A. Giostri | Politecnico di Milano (original) (raw)

Papers by A. Giostri

Renewable Energy, 2019

This paper studies a small-scale CSP system composed of a solar tower and a recuperative air micr... more This paper studies a small-scale CSP system composed of a solar tower and a recuperative air micro gas turbine (i.e. net power in the 100e200 kW e range). A code is developed to determine the optical performance of the heliostat field coupled with a secondary concentrator, while another code computes the thermal engine performance. The 832 m 2 heliostat field layout is taken from a real plant, while the secondary optics is studied to maximize the optical-thermal efficiency. The selected secondary concentrator (CPC), with an aperture diameter of 0.5 m and an acceptance angle of 35 tilted of 52.5 , guarantees an overall optical efficiency of 77.9% in design conditions (Spring equinox, solar noon) and of 66.9% on yearly basis. For every Effective DNI (EDNI) and ambient temperature the turbine operation is optimized allowing to achieve a yearly solar-to-electricity efficiency of 16.3%. Summing up the cost of each component, an overall plant cost of about 2300 V/kW (peak) and a LCOE of 175 V/MWh are obtained. A sensitivity analysis on design EDNI, impacting on turbine size, is performed showing that its reduction from 700 W/m 2 to 550 W/m 2 allows reducing the LCOE down to 158 V/MWh, a value competitive with large-scale solar towers. The possibility of hybridization of plant (i.e. improving the gas turbine power output in selected hours, by means of biomethane or natural gas combustion) was considered to further reduce the LCOE.

Energy, 2017

This paper investigates the integration of a district heating heat pump for the production of abo... more This paper investigates the integration of a district heating heat pump for the production of about 4.65 MW th with the drinking water networkeplaying the role of low temperature heat source-as an alternative to conventional fossil fuel heating. The heat recovery reduces water temperature from 15 C to 12 C, thus requiring partial reheating by the drinking water end-user that needs to be estimated to evaluate the energetic convenience of this solution. Heat transfer between water mains and surrounding soil is considered by a proper thermal model computing the temperature vs. time profile at nodes. The developed model, which exploits Epanet to simulate the water network, compares the primary energy consumption and CO 2 emissions of the studied system with a conventional district heating solution. Each component, which constitute the overall system, (i.e. heat pump, water network, heating by water enduser etc.) is analyzed and modelled. Assuming a fossil fuel based scenario, the investigated heat pump system reduces the overall primary energy consumption and CO 2 emission by about 3%. This value boosts to 41% in case all the electricity generation relies on renewables, thus proving this solution is a promising alternative to conventional district heating in future energy scenarios dominated by renewables.

Renewable Energy, 2016

This paper investigates the smart integration of a 500 ha microalgae culturing facility with a la... more This paper investigates the smart integration of a 500 ha microalgae culturing facility with a large scale coal power plant (758.6 MW e): a fraction of the CO 2 contained in the coal plant flue gases is used for the algal cultivation, a fraction of the low-temperature flue gas heat available is used for the biomass drying, finally the produced biomass is co-fired in the coal plant. The produced algal biomass represents approximately 1% of the boiler heat input. Through the solution of energy and mass balances of each plant component, the overall system performances in terms of net energy ratio (NER) and CO 2 emissions reduction are obtained. The computed NER (1.92) guarantees an energy harvest almost twice the energetic cost needed to produce the microalgal fuel. The total CO 2 emissions are reduced of approximately 0.48%, identifying microalgae cofiring as a solution able to reduce the environmental impact of electricity generation. A simplified economic analysis has allowed an estimate of the algal system investment cost (about 235 kV ha À1) and of the levelized cost of electricity (LCOE) (554.4 V MWh À1). A set of sensitivity analyses is finally performed to investigate the influence of the initial hypotheses on the results.

