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Monitoring is the repeated measurement of electrical, environmental, or battery parameters at certain intervals. PV-system monitoring can serve several purposes. Primarily, it provides information about system status and alerts users to possible problems. Owners and installers also monitor system performance to ensure that energy production meets load requirements and justifies the system cost. Monitoring also includes short-term measurements for troubleshooting. Production-based financial incentives and renewable energy certificate (REC) programs rely on accurate system output measurements to appropriately award incentives. Utilities monitor interactive PV systems to determine the energy exchanged between the customer and the utility grid for billing purposes. Measured Parameters: A variety of parameters may be measured by monitoring equipment in PV systems. The number and types of parameters depend on the system configuration and size and the intended use of the information. Electrical Parameters. Measuring electrical parameters is the most important type of monitoring. At a minimum, electrical power and energy are measured, though various voltage and current measurements are also common. These parameters are the basic indicators of array and inverter performance and are extensively used to troubleshoot system problems. Performance is based on comparisons with expected output (based on sizing calculations) and baseline measurements taken during commissioning. Energy is also often measured (in kilowatt- hours) on daily, monthly, and total cumulative bases. These measurements are particularly useful for the inverter output circuit, but may be used elsewhere. In interactive systems, the total load requirements are the energy supplied by the PV system plus any energy imported from the grid. In stand-alone systems, energy flow into and out of batteries is measured with ampere-hour meters. There are three primary locations in a PV system for measuring electrical parameters: the array output circuit, the inverter output circuit, and the battery-bank output circuit (if applicable). 8. Since the inverter is connected to all three circuits, most modern inverters include integrated monitoring functions as standard features. If this is not the case, external monitoring equipment can be added to measure electrical parameters. For temporary use, such as for troubleshooting, handheld test instruments are used. System designers and equipment manufacturers sometimes incorporate test points into circuits for safe and easy access by test instruments. For some installations, permanently installed meters are used. Depending on the system configuration, electrical parameters may also be measured at other parts of the system, such as PV source circuits, the charge-controller output circuit, and within the power-distribution system. A current transformer consists of a toroidal coil in which a proportionally smaller current is induced from the higher current in the conductors passing through it. These devices are used to monitor current flow in various applications. As part of a service contract a technician may monitor a PV system remotely The monitoring system may be configured to trigger a service call for certain events or if the measured parameters fall outside the normal range -- The three most important points for measuring voltage and current information are the array output circuit, inverter output circuit, and charge controller circuit (if applicable). AMMETER VOLTMETER; VOLTMETER INVERTER; -AMMETER V; INVERTER OUTPUT CIRCUIT I PV OUTPUT I CIRCUIT VOLTMETER CHARGE CONTROLLER CIRCUIT --- Environmental Parameters. Including environmental parameters in monitoring allows system output to be correlated with weather conditions. These parameters usually include irradiance and ambient temperature. For example, current output from a PV device increases proportionally with irradiance. However, if the current measurements don’t correlate with the irradiance measurements, there may be a problem with the array, such as excessive shading, soiling, or blown source circuit fuses. For an accurate representation of the array's environmental conditions, all sensors should be placed as close to the array as possible and in the same plane. By adding a special temperature sensor to the back surface of a module, cell temperature can also be measured. This information can then be used to determine the temperature-rise coefficient for this installation. Battery Parameters. Sophisticated monitoring systems may have the capability to automatically measure battery specific gravity and water levels. This feature is usually employed for only the largest battery-based systems, where the large number of batteries makes manual battery tests impractical. The battery bank may require manual maintenance only when the monitoring system indicates an out-of-range measurement. --19. Sensors for measuring irradiance and other parameters allow technicians to correlate PV system output with weather conditions. Monitoring Output In order to be useful, measurements must be displayed in some form. Monitoring of a PV system can be as simple as LED status indicators on a component or as complex as a separate data network measuring and recording multiple parameters. Indicators. The simplest type of monitoring employs small indicator lights to show the status of components and their functions. These are usually LEDs of different colors. For example, an LED may indicate that the battery bank is fully charged, even if the charge controller also displays the actual battery-bank voltage. 0. Indicators on major components may indicate normal operation, ground faults, low-voltage load disconnect, battery charging, battery discharging, battery equalizing, or component malfunctions. For efficiency of space on the front panel, indicator LEDs may have multiple meanings depending on their colors (for bicolor LEDs) and the rate at which they blink. --20. Equipment status indicators may have multiple functions. Display Screens. Most inverters and charge controllers include small display screens. This is often in addition to a few indicator lights. The display typically cycles through the various measurements and displays the present values. Some inverter manufacturers provide the option of adding a remote display unit to view these parameters from a distant location. The connection to remote units may be wired or wireless. Data-Acquisition Systems. The most sophisticated monitoring systems include data acquisition. Data acquisition is the recording and processing of data from a monitoring system. The same types of parameters may be measured as with other monitoring systems, but the data is recorded at regular time intervals and stored for future analysis. Data acquisition generates a wealth of information and provides a much more complete picture of system performance than measurements at isolated moments in time. As the primary electrical interface device in most PV systems, the inverter is the core of most data-acquisition systems. Some inverters include data acquisition as an on-board feature and others rely on separate computer software to read the data output at intervals and save the data to a storage device. Some data-acquisition systems employ separate units to collect and process the data from multiple sources. In addition to taking measurements from the inverter, these systems may allow a variety of other sensors to be added, such as irradiance and temperature. Such a system requires the added time and expense of separate data wiring that connects each sensor and the data-acquisition unit, but provides much more information. Using computer software, this data can then be plotted to illustrate the changes of values over time. 1. This facilitates spotting trends and correlations between parameters. When troubleshooting, data- acquisition systems are invaluable tools. They allow the technician to review past records and identify slow trends over time or short- term events that may have impaired system performance. By connecting the computer or data-acquisition unit to the Internet, the raw data and plots can also be made available to users through web sites. Several leading inverter manufacturers and independent companies offer data acquisition equipment and sensors for interfacing directly with system components. --21. Data-acquisition systems gather, record, and process information from many sources that can be used to observe trends or problems in PV system operation. Monitoring Data Plots Next: PV Systems: Troubleshooting Prev: Maintenance |