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This study investigates primary energy use and CO₂ emission reduction potential resulting from the integration of solar thermal heating in biomass-based district heating systems in high-latitude regions. A newly commissioned solar thermal system based on parabolic trough collectors for an existing district heating network in Häarnösand, Sweden, is used as a case study, and its hourly one-year measured data are used as inputs for the analysis. The changes in operation and fuel use for local district heat production are extended to a regional context, considering the short- and long-term perspectives of the energy system. The results show that during the studied period, the solar water heating system provided 335 MWh of heat to the existing district heating system with a supply/return temperature of approximately 80/45 °C. Consequently, 339–382 MWh of biomass fuel consumption could be reducedannually with such an installation, depending on the district heat production technologies being substituted. An annual CO₂ reduction of 65.3–189 tons can be achieved in an overall energy system perspective when the saved biomass substitutes fossil fuels. The reduction of CO₂ emission depends on the fuels being substituted and energy conversion technology.

Currently, companies in the solar heating sector may choose from a wide range of tools for modelling and simulating solar thermal power. However, due to the deviant design of some collectors, conventional simulation tools may be inadequate in correctly assessing the performance of such collectors. This study aims to test and validate an in-house simulation model for T160 PTC collectors developed by the company Absolicon Solar Collector AB by comparing measured data with simulated results. A solar district heating (SDH) plant in Härnösand, Sweden featuring 192 parabolic trough collectors (PTC) is used as a case study for the validation. Operational data such as weather data,solar heat production and collector loop/ambient temperatures were collected from the facilities of Absolicon. The data was compiled and simulated using a Python model developed for the T160 collectors. The study shows anacceptable correlation between simulated and measured data during periods with high DNI where a relatively highamount of heat is delivered to the district heating. Deviations are present during periods of low DNI and can bederived from inadequate assessments of heat losses from the piping of the installation in addition to inaccurate measurement data.