Sustainability Assessment of Most Relevant Solar Thermal Heat Systems
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Solar thermal heat systems are of high relevance and interest for the supply of low temperature heat for different purposes. Especially, hot water systems are dominating the solar-thermal market with non-pumped systems gaining more and more importance. The main objective of this paper is to assess most relevant small and medium sized as well as large scale district solar-thermal heat systems as to their sustainable development metrics. While 2017 about 94% of the energy provided by solar thermal systems was used for domestic hot water, currently a trend to larger solar thermal systems with seasonal storage coupled to district heating networks is discernible. Solar thermal at present contributes about 1% to total heat consumption. The share of solar district heating and solar process heat applications is steadily increasing despite it is still only representing 3 % of the global market (Weiss and Spörk-Dür, 2018). The potential contribution is much larger. Many national governments seek to realize this potential by offering subsidies and feed-in-tariffs. Assessing sustainable development for solar thermal heat systems is a complex discipline. The best heat system depends to a large extend on the climate region. If solar heat is intermittend, seasonal, economic storage of heat is advantageous. Significant cost reductions of solar thermal systems and a shift towards polymeric materials to regain market growth and to improve ecological performance is required. For the assessment a 5-step methodology developed by Ashby et al. (2016) is used.