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This paper presents the design of a novel high-temperature solar assisted triple-pressure level combined cycle power plant. The system includes innovative high-temperature flat plate evacuated solar thermal collectors, a double stage lithium bromide/water absorption chiller, pumps, heat exchangers, storage tanks, mixers, diverters, controllers and a triple-pressure combined cycle power plant. This novel layout uses high-vacuum non-concentrating flat plate solar thermal collectors driving a double effect absorption chiller, leading to an overall high coefficient of performance for the solar cooling section. The provided cooling energy is used to cool gas turbine inlet air to enhance system efficiency and electrical capacity. This effect is mainly performed during central hours of the day when the conventional gas-fired combined cycles dramatically suffer for efficiency and capacity reduction, as a consequence of the corresponding increase of external air temperature. Such increase is related to the higher availability of solar radiation. This technology may be a viable solution, especially for hot and dry areas, in terms of primary energy savings and increased revenues. This prototypal system was numerically analysed for a combined cycle with a rated electrical power of 99 MWe and an electrical efficiency of 56%, developing a dynamic simulation model and detailed thermo-economic optimizations. Special attention is also paid to the design of novel control strategies aiming at maximizing the solar cooling effect. The results of the dynamic simulations show a very high average thermal efficiency of the solar collectors, equal to 34%. Implications of the performed work allowed an increase of the power output up to 5.5% and a satisfactory payback period equal to 10.7 years. [ABSTRACT FROM AUTHOR]

This paper presents the design of a novel Solar Assisted Combined Cycle power plant. The system includes a solar loop equipped with a double stage absorption chiller driven by high-temperature high-vacuum non-concentrating flat-plate solar thermal collectors. The solar loop is coupled to a single-pressure Combined Cycle power plant. The cooling energy produced by the absorption chiller is used to cool gas turbine inlet air, aiming at enhancing system efficiency and electrical capacity. This Solar Assisted Combined Cycle arrangement is analysed through a dynamic system simulation and a thermoeconomic analysis is also performed aiming at determining the optimal set of design and operating parameters. The paper has the objective to prove the technical, energetic and economic feasibility of this technology, especially for hot and dry areas, with respect to other alternative air cooling configurations. In addition, solar collectors operating temperatures are high enough to drive a two stage absorption chiller, showing a Coefficient of Performance roughly two times higher than the one of a conventional single stage absorption chiller. This original configuration was numerically analysed in TRNSYS environment, developing a suitable dynamic simulation model in order to predict system performances. Suitable dynamic models are implemented for all the components included in the system. Special attention is also paid to the design of novel control strategies aiming at maximizing the utilization of solar energy for cooling purposes. In particular, a special control strategy managing cooling water flow is implemented in order to limit as much as possible water condensation within the cooling coil. The simulation also includes a detailed thermoeconomic model which accurately evaluates system capital and operating costs as a function of design and operating parameters. The simulations results show that a very high thermal efficiency of solar collectors, on average equal to 34%, is achieved. Results from the economic point of view were also satisfactory. In fact, the pay back period was about 8 years in the best case. Finally, in order to analyse the effects of the variation of the main design parameters, a parametric analysis is also presented. Such analysis shows that high solar radiation and low ambient humidity are crucial in order to achieve acceptable economic profitability indexes. [ABSTRACT FROM AUTHOR]

