FIELD OF INVENTION
The present invention relates in general to a single PV module power measurement system. More particularly, this invention single PV module power performance measurement device capable of monitoring performance of PV module under normal operating conditions and estimating performance of PV module under standard test conditions (STC).
BACKGROUND OF THE INVENTION
The generation capability of a PV module is dependent on the intensity of the solar irradiation, angle of incidence, temperature and other atmospheric parameters. The electrical performance of crystalline silicon and thin film PV modules are measured under standard test conditions (STC), ensuring a relatively independent comparison and output evaluation of different solar PV modules. STC is an industry-wide standard to indicate the performance of PV modules and specifies a cell temperature of 25°C and an irradiance of 1000 W/m2 with an air mass 1.5 (AM1.5) spectrum. These correspond to the irradiance and spectrum of sunlight incident on a clear day, upon a sun-facing 37°-tilted surface with the sun at an angle of 41.81° above the horizon. This condition approximately represents solar noon near the spring and autumn equinoxes in the continental United States with surface of the cell aimed directly at the sun. STC-based performance measurements are applied in the flash tests of many solar PV module manufacturers. However, this equipment is expensive and can’t be afforded by small PV module manufacturer and EPC contractors. Moreover, rating specified for PV module at STC are seldom met in actual field condition due to change in various atmospheric parameter such as temperature, irradiance etc. Hence, a suitable concept for development of a monitoring system is needed to evaluate performance of PV module under open field condition as well as performance estimation under STC.

In the state of art, the existing techniques for performance measurement of PV module such as in JP5293648B2 relate the concept of power estimation device, capable of estimating the generated power of a solar panel from the data of an existing receiving power measuring device and dump power measuring device, without the need for installing a new measuring device. The generated power estimation device includes a receiving unit that receives measurement data of the receiving power measuring device and dump power measuring device, a fluctuation period resolving unit that performs fluctuation period resolution by resolving the measurement data received by the receiving unit to an early fluctuation period component and late fluctuation period component based on the past power usage data of consumers, and a transformed and generated power estimation process unit that estimates the generated power of the solar panel based on the results of the fluctuation frequency resolution. The aforesaid invention describes concept for power generation estimating apparatus for estimating the generated power of the solar panels but does not specify estimation of generated power under standard test condition (STC).
Further, in another instance, US20120053867A1 relates to a system and methods for measuring the performance of individual strings of photovoltaic (PV) modules in a PV array, including a string combiner box with integrated capability for measurement of string current versus voltage (I-V) characteristics. The system includes calibrated solar insolation reference devices; environmental meters; and system computer. The string combiner box allows: high precision string performance measurement during normal power generating operation; isolation of individual strings or groups of strings; and the performance of high-precision full I-V sweeps on individual strings. Methods are provided to analyze measured I-V curves to compensate for the effects of temperature and other variables thereby increasing PV module performance measurement accuracy. Methods are further provided to incorporate data from insolation reference devices and/or environmental meters to extract meaningful parameters from collected data regarding PV module efficiency and degradation, and track string-

level performance and degradation over extended periods of time. This invention describes method for measurement of performance parameters on string level under normal operating condition.
The prior arts do not disclose techniques for measurement of performance of solar/PV module under "real-world" solar and climatic conditions and estimation of performance parameters under standard test conditions. Therefore, in order to overcome the above mentioned drawbacks, there is a need to develop a power performance measurement device for a single PV module operating in actual field conditions.
OBJECTS OF THE INVENTION
An object of the invention is to overcome the drawbacks existing in prior art devices and methods.
Another primary object of the invention is to provide a low cost-portable power performance measurement device capable of being deployed and operated in actual field to test any type of PV module for performance evaluation and estimate rating at standard test conditions (STC).
Still another object of the invention is to provide a low cost-portable power performance measurement device for estimation of performance of PV module with respect to time.
Yet another object of the present invention is to provide a low cost-portable power performance measurement device for comparing performances of distinct PV modules.
SUMMARY OF THE INVENTION
The present application discloses a power performance measurement device for a single PV module. In an aspect, the device includes sensor units operatively

