Levelized cost of heat for solar thermal applications in households

The use of the levelized cost of heat (LCoH) indicator is growing in the thermal engineering literature. In the field of solar thermal systems engineering, existing studies apply different methodologies for LCoH calculations, which leads to difficulties in comparing the results obtained. To facilitate and harmonise future works, the complexity of solar thermal systems is analysed in detail in this study to define possible system boundaries for the parameters of the LCoH equation. For this purpose, energy streams with and within a building are analysed based on standards dealing with energy use in buildings, and four possible system boundaries for energy are identified. Similarly, four commonly used physical system boundaries are identified for the costs when considering the heating system as a whole. A further distinction is introduced between the conventional and the innovative parts of the heating system, when the focus is only on the core components, i.e. the heat production units and storage. As a result of the investigations, a nomenclature is proposed to differentiate the LCoH values from each other. The study also shows with examples that the LCoH is not necessarily the most appropriate indicator for economic comparisons and suggests some ways to extend its scope of application.