Energy Procedia, 2014

Solar tower based plants are seen as a promising technology to reduce the cost of electricity fro... more Solar tower based plants are seen as a promising technology to reduce the cost of electricity from solar radiation. This paper assesses the design and overall yearly performances of two different solar tower concepts featuring two commercial plants running in Spain. The first plant investigated is based on Direct Steam Generation and a cavity receiver (PS-10 type). The second plant considers an external cylindrical receiver with molten salts as heat transfer fluid and storage system (Gemasolar type). About the optical assessment performed with DELSOL3, a calibration of heliostat aim points was performed to match available flux maps on the receiver. Moving to results, the PS-10 type has higher optical performances both nominal design and yearly average. This is due both to the field size and orientation which guarantee a higher efficiency and to the receiver concept itself. About power production, the molten salts allow higher temperature and consequently conversion efficiency than PS-10. The solar-to-electricity efficiency is equal to 18.7% vs. 16.4% of DSG cavity plant. The obtained results are strictly related to the set of assumptions made on each plant component: when available real plant data where used. The two solar tower plants results were also compared to corresponding commercial linear focus plants featuring the same power block concept. Gemasolar type shows a higher solar-to-electricity efficiency compared to a parabolic trough plant with storage (18.7% vs. 15.4%) because of the higher maximum temperatures and, consequently, power block efficiency. PS-10 is better than a linear Fresnel DSG (16.4% vs. 10.4%) because of the higher optical performances.

The paper deals with the development and testing of an innovative code for the performance predic... more The paper deals with the development and testing of an innovative code for the performance prediction of solar trough based CSP plants in off-design conditions. The code is developed in MS Visual Basic 6.0 with Excel as user interface. The proposed code originates from a previously presented algorithm for on-design sizing and cost estimation of the solar field lay-out, as well as of the main components of the plant, including connecting piping and the steam cycle. Off-design calculation starts from data obtained through the on-design algorithm and considers steady-state situations. Both models are implemented in the same software, named PATTO (PArabolic Trough Thermodynamic Optimization), which is very flexible: the optical-thermal model of collectors can simulate different kinds of parabolic trough systems in commerce, including a combination of various mirrors, receivers and supports. The code is also flexible in terms of working fluid, temperature and pressure range, and can also simulate direct steam generation plants (DSG). Regarding the power block, a conventional steam cycle with super-heater, eventually a re-heater section, and up to seven regenerative bleedings is adopted. The off-design model calculates thermal performance of collectors taking into account proper correlations for convective heat transfer coefficients, considering also boiling regime in DSG configurations. Solar plant heat and mass balances and performances at off-design conditions are estimated by accounting for the constraints imposed by the available heat transfer areas in heat exchangers and condenser, as well as the characteristic curve of the steam turbine. The numerical model can be used for a single calculation in a specific off-design condition, as well as for a whole year estimation of energy balances with an hourly resolution. The model is tested towards real applications and reference values found in literature; in particular, focusing on SEGS VI plant in the USA and SAM® code. Annual energy balances with ambient condition taken from TMY3 database are obtained, showing good accuracy of predicted performances. The code potentiality in the design process reveals twofold: it can be used for plant optimization in feasibility studies; moreover it is useful to find the best control strategy of a plant, especially the mass flow of heat transfer fluid in each operating condition.Copyright © 2010 by ASME

Solar Energy, 2012

ABSTRACT Solar thermal plants are among the most promising technologies to replace fossil fuel st... more ABSTRACT Solar thermal plants are among the most promising technologies to replace fossil fuel stationary applications, and within solar thermal technologies, parabolic troughs are considered the most mature application in the market. This paper compares different solar field technologies, in terms of both performance at design conditions and annual energy production; an in-house code, PATTO, was used to perform energy balances. We considered a reference case reflecting state-of-the-art Nevada Solar One, which showed a design efficiency and annual average efficiency of 22.4% and 15.3%, respectively, in agreement with actual performance. If solar salts are used as heat-transfer fluid instead of synthetic oil (e.g. ARCHIMEDE plant), the efficiency improved within the range of 6% due to the higher maximum temperature. Further thermodynamic advantages can be achieved with a direct steam generation plant; the main drawback is the more complex transient control and no commercially available storage systems. We propose the innovative Milan configuration, which combines advantages of direct steam evaporation and the use of a heat-transfer fluid, to investigate both synthetic oil and solar salts for steam superheating and reheating. Results for this configuration are very promising, with a sun-to-electric annual average efficiency of 17.8%, which is 16% higher than the reference case. Detailed daily simulations showed that advantages are more significant at low radiation. However, the plant should be optimized on an economic basis and we will discuss this in a future paper.

