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Trends for heating energy in European Cities are the decarbonization of energy sources and the reduction of heat loads. District heating (DH) networks are key systems to reach the targets due to the cost competitiveness and high performance levels they show. However, DH networks require a conversion to adapt for the need of the future. It is necessary to reduce the operation temperature so that it is possible to increase the performance of renewable systems and operation criteria needs to be adopted for the introduction of weather-dependent, distributed heat sources such as solar systems. In this paper is presented the RELaTED, a novel DH networks scheme with decentralized Ultra-Low Temperature performance. This way, it is possible the adaptation of new and existing networks to several operational schemes. Transitory phases for the conversion of actual DH and how this affects the whole system are discussed along the paper.

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.

Abstract Renewable energy generation is inherently variable. For example, solar energy shows seasonal (summer–winter), daily (day–night), and hourly (clouds) variations. Thermal energy storage (TES) systems correct this mismatch between the supply and demand of the thermal energy. Hence, TES is a key cross-sectional technology with growing present and future importance for utilizing volatile renewable sources (e.g., wind and photovoltaics) and energy efficiency improvements. This chapter gives a broad overview of different options and challenges for TES utilization in a high-temperature field. The chapter structure follows the value chain of TES development from material via component to system integration research and development aspects. The structure of this chapter is based on the classification commonly adopted in the academic literature, which distinguishes between three major TES types: sensible, latent, and thermochemical storage. The chapter focuses on high-temperature applications in the area of concentrating solar power generation and operation temperatures beyond 300°C.