This paper presents a detailed exergetic analysis of a novel high-temperature Solar Assisted Combined Cycle (SACC) power plant. The system includes a solar field consisting of innovative high-temperature flat plate evacuated solar thermal collectors, a double stage LiBr-H2O absorption chiller, pumps, heat exchangers, storage tanks, mixers, diverters, controllers and a simple single-pressure Combined Cycle (CC) power plant. Here, a high temperature solar cooling system is coupled with a conventional combined cycle, in order to pre-cool gas turbine inlet air in order to enhance system efficiency and electrical capacity. In this paper, the system is analyzed from an exergetic point of view, on the basis of an energy-economic model presented in a recent work, where the obtained main results show that SACC exhibits a higher electrical production and efficiency with respect to the conventional CC. The system performance is evaluated by a dynamic simulation, where detailed simulation models are implemented for all the components included in the system. In addition, for all the components and for the system as whole, energy and exergy balances are implemented in order to calculate the magnitude of the irreversibilities within the system. In fact, exergy analysis is used in order to assess: exergy destructions and exergetic efficiencies. Such parameters are used in order to evaluate the magnitude of the irreversibilities in the system and to identify the sources of such irreversibilities. Exergetic efficiencies and exergy destructions are dynamically calculated for the 1-year operation of the system. Similarly, exergetic results are also integrated on weekly and yearly bases in order to evaluate the corresponding irreversibilities. The results showed that the components of the Joule cycle (combustor, turbine and compressor) are the major sources of irreversibilities. System overall exergetic efficiency was around 48%. Average weekly solar collector exergetic efficiency ranged from 6.5% to 14.5%, significantly increasing during the summer season. Conversely, absorption chiller exergy efficiency varies from 7.7% to 20.2%, being higher during the winter season. Combustor exergy efficiency is stably close to 68%, whereas the exergy efficiencies of the remaining components are higher than 80%. [ABSTRACT FROM AUTHOR]

In this work, a dynamic model of a high-temperature integrated solar combined cycle power plant is presented. The system includes a three-pressure combined cycle power plant coupled to parabolic trough solar collectors. Thermal storage, a heat solar steam generator, pumps, heat exchangers, and several controllers are also included in the system. Solar energy is used to produce additional steam to be supplied to the steam turbine of the combined cycle power plant. The integrated solar combined cycle system is based on the heat transfer fluid arrangement, exploiting solar energy to produce steam. The analysis is developed by a dynamic simulation model including detailed algorithms for the calculation of the performances of system components. Special control strategies are included in the model in order to accurately manage the steam production of the heat solar steam generator. The paper presents a thermo-economic and environmental comparison between the integrated solar combined cycle and a conventional combined cycle, powered by fossil fuels, based on dynamic simulations. A case study, referred to a plant with a maximum power of around 100 MW, located in Almeria (Southern Spain), is presented and discussed. A parametric analysis was also performed to show the effect of the variation of total solar field reflector area on the system performance. For the case under evaluation, a simple pay-back of 15 years was found, for a solar field aperture area of 80 000 m 2 ; however, the parametric analysis suggests that a smallest solar field area should be used under the hypotheses of the case study. [ABSTRACT FROM AUTHOR]

In this paper, a detailed numerical analysis of a Combined Cooling, Heating and Power system is presented, aiming at determining its optimal operating strategy in a real industrial application. The system layout includes a reciprocating engine, fuelled by natural gas, heat exchangers for waste-heat recovery, pumps, storage tanks, a single-effect water lithium bromide absorption chiller, a cooling tower, a back-up vapour-compression electric chiller, mixers and valves. A dynamic simulation model of the whole system was developed in TRNSYS. A case study was analysed, referred to a real industrial application, where the system under evaluation should be installed in the near future, providing electricity, mainly used for the production process, and space cooling. Real measured data were used to estimate the electric energy demand of the factory. A detailed building simulation model was used to calculate heating and cooling demands. A detailed economic analysis was carried out, aiming at evaluating: (i) the optimal size of the Combined Cooling, Heating and Power system; (ii) the optimum control strategy, from a thermo-economic point of view, comparing three different cases: Base-Load operation, electric load tracking and a new hybrid strategy based on the simultaneous tracking of electric and thermal-loads. The results showed that the optimal capacity of the system was lower than that selected by the designers of the real unit to be installed. The hybrid control strategy obtained the best profitability, achieving a simple pay-back period equal to 3.8 years, compared to 4.1 years achieved in case of electric-load tracking. [ABSTRACT FROM AUTHOR]

