A stand-alone power production plant comprising a concentrated solar power unit merged into a combined cycle gas turbine plant integrated with a photovoltaic power unit

Abstract

A stand-alone power production plant with a high solar based renewable integration is disclosed. The power production plant comprises at least one electrical power unit connected to a combined cycle gas turbine plant and to a photovoltaic power unit and a concentrated solar power unit is merged into the combined cycle gas turbine plant. A thermal storage unit is also part of the power production plant, to collect heat from the CSP and optionally from the PV unit and to supply heat to the second thermodynamic cycle. Also disclosed are methods for operating the power production plant by minimizing and even zeroing both long-term and short-term fluctuations.

Description

A stand-alone power production plant comprising a concentrated solar power unit merged into a combined cycle gas turbine plant integrated with a photovoltaic power unitDescriptionTECHNICAL FIELD

[0001] The present disclosure concerns power production systems and methods. Embodiments disclosed herein specifically concern power production systems comprising a concentrated solar power unit merged into a combined cycle power plant integrated with a photovoltaic power unit, the power production system being configured to work in islanded configuration, i.e. being able to operate without the need for energy from an electrical network. Also disclosed herein are methods for operating the above power production systems by reducing fuel consumption and increasing overall flexibility and reliability through maximization of two solar-based renewable integration.BACKGROUND ART

[0002] A combined cycle power plants is an assembly of heat engines that work in tandem from the same source of heat, converting it into mechanical energy. Mechanical energy is generally used to drive a generator to produce power. On land, when used to make electricity the most common type is called a combined cycle gas turbine (CCGT) plant. The same principle is also used for marine propulsion, where it is called a combined gas and steam (COGAS) plant. Combining two or more thermodynamic cycles improves overall efficiency, which reduces fuel costs. The principle is that after completing its cycle, also called topping cycle, in the first engine, the working fluid (the exhaust) is still hot enough that a second subsequent heat engine can extract energy from the heat in the exhaust through a second thermodynamic cycle, also called bottoming cycle. Usually the heat passes through a heat exchanger so that the two engines can use different working fluids. Typically, the working fluid of the bottoming cycle is steam and the bottoming cycle comprises a steam generator, wherein steam is generated by heat recovered by the topping cycle and which is called Heat Recovery Steam Generator (HRSG) and one or more steam turbines. By generating power from multiple streams of work, the overall efficiency can be increased by 50-60%. Heatengines can only use part of the energy from their fuel, so in a non-combined cycle heat engine, the remaining heat (i.e., hot exhaust gas) from combustion is wasted.

[0003] Combined cycle gas turbines main advantages comprise efficiency (CCGTs are considered the most efficient fossil fuel-to-electricity converters), high flexibility, a generally low LCOE (Levelized Cost of Energy), which is largely dominated by fuel cost and varies depending on the natural gas price at a specific location. The main drawback is the high level of generated carbon emissions.

[0004] In the last years, due to the increased contribution of renewable energy generation, and intermittency being a nature of such kind of generation, grid reliability is compromised. Accordingly high flexibility, efficient partial load operation and reduced minimum operation load became crucial features for combined cycles. Partial load operation is generally characterized by efficiency reduction relative to full load operation. It is generally due to the decrease in the gas turbine efficiency, which is accounted for the lower pressure ratio and firing temperature at partial load. Therefore, hybridizing CCGT with renewable generation can be considered an attractive option for reducing emissions.

[0005] Solar PhotoVoltaic (PV) is a technology allowing the conversion of solar light into electricity. Solar PV has specific advantages as an energy source: once installed, its operation generates no pollution and no CO2 gas emissions and it allows scalability in respect of power needs.

[0006] Moreover, solar photovoltaic is a technology whose costs have been decreasing and are expected to continue decreasing, thus providing competitive LCOE values, but with relatively low capacity factors as electrical storage systems remain not cost- effective.