Renewable Energy, 2011

This paper presents the development and testing of an innovative code for the prediction of therm... more This paper presents the development and testing of an innovative code for the prediction of thermodynamic performances at nominal conditions, as well as a preliminary plant sizing and investment costs estimation for different parabolic trough solar fields. Part A of the paper presented in detail the model and validated it toward existing plants. This part discusses potentialities of the PATTO code (Parabolic Trough Thermodynamic Optimization) in terms of the capability (i) to compare the HCEs performances of various manufacturers, (ii) to accomplish an economic analysis and evaluate the specific investment costs of different technologies, (iii) to carry out a sensitivity analysis on the HCE performances and (iv) to implement innovative plant configurations. The potentiality of the economic analysis has been tested toward the recently built Nevada Solar One plant, while the sensitivity analysis of collector performances has been validated with a parametric study found in literature. PATTO allowed to propose and test an original hybrid solution with potential thermodynamic and economic advantages: results obtained by the code at nominal conditions show an efficiency gain of 1.2% points and potential investment costs saving of 6.5% with respect to a state-of-the-art reference plant.

Journal of Solar Energy Engineering, 2012

Parabolic trough (PT) technology can be considered the state of the art for solar thermal power p... more Parabolic trough (PT) technology can be considered the state of the art for solar thermal power plants thanks to the almost 30 yr of experience gained in SEGS and, recently, Nevada Solar One plants in the United States and Andasol plant in Spain. One of the major issues that limits the wide diffusion of this technology is the high investment cost of the solar field and, particularly, of the solar collector. For this reason, research has focused on developing new solutions that aim to reduce costs. This paper compares, at nominal conditions, commercial Fresnel technology for direct steam generation with conventional parabolic trough technology based on synthetic oil as heat-transfer. The comparison addresses nominal conditions as well as annual average performance. In both technologies, no thermal storage system is considered. Performance is calculated by Thermoflex®, a commercial code, with a dedicated component to evaluate solar plant. Results will show that, at nominal conditions,...

Journal of Solar Energy Engineering, 2011

This paper deals with the development and testing of an innovative code for the performance predi... more This paper deals with the development and testing of an innovative code for the performance prediction of solar trough based concentrated solar power (CSP) plants in off-design conditions. Off-design calculation starts from data obtained through the on-design algorithm and considers steady-state situations. The model is implemented in flexible software, named patto (parabolic trough thermodynamic optimization): the optical-thermal collector model can simulate different types of parabolic trough systems in commerce, including a combination of various mirrors, receivers and supports. The code is also flexible in terms of working fluid, temperature and pressure range, and can also simulate direct steam generation (DSG) plants. Solar plant heat and mass balances and performance at off-design conditions are estimated by accounting for the constraints imposed by the available heat transfer areas in heat exchangers, as well as by the characteristic curve of the steam turbine. The numerical...

Renewable Energy, 2019

In the present scenario of ever-increasing world electric power demand with increased attention t... more In the present scenario of ever-increasing world electric power demand with increased attention to environmental issues, Ocean Thermal Energy Conversion (OTEC) plants, because of their enormous potential, are gaining interest. In the present work, a techno-economic analysis of closed OTEC (CC-OTEC) cycles for electric power production is conducted. The effect of working fluid selection and number of evaporation levels from the techno-economic point of view are observed with simplified numerical models. A more detailed analysis of the single level power plant with the selected working fluid is also reported. Sizing of heat exchangers in the configuration found by this detailed analysis is conducted and capital cost estimation for the power plant has been assessed. With the introduction of simplifying assumptions on electric energy produced by the plant, the levelized cost of energy (LCOE) is finally calculated.

