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Introduction of more and more intermittent power sources to the power systems may affect the power system reliability. The objective of the paper is to develop the reliability importance measures, which would identify which power plants contribute more and which less to the power system reliability. The loss of load expectation relative increase factor for certain power plant shows how much the loss of load expectation is increased in the case if this power plant would become totally unavailable. The loss of load expectation relative decrease factor for certain power plant shows how much the loss of load expectation is decreased in the case if this power plant would become totally available. The importance factors have been developed and evaluated on a case study of small example power system. The results show the importance factors for specific generators in the power system. The deficiency of the approach is that the importance factors cannot represent the operation regime of the power plants, which follow the daily load diagram.

This work deals whit an energy storage device as a part of electric energy production system based on renewable energy sources. The system supplies given load with known load diagram. Operational diagrams of individual units in the system are determined in an optimization procedure. The optimization goal is to supply given load with minimal use of conventional energy delivered from electric grid. Optimization is performed by a stochastic search algorithm called Differential Evolution [1] for the system consisting of a solar power plant, wind turbine unit, flow battery (VRB unit), load and the electric grid. Individual elements are described in [2]-[7]. The optimization input data are given weather forecasting and forecasted load diagram.

European countries are promoting the use of renewable energy sources in order to reduce their dependence on imported energy. Renewable sources of energy are a promising solution, but there are downsides too. The integration of renewable energy sources causes problems with the electric power systems, as their energy production is meteorologically dependent. In this paper a system is introduced that represents a solution to this problem, with the activation of users of the distribution part of the electricity network. The system connects the users of the distribution network that are willing to participate in the system environment based on market rules. The participation allows users to offer an adaptation of their consumption of electric energy or production in return for financial incentives. The system accepts or rejects the user%s energy adaptation offers on the basis of market principles that are driven by the optimization method (genetic algorithms in the presented case). The system optimizes the total cost amount that is reflected in the integration of a larger portion of the renewable energy sources into the electric energy system. Testing the results of the system operation demonstrates that the developed solution has improved the integration of renewable energy sources and has enabled users to profit from their adaptation to energy consumption or production.

Abstract The decarbonisation of energy systems is one of the important issues of the present energy policies. One of the ways of achieving this is to focus on local energy systems, thus ensuring as much as possible their heat and power self-sufficiency by applying local renewable resource integration and transformation of the renewable energy. Increasing the share of renewables within the local energy balance could be accomplished by using a variety of approaches. One possibility is combining the Locally Integrated Energy Sectors' concept with the novel management and organisation of a renewables-based network. As a first priority, the proposed comprehensive approach focuses on increasing the energy efficiency of municipal heat and power systems using the Locally Integrated Energy Sectors' concept, which is followed by the integration of renewable energy sources with the establishment of a renewable-based network. The proposed approach is illustrated by a case study of district heating based on wood biomass for the municipality Ormož, Slovenia by integrating various end-users from different sectors.

The main objective of this paper is a presentation of an improved probabilistic approach for estimating the additional operating reserve in modern power systems with a large share of renewable energy sources. A reliable operation of modern power systems can be ensured by application of the proposed method. Results show that the power-generation reliability in modern power systems and consequently the required additional operating reserve significantly depend on the variable and uncertain power generation of the renewable energy sources.

Abstract A hybrid energy system, based on renewable energy sources and with hydrogen storage, can become an alternative for stand-alone electricity and heat supply. The objective of this work is to evaluate the feasibility of a completely renewable supply of power and heat for an isolated household, and a comparison to reference and alternative energy supply scenarios. In this paper, an energy system using fossil and renewable energy sources is compared to a system using only renewable energy sources (solar and wind) with hydrogen-based energy storage technologies. A reference household in Slovenia's coastal region was used for modelling and numerical simulation. Simulations and optimal energy system identification were conducted by considering the geographical location and availability of energy sources, load dynamics, and components' technical and economical characteristics. A household with electricity consumption of 11 kWh/day, hourly peak power demand of 3.8 kW and 660 L of oil-equivalent yearly heat demand was considered as the stand-alone load. The results show that 100% renewable electricity and heat supply of a reference household is technically feasible and is more cost-effective, compared to systems utilising fossil heat.

Abstract In this paper we present an improved probabilistic approach for estimating the additional operating reserve in power systems with installed renewable energy sources. This approach uses a novel method for determining the reliability of power systems, where the variable generation of renewable energy sources and the ageing of generating units are considered. The new approach also takes into account the fact that several generating units can share the same source of failure, which causes them to fail or become unavailable simultaneously. Improvements are achieved by the implementation of common cause failures. The obtained results of the reliability analyses are basis for estimating the additional operating reserve in the power system, so that the system operation is supplemented with the proposed reliability criteria. The presented approach is tested on an IEEE Reliability Test System where the one-day-ahead circumstances are observed. The results show that the required additional operating reserve depends primarily on the power generation of the renewable energy sources and on the unavailabilities of the generating units, which are influenced by ageing and by common cause failures. The results show that the new method is suitable for achieving reliable power systems in the future, where a high penetration of variable renewable energy sources is expected.