[0007] Hybridization of CCGT with PV has been proposed as a way to reduce carbon emissions. The hybridization of PV-CCGT is performed on operational level so that, whenever PV production is available, it is prioritized and the CCGT plant ramps down in order to accommodate the PV production, while the whole plant provides a required specific output by means of smart dispatch control. The advantage of this hybridization is the reduction of carbon emissions generated from the CCGT, in addition to the reduction of OpEx, as less fuel is burnt with higher PV integration. PV and CCGT, asgenerators in a grid where the plants operation is managed on the grid level are operated so that PV capacities are recruited when available and CCGT are recruited to cover the demand unmet by the renewable intermittent generators. The relatively fast response, especially for gas turbines of the topping cycle of the CCGT, is the feature that allows this functionality. In fact, even if both gas turbines of the topping cycle operating at higher temperatures and steam turbines of the bottoming cycle operating at lower temperatures can technically respond against the fluctuations, however gas turbines are much faster, while steam turbines respond with some delay. To optimize the integration between CCGT and PV, the fast response of the gas turbines and the slow response of the steam turbines has to be coordinated with each other. As a consequence, complex control systems are needed. An advantage of the hybridization of CCGT with PV is providing the possibility of sharing electrical interconnection lines and infrastructure in order to reduce costs.

[0008] A critical problem of PV system integration with CCGT is the mechanical effect imposed to the HRSG system, i.e. the bottoming cycle, due to the PV fluctuations. In fact, a decrease in the PV production causes the need of an increased energy from the CCGT, in order to maintain the overall energy production constant. In particular, the gas turbine of the topping cycle of the CCGT is operated to produce additional energy in order to respond to the decrease in the PV production. At the same time, the exhaust from the topping cycle is also increased, with a surplus of heat that is transferred to the steam of the bottoming cycle. The working fluid of the bottoming cycle is consequently heated at a higher temperature and the whole bottoming cycle undergoes a thermal stress. Additionally, the output of the bottoming cycle is also increased, and in order to maintain constant the required specific overall output of the PV-CCGT integrated system a smart dispatch control is needed.

[0009] On the other hand, PV needs to be curtailed during peak-solar irradiation days or hours, because of high cost of inverters. As a consequence, whenever PV would be able to produce its maximum (rated) electricity output during the peak-irradiance days, PV curtailment would be a considerable energy loss, especially when high amount of PV is integrated in the system. Therefore, PV system integration with CCGT negatively affect the operation costs of the system, due to PV curtailment, and the maintenance costs, due to thermal stress to HRSG that negatively affects its lifetime and mayhave an adverse environmental impact in case the CCGT has to be operated at higher regimes due to a decrease in PV production.

[0010] As a consequence, PV integration with CCGT in an islanded configuration has never been considered and implemented, due to its technical complications.

[0011] Accordingly, an improved system for stand-alone power production to address the issues of the systems of the current art would be beneficial and would be welcomed in the technology. More in general, it would be desirable to provide systems adapted to more efficiently address problems entailed by fluctuations of power production from the photovoltaic source, by increasing overall flexibility and reliability as well as zeroing the adverse effect of PV fluctuations on mechanical part of HRSG. As a consequence, the ST would work steadily with constant power factor instead of permanent fluctuations, which eliminate ST complexity and technical issues.SUMMARY

[0012] In one aspect, the subject matter disclosed herein is directed to a power production plant comprising a Concentrated Solar Power (CSP) unit merged into a Combined Cycle Gas Turbine (CCGT) power plant integrated with a Photovoltaic (PV) power plant. A Thermal Energy Storage (TES) is also present and it is shared between the CSP and the CCGT. The TES is optionally also receiving heat from the PV, via an electrical heater. An Electrical Battery Storage System (BESS) is preferably utilized for spinning reserve, not as a medium to shift the load. The system disclosed herein is able to supply any kind of load in an islanded-mode grid. In particular, the system allows to provide a constant load profile to be utilized for LNG application. Moreover, the system is applicable for both brownfield and greenfield projects. In particular, the exhaust gas of the topping cycle of the CCGT can be used to supply heat to the bottoming cycle only, to the thermal energy storage only or to both the bottoming cycle and the thermal energy storage.

[0013] In one aspect, the optional electrical heater is an electrical resistor connected to an electrical circuit of the photovoltaic power unit, the electrical resistor being in direct contact with the heat storage fluid of the thermal energy storage unit.

