a b s t r a c tThis paper provides a solution for managing excess heat production in trigeneration and thus, increases the power plant yearly efficiency. An optimization model for combining biomass trigeneration energy system and pit thermal energy storage has been developed. Furthermore, double piping district heating and cooling network in the residential area without industry consumers was assumed, thus allowing simultaneous flow of the heating and cooling energy. As a consequence, the model is easy to adopt in different regions. Degree-hour method was used for calculation of hourly heating and cooling energy demand. The system covers all the yearly heating and cooling energy needs, while it is assumed that all the electricity can be transferred to the grid due to its renewable origin. The system was modeled in MatlabÓ on hourly basis and hybrid optimization model was used to maximize the net present value (NPV), which was the objective function of the optimization. Economic figures become favorable if the economy-of-scale of both power plant and pit thermal energy storage can be utilized. The results show that the pit thermal energy storage was an excellent option for storing energy and shaving peaks in energy demand. Finally, possible switch from feed-in tariffs to feed-in premiums was assessed and possible subsidy savings have been calculated. The savings are potentially large and can be used for supporting other renewable energy projects.

Island communities require in-detail mapping of resources available for exploitation for energy purposes, since infrastructure and connections to the mainland present, in most cases, a weak point of the island energy supply. As the present energy supply on Croatian islands relies mostly on fossil fuels and electricity from the mainland, it becomes obvious that exploitation of renewable energy sources is the only solution that leads towards self-sufficiency and sustainable development. In order to design a self-sufficient and sustainable island, three major technological changes are needed: integration of renewable energy sources alongside with energy savings and improvements in energy efficiency in the energy production. Analyses for several other Croatian islands have been performed using Renewislands/ADEG methodology in order to assess all possible outcomes. The scenarios in these cases have shown that islands can become selfsufficient through combining renewable technologies and energy storage systems. Energy storage systems will be crucial for achieving desired objectives in terms of energy independence from the mainland and in general import of fossil fuels. The analysis conducted for the island of Hvar will result in creation of several scenarios which will clearly point out the favorable solutions for improvement of both security of energy supply and covering the majority of energy demand with renewable energy sources and storage technologies. Also, when talking about implementation of renewable technologies on island of Hvar, an optimal mix of technologies must be applied in order to avoid excess costs and to achieve minimal impact on environment in terms of visual pollution. V C 2013 AIP Publishing LLC.

Industry represents one of the most interesting sectors when analysing Croatian final energy demand. Croatian industry represents 20% of nation's GDP and employs 25% of total labour force making it a significant subject for the economy. Today, with around 60 PJ of final energy demand it is the third most energy intensive sector in Croatia after transport and households. Implementing mechanisms that would lead to improvements in energy efficiency in this sector seems relevant. Through this paper, long-term energy demand projections for Croatian industry will be shown. The central point for development of the model will be parameters influencing the industry in Croatia. Energy demand predictions in this paper are based upon bottom-up approach model. IED model produces results which can be compared to Croatian National Energy Strategy. One of the conclusions shown in this paper is significant possibilities for energy efficiency improvements and lower energy demand in the future.

Project SMART (Strategies to Promote Small-Scale Hydro Electricity Production in Europe) from the Intelligent Energy Europe (IEE) program, in which 7 institutions from 5 European states participate, pointed to the important barriers for the expansion of small hydro power plants (SHP) in Europe. One of the main barriers is the lack of suitable methodology and software able to create a clear view of the SHP potential in the given territory, as well as a complete techno-economic analysis for certain locations. Worldwide, there are a certain number of software for this purpose, and will be presented in this paper. However, in practical application for concrete cases, they show certain disadvantages. For example, one software is not able to take into account all the specifics of watercourses and plants; another does not have the option of selecting all types of turbines; in others, the calculation models are based on a limited number of equations that do not describe all possible cases; in some, economic analysis is oversimplified, etc. The aim of this paper is to develop software that is more comprehensive than any existing software. A new software for the techno-economic analysis of SHP is developed using Python and will be presented in this paper. The software is very useful for experts in the field of SHP, but also much wider, for decision-makers, potential investors, and stakeholders, especially in developing countries. It will improve water resources management, disseminate opportunities to investors, and increase the interest of stakeholders to invest in SHP, resulting in their wider use. The software is tested on location for SHP in the Republic of Croatia by comparison with the results obtained by the usual classical calculation. The agreement of the results is satisfactory.