• Energy Research
• 12. Responsible consumption close

Abstract The coupling of the heating and the electricity sectors is of utmost importance when it comes to the achievement of the decarbonisation and the energy efficiency targets set for the 2020 and 2030 in the EU. Centralised cogeneration plants connected to district heat networks are fundamental element of this coupling. Despite the efficiency benefits, the effects of introducing combined generation to the power system are sometimes adverse. Reduced flexibility caused by contractual obligations to deliver heat may not always facilitate the penetration of renewable energy in the energy system. Thermal storage is acknowledged as a solution to the above. This work investigates the optimal operation of cogeneration plants combined with thermal storage. To do so, a combined heat and power (CHP) plant model is formulated and incorporated into Dispa-SET, a JRC in-house unit commitment and dispatch model. The cogeneration model sets technical feasible operational regions for different heat uses defined by temperature requirements. Different energy system scenarios are used to assess the implications of the heating–electricity coupling to the flexibility of the power system and to the achievement of the decarbonisation goals in an existing non interconnected power system where CHP plants provide heating and electricity to nearby energy dense areas. The analysis indicates that the utilisation of CHP plants contributes to improve the overall system efficiency and reduce total cost of the system. In addition, the incorporation of thermal storage increases the penetration of renewable energy in the system.

Abstract The present paper focuses both on the thermodynamic and on the economic optimization of a small scale ORC in waste heat recovery application. A sizing model of the ORC is proposed, capable of predicting the cycle performance with different working fluids and different components sizes. The working fluids considered are R245fa, R123, n-butane, n-pentane and R1234yf and Solkatherm. Results indicate that, for the same fluid, the objective functions (economics profitability, thermodynamic efficiency) lead to different optimal working conditions in terms of evaporating temperature: the operating point for maximum power doesn’t correspond to that of the minimum specific investment cost: The economical optimum is obtained for n-butane with a specific cost of 2136 €/kW, a net output power of 4.2 kW, and an overall efficiency of 4.47%, while the thermodynamic optimum is obtained for the same fluid with an overall efficiency of 5.22%. It is also noted that the two optimizations can even lead to the selection of a different working fluid. This is mainly due to additional fluid properties that are not taken into account in the thermodynamic optimization, such as the fluid density: a lower density leads to the selection of bigger components which increases the cost and decreases the economical profitability.

Abstract This contribution experimentally evaluates and compares the performance of an ORC (organic Rankine cycle) system for stationary bottoming WHR (waste heat recovery) application operating with two different working fluids, SES36 and R245fa. The test rig is a regenerative cycle equipped with a single screw expander modified from a standard compressor characterized by a nominal shaft power of 11 kW. A total of 36 and 43 steady-state points are collected for SES36 and R245fa respectively, over a wide range of operating conditions by changing the expander rotational speed, the pump frequency and the cooling condenser flow rate. The performances of the ORC components are individually evaluated. A maximum expander isentropic efficiency of 60% is reached using SES36 at 3000 rpm, and a value of 52% is reached with R245fa at 3000 rpm. However, for a given pressure ratio the expander output power is higher with R245fa than with SES36. The overall performance of the ORC unit are investigated in terms of first and second law efficiencies and net output power for the two fluids. The results experimentally demonstrate the correlation between the working fluid critical temperature and the ORC unit working characteristics for low temperature waste heat recovery applications. Open experimental data are provided for both fluids.

Abstract Harvesting the waste heat from industrial processes or power plants is a very effective way to increase the efficiency of an energy system. Available usually as low-grade heat, it needs to be transferred to the points of consumption in order to be utilized. Feasible heat transmission distance is usually estimated by empiricism or by considering a limited number of parameters with the lack of a methodological tool to estimate this distance based on actual generic data. This work analyzes the particularities of long distance heat transmission by using a detailed techno-economic model for the estimation of heat transport costs including all relevant capital and operating expenditures. Sensitivity analysis is conducted to show the effect of transmission distance, supply temperatures and market prices, covering the most common technical and economic parameters found in literature. This model is also used to identify the maximum economically feasible transmission distance that meets a specified economic criterion and to derive a ‘rule of thumb’ equation.

