## 5 Heating Systems and Renewable Energy Solutions in Serbia  
After the fall of the Berlin wall, socialistic countries focused on political and economic transition. Part of transition included also the transition of the energy sector, which needed legislation, restructuring, liberalization and privatization, as well as investment [52]. Indeed, the transition in the energy sector did not contain different elements from those in other sectors. Compared to many other ex-socialist countries, transition in Serbia started later because of complex issues regarding territorial conflicts, civil war, economic embargo and political crisis. Even though transitional process started in 2000, there are still legacies originating from socialist era, as well as new-developed trends from transitional era, which strongly influence actual social, political and economic dynamics in Serbia [53; 54]. The biggest part of energy consumption in Serbia goes to residential and commercial buildings with around 46%, and they are followed by industry and transport [55] (p. 36). Energy in buildings is mostly used for heating (around 62%), followed by energy spent for lighting and warm water [55] (p. 37). Many post-socialist countries still rely on district heating systems operating on fuel oil and are built during socialist era [56]. Cities with a high population density are more favourable places for district heating because of lower distribution costs per household. \"With higher number of heating consumers and a small object density, i.e., large number of  
apartments per object, district heating system is a better solution\". [57] (p. 151)  
It is also expected that post-socialist states reduce plant-level CO\({}_{2}\) emission during the transitional process [58]. Investing in RES can also be motivated by reducing citizens' energy bills [59]. Cost approach was not always considered in socialist states and their former planned economies [49] (p. 626). Most local heating plants in former Yugoslavia were fuelled by heavy oil and/or natural gas [60; 61]. District heating systems are present in bigger Serbian cities, while individual heating solutions prevail in small towns [62]. District heating in Belgrade for instance [63] is in the phase of renovation and gains the importance again after the turbulent 1990s. Still, district heating systems, not only in Serbia, but in the whole region of Western Balkans, are based on using fossil fuels [64] (p. 30). District heating in the Republic of Serbia is used in the bigger urban centres, and is supplied by heat produced by larger heating plants. This heating systems mostly uses coal, wood, oil fuels and gaseous fuels as primary energy source [65]. District heating plants were built in the socialist era, as a heating solution for growing cities. District heating systems are located in 55 cities, towns and municipalities in Serbia [66]. The situation in small Serbian cities is different because they are not dependent on huge heating systems. Their heating structure is very heterogeneous, but also more flexible than in residential complex of big cities. Smaller towns in Serbia, like Ub for instance, do not have such large heating plants, and they are not dependent on district heating systems. Therefore, smaller cities in Serbia are favourable areas for introduction and usage of renewable energy solutions. According to data from 2002 [67], dominant energy source for space heating was coal. Around 36% of energy for space heating came from this source. Today natural gas is the most favourable fuel for domestic heating, while traditional fuels dominate in rural and low-income urban households [68]. Around 22% of occupied dwellings in Serbia are connected to district heating systems, around 21% use central heating, while around 57% are without district and central heating (see Figure 1). [PERSON] et al. [55] (p. 36) wrote that 26% of the households are connected to district heating systems, 30% use electricity for heating, 20% wood, 15% coal, while less than 6% use gas.