IEEE Transactions on Industrial Electronics, Oct 1, 2009
In this paper, a solution is described that makes it possible for wind turbines using doubly-fed ... more In this paper, a solution is described that makes it possible for wind turbines using doubly-fed induction generators to stay connected to the grid during grid faults. The key of the solution is to limit the high current in the rotor in order to protect the converter and to provide a bypass for this current via a set of resistors that are connected to the rotor windings. With these resistors, it is possible to ride through grid faults without disconnecting the turbine from the grid. Because the generator and converter stay connected, the synchronism of operation remains established during and after the fault and normal operation can be continued immediately after the fault has been cleared. An additional feature is that reactive power can be supplied to the grid during long dips in order to facilitate voltage restoration. A control strategy has been developed that takes care of the transition back to normal operation. Without special control action, large transients would occur.
IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society, Oct 1, 2018
In this paper, an energy management strategy based on microgrid power forecasting is applied to a... more In this paper, an energy management strategy based on microgrid power forecasting is applied to a residential grid-connected electro-thermal microgrid with the aim of smoothing the power profile exchanged with the grid. The microgrid architecture under study considers electrical and thermal renewable generation, energy storage system (ESS), and loads. The proposed strategy manages the energy stored in the ESS to cover part of the energy required by the thermal generation system for supplying domestic hot water to the residence. The simulation results using real data and the comparison with previous strategy have demonstrated the effectiveness of the proposed strategy.
Due to high competitiveness in the PV sector, despite the low degradation rate of crystalline sil... more Due to high competitiveness in the PV sector, despite the low degradation rate of crystalline silicon PV modules (below 0.5%/year), it is still important for utilities to know its actual value due to its impact on energy yield and hence, profitability, over the lifetime of a PV plant. However, uncertainties related to both the influence of downtime periods due to problems that may appear under normal operation of a commercial PV plant and to the measurement of degradation rates at PV plant level make this a challenging task. In order to obtain a significant value, in this paper, three measuring methods with different uncertainty sources are used for 82 MWp of PV modules on different locations in Spain and Portugal over 10 years. According to the different methods used and PV plants analyzed, excluding PV plants with problems, a range of degradation rates between 0.01 and 0.47%/year has been found. The overall average value observed is 0.27%/year. The findings of this work have also revealed the great importance of good operation and maintenance practices in order to keep overall low degradation rates.
Short-term variability in the power generated by large grid-connected photovoltaic (PV) plants ca... more Short-term variability in the power generated by large grid-connected photovoltaic (PV) plants can negatively affect power quality and the network reliability. New grid-codes require combining the PV generator with some form of energy storage technology in order to reduce short-term PV power fluctuation. This paper proposes an effective method in order to calculate, for any PV plant size and maximum allowable ramp-rate, the maximum power and the minimum energy storage requirements alike. The general validity of this method is corroborated with extensive simulation exercises performed with real 5-s one year data of 500 kW inverters at the 38.5 MW Amaraleja (Portugal) PV plant and two other PV plants located in Navarra (Spain), at a distance of more than 660 km from Amaraleja.
An increasing number of grid codes are requiring the limitation of the PV output power fluctuatio... more An increasing number of grid codes are requiring the limitation of the PV output power fluctuation over a given time scale. Batteries represent the most obvious solution to smooth power fluctuations, with the corresponding negative impact on the PV energy cost. However, short-term forecasting is currently being proposed as a tool to reduce battery capacity requirements or even completely remove it. Although these solutions decrease or avoid the battery cost, it also entails some energy curtailment losses which obviously raise the final cost of PV energy. This energy losses, currently unknown, are independent of the forecasting accuracy and represent the minimal additional cost in the hypothetical case of a perfect prediction. Thus, this paper compares Levelized Cost of Energy (LCOE) of three ramp-rate control strategies in order to determine which would give the lowest cost: battery-based, ideal short-term forecasting, or a combination of both. Results show that curtailment losses would be small enough to make battery-less strategy an appropriate choice, so it is worthwhile improving short-term forecasting in view of the potential LCOE savings. Database is taken from high resolution measurements recorded for over a year at 8 PV plants ranging from 1 to 46 MWp.
