Abstract:
A monitoring system and method for monitoring performance of individual powers sources in a distributed power source system. A monitoring module is coupled to each of the power sources, or to each string of serially connected power sources, to monitor and collect data regarding current, voltage, temperature and other environmental factors at the power source. The collected data is transmitted over a power line to a central analysis station for analysis. Data collected from each source indicates malfunction or degradation at the source. Comparison of data collected from adjacent sources filters for environmental factors impacting neighboring sources such as cloudy days for a solar panel. Comparison of data collected from the same source at different times indicates soiling or degradation of the source with time or periodic events such as a moving shade from an adjacent building.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application a continuation of U.S. patent application Ser. No. 13/901,890 filed May 24, 2013, titled “Monitoring of Distributed Power Harvesting Systems Using DC Power Sources,” which is a continuation of U.S. patent application Ser. No. 11/951,419 filed Dec. 6, 2007, titled “Monitoring of Distributed Power Harvesting Systems Using DC Power Sources”, which claims priority to U.S. Provisional Patent Applications, Ser. No. 60/868,851, filed Dec. 6, 2006, and titled “Distributed Solar Array Monitoring, Management and Maintenance,” Ser. No. 60/868,893, filed Dec. 6, 2006, and titled “Distributed Power Harvesting System for Distributed Power Sources,” 60/868,962, filed Dec. 7, 2006, and titled “System, Method and Apparatus for Chemically Independent Battery,” Ser. No. 60/908,095, filed Mar. 26, 2007, and titled “System and Method for Power Harvesting from Distributed Power Sources,” and Ser. No. 60/916,815, filed May 9, 2007, and titled “Harvesting Power from Direct Current Power Sources.” The entire contents of the above-identified applications are incorporated herein by reference. Further, this application is related to ordinary U.S. patent application Ser. No. 11/950,224, filed Dec. 4, 2007, titled “Current Bypass for Distributed Power Harvesting Systems Using DC Power Sources,” patent application Ser. No. 11/950,271, filed Dec. 4, 2007, titled “Distributed Power Harvesting Systems Using DC Power Sources,” patent application Ser. No. 11/950,307, filed Dec. 4, 2007, titled “A Method for Distributed Power Harvesting Using DC Power Sources,” “Removable Component Cartridge for Increasing Reliability in Power Harvesting Systems,” and “Battery Power Delivery Module,” that are filed in at the U.S. Patent and Trademark Office on Dec. 6, 2007 and incorporates the entire content of these applications by this reference. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The field of the invention generally relates to management of distributed DC power sources and, more particularly, to monitoring of distributed DC power sources, such as solar cell array, fuel cells, batteries, and similar applications. 
         [0004]    2. Related Arts 
         [0005]    The recent increased interest in renewable energy has led to increased research in systems for distributed generation of energy, such as photovoltaic cells (PV), fuel cells, batteries (e.g., for hybrid cars), etc. Various topologies have been proposed for connecting these power sources to the load, taking into consideration various parameters, such as voltage/current requirements, operating conditions, reliability, safety, costs, etc. For example, most of these sources provide low voltage output (normally lower than 3V), so that many of them need to be connected serially to achieve the required operating voltage. Conversely, a serial connection may fail to provide the required current, so that several strings of serial connections may need to be connected in parallel to provide the required current. 
         [0006]    It is also known that power generation from each of these sources depends on manufacturing, operating, and environmental conditions. For example, various inconsistencies in manufacturing may cause two identical sources to provide different output characteristics. Similarly, two identical sources may react differently to operating and/or environmental conditions, such as load, temperature, etc. In practical installations, different source may also experience different environmental conditions, e.g., in solar power installations some panels may be exposed to full sun, while others be shaded, thereby delivering different power output. While these problems and the solutions provided by the subject invention are applicable to any distributed power system, the following discussion turns to solar energy so as to provide better understanding by way of a concrete example. 
         [0007]    A conventional installation of solar power system  10  is illustrated in  FIG. 1 . Since the voltage provided by each individual solar panel  101  is low, several panels are connected in series to form a string of panels  103 . For a large installation, when higher current is required, several strings  103  may be connected in parallel to form the overall system  10 . The solar panels are mounted outdoors, and their leads are connected to a maximum power point tracking (MPPT) module  107  and then to an inverter box  104 . The MPPT  107  is typically implemented as part of the inverter  104 . 
         [0008]    The harvested power from the DC sources is delivered to the inverter  104 , which converts the fluctuating direct-current (DC) into alternating-current (AC) having a desired voltage and frequency, which, for residential application, is usually 11OV or 220V at 60 Hz or 220V at 50 Hz. The AC current from the inverter  104  may then be used for operating electric appliances or fed to the power grid. Alternatively, if the installation is not tied to the grid, the power extracted from the inverter may be directed to a conversion and charge/discharge circuit to store the excess power created as charge in batteries. In case of a battery-tied application, the inversion stage might be skipped altogether, and the DC output of the MPPT stage  107  may be fed into the charge/discharge circuit. 
         [0009]      FIG. 2  illustrates one serial string of DC sources, e.g., solar panels  201   a - 201   d , connected to MPPT circuit  207  and inverter  204 . The current versus voltage (IV) characteristics are plotted ( 21 Oa- 21 Od) to the left of each DC source  201 . For each DC source  201 , the current decreases as the output voltage increases. At some voltage value the current goes to zero, and in some applications may assume a negative value, meaning that the source becomes a sink. Bypass diodes are used to prevent the source from becoming a sink. The power output of each source  201 , which is equal to the product of current and voltage (P=I*V), varies depending on the voltage drawn from the source. At a certain current and voltage, the power reaches its maximum. It is desirable to operate a power generating cell at this maximum power point. The purpose of the MPPT is to find this point and operate the system at this point so as to draw the maximum power from the sources. 
         [0010]    Various environmental and operational conditions impact the power output of DC power sources. For example, the solar energy incident on various panels, ambient temperature and other factors impact the power extracted from each panel. Depending on the number and type of panels used, the extracted power may vary widely in the voltage and current. Changes in temperature, solar irradiance and shading, either from near objects such as trees or far objects such as clouds, can cause power losses. Owners and even professional installers find it difficult to verify the correct operation of the system. With time, many more factors, such as aging, dust and dirt collection and module degradation affect the performance of the solar array. 
         [0011]    Data collected at the inverter  104  is not sufficient to provide proper monitoring of the operation of the system. Moreover, when the system experiences power loss, it is desirable to ascertain whether it is due to environmental conditions or from malfunctions and/or poor maintenance of the components of the solar array. Furthermore, it is desirable to easily locate the particular solar panel that may be responsible for the power loss. However, to collect information from each panel requires some means of communication to a central data gathering system. The data gathering system needs to be able to control data transmission, avoid transmission collisions, and ascertain each sender of data. Such a requirement can be most easily accomplished using a duplex transmission method. However, a duplex transmission method requires additional transmission lines and complicates the system. On the other hand, one-way transmission is prone to collisions and makes it difficult to compare data transmitted from the various sources. 