interfaced with a PV module for measuring parameters indicative of temperature, irradiance, current and voltage of the PV module in real-time. Further, the sensor unit in communication with a measurement unit configured to measure performance parameters of the PV module. Further, in an aspect, the measurement unit comprises a control unit configured to receive the sensed parameters of temperature, irradiance, current and voltage. The control unit is further configured to compute current-voltage (IV) measurement of the PV module by varying connected load. Furthermore, the control unit is configured to compute and apply compensating factors for each of said parameters for computing power rating of the PV module at standard test conditions (STC). Further, the control unit is configured to apply derating factor based on age of the PV module for computing standard test conditions (STC) rating. Furthermore, in an aspect, the measurement unit comprises a storage unit configured to store information comprising the aforesaid sensed parameters, the current-voltage (IV) measurements, the power rating of the PV module at normal operating condition and the standard test conditions (STC) rating. Further, in aspect, the measurement unit comprises a communication unit, in operation with the control unit configured to transmit the stored information to a monitoring unit which is configured to monitor, display and alert user of events and trends related to the performance rating of the PV module.
In another aspect, the present application discloses a method for measuring power performance of a single PV module at standard test conditions (STC). In an aspect, the method includes the step of generating, in real-time, a first sensor signal, a second sensor signal, a third sensor signal and a fourth sensor signal indicative of temperature, irradiance, current and voltage of the PV module respectively. Further, the method includes the steps of computing current-voltage (IV) measurement of the PV module based on the third signal and the fourth signal, computing and applying compensating factors for each of said temperature, irradiance, current and voltage for computing power rating of the PV module at standard test conditions (STC) and applying derating factor

based on age of the PV module for computing standard test conditions (STC) rating. Furthermore, in an aspect, the method includes storing information comprising said parameters, the current-voltage (IV) measurements, the power rating of the PV module at standard test conditions (STC) and the standard test conditions (STC) rating. Further, the method includes transmitting the stored information for monitoring, displaying and alerting user of events and trends related to the performance rating of the PV module.
The above and additional advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description when taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The above brief description, as well as further objects, features and advantages, of the present invention can be fully appreciated by reference to the following detailed description. These features of the present invention will become more apparent upon reference to the drawings, wherein:
Fig. 1: Illustrates a block diagram of the power performance measurement
system including a power performance measurement device and a PV module according to an embodiment of the present invention.
Fig. 2: Illustrates a flowchart describing the method steps implemented for
measuring power performance of a single PV module at standard test conditions (STC) according to an embodiment of the present invention.
DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION
Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention which may be embodied in other specific

structure. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.
It will be apparent, however, to one of ordinary skill in the art that the present invention may be practiced without specific details of the well known components and techniques. In other instances, well known components/units have not been described in detail but rather in a block diagram in order to avoid unnecessarily obscuring the present invention. Further specific numeric references should not be interpreted as a literal sequential order. Thus, the specific details set forth are merely exemplary. The specific details may be varied from and still be contemplated to be within the scope of the present invention. The features discussed in an embodiment may be implemented in another embodiment.
Moreover, occasional references to the conventional devices are made in order to better distinguish the present inventive disclosure discussed later in greater detail. Few of the details pertaining to the PV module 2 power measurement techniques are well-known in the art, and therefore, are described herein only in the detail required to fully disclose the present invention. The present invention will be described in detail below with reference to embodiments as shown in the drawings.
Turning now to Figures, Fig. 1 illustrates a block diagram of the power performance measurement system including a power performance measurement device and a PV module 2 according to an embodiment of the present invention. The working of the device can be better understood with the help of block diagram as shown in Fig. 1. In an aspect, the block diagram as illustrated in Fig. 1 can be segregated into functional blocks namely a sensor unit 1, a measurement unit 3 further having a control unit 4; a storage unit 5; a

communication unit 6, a monitoring unit 7 among others. In an embodiment, the device is a portable, mobile and transportable PV module 2 power performance measurement device. Further, in an embodiment, the device may work as a system in which the monitoring unit 7 may be remotely located.
In an embodiment, the sensor unit 1 is operatively interfaced in series connection with a PV module 2 for measuring parameters indicative of temperature, irradiance, current and voltage of the PV module 2 in real-time. Herein, it is observed that the electrical performance and characteristic curves of solar panels are dependent mainly on solar irradiance and cell temperature. The change in irradiance affects the module current the most, as the current is directly dependent on the irradiance whereas module voltage remains relatively constant. Similarly, with rise in temperature, voltage drops at very faster pace whereas current remains relatively constant. The electric output performance of crystalline silicon and thin film PV modules 2 are generally measured under standard test conditions (STC), ensuring a relatively independent comparison and output evaluation of different solar PV modules 2. However, Solar module deployed in actual field represent more realistic measure of PV output because the conditions better reflect "real-world" solar and climatic conditions, compared to the STC rating.
Further, in an aspect, the sensor unit 1 comprises a thermocouple sensor coupled to back of the PV module 2 for measuring the temperature, a pyranometer coupled to plane of the PV module 2 for measuring the irradiance, a voltage transducer connected across the PV module 2 for measuring the voltage across the PV module 2, and a current sensor for measuring the current across terminals of the PV module 2. Furthermore, the sensor unit 1 is in communication with a measurement unit 3 which is configured to measure performance parameters of the PV module 2. In an aspect, the measurement unit 3 has a control unit 4. The control unit 4 is configured to receive the

