The main objective of this paper is to evaluate energy and environmental benefits of the large-scale solar heating system connection with district heating system. The assessment of fossil fuels substitution by the solar energy for the hot water production for domestic use, during the summer period, is done. Hot water for district heating and domestic use is produced in heating plant "Cerak" placed in the suburb of Belgrade. The existing production and distribution system are based on fossil fuel energy, mainly on the natural gas. in the first phase of the project plan was to install about 10,000 m(2) of solar collectors to substitute nearly 25% of natural gas consumption. During the summer period, the saving of natural gas calculated for presented system is approximately 430,000 m(3) and in this way 900 t of the CO(2) emissions would be reduced. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.