Pilots for the seasonal thermal energy storage of solar energy on a local basis are few in Finland, even if international demonstrations show that the utilization level of solar energy can exceed 50% of the annual local heat requirement in similar climate zones. This study presents options for heat and electricity generation based on local energy systems and utilizing seasonal thermal energy storages. Energy needs and production on Vartiosaari district in Helsinki in Finland were explored as a case area. The project studied the impacts of introducing solar thermal energy on local energy self-sufficiency and emissions from heating energy supply, if excess solar heat in the summer is stored using borehole thermal energy storage or tank storage for use in the winter. Around 60% self-sufficiency in heat production would have been achieved in the scenarios studied. In addition, carbon dioxide emissions could be reduced by around 50%, and sulphur dioxide and particulate emissions by up to 70% compared to the business-as-usual situation. (C) 2017 Elsevier Ltd. All rights reserved.