sensed parameters of temperature, irradiance, current and voltage as sensed by the sensor unit 1. Further, the control unit 4 measures current-voltage (IV) relationship of the PV module 2. In an aspect, when the control unit 4 computes current-voltage (IV) relationship of the PV module 2 a module level power optimizer (MPP) 8/Maximum Power Point Tracker (MPPT) 8 is attached to the PV module 2 for keeping the PV module 2 at maximum power point (MPP). Further, in an aspect, the PV module 2 output is connected to a suitable load and the current sensor is connected in series. Furthermore, in another aspect, a Voltage transducer is connected across PV module 2, to measure potential and to minimize voltage drop in connecting wires. From the PV module 2, current – voltage (IV) curve is measured at regular intervals by varying the load from minimum to maximum. In essence, PV module 2 temperature is measured with a thermocouple sensor fixed to the back of PV module 2 and an irradiance measurement is taken from pyranometer installed in the plane of PV module 2. Furthermore, the control unit 4 is configured to sample irradiance and weather data at predefined intervals. The data is processed for computation of a compensating factor and the compensating factor is subsequently applied for each of said parameters for computing/calculating power rating of the PV module 2 at standard test conditions (STC). After the above step the control unit 4 applies derating factor, calculated on predefined value which is based on age of the PV module 2, for computing standard test conditions (STC) rating. In essence, Performance of PV module is compared by its rating at STC, higher the rating, better the performance. Furthermore, in an aspect, the measurement unit 3 further comprises a storage unit 5 configured to store information comprising: said parameters, the current-voltage (IV) measurements, the power rating of the PV module 2 at standard test conditions (STC) and power rating at normal operating condition. Further, the measurement unit 3 comprises a communication unit 6, in operation with the control unit 4 configured to transmit the stored information to a monitoring unit 7 configured to monitor, display and alert user of events and trends related to the performance rating of the PV module 2. In an aspect, the monitoring unit 7 may be remotely located.

In another aspect, the device is housed in a rugged box for portability. In a further aspect, the control unit 4 may be implemented in the form of a microcontroller configured to implement the methods. In yet another aspect, the communication unit 6 may be implemented by wired or wireless mode of communication. In another aspect, the monitoring unit 7 is a display device.
Further, Fig. 2 a flowchart describing the method steps implemented for measuring power of a single PV module 2 at standard test conditions (STC) according to an embodiment of the present invention. In step 2A, the method starts with the step of generating, in real-time, a first sensor signal, a second sensor signal, a third sensor signal and a fourth sensor signal indicative of temperature, irradiance, current and voltage of the PV module 2 respectively. In an aspect, the first sensor signal is generated from a thermocouple sensor coupled to back of the PV module 2 for measuring the cell temperature. Further, in an aspect, the second sensor signal is generated from a pyranometer coupled to plane of the PV module 2 for measuring the irradiance. Further, the third sensor signal is generated from a voltage transducer connected across the PV module 2 for measuring the voltage across the PV module 2. Furthermore, the fourth sensor signal is generated from a current sensor connected in series with PV module for measuring the current of the PV module 2. Further, in step 2B current-voltage (IV) measurement of the PV module 2 by varying connected load.
In step 2C, the method comprises computing and applying compensating factors for each of said temperature, irradiance, current and voltage for computing power rating of the PV module 2 at standard test conditions (STC). Further, in an aspect, the computing current-voltage (IV) relationship of the PV module 2 comprises providing a module level power optimizer 8 for keeping the PV module 2 at maximum power point (MPP), and the computing current-

voltage (IV) relationship of the PV module 2 comprises connecting a varying load in series across the PV module 2. In an aspect, varying load comprises varying load from minimum to maximum.
In step 2D, the method includes applying derating factor based on age of the PV module 2 for computing standard test conditions (STC) rating. Further, in step 2E, the step involves storing information comprising the above parameters, the current-voltage (IV) measurements, the power rating of the PV module 2 at standard test conditions (STC). Furthermore, the step 2E includes transmitting the stored information for monitoring, displaying and alerting user of events and trends related to the performance rating of the PV module 2.
In essence, the power performance of the PV module 2 at standard test conditions (STC) is estimated based on the computed power rating of the PV module 2 at normal operating condition and applying compensating and derating factors.
The foregoing is considered as illustrative only of the principles of the invention. Furthermore, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.