ABSTRACT Solar thermal plants are among the most promising technologies to replace fossil fuel st... more ABSTRACT Solar thermal plants are among the most promising technologies to replace fossil fuel stationary applications, and within solar thermal technologies, parabolic troughs are considered the most mature application in the market. This paper compares different solar field technologies, in terms of both performance at design conditions and annual energy production; an in-house code, PATTO, was used to perform energy balances. We considered a reference case reflecting state-of-the-art Nevada Solar One, which showed a design efficiency and annual average efficiency of 22.4% and 15.3%, respectively, in agreement with actual performance. If solar salts are used as heat-transfer fluid instead of synthetic oil (e.g. ARCHIMEDE plant), the efficiency improved within the range of 6% due to the higher maximum temperature. Further thermodynamic advantages can be achieved with a direct steam generation plant; the main drawback is the more complex transient control and no commercially available storage systems. We propose the innovative Milan configuration, which combines advantages of direct steam evaporation and the use of a heat-transfer fluid, to investigate both synthetic oil and solar salts for steam superheating and reheating. Results for this configuration are very promising, with a sun-to-electric annual average efficiency of 17.8%, which is 16% higher than the reference case. Detailed daily simulations showed that advantages are more significant at low radiation. However, the plant should be optimized on an economic basis and we will discuss this in a future paper.

Journal of Solar Energy Engineering, 2012

Parabolic trough can be considered the state of the art for solar thermal power plants thanks to ... more Parabolic trough can be considered the state of the art for solar thermal power plants thanks to the almost 30 years experience gained in SEGS and, recently, Nevada Solar One plants in US and Andasol plants in Spain. One of the major issues that limits the wide diffusion of this technology is the high investment cost of the solar field and, particularly, of the solar collector. For this reason, since several years research activity has been trying to develop new solutions with the aim of cost reduction. This work compares commercial Fresnel technology with conventional parabolic trough plant based on synthetic oil as heat transfer fluid at nominal conditions and evaluates yearly average performances. In both technologies, no thermal storage system is considered. In addition, for Fresnel, a Direct Steam Generation (DSG) case is investigated. Performances are calculated by a commercial code, Thermoflex ® , with dedicated component to evaluate solar plant. Results will show that, at nominal conditions, Fresnel technology have an optical efficiency of 67% which is lower than 75% of parabolic trough. Calculated net electric efficiency is about 19.25%, while parabolic trough technology achieves 23.6%. In off-design conditions, the gap between Fresnel and parabolic trough increases because the former is significantly affected by high radiation incident angles. The calculated sunto-electric annual average efficiency for Fresnel plant is 10.2%, consequence of the average optical efficiency of 38.8%, while parabolic trough achieve an overall efficiency of 16%, with an optical one of 52.7%. An additional case with Fresnel collector and synthetic oil outlines differences among investigated cases.

Journal of Solar Energy Engineering, 2012

ABSTRACT This paper deals with the development and testing of an innovative code for the performa... more ABSTRACT This paper deals with the development and testing of an innovative code for the performance prediction of solar trough based concentrated solar power (CSP) plants in off-design conditions. Off-design calculation starts from data obtained through the on-design algorithm and considers steady-state situations. The model is implemented in flexible software, named patto (parabolic trough thermodynamic optimization): the optical-thermal collector model can simulate different types of parabolic trough systems in commerce, including a combination of various mirrors, receivers and supports. The code is also flexible in terms of working fluid, temperature and pressure range, and can also simulate direct steam generation (DSG) plants. Solar plant heat and mass balances and performance at off-design conditions are estimated by accounting for the constraints imposed by the available heat transfer areas in heat exchangers, as well as by the characteristic curve of the steam turbine. The numerical model can be used e

Renewable Energy, 2011

This paper presents the development and testing of an innovative code for the prediction of therm... more This paper presents the development and testing of an innovative code for the prediction of thermodynamic performances at nominal conditions, as well as a preliminary plant sizing and investment costs estimation for different parabolic trough solar fields. Part A of the paper presented in detail the model and validated it toward existing plants. This part discusses potentialities of the PATTO code (Parabolic Trough Thermodynamic Optimization) in terms of the capability (i) to compare the HCEs performances of various manufacturers, (ii) to accomplish an economic analysis and evaluate the specific investment costs of different technologies, (iii) to carry out a sensitivity analysis on the HCE performances and (iv) to implement innovative plant configurations. The potentiality of the economic analysis has been tested toward the recently built Nevada Solar One plant, while the sensitivity analysis of collector performances has been validated with a parametric study found in literature. PATTO allowed to propose and test an original hybrid solution with potential thermodynamic and economic advantages: results obtained by the code at nominal conditions show an efficiency gain of 1.2% points and potential investment costs saving of 6.5% with respect to a state-of-the-art reference plant.