         [0012]    Consequently, conventional methods in the field of solar array monitoring focus mainly on the collection of the output parameters from the overall solar array. Due to the wide variability of power output of such systems, and the wide range of environmental conditions that affect the power output, the output parameters from the overall system are not sufficient to verify whether the solar array is operating at peak power production. Local disturbances, such as faulty installation, improper maintenance, reliability issues and obstructions might cause locals power losses which are difficult to detect from overall monitoring parameters. 
         [0013]    For further discussion of the above issues relating to distributed power sources and solar panels, the reader is highly encouraged to review the following literature, which may or may not be prior art.
       Cascade DC-DC Converter Connection of Photovoltaic Modules, G. R. Walker and P. C. Sernia,  Power Electronics Specialists Conference,  2002. ( PESCO 2), Vol. 1 IEEE, Cairns, Australia, pp. 24-29.   Topology for Decentralized Solar Energy Inverters with a Low Voltage AC-Bus, Bjorn Lindgren.   Integrated Photovoltaic Maximum Power Point Tracking Converter, Johan H. R. Enslin et al., IEEE Transactions on Industrial Electronics, Vol. 44, No. 6, December 1997.   A New Distributed Converter Interface for PV Panels, R. Alonso et al., 20th European Photovoltaic Solar Energy Conference, 6-10 Jun. 2005, Barcelona, Spain.   Intelligent PV Module for Grid-Connected PV Systems, Eduardo Roman, et al., IEEE Transactions on Industrial Electronics, Vol. 53, No. 4, August 2006. Also in Spanish patent application ES2249147.   A Modular Fuel Cell, Modular DC-DC Converter Concept for High Performance and Enhanced Reliability, L. Palma and P. Enjeti, Power Electronics Specialists Conference, 2007, PESC 2007, IEEE Volume, Issue, 17-21 Jun. 2007 Page(s): 2633-2638. Digital Object Identifier 10.1109/PESC.2007.4342432.   Experimental Results of intelligent PV Module for Grid-Connected PV Systems, R. Alonso et al., Twenty first European Photovoltaic Solar Energy Conference, Proceedings of the International Conference held in Dresden, Germany, 4-8 Sep. 2006.   Cascaded DC-DC Converter Connection of Photovoltaic Modules, G. R. Walker and P. C. Semia, IEEE Transactions on Power Electronics, Vol. 19, No. 4, July 2004.   Cost Effectiveness of Shadow Tolerant Photovoltaic Systems, Quaschning, V.; Piske, R.; Hanitsch, R., Euronsun 96, Freiburg, Sep. 16-19, 1996.   Evaluation Test results of a New Distributed MPPT Converter, R. Orduz and M. A. Egido, 22nd European Photovoltaic Solar Energy Conference, 3-7 Sep. 2007, Milan, Italy.   Energy Integrated Management System for PV Applications, S. Uriarte et al., 20th European Photovoltaic Solar Energy Conference, 6-10 Jun. 2005, Barcelona, Spain.   U.S. Published Application 2006/0185727       
 
       SUMMARY 
       [0026]    The following summary of the invention is provided in order to provide a basic understanding of some aspects and features of the invention. This summary is not an extensive overview of the invention, and as such it is not intended to particularly identify key or critical elements of the invention, or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented below. 
         [0027]    According to aspects of the invention, there is provided a monitoring system employing one-way transmission. Collisions are avoided or minimized by a novel transmission timing scheme. The novel transmission method also voids the necessity to synchronize the transmission of data. According to aspects of the invention, each transmission carries a unique ID of the data source. The data is collected and stored at a central analysis system, and various analysis is performed on the data to ascertain the operation parameters of each transmission source and of the entire system. According to further aspects of the invention, a mechanism for sending an interrupt message is provided. When a fault is detected in any of the power sources, an interrupt message may be sent that overrides all other messages, so that the fault may be detected immediately. According to aspects of the invention, all data transmission is done using power line communication (PLC). Alternatively, other modes of transmission may be used, such as wireless or dedicated transmission lines, such as Ethernet, RS232, RE485, etc. 
         [0028]    According to aspects of the invention, a monitoring system for distributed DC power installation is provided, comprising: a plurality of power sources; a plurality of monitoring modules, each monitoring module associated with one of the power sources and collecting performance data of the associated power source; a plurality of transmitters, each transmitter associated with one of the monitoring modules and transmitting the performance data; a plurality of controllers, each associated with one of the transmitters and controlling transmission events according to elapsed time from timer initialization. Each of the power sources may be connected to a power line and wherein each transmitter transmits the performance data over the power line. Each of the monitoring modules comprises: a current measurement module for collecting the current data; and a voltage measurement module for collecting the voltage data. Each of the monitoring modules may further comprise a temperature sensor module for sensing the temperature data at the power source. Each of the monitoring modules may further comprise an arc detection module for detecting arcing at the power source. Each of the monitoring modules may further comprise a timer, and wherein each controller initializes the timer whenever the associated power source starts to generate power. Each of the monitoring modules may further comprise a randomizer for varying time increments for controlling transmission events. The monitoring system may further comprise a memory storing the performance data accumulated since timer initialization. The monitoring system may further comprise: a central analysis station; and, a communication translator for receiving the performance data from the monitoring modules and transmitting the performance data to the central analysis station. The central analysis station may analyze fault detection. The central analysis station may compare measured power to expected power determined based on external data. Each of the power sources may comprise a solar panel. Each of the power sources may comprise a string of serially connected solar panels. Each of the monitoring modules may comprise a current measurement module for collecting current data. The monitoring system may further comprise: a connection box for parallel coupling all of the string of serially connected solar panels; and, a voltage measuring module measuring the voltage of the parallel coupling. The monitoring system may further comprise: a connection box for parallel coupling all of the string of serially connected solar panels; and, total current measuring module measuring the total current of the parallel coupling. The monitoring system may detect current leakage by comparing output of the total current measuring module to the sum of current measuring modules of each of the monitoring modules. 