[0014] In still another aspect, the photovoltaic power unit includes a damping-filterconfigured to separate high-frequency fluctuations of photovoltaic power and to direct said high-frequency fluctuations to the electrical heater of the thermal energy storage unit or the BESS, instead of to the PV electrical output. This keeps the PV electrical output to the grid steadier (removing high frequency fluctuations). Without this filter, the high frequency power variations and the fast power variations of the PV should be compensated by the electrical output of GT. As a result, by using the filter, GT output will also remain steady in response to short-term fluctuations of the sun irradiation, which is beneficial in terms of GT control and maintenance. On the other end, the BESS can also be used to inject power to damp high frequencies.

[0015] The power production plant herein disclosed demonstrated to solve all the above specified technical problems of the prior art. Moreover, the power production plant herein disclosed also introduces a flexible system, which allows to realize the maximization of PV penetration to CCGT plant stably and let the maximum clean penetration (total PV and CSP) in accordance with climate agreements. In terms of economic benefits, the power production plant herein disclosed allows for a noticeable reduction in terms of normalized operational cost (Euro / MWh) compared to hybridization of PV with CCGT, with a very reasonable investment cost, as the system has an intrinsic capability, which allows to minimize the investment cost.

[0016] Moreover, the power production plant herein disclosed is able to reduce the capacity factor (and therefore production) of the topping cycle, consequently reducing fuel consumption and carbon tax, and at the same time increase the capacity factor of the bottoming cycle by adding clean energy obtained by CSP and TES, because steam turbines of the bottoming cycle are operated at their full capacity to produce power.

[0017] Increasing the capacity factor of the CCGT also has a direct effect on normalized capital cost (Euro / MW).

[0018] In another aspect, the subject matter disclosed herein concerns a method for controlling a power production plant comprising at least one electrical power generator connected to a combined cycle gas turbine plant, which is merged with a concentrated solar power unit, and the electrical power generator being also connected to a photovoltaic power unit, the plant comprising a thermal storage unit to collect heat from the CSP and optionally from the PV unit and to supply heat to the second thermodynamiccycle, the method comprising the steps of:- supplying heat of the exhaust gas from the topping cycle of the CCGT to the bottoming cycle of the CCGT; and / or- supplying heat of the exhaust gas from the topping cycle of the CCGT to the thermal storage unit; and- supplying heat of the thermal storage unit to the HRSG; and wherein the method can further comprise the steps of:- decreasing the amount of fuel supplied to the topping cycle of the CCGT during the day to reduce power production and compensate the increased power production by the PV unit; and- increasing the amount of heat from the thermal storage unit to the HRSG to compensate the decreased amount of heat of the exhaust gas from the first thermodynamic cycle unit to the HRSG; and wherein the method can also further comprise the steps of:- supplying power produced by the PV in excess with respect to the design conditions to the TES unit.BRIEF DESCRIPTION OF THE DRAWINGS

[0019] A more complete appreciation of the disclosed embodiments of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:Fig.1 illustrates a block diagram of a power production plant, according to a first embodiment;Fig.2 illustrates a block diagram of a power production plant, according to a second embodiment;Fig.3 illustrates a diagram showing power production contribution, during a sunny day, of a GT, ST and PV unit, according to an integrated GTCC+PV of the prior art;Fig.4 illustrates a diagram showing HRSG input heat from the GT, during a sunny day, on an hourly basis, according to an integrated GTCC+PV of the prior art;Fig.5 illustrates a diagram showing power production contribution, during a sunny day, of a GT, ST and PV unit of a power production plant according to the present disclosure; andFig.6 illustrates an exemplary diagram showing HRSG input heat from the GT and the TES, consequent to fluctuation of sun irradiation in a partly cloudy day, according to the present disclosure.DETAILED DESCRIPTION OF EMBODIMENTS

[0020] According to one aspect, the present subject matter is directed to systems and methods for producing power by maximizing solar-based renewable penetration to a combined cycle gas turbine plant and assuring stability of the system by increasing overall flexibility and reliability. Specifically, in one exemplary embodiment disclosed herein a power production plant is provided, the plant comprising a concentrated solar power unit merged into a combined cycle power plant integrated with a photovoltaic power unit, wherein the power production plant is configured to work in islanded configuration. In particular, the power production plant includes a Thermal Energy Storage (TES), shared among the concentrated solar power unit and the combined cycle power plant. Optionally, according to one aspect, the TES is also configured to receive heat from the photovoltaic power unit, for exemplary purposes by means of an electrical heater. The exhaust gas of the topping cycle of the Combined Cycle Gas Turbine plant (CCGT) can be used to supply heat to the bottoming cycle only, to the thermal energy storage only or to both the bottoming cycle and the thermal energy storage.