The worldwide growth of the PV market has been almost exponential during the last years. Together... more The worldwide growth of the PV market has been almost exponential during the last years. Together with conventional crystalline (c-Si) PV modules, "new" commercially available PV technologies such as copper indium selenide (CIS) based solar cells have appeared achieving a similar efficiency comparable to c-Si at similar production cost. In addition to the use of cheaper materials, CIS solar cells manufacturers claim some enhancements such as lower temperature coefficient or higher absorption of diffuse light that achieve to reduce the cost of electrical energy. Although several papers deal with this topic, little is known about real comparisons between CIS technology and conventional crystalline at a PV generator level with real test conditions. This paper analyses the in-field performance and degradation of a commercially available CIS solar based PV generator compared to a conventional c-Si one during four years of operation attributing the differences observed to the possible factors that can influence in both technologies.
Appropriate voltage control is essential in order to extend the useful life of a battery. However... more Appropriate voltage control is essential in order to extend the useful life of a battery. However, when universal chargers are used, the design of this control becomes more complicated, given the fact that the battery impedance value may vary considerably, depending not only on the operating point but also on the type, size, and aging level of the battery. This paper first shows how the voltage regulation can become extremely variable or even unstable when the controller is designed according to the proposals in the literature. We then go on to propose the emulation of a series and parallel impedance with the battery, which is easy to implement and achieves a control that is completely independent of the battery connected. The simulation results obtained for batteries with resistances ranging from 10 m to 1 , show the problems with existing controls and confirm that the proposed control response is similar for all the possible range of battery resistance.
Energy storage systems (ESS) have been widely proposed as a solution for smoothing out photovolta... more Energy storage systems (ESS) have been widely proposed as a solution for smoothing out photovoltaic (PV) power fluctuations and complying with new regulations that limit the maximum fluctuation over a given period, typically 10%/min, evaluated over a shorter period of time, such as one second. Although ramp-rate control is one of the most used strategies it does require symmetric charge-discharge power capabilities, which most commercially available batteries do not have. This can lead to non-compliance with the regulations and is a problem that has not yet been sufficiently studied. Furthermore, delays in the communication system between the measurement of the actual PV power, the PLC calculation time and the battery converter response time can lead to a failure to comply with the maximum ramp rate limit, bringing to light the need for faster systems. These two problems are addressed herein, and solutions are presented and validated with 1 s experimental data from a 122.4 kWp PV array section coupled to a 100 kW/56 kWh lithium-ion battery within a 1.18 MWp PV plant in northern Spain.
Progress in Photovoltaics: Research and Applications
Durability of photovoltaic (PV) modules is of great concern not only from the point of view of co... more Durability of photovoltaic (PV) modules is of great concern not only from the point of view of cost‐effectiveness but also from the point of view of safety and sustainability. The backsheet of a PV module is one of the most critical parts of the PV module from the point of view of protection and also one of the most important sources of PV modules' failure; hence, it is of great importance to understand its different forms of failure. In this paper we analyze the case of an 8‐MW PV plant, which had suffered a rapid degradation of their PV modules' backsheets. The case is especially relevant as all the PV modules are from the same model and manufacturer but with different backsheet materials (polyamide and fluoropolymer) and different times of exposure: on one hand, all PV modules originally installed in the plant (i.e., 6 years under operation when tested), and also, extra modules that had been stored indoors for replacement and had been mounted in the plant for less than 1 ...
2022 IEEE International Conference on Environment and Electrical Engineering and 2022 IEEE Industrial and Commercial Power Systems Europe (EEEIC / I&CPS Europe)
IECON 2016 - 42nd Annual Conference of the IEEE Industrial Electronics Society
The changeability in the power produced by utility-scale PV plants caused by passing clouds can c... more The changeability in the power produced by utility-scale PV plants caused by passing clouds can compromise power quality and reliability. Hence, some kind of energy storage systems (ESS) are required to reduce power variations below the limits imposed by new grid codes regulations. Here, we propose a novel control strategy to smooth out the fluctuations by using an energy storage system, namely dynamic ramp-rate control, which provides simultaneously a simple state of charge (SOC) control and 30 % less cycling degradation than classic ramp-rate control, as only is triggered when a fluctuation takes place. In addition, the strategy parameters can be tuned in order to reduce the capacity requirements by only modifying the SOC band values wherein the strategy is active. The novel techinque has been shown to work effectively with 5-s real power measurements recorded at the Amareleja PV plant (45.6 MWp, Portugal).
