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Following a strategic orientation towards sustainable development, the Government of the Republic of Croatia has changed its energy legislation and has put forward a framework for the systematic development and increased use of renewable energy sources and cogeneration. This paper focuses on changes in the regulatory context relevant to the cogeneration sector and also analyses the impact of energy market transition on cogeneration viability in municipal district heating, industry, services and the residential sector. Particular attention has been paid to the expected changes of heat, electricity and gas prices. We present a simple model for quantitative prediction of the cogeneration system profitability at different power levels under given national circumstances. Our findings support a need for a strong institutional support for initial penetration of the micro-cogeneration technologies into the Croatian energy system. [Copyright &y& Elsevier]

• District heating and cooling play a vital role in the EU's decarbonisation effort. • The H2RES tool has been upgraded to including district cooling. • Power to heat is a valuable demand response tool. • Wind and PV could cover up to 73% of Croatia's electricity demand in some scenarios. • District cooling has a significant positive impact on the reduction of curtailment. Europe's decarbonisation ambitions can't be achieved without the full and rapid decarbonisation of its buildings which represent over 36% of its greenhouse gas emissions, the majority of which are linked to space heating and domestic hot water preparation. District heating, and in recent times, cooling must play a large role in satisfying this demand, especially in densely populated urban areas which already hold over half of the World's population. Besides the decarbonisation potential linked to heating and cooling production, these systems hold a strong potential for increased flexibility in the power sector using power to heat technologies thus increasing the potential for the utilization of intermittent renewables such as wind and solar. The goal of this research is to demonstrate the impact district heating and cooling can have on the potential for the utilization of intermittent renewable electricity sources in mild and Mediterranean climates, which traditionally have lower shares of district energy systems. Additionally, this paper presents the newly implemented capabilities of the H2RES linear optimization tool to model district cooling systems alongside the existing capacity to model district heating systems. The results demonstrate a significant capacity of district heating and cooling systems to act as demand response tools thus greatly increasing the potential for the utilization of wind and PV for electricity generation. In some scenarios, up to 73% of the total electricity demand could be covered with wind and PV and a production of excess electricity of only 5% on an annual basis. The Republic of Croatia has been used as a case study for this research. [ABSTRACT FROM AUTHOR]

The penetration of intermittent renewable energy sources, for instances wind power, in the power system of isolated islands is limited, even when there is large potential. The wind power that cannot be directly injected in the power grid is usually curtailed. In addition, some islands need to desalinate seawater to produce fresh water, increasing the pressure on the power system, because desalination needs electricity. Nevertheless, the water scarcity problem of an island can be part of the solution of the problem of its integration of intermittent renewable energy sources. To tackle this issue, a system was proposed to use the excess wind power in desalination units and in a pumped hydro storage, resulting in an integrated power and water supply system that would minimize the wind power curtailed. This paper proposes a methodology to optimize the size and operational strategy of this wind powered desalination and pumped hydro storage system. The objective is to minimize the total annualized production costs, maximize the percentage of renewable energy sources in the total power production and minimize the wind power curtailed. To solve this optimization problem, a derivative free multiobjective optimization method (Direct MultiSearch) is used. This methodology is applied to the integrated power and water supply system proposed for the island of S. Vicente, in Cape Verde. The results show that the penetration of renewable energy sources can reach 84% with a 27% decrease of power and water production costs and 67% decrease of CO 2 emissions, in relation to the values foreseen for 2020. [ABSTRACT FROM AUTHOR]

This 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 Matlab© 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. [ABSTRACT FROM AUTHOR]

Transition and decarbonization of the energy sector require the utilisation of new technologies and energy sources. Higher penetration of intermittent renewable energy sources implies the installation of energy storage, to store electricity excess and enhanced system efficiency. These electricity surpluses that will occur more often in the future energy system could be effectively utilized for the production of alternative fuels. Most of the alternative fuels that are considered for future applications are already known chemicals or products, nowadays used for other purposes. Another great advantage of some alternative fuels lies in their possibilities to act as an energy carrier. This feature might be crucial while discussing their utilisation potential and further development. Fuels which can simultaneously be used for power generation and as an energy carrier will have a more important role in the future and are likely to be utilized on a greater scale. Renewable energy source like biomass, on the other hand, is already widely used, and their role in the future system is not questionable. Even though significant increment in biomass consumption raises serious concerns about its sustainability, and seeks for new approaches. In this work, the authors tried to review alternative fuel characteristics, alongside their utilisation and production opportunities. To come up with the optimal solutions, the authors compared various proposed alternative fuels, alongside their advantages and drawbacks with an aim to find the most appropriate role for each fuel. • Decarbonization of the energy sector requires the utilisation of alternative fuels. • Alternative fuels are complementary, but not competitive amongst themselves. • Carbon neutral fuels are strongly prioritized in future energy systems. • Future research focus should be shifted to couple fuel synthesis with renewables. [ABSTRACT FROM AUTHOR]