[0021] Embodiments disclosed herein provide for large-scale Photo Voltaic unit (PV) integration to CCGT in islanded power systems, by maximization of two solarbased renewable integration, without the necessity to utilize expensive Electrical Battery Storage System (BESS) or a big TES to shift the demand. Heat produced by Concentrated Solar Power (CSP) mirrors, heat produced by surplus energy of PV, and, depending on the configuration of the system and the operating conditions, no heat or some or all the heat produced by Gas Turbine (GT) exhaust are fed directly into the thermal storage. This combination creates a heat input for TES, which will be directly consumed at TES output by feeding to a Steam Turbine (ST) (alternatively in combination with heat produced by GT exhaust). This reduces TES to store energy and minimize considerably the size of TES.

[0022] Conveniently, according to the system disclosed herein, the size of TES can be extremely reduced compared to the big TES that are needed in the stand-alone CSPof the prior art to maintain the energy. The size of the TES in the system disclosed herein is reduced around 30-40 times with respect to the size of the TES of the standalone CSP of the prior art.

[0023] Moreover, integration of the CSP in the system disclosed herein does not need for dedicated power apparatuses, including a dedicated Heat Recovery Steam Generator (HRSG) and ST, since the system disclosed herein allows CSP to provide heat to the same ST and HRSG of the CCGT. Furthermore, the TES size can be significantly reduced. Therefore, CSP investment cost is considerably reduced compared to a standalone CSP, with increased economic feasibility.

[0024] An additional advantage of the power production systems disclosed herein is that HRSG thermal stress due to fluctuations of solar-based energy production from PV and consequent increase of GT operation can be significantly reduced or even zeroed. Consequently, the lifetime of the HRSG is increased and maintenance is reduced.

[0025] Finally, whenever PV produces its maximum (rated) electricity output, i.e. during the peak-irradiance days, PV curtailment and consequent energy loss can be avoided, the excess power being converted directly to heat inside TES. Conversion of excess power from the PV to heat inside the TES is preferably obtained via an inexpensive Electrical Resistor (ER). Such a solution allows to save operational cost and at the same time leads to a reduction for CSP investment cost.

[0026] Reference now will be made in detail to embodiments of the disclosure, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the disclosure, not limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. Reference throughout the specification to “one embodiment” or “an embodiment” or “some embodiments” means that the particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrase “in one embodiment” or “in an embodiment” or “in some embodiments” in various places throughout the specification is not necessarily referring to the same embodiment s). Further, the particular features, structures or characteristics may be combined in anysuitable manner in one or more embodiments.

[0027] When introducing elements of various embodiments the articles “a”, “an”, “the”, and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including”, and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[0028] Referring now to the drawings, Fig.1 shows a block diagram of an exemplary stand-alone power production plant according to the present disclosure. In particular, the stand-alone power production plant comprises an electrical power unit 10 connected to electrical power generators of a combined cycle gas turbine unit 20 through a first power line 61 and a second power line 62 and to a photovoltaic power unit 30 through a third power line 63. The power production plant also comprises a thermal energy storage unit 40, the thermal energy storage unit 40 comprising a heat storage fluid and being configured to collect, store and supply heat from and to the combined cycle gas turbine unit 20.

[0029] Additionally, the power production plant further comprises a concentrated solar power unit 50, configured to supply heat to the thermal energy storage unit 40 through a heat transfer line 71. Heat transfer from the concentrated solar power unit 50 to the thermal energy storage unit 40 can be obtained through any technology according to the prior art.

[0030] In particular, the combined cycle gas turbine unit 20 includes a first thermodynamic cycle unit 21, which is connected to the electrical power unit 10 through the electrical line 61, and a second thermodynamic cycle unit 22, which is connected to the electrical power unit 10 through the electrical line 62.