         [0029]    According to aspects of the invention, a method for monitoring distributed power harvesting systems including DC power sources is provided, the method comprising: individually monitoring power generation at each of the DC power sources and, when power generation passes a threshold at one of the DC power sources, performing the steps: initializing a timer for the power source; collecting performance data for the power source; monitoring passage of time period of the timer and, when the time period reached a setup time, transmitting the collected performance data to a central analysis station. Collecting performance data may further comprise storing the performance data in memory, and wherein transmitting the collected performance data comprises transmitting the collected performance data accumulated since initialization of the timer. Collecting performance data may comprise measuring at least one of output voltage and output current. The method may further comprise comparing performance data for at least one of the DC power sources to performance data from the same DC power source at a different time. The method may further comprise comparing performance data for at least one of the DC power sources to performance data from adjacent ones of the DC power sources. The method may further comprise comparing performance data for at least one of the DC power sources to expected performance data based on external parameters. Monitoring passage of time period may further comprise introducing randomness to the setup time. The method may further comprise serially connecting a plurality of solar panels to form each of the DC power sources. Transmitting the collected performance data may comprise sending the collected performance data over a power line. 
         [0030]    According to aspects of the invention, a distributed DC power harvesting system is provided, comprising: a plurality of solar panels serially connected to form a string of panels coupled to a power line; at least one monitoring module connected to the string of panels and gathering performance data from at least one solar panel, the monitoring module comprising: a transmitter for transmitting the performance data over the power line; a controller for controlling transmission events of the transmitter according to elapsed time from timer initialization; and, a receiving station coupled to the power line and receiving the performance data from the transmitter. The receiving station may further comprise at least one of a voltage and current sensor. The receiving station may further comprise a transmitter for relaying at least the performance data received from the power line. The transmitter may comprise a wireless transmitter. The monitoring module may comprise and least one of: a current measurement module for collecting current data from at least one solar panel; and a voltage measurement module for collecting voltage data from at least one solar panel. The monitoring module may further comprise a temperature sensor. The monitoring module may further comprise a timer, and wherein the controller initializes the timer whenever an associated panel starts to generate power. The monitoring module may further comprise a randomizer for varying time increments for controlling transmission events. The system may further comprise a memory storing the performance data accumulated since timer initialization. The system may further comprise: one or more additional string of panels; a connection box for parallel coupling of the string of panels and the one or more additional string of panels; and, a voltage measuring module measuring the voltage of the parallel coupling. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    The accompanying drawings, which are incorporated in and constitute a part of this specification, exemplify the embodiments of the present invention and, together with the description, serve to explain and illustrate principles of the invention. The drawings are intended to illustrate major features of the exemplary embodiments in a diagrammatic manner. The drawings are not intended to depict every feature of actual embodiments nor relative dimensions of the depicted elements, and are not drawn to scale. 
           [0032]      FIG. 1  illustrates a conventional solar power system. 
           [0033]      FIG. 2  illustrates one serial string of DC sources and current versus voltage characteristic curve for the solar panels. 
           [0034]      FIG. 3A  illustrates a monitoring module according to aspects of the invention. 
           [0035]      FIG. 3B  is a flow chart illustrating a method for transmission of data according to various aspects. 
           [0036]      FIG. 4  shows a communication and analysis system, according to aspects of the invention, being associated with the monitoring module of  FIG. 3A . 
           [0037]      FIG. 5  shows a distributed power harvesting system, including a monitoring module, according to aspects of the invention. 
           [0038]      FIG. 6  illustrates a solar system according to another embodiment of the invention. 
           [0039]      FIG. 7  illustrates a power converter, according to aspects of the invention. 
           [0040]      FIG. 8  illustrates a typical centralized solar field installation. 
           [0041]      FIG. 9  illustrates a solar field installation implementing monitoring according to an embodiment of the invention. 
           [0042]      FIG. 10  illustrates a solar field installation implementing monitoring according to another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0043]    Aspects of the present invention provide a monitoring system for solar panel system. The monitoring system includes modules that may be attached to each solar panel of the solar system. The monitoring module will monitor several parameters including, etc., panel voltage, panel current, panel temperature, lighting conditions, spatial orientation (e.g., tilt), and other parameters. The information from each monitoring module may be transmitted to a central management unit together with a unique module ID. The transmission may be done over the powerlines, in wireless form, or with dedicated wiring—such as Ethernet, RS-232, RS-485 or other. In one aspect of the invention, transmission is done as power line communication in a one-way implementation. Collisions are avoided or minimized by using a unique transmission timing mechanism. 
         [0044]    The central management unit may analyze the data from all solar panels. The monitoring system can be implemented at the string level, at the panel level or even at the cell level. The principle applicable at the panel level monitoring may be applied for string level and cell level. Moreover, the innovative monitoring system may be used in small installation, such as residential solar panel installations, and large installations, such as large solar panel field power plants. 
         [0045]    Analysis of the data may enable detection and pinpointing of most of the common failures associated with solar array power loss. Further, smart analysis of current and historical data can also be used to suggest corrective measures such as cleaning or replacing a specific portion of the solar array. The system can also detect normal power losses caused by environmental conditions and prevent costly and difficult solar array testing. Additionally, analysis of the data can lead to suggestion for environmental corrective actions. For example, it may suggest changing the tilt or location of specific panels, or removing of obstacles that block the sun under certain conditions not realized at the time of installation. 
         [0046]      FIG. 3A  shows a monitoring module according to aspects of the invention. The exemplary monitoring module  300 , according to aspect of the invention, is used to collect and transmit date from each solar panel, such as the solar panel  101  of  FIG. 1 . Data from all monitoring modules is transmitted via a communication system to a central analysis station, which analyzes the data and displays the status of the solar array. 
         [0047]    The monitoring module  300  includes several sub-modules. The sub-modules within the monitoring module  300  include a current measurement module  301 , a microcontroller  302 , a communication module  303 , a voltage measurement module  304 , a random access memory (RAM) module, a non-volatile RAM or NVRAM module  306 , a temperature sensor  307  and one or more external sensor interfaces  308 . 
         [0048]    The microcontroller module  302  is coupled to the other modules and controls the other modules. In one exemplary aspect shown in  FIG. 3A , the current measurement module  301  is located in series with the input and output ports to the monitoring module  300 . The location of the current measurement module  301  may vary depending on the type of current measurement device used in the module. In the exemplary aspect shown, the voltage measurement module  304  is located in parallel across the input port to the monitoring module  300 . Voltage measurement devices are usually placed in parallel with the component whose voltage is being measured. In the exemplary aspect shown, the communication module  303  is shown as located in parallel with the output ports of the monitoring module  300 . There is no requirement for a particular location for this module and the location shown is arbitrary. The sensor modules while coupled to the microcontroller module  302 , are not shown as coupled to the input or output ports of the monitoring module  300 . These sensor modules, however, may derive power from the panel connected to the monitoring module  300  and, therefore, may be located along a circuit path from the input to the output ports of the monitoring module  300 . A power unit may be used to feed monitoring module  300 . The power may be derived from one of many power sources, such as batteries or feed-in from another location. In one embodiment the monitoring module  300  may be fed from power harvested from the solar panel being monitored. 
         [0049]    In various aspects of the invention, inclusion of some of the modules, such as the temperature sensor  307 , is optional. 