We claim:
1. A power performance measurement device for a single PV module (2) at standard test conditions (STC), the device comprising:
a sensor unit (1) operatively interfaced with a PV module (2) for measuring parameters indicative of temperature, irradiance, current and voltage of the PV module (2) in real-time, said sensor unit (1) in communication with a measurement unit (3) configured to measure performance parameters of the PV module (2), wherein the measurement unit (3) comprises:
a control unit (4) configured to:
receive said sensed parameters of temperature, irradiance, current and voltage,
compute current-voltage (IV) measurement of the PV module (2) at regular intervals by varying load from minimum to maximum,
compute and apply compensating factors for each of said parameters for computing power rating of the PV module (2) at standard test conditions (STC),
apply derating factor based on age of the PV module (2) for computing standard test conditions (STC) rating,
a storage unit (5) configured to store information comprising: said parameters, the current-voltage (IV) measurements, the power rating of the PV module (2) at standard test conditions (STC) and the standard test conditions (STC) rating,

a communication unit (6), in operation with the control unit (4) configured to transmit the stored information to a monitoring unit (7) configured to monitor, display and alert user of events and trends related to the performance rating of the PV module (2).
2. The device as claimed in claim 1, wherein the sensor unit (1) comprises: a thermocouple sensor coupled to back of the PV module (2) for measuring the temperature, a pyranometer coupled to plane of the PV module for measuring the irradiance, a voltage transducer connected across the PV module (2) for measuring the voltage across the PV module (2), and a current sensor in series with PV module for measuring the current.
3. The device as claimed in claim 1, wherein the computing current-voltage (IV) relationship of the PV module (2) comprises providing a module level power optimizer (8) for keeping the PV module (2) at maximum power point (MPP), and wherein the computing current-voltage (IV) relationship of the PV module (2) comprises connecting a varying load across the PV module (2).
4. The device as claimed in claim 1, wherein the device is housed in a rugged box for portability.
5. A method for measuring power performance of a single PV module at standard test conditions (STC), the method comprising:
generating, in real-time, a first sensor signal, a second sensor signal, a third sensor signal and a fourth sensor signal indicative of temperature, irradiance, current and voltage of the PV module (2) respectively;

computing current-voltage (IV) measurement of the PV module (2) based on the third signal and the fourth signal;
computing and applying compensating factors for each of said temperature, irradiance, current and voltage for computing power rating of the PV module (2) at standard test conditions (STC);
applying derating factor based on age of the PV module (2) for computing standard test conditions (STC) rating;
storing information comprising said parameters, the current-voltage (IV) measurements, the power rating of the PV module (2) at standard test conditions (STC) and the standard test conditions (STC) rating;
transmitting the stored information for monitoring, displaying and alerting user of events and trends related to the performance rating of the PV module (2).
6. The method as claimed in claim 5, wherein the first sensor signal is generated from a thermocouple sensor coupled to back of the PV module (2) for measuring the temperature, wherein the second sensor signal is generated from a pyranometer coupled to plane of the PV module (2) for measuring the irradiance, wherein the third sensor signal is generated from a voltage transducer connected across the PV module (2) for measuring the voltage across the PV module (2), and wherein the fourth sensor signal is generated from a current sensor for measuring the current across terminals of the PV module (2).
7. The method as claimed in claim 5, wherein the computing current-voltage (IV) relationship of the PV module (2) comprises providing a module level

power optimizer (8) for keeping the PV module (2) at maximum power point (MPP), and wherein the computing current-voltage (IV) relationship of the PV module (2) comprises connecting a varying load in series across the PV module (2).
8. The method as claimed in claim 5, wherein the power performance of the PV module (2) is estimated based on the computed power rating of the PV module (2) at standard test conditions (STC) and standard test conditions (STC) rating.
9. The method as claimed in claim 6, wherein the current sensor is connected in series with the PV module (2).