Celje deals with heavily polluted air, which is the result of several factors such as industrial activity, heavy transit traffic, high number of old and inefficient individual heating systems and building stock, and unfortunate climate conditions related to its location in a valley. The municipality was thus in great need of developing a new local energy concept (LEK) and strategy to reduce Celje‘s energy consumption and CO2 emissions and to increase its use of renewable energy sources (RES), ultimately improving the overall air quality.