2018 IEEE International Conference on Environment and Electrical Engineering and 2018 IEEE Industrial and Commercial Power Systems Europe (EEEIC / I&CPS Europe), 2018
This paper proposes a method for measuring the degradation rate of crystalline silicon PV modules... more This paper proposes a method for measuring the degradation rate of crystalline silicon PV modules at plant level in two different ways as a form of verification. As actual levels of degradation rate have been observed to be as low as 0.2%/a, the uncertainties make it difficult to measure this value accurately at plant level. However, despite the low value, it is still important to know the actual degradation rate due to its impact on energy yield. In this paper, two ways of measuring the degradation rate at plant level are proposed. These two methods, with different uncertainty sources, are proposed to be used jointly in order to have a better approach to the real value. Finally, an example of measurement in a 1.78 MW PV plant is presented.
2018 20th European Conference on Power Electronics and Applications (EPE'18 ECCE Europe), 2018
The changeability in the power produced by utility-scale PV plants caused by shadows due to passi... more The changeability in the power produced by utility-scale PV plants caused by shadows due to passing clouds can compromise grid stability. Traditionally, some kind of energy storage systems (ESS) is proposed as the solution to reduce power variations below the limits imposed by new grid codes regulations. However, recent short-term forecast sources open the door to control the variability without batteries, using only inverter limitation. This option entails some energy curtailment losses that has not been yet addressed. This paper quantifies these losses for the first time using a meaningful database of 5 s one year data for a 38.5 MW PV plant in a perfect forecast scenery. Finally, we compare the economic cost of installing a lithium-ion battery vs. the inverter limitation solution. The results obtained indicate that battery-less strategies must not be neglected for ramp-rate control, since they can be more cost-effective using perfect forecast for any ramp value.
In-field photovoltaic (PV) module and array characterization is becoming increasingly important w... more In-field photovoltaic (PV) module and array characterization is becoming increasingly important within the particular framework of quality assurance procedures at large commercial PV plants. In this context, the correct measurement of the module temperature is critical in order to reduce uncertainty and increase repeatability of results. In the case of large PV array characterization, the measurement provided by the sensors may not be representative of the PV array as a whole given the great diversity of operating conditions occurring throughout its surface area. Spatial temperature differences within a PV array of less than 5 K are typically considered in practice. However, the temperature differences observed at a commercial PV plant in Amareleja (Portugal) are more than twice those typically assumed. Such high differences may considerably increase the uncertainty in the determination of the PV array operating temperature and, hence, in its standard test conditions power characterization. This paper quantifies the uncertainty associated with the in-field measurement of the operating temperature of large PV arrays and their individual PV modules as a function of the type, number, and location of the temperature sensors used. Furthermore, the incident irradiance and particular wind speed conditions over the PV array have been clearly identified as the main causes of these temperature differences, showing that the optimum conditions to perform the PV array characterization do not correspond to low wind speed conditions, as recommended by many authors.
Large Scale Grid Integration of Renewable Energy Sources
This chapter will study the dynamics of irradiance and the power delivered to the grid by PV plan... more This chapter will study the dynamics of irradiance and the power delivered to the grid by PV plants in time frames of less than 10 min, paying particular attention to the influence of PV plant size and geographic dispersion on magnitude and duration. We are now going to present some general models which make it possible to simulate the power fluctuations of either a power plant or a group of power plants, based solely on irradiance measurements. Finally, we shall study the control strategies required to compensate these fluctuations, based on storage systems installed in the PV plants, analysing the energy and power requirements to compensate these variations.
This paper presents the design of a low complexity Fuzzy Logic Controller of only 25-rules to be ... more This paper presents the design of a low complexity Fuzzy Logic Controller of only 25-rules to be embedded in an Energy Management System for a residential grid-connected microgrid including Renewable Energy Sources and storage capability. The system assumes that neither the renewable generation nor the load demand is controllable. The main goal of the design is to minimize the grid power profile fluctuations while keeping the Battery State of Charge within secure limits. Instead of using forecasting-based methods, the proposed approach uses both the microgrid energy rate-of-change and the battery SOC to increase, decrease or maintain the power delivered/absorbed by the mains. The controller design parameters (membership functions and rule-base) are adjusted to optimize a pre-defined set of quality criteria of the microgrid behavior. A comparison with other proposals seeking the same goal is presented at simulation level, whereas the features of the proposed design are experimentally tested on a real residential microgrid implemented at the Public University of Navarre.