[0031] The first thermodynamic cycle unit 21 includes one or more gas turbines producing kinetic energy and an exhaust gas, wherein kinetic energy is transferred to the electrical power unit 10 and wherein the exhaust gas is directed to a heat exchanger 223 through a second heat transfer line 72. The second thermodynamic cycle unit 22 includes one or more heat recovery steam generators 221, wherein a working fluid is processed in a closed circuit comprising the heat exchanger 223 configured to exchange heat between the exhaust gas from the first thermodynamic cycle unit 21 andthe working fluid of the second thermodynamic cycle unit 22. The second thermodynamic cycle unit 22 further comprises an additional heat exchanger 224 configured to exchange heat between the heat storage fluid of the thermal energy storage unit 40 and the working fluid of the second thermodynamic cycle unit 22, through the heat transfer line 73. The heat exchangers 223, 224 can be arranged on the closed circuit in any configuration depending on the temperature of the heat stream of the heat transfer line 72 and the heat transfer line 73, so that evaporation of the working fluid can be obtained through thermal exchange with the heat transfer line at higher temperature. Finally, the second thermodynamic cycle unit 22 comprises an expansion unit 222, namely one or more steam turbines ST, configured to expand the working fluid vapor and produce kinetic energy that is transferred to the electrical power unit 10, and a condenser 225 to condense the working fluid.

[0032] Additionally, the exhaust gas of the first thermodynamic cycle unit 21 is directed through a heat transfer line 74 to the thermal energy storage unit 40. According to different embodiments, rather than to supply heat to both the second thermodynamic cycle unit 22 and the thermal energy storage unit 40, the exhaust gas of the first thermodynamic cycle unit 21 can be used to alternatively supply heat only to the second thermodynamic cycle unit 22 or only to the thermal energy storage unit 40.

[0033] The power production plant comprises an electrical battery storage system 32, connected to the electrical power unit 10 through the third power line 63, to stabilize the system, mainly, but not necessarily, in response to PV fluctuation.

[0034] In one embodiment, the electrical battery storage system 32 is configured to supply spinning reserve to the electrical power unit 10 through the third power line 63.

[0035] In one embodiment, the mirrors of the concentrated solar power unit 50 are configured to concentrate solar irradiation into a receiver 51 configured to exchange heat with the heat storage fluid of the thermal energy storage unit 40.

[0036] While in the block diagram of Fig.1 described so far, the first thermodynamic cycle unit 21 is configured to supply heat both to the second thermodynamic cycle unit 22 and to the thermal energy storage unit 40, in another embodiment the first thermodynamic cycle unit 21 can be configured to supply heat only to the second thermodynamic cycle unit 22 and in still another embodiment the first thermodynamic cycle unit21 can be configured to supply heat only to the thermal energy storage unit 40.

[0037] With continuing reference to Fig. l, Fig.2 shows a schematic of another exemplary power production plant according to the present disclosure. The same reference numbers designate the same or corresponding parts, elements or components already illustrated in Fig.1 and described above, and which will not be described again. According to the embodiment of Fig.2, the thermal energy storage unit 40 is configured to collect and store heat also from the photovoltaic power unit 30. In particular, heat is transferred from the photovoltaic power unit 30 to the thermal energy storage unit 40 by means of a fourth power line 64 conveying power produced by the photovoltaic power unit 30 to an electrical heater 41 that is in direct contact with the heat storage fluid of the thermal energy storage unit 40. Conveniently, the electrical heater 41 is an electrical resistor 41.

[0038] In another embodiment, the photovoltaic power unit 30 includes a dampingfilter 31, namely a resistor-capacitor circuit 31, configured to separate photovoltaic power fluctuations and to direct said fluctuations to the electrical heater 41 of the thermal energy storage unit 40, instead of directing it to the electrical power unit 10. This embodiment allows to keep the PV electrical output to the grid steadier (removing fluctuations). Without this damping-filter 31, all these power variations of PV 30 should be compensated by the electrical output of the GT. As a result, by using the damping-filter 31, GT output will also remain steady, which is not only beneficial in terms of GT control but also in terms of GT maintenance.

[0039] In one embodiment BESS and ER can be operated to cooperate with each other, in order to control the electrical output of the PV.

[0040] The operation of the power production plant disclosed herein can be better understood with reference to the following examples.