         [0050]    The monitoring module  300  can be implemented using discrete components or may be integrated to obtain an application specific integrated circuit (ASIC). 
         [0051]    The measurement modules  301 ,  304  and the sensor modules  307 ,  308  may have filter circuits and analog to digital conversion circuits associated with them.  FIG. 3A  shows low-pass filter and analog to digital conversion circuits  311 ,  314 ,  317 ,  318  each associated with a corresponding measurement and sensor module. 
         [0052]    Current and voltage measurement modules  301 ,  304  are used to collect current and voltage data. The collected data is transferred to the microcontroller module  302 . The microcontroller module  302  may be a digital state machine. The microcontroller stores the collected information in its local RAM  305 . Pre-defined data, stored in the NVRAM module  306 , may be used to control the activity of the microcontroller  302 . 
         [0053]    The data collected by the current and voltage measurement modules  301 ,  304  and transferred to the microcontroller  302  may be subsequently transmitted to a central analysis station described below with respect to  FIG. 4 . The communication module  303  is used to transmit the data from the microcontroller  302  or from storage in RAM  305  to outside of the monitoring module  300 . 
         [0054]    The current measurement module  301  may be implemented by various techniques used to measure current. In one aspect of the invention, the current measurement module  301  is implemented using a very low value resistor. The voltage across the resistor will be proportional to the current flowing through the resistor. In another aspect of the invention, the current measurement module  301  is implemented using current probes which use the Hall Effect to measure the current through a conductor without the need to add a series resistor. After translating the current to voltage, the data passes through a low pass filter and is digitized. The low-pass filter and the analog to digital converter associated with the current measurement module  301  are shown as module  311  in  FIG. 3A . As with the voltage measurement module, care must be taken to choose the correct resolution and sample rate for the analog to digital converter. If the current sensing technique does not require a series connection, then the monitoring module  300  may be connected to the panel in parallel. For a parallel connection, there is no need to disconnect the panel during the connection. 
         [0055]    In one aspect of the invention, the voltage measurement module  304  uses simple parallel voltage measurement techniques in order to measure the voltage output of the solar panel. The analog voltage is passed through a low pass filter in order to minimize aliasing. The data is then digitized using an analog to digital converter. The low-pass filter and the analog to digital converter associated with the voltage measurement module  304  are shown as module  314  in  FIG. 3A . The analog to digital converter  314  has sufficient resolution to correctly evaluate the voltage from the solar panel. The low-pass filter makes it possible for low sample rates to be sufficient for evaluating the state of the panel. 
         [0056]    The optional temperature measurement module  307  enables the system to use temperature data in the analysis process. The temperature may be indicative of several types of failures and problems. Furthermore, the panel temperature is a factor in the power output from the panel and in the overall power production. 
         [0057]    The one or more external sensor interfaces  308  enable connecting various external sensors to the monitoring module  300 . These sensors are optional and may be used where they enable enhanced analysis of the state of the solar array. Examples of external sensors that may be used at the external sensor interfaces  308 , include ambient temperature sensor, solar irradiance sensors, spatial orientation such as tilt sensor, sensors from neighboring panels and the like. When a type of sensor is regularly used, then it may be integrated into the monitoring module  300  instead of being an external component. 
         [0058]    The microcontroller module  302  manages the monitoring process. The tasks performed by the microcontroller module  302  includes gathering information from the current and voltage measurement modules  301 ,  304 , storing the information in local memory  305 ,  306  and transmitting the stored information to outside of the monitoring module  300 . The microcontroller module  302  uses the information stored in memory in order to control its operation. This operating information may be stored in the non-volatile memory of the NVRAM module  306 , to preserve the information even when power-loss occurs. Information in the NVRAM module  306  may include information about the microcontroller module  302  such as the serial number, the type of communication bus used, the status update rate and the ID of the central analysis station to which the data is transmitted. This information may be added to the parameters collected by the measurement modules  301 ,  304  before transmission out of the monitoring module  300 . 
         [0059]    The installation process of the monitoring module  300  includes connecting each of the monitoring modules  300  to a panel such as the solar panel  101  of  FIG. 1  or the solar panel  505  of  FIG. 5 . The measurement features of the monitoring module  300  may be used to ensure that the panel and the monitoring module are properly connected and to record the serial number of the monitoring module  300  or the microcontroller within the monitoring module. The measurement features  301 ,  304 , or other sensors, such as GPS, tilt etc., may also be used to determined physical location of the connection and the array connection topology. These parameters may be used by an analysis software at the central analysis station  403  to detect problems in the solar panels and the array. 
         [0060]    The monitoring module  300  may be installed during the installation of the solar array or retrofitted to an existing installation. In both cases the monitoring module may be connected to the panel junction connection box or to the cables between the panels. The monitoring module may be provided with the connectors and cabling needed to enable easy installation and connection to the panels and cables. 
         [0061]    The monitoring module  300  shown in  FIG. 3A  collects current, voltage and some other optional types of data from each of the panels in a distributed DC power harvesting system. Data from each panel is subsequently transmitted for analysis. The communication module  303  connects the microcontroller module  302  to the communication bus that is described below with reference in  FIG. 4 . The communication from each monitoring module  300  is performed using conventional power line communication technique (also known as power line carrier). However, a unique transmission timing is utilized in order to avoid or minimize collisions. This technique will be explained with reference to a specific example of a monitor connected to a solar panel. 
         [0062]    When the solar panel “wakes”, i.e., starts to receive sun light and generate output power, the monitor initializes a timer to time to. The monitor may or may not send data at the initialization time. Then, the monitor collects data continuously, but transmits collected data only after a given period has past from t 0  or from the last transmission. For example, the monitor may transmit data every 15 minutes. Since the panels are spatially separated, they will most likely wake at different times, introducing randomness to the transmission time, so that each panel would transmit according to its own timer. That is, each monitor would transmit data at: 
         [0000]    
       
      
       t 
       0 
       +xC,  
      
     
         [0000]    where x is a whole natural number and Cis a set constant, say 15 minutes. However, for each panel t 0  may be at a different time every morning 
         [0063]    As can be appreciated from the above, using the wake up time of the panel to initiate the timer introduces a measure of randomness that helps avoid collisions. According to another embodiment of the invention, another measure of randomness is introduced in the counter. For example, the transmission time may be calculated as t 0 +xC+ E , where  E  is a random number provided by a random number generator, etc. Alternatively, the transmission time may be calculated as t0+x(C+ E ). Notably, the random number should be generated separately to each module to prevent the chance that two panels wake at the same time and increment the counter at the same rate, thereby colliding on each transmission attempt. This random element may be reintroduced for each time a transmission is sent. Other methods of introducing randomness may also be used. 