Renewable Energy, 2019

This paper studies a small-scale CSP system composed of a solar tower and a recuperative air micr... more This paper studies a small-scale CSP system composed of a solar tower and a recuperative air micro gas turbine (i.e. net power in the 100e200 kW e range). A code is developed to determine the optical performance of the heliostat field coupled with a secondary concentrator, while another code computes the thermal engine performance. The 832 m 2 heliostat field layout is taken from a real plant, while the secondary optics is studied to maximize the optical-thermal efficiency. The selected secondary concentrator (CPC), with an aperture diameter of 0.5 m and an acceptance angle of 35 tilted of 52.5 , guarantees an overall optical efficiency of 77.9% in design conditions (Spring equinox, solar noon) and of 66.9% on yearly basis. For every Effective DNI (EDNI) and ambient temperature the turbine operation is optimized allowing to achieve a yearly solar-to-electricity efficiency of 16.3%. Summing up the cost of each component, an overall plant cost of about 2300 V/kW (peak) and a LCOE of 175 V/MWh are obtained. A sensitivity analysis on design EDNI, impacting on turbine size, is performed showing that its reduction from 700 W/m 2 to 550 W/m 2 allows reducing the LCOE down to 158 V/MWh, a value competitive with large-scale solar towers. The possibility of hybridization of plant (i.e. improving the gas turbine power output in selected hours, by means of biomethane or natural gas combustion) was considered to further reduce the LCOE.

Energy, 2017

This paper investigates the integration of a district heating heat pump for the production of abo... more This paper investigates the integration of a district heating heat pump for the production of about 4.65 MW th with the drinking water networkeplaying the role of low temperature heat source-as an alternative to conventional fossil fuel heating. The heat recovery reduces water temperature from 15 C to 12 C, thus requiring partial reheating by the drinking water end-user that needs to be estimated to evaluate the energetic convenience of this solution. Heat transfer between water mains and surrounding soil is considered by a proper thermal model computing the temperature vs. time profile at nodes. The developed model, which exploits Epanet to simulate the water network, compares the primary energy consumption and CO 2 emissions of the studied system with a conventional district heating solution. Each component, which constitute the overall system, (i.e. heat pump, water network, heating by water enduser etc.) is analyzed and modelled. Assuming a fossil fuel based scenario, the investigated heat pump system reduces the overall primary energy consumption and CO 2 emission by about 3%. This value boosts to 41% in case all the electricity generation relies on renewables, thus proving this solution is a promising alternative to conventional district heating in future energy scenarios dominated by renewables.

Renewable Energy, 2016

This paper investigates the smart integration of a 500 ha microalgae culturing facility with a la... more This paper investigates the smart integration of a 500 ha microalgae culturing facility with a large scale coal power plant (758.6 MW e): a fraction of the CO 2 contained in the coal plant flue gases is used for the algal cultivation, a fraction of the low-temperature flue gas heat available is used for the biomass drying, finally the produced biomass is co-fired in the coal plant. The produced algal biomass represents approximately 1% of the boiler heat input. Through the solution of energy and mass balances of each plant component, the overall system performances in terms of net energy ratio (NER) and CO 2 emissions reduction are obtained. The computed NER (1.92) guarantees an energy harvest almost twice the energetic cost needed to produce the microalgal fuel. The total CO 2 emissions are reduced of approximately 0.48%, identifying microalgae cofiring as a solution able to reduce the environmental impact of electricity generation. A simplified economic analysis has allowed an estimate of the algal system investment cost (about 235 kV ha À1) and of the levelized cost of electricity (LCOE) (554.4 V MWh À1). A set of sensitivity analyses is finally performed to investigate the influence of the initial hypotheses on the results.

