Sustainable energy development becomes one of the crucial issues for every municipality. Reductions of fossil fuels which are used in public buildings together with grow of investments in energy efficiency and renewable energy creates strong challenge for local municipality government. Preservation of local cultural heritage and local architecture recognition could be in danger by non organized investments in „?green?? technology. Simultaneously, overprotected and overregulated reconstruction of cultural heritage buildings usually do not lead to diminishment of energy consumption. Authors of this paper analyzed recent sustainable energy project in the city of Rijeka Municipality building, which was originally built in 1915. Although Municipality building is located in the center of the city and protected as cultural heritage, Conservatory department in Rijeka and Municipality, together with investor Energo Ltd. created solutions which have satisfied all included parties. In the year 2009 first photovoltaic power plant of 9.9 kWp has been installed and put in service on the upper terrace of the building. That was technically and financially acceptable for the owner of the building, as well as for the investor. Next year, City of Rijeka accepted Sustainable energy action plan (SEAP) and started with implementation of smart metering in that same building. Further analyses of those projects lead to conclusion that similar investments could be carried out in order to match energy sustainability and economic feasibility in cultural protected buildings.