         [0064]      FIG. 3B  is a flow chart illustrating a method for transmission of data by the monitor  300  of  FIG. 3A . At step  340  it is checked whether the panel has awaken (i.e., receives light and generates power at a predetermined level). If so, the process proceeds to step  342  where the timer is initialized and the counting is started. Data, such as current, voltage, temperature, illumination, power output, etc., is then collected and stored, e.g., in RAM  305 , at step  344 , which continues so long as the timer progresses and the panel has not gone to sleep ( 352 ). As explained above, optionally a further randomization is introduced, which is shown by step  346 . Then at step  348  it is determined whether the time for transmitting data has been reached and, if so, the data is transmitted at step  350 . In this particular example, the data that is transmitted is the data accumulated since initialization of the timer. However, other methodologies may be implemented. For example, the data may be data accumulated since last transmission or current data reading. At step  352  it is checked whether the panel assumed the sleep mode, e.g., illumination or power generation is below a threshold. If so, the process ends. Otherwise, counting and transmission of data continues. 
         [0065]    The above schemes minimize or avoid collisions. However, if a collision does occur, since the transmission is only one way, the central system would not get the data and would not know what data was lost, and the sending monitors would also have no way of knowing that the data never reached the central system. As a result, when the central system analyzes the data and compares data from one panel to another, errors may be introduced if some data transmission was lost due to collision. For example, if the central unit tries to compare power generated by several panels between 1 pm and 2 pm, the comparison would be inaccurate if data from two or more panels collided at 1:30 pm and is missing from the calculation. 
         [0066]    To avoid this problem, a scheme is adopted wherein the data is accumulated at each monitor. Then, at each transmission, the accumulated total value of the data is transmitted. For example, at time t 15  the power generated from wake to wake plus 15 minutes is transmitted. At time ho the power generated from wake to wake plus 30 minutes is transmitted, and so on. In this way, even if one or more transmission was not received by the central unit, the central unit can reconstruct the missing data by, for example, extrapolating it from the data from all of the transmissions that were received. Similar extrapolation may be done in order to put data that arrived at different times from different panels in order to compare between panels on a unified time-base. E.g. Curves of power production from the monitors could be extrapolated for each panel based on the data points that arrived, and then these curves could be compared in order to detect power anomalies or other problems and phenomena. 
         [0067]    According to a further aspect of the invention, an interrupt message may be sent, which overrules all other messages. An interrupt message may be sent by any monitoring module  300 , for example, whenever a rapid corrective action may be required. This may be when power drops suddenly, as due to malfunction, panel breakage due to hail storms or other cause, etc. The interrupt message may be sent at any time, regardless of the counter&#39;s position. In connection with the interrupt message, according to an aspect of the invention a wide band noise detector is implemented in the module  300 . When the wideband noise detector detects noise above a certain threshold, it sends an interrupt message. Notably, this feature is implemented to identify arcing that may be caused due to an open connection in the system. That is, since the system voltage is relatively high, e.g., 400-600V, if a connection becomes separated, and potential may arc through the air. Such arcing can be detected as wideband noise. The wideband noise detector may be implemented as part of the controller  102 , as shown in  FIG. 3A , or as a separate unit. 
         [0068]    Additionally, to assist in locating faults and deleterious conditions, each monitor has a unique ID, which is transmitted together with the data. In this way, the central unit can easily monitor each panel individually and the physical location of the panel corresponding to each data stream can be easily ascertained. Thus, for example, if every day at 2 pm there is power drop at one or more panels, their physical location can be easily ascertained by using the unique ID transmitted with the data. Then the status of the panels can be evaluated to see whether there is an obstacle that obscures the sun every day at 2 pm. Furthermore, if a geographic information sensor (such as a GPS) is attached to the monitoring module, it could directly transmit its location so the obstruction may be found and removed. 
         [0069]    The central analysis unit may also use the ID information to perform data analysis by comparing the data from the particular panel to expected data obtained from external sources. That is, if the central analysis system knows the location, temperature, tilt, etc., of the panel having the particular ID, it may calculate expected power from this panel at the current prevailing conditions. If the data received from the panel substantially deviates from the expected power output, it may determine that the panel is faulty or some factors cause it to lose power. This is especially a beneficial feature in the topology of the embodiment described herein, since the maximum power point tracking is performed on an individual panel basis, so the power obtained should be commensurable with the expected power. That is, there is no error introduced due to tracking maximum power point on an average of several panels. 
         [0070]      FIG. 4  shows a communication and analysis system, according to aspects of the invention, being associated with the monitoring module of  FIG. 3A .  FIG. 4  shows a system used for collecting data from each of the panels in a distributed power system and subsequent analysis of collected data. The system of  FIG. 4  includes a number of panels  401  that generate power. Each panel includes a monitoring module such as the monitoring module  300 . Data collected by the monitoring modules at the panels  402  are communicated by a module communication bus  404  to a communication translator  401 . The communication translator  401  sends the date to a central analysis station  403  via a communication link  403 . The central analysis station  403  receives the data that is transmitted via the communication bus  404 , analyzes the data and displays the status of the panels corresponding to the time the data was collected. 
         [0071]    In  FIG. 4 , one module communication bus  404  is shown for transmitting data from the monitoring modules  300  from a number of panels  402 . The data may be transmitted on a single bus in the manner described above which eliminates or minimizes collisions. However, other transmission methods may be used. For example, the data from several panels may be multiplexed on the same module communication bus. Alternatively, each monitoring module  300  includes a separate module communication bus  404 . The module communication buses  404  from the different monitoring modules carry the data from each monitoring module  300  to the communication translator  401 . 
         [0072]    The module communication bus  404  can be implemented in different ways. In one aspect of the invention, an off-the-shelf communication bus such as Ethernet, RS232 or RS485 is used. Using an off-the-shelf communication bus simplifies the design of the communication module  303  of the monitoring module  300  but requires separate cables. Other methods such as wireless communications or power line communications may also be used. When wired communication is used between the monitoring modules  300  and the communication translator  401 , the communication translator  401  may be located in close physical proximity to the panels to reduce the length of the module communication bus  404  or buses. When wireless communication is used between the monitoring modules  300  and the communication translator  401 , the communication translator  401  need not be in close physical proximity to the panels. 
         [0073]    The communication translator  401  is used to convert the module communication bus or buses  404  to a standard communication protocol and physical layer. This enables receiving data from the monitoring module  300  on various data terminals, such as a computer or PDA. The central analysis station  403  may then be implemented as a software that is run on a standard PC, an embedded platform or a proprietary device. 
         [0074]    In one aspect of the invention, unidirectional power line communication is used from the monitoring modules  300  to the central analysis station  403 . With unidirectional communication, a mechanism for preventing cross-talk between the monitoring modules  300  may be provided. Such a mechanism may be implemented in the form of transmitting data from each of the monitoring modules  300  at preset times as explained with respect to  FIG. 3B . In one aspect of the invention, a collision detection algorithm may be used to ensure the data is received without collisions at the central analysis station  403 . 