The ongoing climate change, together with the global increase in energy consumption and unpredictable fossil fuel prices have been the main drivers for the implementation of power exchange, market coupling, energy efficiency measures and larger use of renewable energy. All these targets bring up the need for the development of new modelling frameworks and governance systems that will be based on competitive, secure and sustainable national action plans. For this purpose, the Dispa-SET model has been applied to six countries in the Western Balkans region. In the first scenario, the model has been validated for the year 2010. The second scenario has been developed according to the targets from national energy strategies for the years 2020 and 2030, while the third scenario has been developed with the purpose of determining the maximum share of renewable energy sources in the regional power mix. Simulation results indicate that the integration of additional wind and solar capacities, compared to the short and long-term national strategies for the years 2020 and 2030, can be achieved without compromising the stability of the system.

Abstract The relevance of sector coupling is increasing when shifting from the current highly centralised and mainly fossil fuel-based energy system to a more decentralized and renewable energy system. Cross-sectoral linkages are already recognized as a cost-effective decarbonisation strategy that provides significant flexibility to the system. Modelling such cross-sectoral interconnections is thus highly relevant. In this work, these interactions are considered in a long-term perspective by uni-directional soft-linking of two models: JRC-EU-TIMES, a long term planning multisectoral model, and Dispa-SET, a unit commitment and optimal dispatch model covering multiple energy sectors such as power, heating & cooling, transportation etc. The impact of sector coupling in future Europe-wide energy systems with high shares of renewables is evaluated through five scenarios. Results show that the contributions of individual sectors are quite diverse. The transport sector provides the highest flexibility potential in terms of power curtailment, load shedding, congestion in the interconnection lines and resulting greenhouse gas emissions reduction. Nevertheless, allowing combinations of multiple flexibility options such as hydro for the long-term, electric vehicles and flexible thermal units for the short-term provides the best solution in terms of system adequacy, greenhouse gas emissions and operational costs.

Abstract District heating has already proven to be a suitable solution for the decarbonisation of the most energy intensive energy sector in Europe, heating and cooling. However, to achieve this, it needs to incorporate renewable and sustainable energy sources into the generation mix which is still dominated by fossil fuels in many countries. Alongside traditional renewables like solar thermal, geothermal and biomass, excess heat from the industrial and service sector has a high untapped potential. Nonetheless, to utilize it in district heating, third party access must be granted. For that reason, a wholesale day ahead heat market has been modelled in this study and validated on a case study in the city of Sisak in Croatia. The idea was twofold: to evaluate the functionality of such a heat market and its effect on the existing system, as well as to analyse the integration of high and low temperature excess heat sources in different conditions, including the use of thermal storage, as well as the competition with low-cost renewables, i.e. solar thermal. The results have shown that the introduction of a wholesale day ahead heat market would ensure the positive total welfare in all the scenarios. The benefit for the demand side and the total welfare would increase even more if excess heat sources are integrated in the system and especially if they are combined with a thermal storage to increase their capacity factor, which would also decrease the competing effect of solar thermal. Finally, it was shown that low temperature excess heat is not feasible in the high temperature district heating and the transfer to the 4th generation district heating is required to feasibly utilise low temperature sources.

Abstract Waste heat recovery systems are today considered as a valuable solution to increase energy efficiency of industrial applications and heavy-duty vehicles, as it uses a thermodynamic organic Rankine cycle system to recover the heat losses to produce electrical or mechanical power. Optimal performance of such machines is often achieved at conditions where complex time-varying nonlinear dynamics are encountered, making the automatic control strategy a fundamental element to maximise the energy efficiency. In this paper the development of a multiple model predictive controller suitable for industrial implementation is presented, and its effectiveness is experimentally validated for the task of maximising output power of a 11 kW el small-scale ORC power unit used in a waste heat recovery application. The main advantage of the proposed controller is the possibility to use different model structures to describe local dynamics without increasing complexity of the optimisation problem. Additionally, experimental results illustrate that the entire operating range of the system might be classified in two regions, a quasi-linear and a highly nonlinear region for ‘high’ and ‘low’ superheating degrees respectively. Closed-loops tests lead to the conclusion that a single linear model predictive controller might only be used under suboptimal operation of low power production (on the quasi-linear region for ‘high’ superheating), otherwise leading to poor performance or even instability. Alternatively, the proposed strategy keeps the cycle stable over the entire range of conditions and allows to increase the net electrical energy produced by at least 6 % , even under drastic waste heat source variations, when operating closer to the minimum allowed superheating degree.