2009 35th Annual Conference of IEEE Industrial Electronics, 2009
... Usually, photovoltaic plants consider the utility grid as infinite storage system capable of ... more ... Usually, photovoltaic plants consider the utility grid as infinite storage system capable of absorb as ... In fact, the system continues delivering electrical energy to the grid during the transient ... 1b shows an example of adaptor circuit connected in parallel to a previously existent PV ...
Progress in Photovoltaics: Research and Applications, 2014
When evaluating the performance of a photovoltaic (PV) system, it is extremely important to corre... more When evaluating the performance of a photovoltaic (PV) system, it is extremely important to correctly measure the plant operating conditions: incident irradiation and cell temperature. At large‐size PV plants, the possible dispersion of the plant operating conditions may affect the representativeness of the values measured at one single point. The available literature contains many observations on irradiance dispersion (typically associated to high temporal resolution experiments) and its effects on the PV power output (unexpected power transients, power fluctuations, etc.). However no studies have been made on the long‐term energy‐related effects of geographic dispersion of solar irradiation, which could affect, for example, to the uncertainty in determining energy performance indexes like PR. This paper analyses the geographical dispersion in the PV operating conditions observed at low temporal resolutions (day, month and year) at two PV plants located, respectively, in the south ...
Short-term variability in the power generated by large grid-connected photovoltaic (PV) plants ca... more Short-term variability in the power generated by large grid-connected photovoltaic (PV) plants can negatively affect power quality and the network reliability. New grid-codes require combining the PV generator with some form of energy storage technology in order to reduce short-term PV power fluctuation. This paper proposes an effective method in order to calculate, for any PV plant size and maximum allowable ramp-rate, the maximum power and the minimum energy storage requirements alike. The general validity of this method is corroborated with extensive simulation exercises performed with real 5-s one year data of 500 kW inverters at the 38.5 MW Amaraleja (Portugal) PV plant and two other PV plants located in Navarra (Spain), at a distance of more than 660 km from Amaraleja.
IEEE Transactions on Industrial Electronics, Oct 1, 2009
In this paper, a solution is described that makes it possible for wind turbines using doubly-fed ... more In this paper, a solution is described that makes it possible for wind turbines using doubly-fed induction generators to stay connected to the grid during grid faults. The key of the solution is to limit the high current in the rotor in order to protect the converter and to provide a bypass for this current via a set of resistors that are connected to the rotor windings. With these resistors, it is possible to ride through grid faults without disconnecting the turbine from the grid. Because the generator and converter stay connected, the synchronism of operation remains established during and after the fault and normal operation can be continued immediately after the fault has been cleared. An additional feature is that reactive power can be supplied to the grid during long dips in order to facilitate voltage restoration. A control strategy has been developed that takes care of the transition back to normal operation. Without special control action, large transients would occur.
IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society, Oct 1, 2018
In this paper, an energy management strategy based on microgrid power forecasting is applied to a... more In this paper, an energy management strategy based on microgrid power forecasting is applied to a residential grid-connected electro-thermal microgrid with the aim of smoothing the power profile exchanged with the grid. The microgrid architecture under study considers electrical and thermal renewable generation, energy storage system (ESS), and loads. The proposed strategy manages the energy stored in the ESS to cover part of the energy required by the thermal generation system for supplying domestic hot water to the residence. The simulation results using real data and the comparison with previous strategy have demonstrated the effectiveness of the proposed strategy.
Due to high competitiveness in the PV sector, despite the low degradation rate of crystalline sil... more Due to high competitiveness in the PV sector, despite the low degradation rate of crystalline silicon PV modules (below 0.5%/year), it is still important for utilities to know its actual value due to its impact on energy yield and hence, profitability, over the lifetime of a PV plant. However, uncertainties related to both the influence of downtime periods due to problems that may appear under normal operation of a commercial PV plant and to the measurement of degradation rates at PV plant level make this a challenging task. In order to obtain a significant value, in this paper, three measuring methods with different uncertainty sources are used for 82 MWp of PV modules on different locations in Spain and Portugal over 10 years. According to the different methods used and PV plants analyzed, excluding PV plants with problems, a range of degradation rates between 0.01 and 0.47%/year has been found. The overall average value observed is 0.27%/year. The findings of this work have also revealed the great importance of good operation and maintenance practices in order to keep overall low degradation rates.