         [0075]    In one aspect of the invention, bidirectional communication is used between the central analysis station  403  and the monitoring modules  300 . With bidirectional communication, the central analysis station  403  may proactively request the data collected by one or more of the monitoring modules  300 . 
         [0076]    The collected data is analyzed at the central analysis station  403 . By analyzing the information from each of the monitoring modules, many causes for power losses can be detected. For example, when energy production from a panel is low on some hours of the day while the adjacent panels produce the same power on all hours, the low performance panel is probably shaded during the low production hours. Panels that produce little power in comparison to their adjacent panels might be constantly shaded, soiled or installed incorrectly. Comparison of the power output of each panel with its corresponding power output a year earlier may indicate that the output has diminished due to dust or soil collected on the panel. Additional data may be gathered from outside sources in order to monitor and evaluate the power production of the array. E.g. irradiance data from satellites, weather data from terrestrial stations, RADAR systems or satellites, or weather and irradiance forecasts based on historical data or computerized models, and so forth. Many more heuristics and algorithmic methods may be used to detect problems and help the owner of the system to pinpoint problems in the array. Having the unique ID transmitted with the data helps identify the panels and their physical location. 
         [0077]      FIG. 5  shows a distributed power harvesting system, including a monitoring module, according to aspects of the invention. Configuration  50  enables connection of multiple power sources, for example solar panels  501  to a single power supply. The series connection of all of the solar panels is connected to an inverter  504 . A central analysis station  500  is shown that is in communication with the monitoring modules  300  coupled to each of the solar panels  501 . Station  500  may be incorporated into the inverter  504  or may be an independent unit. 
         [0078]    In configuration  50 , each solar panel  501  is connected to a separate power converter circuit  505 . Power converter circuit  505  adapts optimally to the power characteristics of the connected solar pane  1501  and transfers the power efficiently from input to output. Power converters  505  can be buck converters, boost converters, buck/boost converters, flyback or forward converters. The converters  505  may also contain a number of component converters, for example a serial connection of a buck and a boost converter. 
         [0079]    Each converter  505  includes a control loop that receives a feedback signal, not from the output current or voltage, but rather from the input coming from the solar panel  501 . An example of such a control loop is a maximum power point tracking (MPPT) loop in solar array applications. The MPPT loop in the converter locks the input voltage and current from each solar panel  501  to its optimal power point. The MPPT loop of the converter  505  operates to perform maximum power point tracking and transfers the input power to its output without imposing a controlled output voltage or output current. 
         [0080]    Each converter  505  may include a monitoring module according to the aspects of the invention. For example, each converter  505  may include the monitoring module  300  of  FIG. 3A . The communication link between the monitoring modules  300  and the central analysis station  500  may be wireless or wired. If wired, the connection may be done to each unit  505  individually or centrally via inverter  504 . Note that there is additional value in monitoring the panels output when coupling it with MPPT tracking power converter  505 , since this guaranties that the power monitored is at maximum power point, and therefore low power reading signify a real problem and are not merely a false-alarm that results from the current draw from a central inverter, which may not be optimal for each panel. Converters  505  can be connected in series or in parallel to form strings and arrays. 
         [0081]    Conventional DC-to-DC converters have a wide input voltage range at the solar panel side and an output voltage predetermined and fixed on installation. In these conventional DC-to-DC voltage converters, the controller monitors the current or voltage at the input, and the voltage at the output. The controller determines the appropriate pulse width modulation (PWM) duty cycle to fix the input voltage to the predetermined value decreasing the duty cycle if the input voltage drops while varying the current extracted from the input. In converters  505 , according to embodiments of the present invention, the controller monitors the voltage and current at its input and determines the PWM in such a way that maximum power is extracted, dynamically tracking the maximum point. In embodiments of the present invention, the feedback loop is closed on the input power in order to track maximum power rather than closing the feedback loop on the output voltage as performed by conventional DC-to-DC voltage converters. 
         [0082]    The outputs of converters  505  are series connected into a single DC output into the inverter  504 , which converts the series connected DC output to an alternating current power supply. If the output is not required to be AC, the inverter may be omitted, or other load, such as a central DC/DC converter or battery charger may be used instead. 
         [0083]    The circuit of  FIG. 5  provides maximum power available during continuous operation from each solar panel  501  by continuously performing MPPT on the output of each solar panel to react to changes in temperature, solar radiance, shading or other performance deterioration factors of each individual solar panel  501 . As shown in  FIG. 1 , conventional solutions for combining power, perform MPPT on strings  103  or arrays of solar panels  101 . As a result of having a separate MPPT circuit in each converter  505 , and for each solar panel  501 , in the embodiments of the present invention, each string  503  in the embodiment shown in  FIG. 5  may have a different number of panels  501  connected in series. Furthermore panels  501  can be installed in different directions, as solar panels  501  do not have to be matched and partial shading degrades the performance of only the shaded panel. According to embodiments of the present invention, the MPPT circuit within the converter  505  harvests the maximum possible power from panel  501  and transfers this power as output regardless of the parameters of other solar panel  501 . 
         [0084]      FIG. 6  illustrates a solar system according to another embodiment of the invention. The embodiment of  FIG. 6  is similar to that of  FIG. 5 , in that panels  601  are connected in series to form strings  603 . The strings  603  are then connected in parallel to inverter  604 . The inverter  604  includes a central analysis station  600  that receives data from reporting modules within converters  605 . Central station  600  also receives data from reporting module  606 , which provides data relating to the entire power delivered from all of the panels. 
         [0085]      FIG. 7  illustrates a power converter, according to aspects of the invention.  FIG. 7  highlights, among others, a monitoring and control functionality of a DC-to-DC converter  705 , according to embodiments of the present invention. A DC voltage source  701  is also shown in the figure. Portions of a simplified buck and boost converter circuit are shown for the converter  705 . The portions shown include the switching transistors  728 ,  730 ,  748  and  750  and the common inductor  708 . Each of the switching transistors is controlled by a power conversion controller  706 . 
         [0086]    The power conversion controller  706  includes the pulse-width modulation (PWM) circuit  733 , and a digital control machine  730  including a protection portion  737 . The power conversion controller  706  is coupled to microcontroller  790 , which includes an MPPT module  719 , and may also optionally include a communication module  709 , a monitoring and logging module  711 , and a protection module  735 . 
