*2.1. Goal and Scope*

The goal of this study is to assess the environmental impacts of an S-LHTES-PCM system and compare it with other common sources of domestic heat in the UK using an attributional LCA. The LHTES system will store heat produced by solar collectors using SAT as the PCM and its purpose is to supply heating and domestic hot water to a household in the UK.

To accomplish the stated aim, the functional unit (FU) selected for the study was 1 kWh of heat produced by the novel S-LHTES-PCM system. This unit was selected because the main purpose of the system is to provide heat. Moreover, this FU allows to compare the results obtained with other energy storage technologies or sources of heat, irrespective of the size of the systems. For example, Oró et al. [18] performed a comparative LCA of three different thermal energy storage systems for solar power plants, and the same FU was selected.

The system boundaries of the study illustrated in Figure 1 are from cradle to grave, including the following activities and stages:

• Production of materials:

	- Hot water tanks, PCM tanks, solar collectors, PCM, piping, pumps, expansion vessels, heat exchangers, valves, stratifier, and the crystallization activation device. On the other hand, the hydronic circuits with the radiators and taps/showers were not included because they are not part of the S-LHTES-PCM system per se and are components that a typical UK household already has.
	- Electricity consumption of the pumps to circulate the water.
	- Disposal of components after they have reached their life expectancy.
	- Transport of all the components from production to the household in the UK and to the treatment plant at the end of life.