[0041] According to a configuration of the prior art, the topping cycle of an exemplary a combined cycle power plant can be provided with a GT with a capacity of 300MW, while the ST has a capacity of 160MW. The system is generally operated in steadily conditions, with both the GT and the ST working at 100% capacity factor during day and night. In fact, since the gas turbine works steadily, also the flue gas from the gas turbine has no fluctuation and therefore supplies a constant heat exchangeto the bottoming cycle through the second heat transfer line. As a consequence, this exemplary plant according to the prior art allows to achieve important advantages, which comprise an efficiency higher than 50%. On the other end, this exemplary plant of the prior art is dependent on fuel cost, which can vary depending on the natural gas price at a specific location. Another drawback of this technology is the higher and higher level of taxation, which is imposed, due to the high level of generated carbon emissions.

[0042] According to a second configuration of the prior art, the combined cycle power plant previously described can be combined with a PV unit, to reduce carbon emissions. On operational level, according to this exemplary configuration, power production from renewable sources is prioritized, meaning that, whenever PV production is available, the CCGT plant ramps down in order to accommodate the PV production, while the whole plant provides a required specific output by means of smart dispatch control. Assuming GT and ST are in perfect coordination against net load variation, the plant location being assumed to be in a place with a high solar irradiation with low variation during the year, such as, for example, in Sudan, calculation being based on hourly solar irradiation data and PV curtailment being calculated 8.7% during sunny days, then the power generation production is represented in Fig. 3, while the exemplary average power production during the lifetime of the power plant is 11% PV, 31% ST and 58% GT. A problem with this exemplary configuration according to the prior art is the fluctuation of heat supplied to the bottoming cycle of the CCGT, due to the non-constant operation of the GT during the day. In fact, since the gas turbine plant ramps down in order to accommodate the PV production, also the flue gas from the gas turbine decreases and therefore supplies a lower heat exchange to the heat recovery steam generator of the bottoming cycle. As a consequence, this exemplary plant according to the prior art involves a fluctuating amount of heat supplied to the HRSG, as shown in Fig. 4, which causes a thermal stresses on the same and consequently reduces the HRSG lifetime. Furthermore, not only ramping up and ramping down shown in figure impose the thermal stress on HRSG. During the day, PV fluctuation also creates thermal stress, which is not drawn in the figure for the sake of simplicity. Moreover, PV curtailment during the central hours of the day causes a considerable energy loss.

[0043] Finally, according to a configuration of the present disclosure, by merging a concentrated solar power unit into the combined cycle power plant integrated with aphotovoltaic power unit previously disclosed, it is possible to achieve at least two technical effects positively contributing to the power plant efficiency. In fact, assuming that a molten salt is used as heat storage fluid of the thermal energy storage unit 40 and CSP is provided with mirrors concentrating the solar radiation into a receiver, arranged in a solar tower, the receiver being configured to exchange heat with the heat storage fluid of the thermal energy storage unit 40, contributing in further reducing carbon emissions, with respect to a power plant wherein the CCGT is integrated only with a PV unit.

[0044] Moreover, by using GT exhaust gas to provide heat to both HRSG and TES it is possible to provide additional flexibility to the system in response to weather / load uncertainty. In fact, making reference to Fig. 6, while the contribution of PV to the power generation production is the same as in the previously described combined cycle power plant integrated with a PV unit, the GT ramping down in order to accommodate the PV production during the hours of sunlight, nevertheless the decreased amount of heat provided by the GT to the HRSG does not involve a corresponding lower power production by the ST, due to the additional heat available from the thermal energy storage unit 40. Therefore, fluctuation of heat provided to the HRSG due to long-term fluctuations of sun irradiation can be greatly reduced and even zeroed.

[0045] In terms of short term / instant fluctuations, a damping-filter 31, namely a high pass filter 31, can be applied to convert the PV fluctuations to heat passed to the thermal storage unit. Lower frequency solar power will be converted to electricity. This can minimize the GT instant fluctuations and improve its control and functionality. This high pass filter 31 should be utilized based on the weather forecast very close to the live operation of the power plant. Moreover, integration with BESS can reduce sudden variations and fluctuations of PV.