         [0087]    A current sensor  703  may be coupled between the DC power source  701  and the converter  705 , and output of the current sensor  703  may be provided to the digital control machine  730  through an associated analog to digital converter  723 . A voltage sensor  704  may be coupled between the DC power source  701  and the converter  705  and output of the voltage sensor  704  may be provided to the digital control machine  730  through an associated analog to digital converter  724 . The current sensor  703  and the voltage sensor  704  are used to monitor current and voltage output from the DC power source, e.g., the solar panel  701 . The measured current and voltage are provided to the digital control machine  730  and are used to maintain the converter input power at the maximum power point. 
         [0088]    The PWM circuit  733  controls the switching transistors of the buck and boost portions of the converter circuit. The PWM circuit may be a digital pulse-width modulation (DPWM) circuit. Outputs of the converter  705  taken at the inductor  708  and at the switching transistor  750  are provided to the digital control machine  730  through analog to digital converters  741 ,  742 , so as to control the PWM circuit  733 . 
         [0089]    A random access memory (RAM) module  715  and a non-volatile random access memory (NVRAM) module  713  may be located outside the microcontroller  706  but coupled to the microcontroller  706 . The unique ID and other related data, such as serial number, manufacturer, manufacturing date, etc., may be stored in the NVRAM. A temperature sensor  779  and one or more external sensor interfaces  707  may be coupled to the microcontroller  706 . The temperature sensor  779  may be used to measure the temperature of the DC power source  701 . A physical interface  717  may be coupled to the microcontroller  706  and used to convert data from the microcontroller into a standard communication protocol and physical layer. An internal power supply unit  739  may be included in the converter  705 . 
         [0090]    In various aspects of the invention, the current sensor  703  may be implemented by various techniques used to measure current. In one aspect of the invention, the current measurement module  703  is implemented using a very low value resistor. The voltage across the resistor will be proportional to the current flowing through the resistor. In another aspect of the invention, the current measurement module  703  is implemented using current probes which use the Hall Effect to measure the current through a conductor without adding a series resistor. After translating the current to voltage, the data may be passed through a low pass filter and then digitized. The analog to digital converter associated with the current sensor  703  is shown as the AID converter  723  in  FIG. 7 . Aliasing effect in the resulting digital data may be avoided by selecting an appropriate resolution and sample rate for the analog to digital converter. If the current sensing technique does not require a series connection, then the current sensor  703  may be connected to the DC power source  701  in parallel. 
         [0091]    In one aspect of the invention, the voltage sensor  704  uses simple parallel voltage measurement techniques in order to measure the voltage output of the solar panel. The analog voltage is passed through a low pass filter in order to minimize aliasing. The data is then digitized using an analog to digital converter. The analog to digital converter associated with the voltage sensor  704  are shown as the AID converter  724  in  FIG. 7 . The AID converter  724  has sufficient resolution to generate an adequately sampled digital signal from the analog voltage measured at the DC power source  701  that may be a solar panel. 
         [0092]    The current and voltage data collected for tracking the maximum power point at the converter input may be used for monitoring purposes also. An analog to digital converter with sufficient resolution may correctly evaluate the panel voltage and current. However, to evaluate the state of the panel, even low sample rates may be sufficient. A low-pass filter makes it possible for low sample rates to be sufficient for evaluating the state of the panel. The current and voltage date may be provided to the monitoring and logging module  711  for analysis. 
         [0093]    The temperature sensor  779  enables the system to use temperature data in the analysis process. The temperature is indicative of some types of failures and problems. Furthermore, in the case that the power source is a solar panel, the panel temperature is a factor in power output production. 
         [0094]    The one or more optional external sensor interfaces  707  enable connecting various external sensors to the converter  705 . External sensors are optionally used to enhance analysis of the state of the solar panel  701 , or a string or an array formed by connecting the solar panels  701 . Examples of external sensors include ambient temperature sensors, solar radiance sensors, and sensors from neighboring panels. External sensors may be integrated into the converter  705  instead of being attached externally. 
         [0095]    In one aspect of the invention, the information acquired from the current and voltage sensors  703 ,  704  and the optional temperature and external sensors  705 ,  707  may be transmitted to a central analysis station for monitoring, control, and analysis using the communications interface  709 . The central analysis station is not shown in the figure. The communication interface  709  connects a microcontroller  706  to a communication bus. The communication bus can be implemented in several ways. In one aspect of the invention, the communication bus is implemented using an off-the-shelf communication bus such as Ethernet or RS422. Other methods such as wireless communications or power line communications may also be used. If bidirectional communication is used, the central analysis station may request the data collected by the microcontroller  706 . Alternatively or in addition, the information acquired from sensors  703 ,  704 ,  705 ,  707  is logged locally using the monitoring and logging module  711  in local memory such as the RAM  715  or the NVRAM  713 . 
         [0096]    Analysis of the information from sensors  703 ,  704 ,  705 ,  707  enables detection and location of many types of failures associated with power loss in solar arrays. Smart analysis can also be used to suggest corrective measures such as cleaning or replacing a specific portion of the solar array. Analysis of sensor information can also detect power losses caused by environmental conditions and prevent costly and difficult solar array testing. 
         [0097]    Consequently, in one aspect of the invention, the microcontroller  706  simultaneously maintains the maximum power point of input power to the converter  705  from the attached DC power source or solar panel  701  based on the MPPT algorithm in the MPPT module  719  and manages the process of gathering the information from sensors  703 ,  704 ,  705 ,  707 . The collected information may be stored in the local memory  713 ,  715  and transmitted to an external central analysis station. In one aspect of the invention, the microcontroller  706  uses previously defined parameters stored in the NVRAM  713  in order to operate. The information stored in the NVRAM  713  may include information about the converter  705  such as serial number, the type of communication bus used, the status update rate and the ID of the central analysis station. This information may be added to the parameters collected by the sensors before transmission. 
         [0098]    The converters  705  may be installed during the installation of the solar array or retrofitted to existing installations. In both cases, the converters  705  may be connected to a panel junction connection box or to cables connecting the panels  701 . Each converter  705  may be provided with the connectors and cabling to enable easy installation and connection to solar panels  701  and panel cables. 
         [0099]    In one aspect of the invention, the physical interface  717  is used to convert to a standard communication protocol and physical layer so that during installation and maintenance, the converter  705  may be connected to one of various data terminals, such as a computer or PDA. Analysis may then be implemented as software which will be run on a standard computer, an embedded platform or a proprietary device. 
         [0100]    The installation process of the converters  705  includes connecting each converter  705  to a solar panel  701 . One or more of the sensors  703 ,  704 ,  705 ,  707  may be used to ensure that the solar panel  701  and the converter  705  are properly coupled together. During installation, parameters such as serial number, physical location and the array connection topology may be stored in the NVRAM  713 . These parameters may be used by analysis software to detect future problems in solar panels  701  and arrays. 