This paper presents a detailed numerical analysis of a trigeneration system serving a hospital, aiming at determining the best economic operating strategy. In this paper, a novel approach is presented aiming at developing a detailed tool to be used to predict the real time performance of the trigeneration system and to optimize its operation designing efficient control strategy. To this scope, a detailed dynamic simulation model was developed in TRNSYS environment. The simulated system provides electrical, thermal and cooling energy. It includes: a natural gas fired reciprocating engine, heat exchangers for waste-heat recovery, a single-stage LiBr-H 2 O Absorption Chiller (ACH), a cooling tower, pumps, a backup boiler, a backup vapor-compression electric chiller, storage tanks, valves, mixers. For such components, suitable control strategies and detailed algorithms were implemented in order to develop a model as much realistic as possible. To this scope, cooling and thermal loads were estimated by implementing detailed building dynamic simulations strictly related to the trigeneration system model. Three different operating strategies were evaluated in order to minimize the plant cost and maximize the performance of the system, namely: Thermal Load Tracking mode (TLT), Maximum Power Thermal Load Tracking mode (MPTLT) and Electricity Load Tracking mode (ELT). In the first one (MPTLT), the thermal power provided by the engine is always lower or equal to the thermal demand; in the second one (TLT), the engine operates according to an On/Off strategy; in the third one (ELT), the electrical power provided by the engine is always lower or equal to the electrical demand. The results of the case study were presented on different time bases (days, weeks, years). Such results show that the ELT control strategy can achieve a better profitability, with a simple payback period, SPB, equal to 4 years. For this strategy, 256 simulations were also performed by varying the main model parameters, in order to determine the combination showing the lowest SPB value and the highest Primary Energy Saving (PES) value. The optimum and the analysis of the optimum response surface was obtained by using Design of Experiments (DoE) method, showing that the best SPB value, equal to 3.9 years, comes out choosing an engine capacity ratio equal to 1, an ACH capacity ratio equal to 1, a hot tank volume equal to 5 m 3 and a cold tank volume equal to 2 m 3 . The best PES value, instead, is equal to 20.6% and comes out selecting an engine capacity ratio equal to 0.5, an ACH capacity ratio equal to 1, a hot tank volume equal to 6 m 3 and a cold tank volume equal to 2 m 3 . [ABSTRACT FROM AUTHOR]

Hospitals are very attractive for Combined Heat and Power (CHP) applications, due to their high and continuous demand for electric and thermal energy. However, both design and control strategies of CHP systems are usually based on an empiric and very simplified approach, and this may lead to non-optimal solutions. The paper presents a novel approach based on the dynamic simulation of a trigeneration system to be installed in a hospital located in Puglia (South Italy), with around 600 beds, aiming to investigate the energy and economic performance of the system, for a given control strategy (electric-load tracking). The system includes a natural gas fired reciprocating engine (with a rated power of 2.0 MW), a single-stage LiBr-H2O absorption chiller (with a cooling capacity of around 770 kW), auxiliary gas-fired boilers and steam generators, electric chillers, cooling towers, heat exchangers, storage tanks and several additional components (pipes, valves, etc.). Suitable control strategies, including proportional–integral–derivative (PID) and ON/OFF controllers, were implemented to optimize the trigeneration performance. The model includes a detailed simulation of the main components of the system and a specific routine for evaluating the heating and cooling demand of the building, based on a 3-D model of the building envelope. All component models were validated against experimental data provided by the manufacturers. Energy and economic models were also included in the simulation tool, to calculate the thermoeconomic performance of the system. The results show an excellent economic performance of the trigeneration system, with a payback period equal to 1.5 years and a profitability index (ratio of the Net Present Value to the capital cost) equal to 3.88, also due to the significant contribution of the subsidies provided by the current Italian regulation for CHP systems (energy savings certificates). [ABSTRACT FROM AUTHOR]