Short-term variability in the power generated by large grid-connected photovoltaic (PV) plants ca... more Short-term variability in the power generated by large grid-connected photovoltaic (PV) plants can negatively affect power quality and the network reliability. New grid-codes require combining the PV generator with some form of energy storage technology in order to reduce short-term PV power fluctuation. This paper proposes an effective method in order to calculate, for any PV plant size and maximum allowable ramp-rate, the maximum power and the minimum energy storage requirements alike. The general validity of this method is corroborated with extensive simulation exercises performed with real 5-s one year data of 500 kW inverters at the 38.5 MW Amaraleja (Portugal) PV plant and two other PV plants located in Navarra (Spain), at a distance of more than 660 km from Amaraleja.
An increasing number of grid codes are requiring the limitation of the PV output power fluctuatio... more An increasing number of grid codes are requiring the limitation of the PV output power fluctuation over a given time scale. Batteries represent the most obvious solution to smooth power fluctuations, with the corresponding negative impact on the PV energy cost. However, short-term forecasting is currently being proposed as a tool to reduce battery capacity requirements or even completely remove it. Although these solutions decrease or avoid the battery cost, it also entails some energy curtailment losses which obviously raise the final cost of PV energy. This energy losses, currently unknown, are independent of the forecasting accuracy and represent the minimal additional cost in the hypothetical case of a perfect prediction. Thus, this paper compares Levelized Cost of Energy (LCOE) of three ramp-rate control strategies in order to determine which would give the lowest cost: battery-based, ideal short-term forecasting, or a combination of both. Results show that curtailment losses would be small enough to make battery-less strategy an appropriate choice, so it is worthwhile improving short-term forecasting in view of the potential LCOE savings. Database is taken from high resolution measurements recorded for over a year at 8 PV plants ranging from 1 to 46 MWp.
The worldwide growth of the PV market has been almost exponential during the last years. Together... more The worldwide growth of the PV market has been almost exponential during the last years. Together with conventional crystalline (c-Si) PV modules, "new" commercially available PV technologies such as copper indium selenide (CIS) based solar cells have appeared achieving a similar efficiency comparable to c-Si at similar production cost. In addition to the use of cheaper materials, CIS solar cells manufacturers claim some enhancements such as lower temperature coefficient or higher absorption of diffuse light that achieve to reduce the cost of electrical energy. Although several papers deal with this topic, little is known about real comparisons between CIS technology and conventional crystalline at a PV generator level with real test conditions. This paper analyses the in-field performance and degradation of a commercially available CIS solar based PV generator compared to a conventional c-Si one during four years of operation attributing the differences observed to the possible factors that can influence in both technologies.
Appropriate voltage control is essential in order to extend the useful life of a battery. However... more Appropriate voltage control is essential in order to extend the useful life of a battery. However, when universal chargers are used, the design of this control becomes more complicated, given the fact that the battery impedance value may vary considerably, depending not only on the operating point but also on the type, size, and aging level of the battery. This paper first shows how the voltage regulation can become extremely variable or even unstable when the controller is designed according to the proposals in the literature. We then go on to propose the emulation of a series and parallel impedance with the battery, which is easy to implement and achieves a control that is completely independent of the battery connected. The simulation results obtained for batteries with resistances ranging from 10 m to 1 , show the problems with existing controls and confirm that the proposed control response is similar for all the possible range of battery resistance.
Energy storage systems (ESS) have been widely proposed as a solution for smoothing out photovolta... more Energy storage systems (ESS) have been widely proposed as a solution for smoothing out photovoltaic (PV) power fluctuations and complying with new regulations that limit the maximum fluctuation over a given period, typically 10%/min, evaluated over a shorter period of time, such as one second. Although ramp-rate control is one of the most used strategies it does require symmetric charge-discharge power capabilities, which most commercially available batteries do not have. This can lead to non-compliance with the regulations and is a problem that has not yet been sufficiently studied. Furthermore, delays in the communication system between the measurement of the actual PV power, the PLC calculation time and the battery converter response time can lead to a failure to comply with the maximum ramp rate limit, bringing to light the need for faster systems. These two problems are addressed herein, and solutions are presented and validated with 1 s experimental data from a 122.4 kWp PV array section coupled to a 100 kW/56 kWh lithium-ion battery within a 1.18 MWp PV plant in northern Spain.