[0046] Additionally, the solution according to the present disclosure allows to avoid any losses due to curtailment during excess sun irradiation. In fact, instant excess fluctuations of sun irradiation do not need to be filtered, rather can be passed to the thermal storage unit and used for the HRSG or to the BESS. Therefore, PV capacity factor is consequently increased, such as solar integration in island-mode.

[0047] The heat supplied by the CSP 50 to the thermal storage unit 40 allows foranother technical effect. In fact, while the temperature of the flue gas from the GT ranges between 420 and 580°C, the temperature of the molten salt of the CSP can vary between 220 and 600°C. Since the efficiency of a thermodynamic system varies proportionally with the inlet temperature, then, in case the temperature of the CSP is higher than the temperature of the flue gas from the GT, this allows to reach a higher efficiency of the ST of the bottoming cycle of the CCGT. ST capacity factor is consequently increased.

[0048] The sizing of the CSP and the TES can be designed to allow the HRSG to be supplied with a constant amount of heat, i.e. the sum of heat from GT and from TES, during the hours of the day and of the night (long term fluctuations) and in any case of fluctuation due to atmospheric conditions (long term fluctuations), thus allowing to operate the HRSG without any thermal stress. In an exemplary power production plant according to the present disclosure, wherein the sizing of the GT, ST and PV is the same previously described, then the CSP can be designed to produce 136MW and the heat storage unit is calculated to need 7 MWh. By making a comparison with a stand alone power production plant based on a CSP and using a TES according to the prior art, the solution of the present disclosure allows for a reduction of about 100 times of the size of the TES compared to a stand-alone CSP with constant output and same daily energy consumption. Higher medium / long term flexibility can be achieved by increasing the size of TES, in order to respond robustly to seasonal fluctuations and uncertainties.

[0049] An additional advantage of the power production plant according to the present disclosure is the possibility to operate the system without the need for a BESS for load shifting, with a saving of 50 times per unit of energy with respect to the solutions of the prior art.

[0050] While aspects of the invention have been described in terms of various specific embodiments, it will be apparent to those of ordinary skill in the art that many modifications, changes, and omissions are possible without departing form the spirt and scope of the claims. In addition, unless specified otherwise herein, the order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments.

Claims

CLAIMS1. A power production plant comprising one or more electrical power units (10) connected to a first thermodynamic cycle unit (21), a second thermodynamic cycle unit (22) and a photovoltaic power unit (30), the photovoltaic power unit (30) being connected to said one or more electrical power units (10); the first thermodynamic cycle unit (21) including one or more gas turbines producing an exhaust gas and kinetic energy that is transferred to one or more electrical power generators forming part of or being connected to said one or more electrical power units (10), the second thermodynamic cycle unit (22) including a closed circuit comprising one or more heat exchangers (223) and one or more heat recovery steam generators (221), configured to heat and to evaporate a working fluid, one or more expansion units (222) configured to expand the working fluid vapor and produce kinetic energy that is transferred to one or more electrical power generators forming part of or being connected to said one or more electrical power units (10), and one or more condensers (225) to condense the working fluid, the first thermodynamic cycle unit (21) operating at a higher temperature than the second thermodynamic cycle unit (22), the power production plant also comprising a thermal energy storage unit (40), the thermal energy storage unit (40) comprising a heat storage fluid and being configured to supply heat to the second thermodynamic cycle unit (22) by means of one or more heat exchangers (224) configured to exchange heat between the heat storage fluid and the working fluid of the second thermodynamic cycle unit (22), wherein the power production plant further comprises a concentrated solar power unit (50), configured to supply heat to the thermal energy storage unit (40).

2. The power production plant of claim 1, wherein the thermal energy storage unit (40) is also configured to collect heat from the photovoltaic power unit (30) by means of an electrical heater (41).

3. The power production plant of claim 1 or 2, wherein one electrical power unit (10) is connected both to the first thermodynamic cycle unit (21) and to the second thermodynamic cycle unit (22), the kinetic energy produced by said one or more gas turbines of the first thermodynamic cycle unit (21) being transferred to one or more electrical power generators forming part of said electrical power unit (10), and the kinetic energy produced by said one or more expansion units (222) of the second thermodynamic cycle unit (22) being transferred to one or more electrical power generators forming part of said electrical power unit (10).

