumulators for load balancing;
• Utilisation of ground heat or coolness.

Prof. Dr. Tadas Zdankus
Dr. Juozas Vaiciunas
Guest Editors

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• heat storage system
• accumulator
• network
• renewable energy
• building heating and cooling
• building energy efficiency
• energy balance
• optimisation
• loadings