Grid connected inverters must be able to reliably detect a loss of grid condition and rapidly disconnect from the grid system. This behavior prevents the formation of an unintentional island (a stand-alone power system with its own generation and loads operating in balance). Current standards (e.g., IEEE 1547 and IEC 62116) specify that the inverter…
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As more PV systems are added to the electrical grid, the requirements for interconnection are changing. New PV inverters are being required to provide advanced functions to help support the robust operation of the electrical system. These functions include: Volt-VAr (voltage regulation) Commanded Power Factor (voltage regulation) Frequency-watt (frequency regulation) Commanded Maximum Power (frequency regulation)…
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Inverter efficiency is the ratio of the usable AC output power to the sum of the DC input power and any AC input power. Typical grid-tied inverter efficiencies exceed 95% under most operating conditions. Efficiency changes as a function of AC output power, DC voltage, and sometimes inverter temperature. Sandia National Laboratories and BEW have…
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Some inverters will automatically decrease their efficiency under conditions of elevated temperature. This behavior is meant to protect the device from conditions that might lead to component failures. There is currently no standard test procedure to characterize this behavior for inverters. In the future, inverter performance characterization should include information on the conditions that lead…
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Conversion from DC to AC power allows this power to be tied to the AC grid. This conversion can be accomplished with high efficiencies but there are energy losses that need to be estimated. There are a number of model algorithms that are used to estimate this conversion efficiency. They will be described and compared…
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The performance of an illuminated PV array or system is characterized by the system’s I-V curve. To harvest power from the system the voltage must be adjusted in order to maximize the power. This function is called Maximum Power Point Tracking (MPPT). MPPTY is typically performed by the inverter or a DC-DC converter. A control…
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DC wiring losses are mainly caused by the ohmic resistance of the cabling that interconnects PV devices and strings, although losses can also occur in connections and fuses. The power loss varies as a function of the array current squared. Differences in cable length or size among parallel strings can introduce differences in voltage drop,…
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Gantner Instruments (Juergen Sutterlueti, http://www.gantner-webportal.com) and Steve Ransome (www.steveransome.com), using outdoor IV measurements on a wide variety of module technologies have developed a PV module performance model based on defining loss factors that affect the shape of the IV curve. Details of this model can be found on publications listed on Ransome’s website. We will include a summary of…
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The PVWatts model is provided by the National Renewable Energy Laboratory (NREL) as an online PV performance modeling application. The equations that underlie PVWatts are really quite simple. There are two primary input variables: Effective irradiance () PV cell temperature () PVWatts relates these two variables to the maximum power point () with two equations…
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PV devices are characterized by their response to light in a reference spectrum. When a device is tested in a lab or outdoors, the spectrum of the light source may not be the same as that of the reference spectrum. The effect of this difference on performance is typically quantified by a spectral mismatch factor.…
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