4. The power production plant of claim 1 or 2, wherein at least one of the one or more electrical power units (10) is connected to the first thermodynamic cycle unit (21), the kinetic energy produced by said one or more gas turbines of the first thermodynamic cycle unit (21) being transferred to one or more electrical power generators connected to said at least one electrical power unit (10), and at least another one of the one or more electrical power units (10) is connected to the second thermodynamic cycle unit (22), the kinetic energy produced by said one or more expansion units (222) of the second thermodynamic cycle unit (22) being transferred to one or more electrical power generators connected to said at least another one of the one or more electrical power units (10).

5. The power production plant of claim 1 or 2, wherein the first thermodynamic cycle unit (21) is configured to: supply heat to the thermal energy storage unit (40) by means of a heat exchanger configured to exchange heat between the exhaust gas from the first thermodynamic cycle unit (21) and the heat storage fluid of the thermal energy storage unit (40); and / or supply heat to the second thermodynamic cycle unit (22) by means of a heat exchanger configured to exchange heat between the exhaust gas from the first thermodynamic cycle unit (21) and the working fluid of the second thermodynamic cycle unit (22).

6. The power production plant of claim 1 or 2, further comprising an electrical battery storage system (32) connected to the electrical power units (10).

7. The power production plant of claim 6, wherein the electrical battery storage system (32) is configured to supply spinning reserve to the electrical power units (10).

8. The power production plant of one or more of the preceding claims, wherein the heat exchanger (223) configured to exchange heat between the exhaust gas from the first thermodynamic cycle unit (21) and the working fluid of the second thermodynamic cycle unit (22) is arranged upstream the heat exchanger (224) configured to exchange heat between the heat storage fluid of the thermal energy storage unit (40) and the working fluid of the second thermodynamic cycle unit (22).

9. The power production plant of one or more of the preceding claims, wherein the heat exchanger (223) that is configured to exchange heat between the exhaust gas from the first thermodynamic cycle unit (21) and the working fluid of the second thermodynamic cycle unit (22) is arranged downstream the heat exchanger (224) that is configured to exchange heat between the heat storage fluid of the thermal energy storage unit (40) and the working fluid of the second thermodynamic cycle unit (22).

10. The power production plant of one or more of the preceding claims, wherein the concentrated solar power unit (50) is configured to concentrate solar irradiation into a receiver (51) configured to directly exchange heat with the heat storage fluid of the thermal energy storage unit (40).

11. The power production plant of claim 10, wherein the concentrated solar power unit (50) is configured to concentrate solar irradiation into a receiver (51) configured to indirectly exchange heat with the heat storage fluid of the thermal energy storage unit (40).

12. The power production plant of one or more of the preceding claims 2-11, wherein the electrical heater (41) is an electrical resistor (41) connected to an electrical circuit of the photovoltaic power unit (30), the electrical resistor (41) being configured to exchange heat with the heat storage fluid of the thermal energy storage unit (40).

13. The power production plant of claim 12, wherein the electrical resistor (41) is in direct contact with the heat storage fluid of the thermal energy storage unit (40).

14. The power production plant of one or more of the preceding claims 2-13, wherein the photovoltaic power unit (30) includes a damping-filter (31) configured to separate fluctuations of photovoltaic power and to direct said fluctuations to the electrical heater (41) of the thermal energy storage unit (40).

15. A method of controlling the power production plant of claims 1-14, the method comprising the steps of: supplying heat of the exhaust gas from the first thermodynamic cycle unit(21) to the heat recovery steam generator; and / or supplying heat of the exhaust gas from the first thermodynamic cycle unit(21) to the thermal storage unit; and supplying heat of the thermal storage unit to the HRSG.

16. The method of claim 15, further comprising the steps of: adjusting the amount of fuel supplied to the first thermodynamic cycle unit (21) during the day to reduce power production and compensate the increased power production by the PV unit (30); and adjusting the amount of heat from the thermal storage unit (40) to the HRSG (221) to compensate the decreased amount of heat of the exhaust gas from the first thermodynamic cycle unit (21) to the HRSG (221).

17. The method of claim 15 or 16, further comprising the steps of: supplying to the TES unit any power produced by the PV in excess with respect to the design conditions.

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