Energy Procedia, 2014

Solar tower based plants are seen as a promising technology to reduce the cost of electricity fro... more Solar tower based plants are seen as a promising technology to reduce the cost of electricity from solar radiation. This paper assesses the design and overall yearly performances of two different solar tower concepts featuring two commercial plants running in Spain. The first plant investigated is based on Direct Steam Generation and a cavity receiver (PS-10 type). The second plant considers an external cylindrical receiver with molten salts as heat transfer fluid and storage system (Gemasolar type). About the optical assessment performed with DELSOL3, a calibration of heliostat aim points was performed to match available flux maps on the receiver. Moving to results, the PS-10 type has higher optical performances both nominal design and yearly average. This is due both to the field size and orientation which guarantee a higher efficiency and to the receiver concept itself. About power production, the molten salts allow higher temperature and consequently conversion efficiency than PS-10. The solar-to-electricity efficiency is equal to 18.7% vs. 16.4% of DSG cavity plant. The obtained results are strictly related to the set of assumptions made on each plant component: when available real plant data where used. The two solar tower plants results were also compared to corresponding commercial linear focus plants featuring the same power block concept. Gemasolar type shows a higher solar-to-electricity efficiency compared to a parabolic trough plant with storage (18.7% vs. 15.4%) because of the higher maximum temperatures and, consequently, power block efficiency. PS-10 is better than a linear Fresnel DSG (16.4% vs. 10.4%) because of the higher optical performances.

The paper deals with the development and testing of an innovative code for the performance predic... more The paper deals with the development and testing of an innovative code for the performance prediction of solar trough based CSP plants in off-design conditions. The code is developed in MS Visual Basic 6.0 with Excel as user interface. The proposed code originates from a previously presented algorithm for on-design sizing and cost estimation of the solar field lay-out, as well as of the main components of the plant, including connecting piping and the steam cycle. Off-design calculation starts from data obtained through the on-design algorithm and considers steady-state situations. Both models are implemented in the same software, named PATTO (PArabolic Trough Thermodynamic Optimization), which is very flexible: the optical-thermal model of collectors can simulate different kinds of parabolic trough systems in commerce, including a combination of various mirrors, receivers and supports. The code is also flexible in terms of working fluid, temperature and pressure range, and can also simulate direct steam generation plants (DSG). Regarding the power block, a conventional steam cycle with super-heater, eventually a re-heater section, and up to seven regenerative bleedings is adopted. The off-design model calculates thermal performance of collectors taking into account proper correlations for convective heat transfer coefficients, considering also boiling regime in DSG configurations. Solar plant heat and mass balances and performances at off-design conditions are estimated by accounting for the constraints imposed by the available heat transfer areas in heat exchangers and condenser, as well as the characteristic curve of the steam turbine. The numerical model can be used for a single calculation in a specific off-design condition, as well as for a whole year estimation of energy balances with an hourly resolution. The model is tested towards real applications and reference values found in literature; in particular, focusing on SEGS VI plant in the USA and SAM® code. Annual energy balances with ambient condition taken from TMY3 database are obtained, showing good accuracy of predicted performances. The code potentiality in the design process reveals twofold: it can be used for plant optimization in feasibility studies; moreover it is useful to find the best control strategy of a plant, especially the mass flow of heat transfer fluid in each operating condition.Copyright © 2010 by ASME

Solar Energy, 2012

ABSTRACT Solar thermal plants are among the most promising technologies to replace fossil fuel st... more ABSTRACT Solar thermal plants are among the most promising technologies to replace fossil fuel stationary applications, and within solar thermal technologies, parabolic troughs are considered the most mature application in the market. This paper compares different solar field technologies, in terms of both performance at design conditions and annual energy production; an in-house code, PATTO, was used to perform energy balances. We considered a reference case reflecting state-of-the-art Nevada Solar One, which showed a design efficiency and annual average efficiency of 22.4% and 15.3%, respectively, in agreement with actual performance. If solar salts are used as heat-transfer fluid instead of synthetic oil (e.g. ARCHIMEDE plant), the efficiency improved within the range of 6% due to the higher maximum temperature. Further thermodynamic advantages can be achieved with a direct steam generation plant; the main drawback is the more complex transient control and no commercially available storage systems. We propose the innovative Milan configuration, which combines advantages of direct steam evaporation and the use of a heat-transfer fluid, to investigate both synthetic oil and solar salts for steam superheating and reheating. Results for this configuration are very promising, with a sun-to-electric annual average efficiency of 17.8%, which is 16% higher than the reference case. Detailed daily simulations showed that advantages are more significant at low radiation. However, the plant should be optimized on an economic basis and we will discuss this in a future paper.