         [0101]    When the DC power sources  701  are solar panels, one of the problems facing installers of photovoltaic solar panel arrays is safety. The solar panels  701  are connected in series during the day when there is sunlight. Therefore, at the final stages of installation, when several solar panels  701  are connected in series, the voltage across a string of panels may reach dangerous levels. Voltages as high as 600V are common in domestic installations. Thus, the installer faces a danger of electrocution. The converters  705  that are connected to the panels  701  may use built-in functionality to prevent such a danger. For example, the converters  705  may limit the output voltage to a safe level until a predetermined minimum load is detected. Only after detecting this predetermined load, the microcontroller  706  ramps up the output voltage from the converter  705 . 
         [0102]    Another method of providing a safety mechanism is to use communications between the converters  705  and the associated inverter for the string or array of panels. This communication, that may be for example a power line communication, may provide a handshake before any significant or potentially dangerous power level is made available. Thus, the converters  705  would wait for an analog or digital signal from the inverter in the associated array before transferring power to inverter. 
         [0103]    The above methodology for monitoring, control and analysis of the DC power sources  701  may be implemented on solar panels or on strings or arrays of solar panels or for other power sources such as batteries and fuel cells. 
         [0104]    The innovative monitoring described so far may be implemented in any solar panel installation, but is particularly beneficial for residential and relatively small installations. On the other hand, for large installations, such as, e.g., 025 megawatt solar field and larger, implementing monitoring on each panel may prove to be prohibitively expensive. Accordingly, the monitoring solution provided herein may be modified for such applications. 
         [0105]      FIG. 8  illustrates a typical centralized solar field installation. In  FIG. 8 , a large field installation is formed by connecting several solar panels  805  in series so as to form a string  810 . Normally 8-20 panels  805  are serially connected to form one string  810 . Then, several strings, e.g., eight or twelve strings are connected in parallel to form a cluster  815 . Several clusters are then connected together in a super cluster junction box  820 , sometimes called a combiner box, to form a super cluster. The super cluster may be connected to a central inverter, or to other super clusters. According to the prior art, monitoring of such a system is done by measuring current and voltage at the output of the super cluster. However, such monitoring detects only major malfunctions and fails to detect smaller problems that, if corrected, can lead to higher efficiency. On the other hand, it has been proposed to provide a monitor at each panel and utilize master-slave arrangement to obtain performance data from each panel. However, such an arrangement is costly both in terms of the additional cost for each monitor on each panel (there are normally hundreds to tens of thousands of panels in large field installations) and in terms of complexity of the transmission requirements. For further background information the reader is directed to U.S. Patent Publication 2006/0162772. 
         [0106]      FIG. 9  illustrates a centralized solar field installation implementing monitoring according to an embodiment of the invention. The system  900  is arranged with panels  905  serially connected to strings  910 , which are connected in parallel to form clusters  915 , which are in tum connected to a super cluster junction box  920 . In the embodiment of  FIG. 9  one monitor  925  is installed for each string  910  of serially connected panels  905 . The monitor  925  may be the same monitor  300  as in  FIG. 3A . On the other hand, in one embodiment the monitor  925  includes only a current probe and transmission means, which may be similar to that of monitor  300 . While in  FIG. 9  the monitor  925  is shown connected to the first panel  905 , it may be connected to any of the serially connected panels in the string  910 . Additionally, one voltage monitor  930  is connected at the super cluster junction box  920 . A power unit may be used to feed monitors  925  and  930 . The power may be derived from one of many power sources, such as batteries or feed-in from another location. In one embodiment monitors  925  and  930  may be fed from power harvested from the cable running through them—the solar panel being monitored in the case of monitor  925 , and the current from one or more entire clusters  915  in the case of combiner box  920 . 
         [0107]    With the arrangement of  FIG. 9 , since each string  910  is connected in parallel to all other strings at the super cluster junction box  920 , the voltage measured by the voltage monitor  930  indicates the voltage of each string  910 . The voltage measurement is sent from the box  920  and the current is sent from each string separately to a central monitoring system (not shown). Alternatively, monitors  925  may send their data over power line communication or in other means to monitor  930 , which then aggregates the data and sends it to central monitoring system. The monitor  930  may transmit the data it receives together with any data it monitors itself to a central monitoring station (not shown) using other transmission methods, such as Ethernet, wireless communication (WiFi, ZigBee, etc.) via one-way or two way communication, as illustrated by the arrow  955 . Consequently, the central monitoring station can calculate the power production from each string. Such monitoring is more sensitive to power drops and other malfunctions at each string. This enables improved identification of failing or malfunctioning panels without the expense of installing monitor at each panel. 
         [0108]    Additionally, rather than utilizing complicated master slave arrangement, in this embodiment the monitors  925  send the data using the power line communication via unidirectional communication method as explained above with respect to  FIGS. 3A and 3B . This way, no dedicated bus is required and collisions are avoided by using the randomizing mechanism discussed above. Since solar fields may be very large and include many thousands or transmitting monitors, it is beneficial to prevent data transmitted in one part of the field to interfere with data transmitted in other parts. In an aspect of the invention, such a separation might me done by introducing capacitors  960  between the output terminals of each super cluster combiner box  920 . This capacitor  920  is used to attenuate the PLC signaling in the super-cluster, and prevent interference with other super-clusters. 
         [0109]      FIG. 10  illustrates a solar field installation implementing monitoring according to another embodiment of the invention. The embodiment of  FIG. 10  is similar to that of  FIG. 9 , except that a current monitor  1035  is added to measure the total current provided by each cluster  1010 . The current measured at current monitor  1035  should be the sum of the current measurements of all of the monitors  1025 . That is, the reading of current monitor should be commensurable to the sum of the reading reported by all of the monitors  1025  (less transmission losses). If an abnormal discrepancy is detected, then it means that at least one of the strings  1010  has problem with current delivery. This may be due to a faulty connector, bad cable isolation, or other factors. Thus, the problem is detected and could easily be pinpointed and fixed. 
         [0110]    Embodiments of the invention, such as those described above, provide a greater degree of fault tolerance, maintenance and serviceability by monitoring, controlling, logging and/or communicating the performance of each solar panel  501 , or strings of solar panels  503 . A microcontroller used in the MPPT circuit of the converter  505 , may include the monitoring module  300  of  FIG. 3A . Then, this microcontroller may also be used to perform the monitoring, logging and communication functions. These functions allow for quick and easy troubleshooting during installation, thereby significantly reducing installation time. These functions are also beneficial for quick detection of problems during maintenance work. Furthermore, by monitoring the operation of each part of the system, preventive maintenance may be performed in a timely manner to avoid downtime of the system. 
         [0111]    The present invention has been described in relation to particular examples, which are intended in all respects to be illustrative rather than restrictive. Those skilled in the art will appreciate that many different combinations of hardware, software, and firmware will be suitable for practicing the present invention. Moreover, other implementations of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims and their equivalents.