Småskalig säsongslagring av solenergi för uppvärmning av byggnader : Simulering av täckningsgrad och lagerutformning för lågenergibyggnader

The sun is a huge energy source with great potential of providing energy to the heating of homes and other buildings in an environmentally sustainable manner. In order to provide buildings with energy from the sun it is necessary to transfer the energy supply over time to when the demand arises. By storing the heat in a seasonal storage, solar energy from the summer can be used in the winter when the demand for heating is greatest. Today's existing plants are mainly in Europe and particularly in Germany. These facilities are designed to supply heat demands greater than 500 MWh and covers about 40-50% of this need which consists of energy for space heating and domestic hot water. How much of the heat demand that is covered, the solar fraction, is partly due to losses from the storage which in turn is connected to the surface area of the storage. The bigger a storage, the smaller the losses are because of the decreasing relationship between surface area and storage volume. Looking at the size of the seasonal storages that are currently in operation, the question if seasonal storage is also suitable for installations designed for heat demands smaller than 500 MWh arises. Jonas Haglund of Architects Skanark AB in Karlstad is planning an accommodation of 40 flats and hopes that the seasonal solar energy can serve as the main energy source for heating and hot water. The building can be constructed according to normal building standards or as a low energy building. Haglund would like to investigate whether the character of the energy demand affects the solar fraction of the storage. Will the solar fraction of the storage change if the energy demand is equivalent to a low energy demand instead of a standard energy demand? The purpose of this study is to investigate the possibility of covering a large fraction of a small-scale annual heat demand corresponding to about 50-500 MWh. The study shall present the solar fractions that can be achieved with different storage concepts when storage size and collector area is varied. The study will also answer how the solar fraction will change if the character of the energy demands changes. These questions are answered by simulations with computational tool COMSOL Multiphysics. The results show that it is possible to obtain solar fractions above 80% with sufficient collector area. Suitable storage volume varies depending on the specific storage concept but generally requires a smaller storage volume of the seasonal storage in a tank compared with the duct storage in clay. Equally suitable collector area varies depending on the storage concept studied. The results show that it is possible to obtain higher solar fractions in the tank storage compared with the duct storage in clay for the same collector area. The result shows also that the character of the energy demand is of great importance for the solar fraction. The solar fraction increases significantly when the low energy demand is to be met, regardless of the storage concept.