Renewable Energy, 2011

This paper presents the development and testing of an innovative code for the prediction of therm... more This paper presents the development and testing of an innovative code for the prediction of thermodynamic performances at nominal conditions, as well as a preliminary plant sizing and investment costs estimation for different parabolic trough solar fields. Part A of the paper presented in detail the model and validated it toward existing plants. This part discusses potentialities of the PATTO code (Parabolic Trough Thermodynamic Optimization) in terms of the capability (i) to compare the HCEs performances of various manufacturers, (ii) to accomplish an economic analysis and evaluate the specific investment costs of different technologies, (iii) to carry out a sensitivity analysis on the HCE performances and (iv) to implement innovative plant configurations. The potentiality of the economic analysis has been tested toward the recently built Nevada Solar One plant, while the sensitivity analysis of collector performances has been validated with a parametric study found in literature. PATTO allowed to propose and test an original hybrid solution with potential thermodynamic and economic advantages: results obtained by the code at nominal conditions show an efficiency gain of 1.2% points and potential investment costs saving of 6.5% with respect to a state-of-the-art reference plant.

Journal of Solar Energy Engineering, 2012

Parabolic trough (PT) technology can be considered the state of the art for solar thermal power p... more Parabolic trough (PT) technology can be considered the state of the art for solar thermal power plants thanks to the almost 30 yr of experience gained in SEGS and, recently, Nevada Solar One plants in the United States and Andasol plant in Spain. One of the major issues that limits the wide diffusion of this technology is the high investment cost of the solar field and, particularly, of the solar collector. For this reason, research has focused on developing new solutions that aim to reduce costs. This paper compares, at nominal conditions, commercial Fresnel technology for direct steam generation with conventional parabolic trough technology based on synthetic oil as heat-transfer. The comparison addresses nominal conditions as well as annual average performance. In both technologies, no thermal storage system is considered. Performance is calculated by Thermoflex®, a commercial code, with a dedicated component to evaluate solar plant. Results will show that, at nominal conditions,...

Journal of Solar Energy Engineering, 2011

This paper deals with the development and testing of an innovative code for the performance predi... more This paper deals with the development and testing of an innovative code for the performance prediction of solar trough based concentrated solar power (CSP) plants in off-design conditions. Off-design calculation starts from data obtained through the on-design algorithm and considers steady-state situations. The model is implemented in flexible software, named patto (parabolic trough thermodynamic optimization): the optical-thermal collector model can simulate different types of parabolic trough systems in commerce, including a combination of various mirrors, receivers and supports. The code is also flexible in terms of working fluid, temperature and pressure range, and can also simulate direct steam generation (DSG) plants. Solar plant heat and mass balances and performance at off-design conditions are estimated by accounting for the constraints imposed by the available heat transfer areas in heat exchangers, as well as by the characteristic curve of the steam turbine. The numerical...

Renewable Energy, 2019

In the present scenario of ever-increasing world electric power demand with increased attention t... more In the present scenario of ever-increasing world electric power demand with increased attention to environmental issues, Ocean Thermal Energy Conversion (OTEC) plants, because of their enormous potential, are gaining interest. In the present work, a techno-economic analysis of closed OTEC (CC-OTEC) cycles for electric power production is conducted. The effect of working fluid selection and number of evaporation levels from the techno-economic point of view are observed with simplified numerical models. A more detailed analysis of the single level power plant with the selected working fluid is also reported. Sizing of heat exchangers in the configuration found by this detailed analysis is conducted and capital cost estimation for the power plant has been assessed. With the introduction of simplifying assumptions on electric energy produced by the plant, the levelized cost of energy (LCOE) is finally calculated.