Progress in Photovoltaics: Research and Applications
Durability of photovoltaic (PV) modules is of great concern not only from the point of view of co... more Durability of photovoltaic (PV) modules is of great concern not only from the point of view of cost‐effectiveness but also from the point of view of safety and sustainability. The backsheet of a PV module is one of the most critical parts of the PV module from the point of view of protection and also one of the most important sources of PV modules' failure; hence, it is of great importance to understand its different forms of failure. In this paper we analyze the case of an 8‐MW PV plant, which had suffered a rapid degradation of their PV modules' backsheets. The case is especially relevant as all the PV modules are from the same model and manufacturer but with different backsheet materials (polyamide and fluoropolymer) and different times of exposure: on one hand, all PV modules originally installed in the plant (i.e., 6 years under operation when tested), and also, extra modules that had been stored indoors for replacement and had been mounted in the plant for less than 1 ...
2022 IEEE International Conference on Environment and Electrical Engineering and 2022 IEEE Industrial and Commercial Power Systems Europe (EEEIC / I&CPS Europe)
IECON 2016 - 42nd Annual Conference of the IEEE Industrial Electronics Society
The changeability in the power produced by utility-scale PV plants caused by passing clouds can c... more The changeability in the power produced by utility-scale PV plants caused by passing clouds can compromise power quality and reliability. Hence, some kind of energy storage systems (ESS) are required to reduce power variations below the limits imposed by new grid codes regulations. Here, we propose a novel control strategy to smooth out the fluctuations by using an energy storage system, namely dynamic ramp-rate control, which provides simultaneously a simple state of charge (SOC) control and 30 % less cycling degradation than classic ramp-rate control, as only is triggered when a fluctuation takes place. In addition, the strategy parameters can be tuned in order to reduce the capacity requirements by only modifying the SOC band values wherein the strategy is active. The novel techinque has been shown to work effectively with 5-s real power measurements recorded at the Amareleja PV plant (45.6 MWp, Portugal).
2018 IEEE International Conference on Environment and Electrical Engineering and 2018 IEEE Industrial and Commercial Power Systems Europe (EEEIC / I&CPS Europe), 2018
This paper proposes a method for measuring the degradation rate of crystalline silicon PV modules... more This paper proposes a method for measuring the degradation rate of crystalline silicon PV modules at plant level in two different ways as a form of verification. As actual levels of degradation rate have been observed to be as low as 0.2%/a, the uncertainties make it difficult to measure this value accurately at plant level. However, despite the low value, it is still important to know the actual degradation rate due to its impact on energy yield. In this paper, two ways of measuring the degradation rate at plant level are proposed. These two methods, with different uncertainty sources, are proposed to be used jointly in order to have a better approach to the real value. Finally, an example of measurement in a 1.78 MW PV plant is presented.
2018 20th European Conference on Power Electronics and Applications (EPE'18 ECCE Europe), 2018
The changeability in the power produced by utility-scale PV plants caused by shadows due to passi... more The changeability in the power produced by utility-scale PV plants caused by shadows due to passing clouds can compromise grid stability. Traditionally, some kind of energy storage systems (ESS) is proposed as the solution to reduce power variations below the limits imposed by new grid codes regulations. However, recent short-term forecast sources open the door to control the variability without batteries, using only inverter limitation. This option entails some energy curtailment losses that has not been yet addressed. This paper quantifies these losses for the first time using a meaningful database of 5 s one year data for a 38.5 MW PV plant in a perfect forecast scenery. Finally, we compare the economic cost of installing a lithium-ion battery vs. the inverter limitation solution. The results obtained indicate that battery-less strategies must not be neglected for ramp-rate control, since they can be more cost-effective using perfect forecast for any ramp value.