ABSTRACT Solar thermal plants are among the most promising technologies to replace fossil fuel st... more ABSTRACT Solar thermal plants are among the most promising technologies to replace fossil fuel stationary applications, and within solar thermal technologies, parabolic troughs are considered the most mature application in the market. This paper compares different solar field technologies, in terms of both performance at design conditions and annual energy production; an in-house code, PATTO, was used to perform energy balances. We considered a reference case reflecting state-of-the-art Nevada Solar One, which showed a design efficiency and annual average efficiency of 22.4% and 15.3%, respectively, in agreement with actual performance. If solar salts are used as heat-transfer fluid instead of synthetic oil (e.g. ARCHIMEDE plant), the efficiency improved within the range of 6% due to the higher maximum temperature. Further thermodynamic advantages can be achieved with a direct steam generation plant; the main drawback is the more complex transient control and no commercially available storage systems. We propose the innovative Milan configuration, which combines advantages of direct steam evaporation and the use of a heat-transfer fluid, to investigate both synthetic oil and solar salts for steam superheating and reheating. Results for this configuration are very promising, with a sun-to-electric annual average efficiency of 17.8%, which is 16% higher than the reference case. Detailed daily simulations showed that advantages are more significant at low radiation. However, the plant should be optimized on an economic basis and we will discuss this in a future paper.

Journal of Solar Energy Engineering, 2012

Parabolic trough can be considered the state of the art for solar thermal power plants thanks to ... more Parabolic trough can be considered the state of the art for solar thermal power plants thanks to the almost 30 years experience gained in SEGS and, recently, Nevada Solar One plants in US and Andasol plants in Spain. One of the major issues that limits the wide diffusion of this technology is the high investment cost of the solar field and, particularly, of the solar collector. For this reason, since several years research activity has been trying to develop new solutions with the aim of cost reduction. This work compares commercial Fresnel technology with conventional parabolic trough plant based on synthetic oil as heat transfer fluid at nominal conditions and evaluates yearly average performances. In both technologies, no thermal storage system is considered. In addition, for Fresnel, a Direct Steam Generation (DSG) case is investigated. Performances are calculated by a commercial code, Thermoflex ® , with dedicated component to evaluate solar plant. Results will show that, at nominal conditions, Fresnel technology have an optical efficiency of 67% which is lower than 75% of parabolic trough. Calculated net electric efficiency is about 19.25%, while parabolic trough technology achieves 23.6%. In off-design conditions, the gap between Fresnel and parabolic trough increases because the former is significantly affected by high radiation incident angles. The calculated sunto-electric annual average efficiency for Fresnel plant is 10.2%, consequence of the average optical efficiency of 38.8%, while parabolic trough achieve an overall efficiency of 16%, with an optical one of 52.7%. An additional case with Fresnel collector and synthetic oil outlines differences among investigated cases.

Journal of Solar Energy Engineering, 2012

ABSTRACT This paper deals with the development and testing of an innovative code for the performa... more ABSTRACT This paper deals with the development and testing of an innovative code for the performance prediction of solar trough based concentrated solar power (CSP) plants in off-design conditions. Off-design calculation starts from data obtained through the on-design algorithm and considers steady-state situations. The model is implemented in flexible software, named patto (parabolic trough thermodynamic optimization): the optical-thermal collector model can simulate different types of parabolic trough systems in commerce, including a combination of various mirrors, receivers and supports. The code is also flexible in terms of working fluid, temperature and pressure range, and can also simulate direct steam generation (DSG) plants. Solar plant heat and mass balances and performance at off-design conditions are estimated by accounting for the constraints imposed by the available heat transfer areas in heat exchangers, as well as by the characteristic curve of the steam turbine. The numerical model can be used e

Renewable Energy, 2011

This paper presents the development and testing of an innovative code for the prediction of therm... more This paper presents the development and testing of an innovative code for the prediction of thermodynamic performances at nominal conditions, as well as a preliminary plant sizing and investment costs estimation for different parabolic trough solar fields. Part A of the paper presented in detail the model and validated it toward existing plants. This part discusses potentialities of the PATTO code (Parabolic Trough Thermodynamic Optimization) in terms of the capability (i) to compare the HCEs performances of various manufacturers, (ii) to accomplish an economic analysis and evaluate the specific investment costs of different technologies, (iii) to carry out a sensitivity analysis on the HCE performances and (iv) to implement innovative plant configurations. The potentiality of the economic analysis has been tested toward the recently built Nevada Solar One plant, while the sensitivity analysis of collector performances has been validated with a parametric study found in literature. PATTO allowed to propose and test an original hybrid solution with potential thermodynamic and economic advantages: results obtained by the code at nominal conditions show an efficiency gain of 1.2% points and potential investment costs saving of 6.5% with respect to a state-of-the-art reference plant.