In-field photovoltaic (PV) module and array characterization is becoming increasingly important w... more In-field photovoltaic (PV) module and array characterization is becoming increasingly important within the particular framework of quality assurance procedures at large commercial PV plants. In this context, the correct measurement of the module temperature is critical in order to reduce uncertainty and increase repeatability of results. In the case of large PV array characterization, the measurement provided by the sensors may not be representative of the PV array as a whole given the great diversity of operating conditions occurring throughout its surface area. Spatial temperature differences within a PV array of less than 5 K are typically considered in practice. However, the temperature differences observed at a commercial PV plant in Amareleja (Portugal) are more than twice those typically assumed. Such high differences may considerably increase the uncertainty in the determination of the PV array operating temperature and, hence, in its standard test conditions power characterization. This paper quantifies the uncertainty associated with the in-field measurement of the operating temperature of large PV arrays and their individual PV modules as a function of the type, number, and location of the temperature sensors used. Furthermore, the incident irradiance and particular wind speed conditions over the PV array have been clearly identified as the main causes of these temperature differences, showing that the optimum conditions to perform the PV array characterization do not correspond to low wind speed conditions, as recommended by many authors.
Large Scale Grid Integration of Renewable Energy Sources
This chapter will study the dynamics of irradiance and the power delivered to the grid by PV plan... more This chapter will study the dynamics of irradiance and the power delivered to the grid by PV plants in time frames of less than 10 min, paying particular attention to the influence of PV plant size and geographic dispersion on magnitude and duration. We are now going to present some general models which make it possible to simulate the power fluctuations of either a power plant or a group of power plants, based solely on irradiance measurements. Finally, we shall study the control strategies required to compensate these fluctuations, based on storage systems installed in the PV plants, analysing the energy and power requirements to compensate these variations.
This paper presents the design of a low complexity Fuzzy Logic Controller of only 25-rules to be ... more This paper presents the design of a low complexity Fuzzy Logic Controller of only 25-rules to be embedded in an Energy Management System for a residential grid-connected microgrid including Renewable Energy Sources and storage capability. The system assumes that neither the renewable generation nor the load demand is controllable. The main goal of the design is to minimize the grid power profile fluctuations while keeping the Battery State of Charge within secure limits. Instead of using forecasting-based methods, the proposed approach uses both the microgrid energy rate-of-change and the battery SOC to increase, decrease or maintain the power delivered/absorbed by the mains. The controller design parameters (membership functions and rule-base) are adjusted to optimize a pre-defined set of quality criteria of the microgrid behavior. A comparison with other proposals seeking the same goal is presented at simulation level, whereas the features of the proposed design are experimentally tested on a real residential microgrid implemented at the Public University of Navarre.
2009 35th Annual Conference of IEEE Industrial Electronics, 2009
... Usually, photovoltaic plants consider the utility grid as infinite storage system capable of ... more ... Usually, photovoltaic plants consider the utility grid as infinite storage system capable of absorb as ... In fact, the system continues delivering electrical energy to the grid during the transient ... 1b shows an example of adaptor circuit connected in parallel to a previously existent PV ...
Progress in Photovoltaics: Research and Applications, 2014
When evaluating the performance of a photovoltaic (PV) system, it is extremely important to corre... more When evaluating the performance of a photovoltaic (PV) system, it is extremely important to correctly measure the plant operating conditions: incident irradiation and cell temperature. At large‐size PV plants, the possible dispersion of the plant operating conditions may affect the representativeness of the values measured at one single point. The available literature contains many observations on irradiance dispersion (typically associated to high temporal resolution experiments) and its effects on the PV power output (unexpected power transients, power fluctuations, etc.). However no studies have been made on the long‐term energy‐related effects of geographic dispersion of solar irradiation, which could affect, for example, to the uncertainty in determining energy performance indexes like PR. This paper analyses the geographical dispersion in the PV operating conditions observed at low temporal resolutions (day, month and year) at two PV plants located, respectively, in the south ...
Short-term variability in the power generated by large grid-connected photovoltaic (PV) plants ca... more Short-term variability in the power generated by large grid-connected photovoltaic (PV) plants can negatively affect power quality and the network reliability. New grid-codes require combining the PV generator with some form of energy storage technology in order to reduce short-term PV power fluctuation. This paper proposes an effective method in order to calculate, for any PV plant size and maximum allowable ramp-rate, the maximum power and the minimum energy storage requirements alike. The general validity of this method is corroborated with extensive simulation exercises performed with real 5-s one year data of 500 kW inverters at the 38.5 MW Amaraleja (Portugal) PV plant and two other PV plants located in Navarra (Spain), at a distance of more than 660 km from Amaraleja.
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