![]() It is best to think of it as an index number that can predict certain pump characteristics. An Index NumberĪs Terry Henshaw stated in “Centrifugal Pump Specific Speed” (Pumps & Systems, September 2011), the definition of specific speed can be confusing. It allows the use of existing design and test data to design similar higher and lower flow pumps because the specific speed of a pump is independent of its size. Many pump designers see specific speed as the most important contributor to centrifugal pump design. Specific speed was first applied to centrifugal pumps in the latter 1800s and was a modified version of one developed for water turbines. For other articles in this series, click here.Įarly centrifugal pump design was heavily influenced by turbine technology during the mid to late 1800s. Latitude of approximately 35 degrees North.Editor's Note: This is the second in a six-part series on centrifugal pump efficiency. Shading loss versus ground cover ratio (GCR) for different tracking options and tilt angles at a The ground or roof area occupied by the array. The GCR is defined as the ratio of the array area to Percentage when you know the ground coverage ratio (GCR). ![]() For fixed arrays or arrays with two-axis tracking, you can use the graph below to estimate a self-shading loss Self-shading with the one-axis tracking option. You specify under Advanced Parameters, so you should not use the shading loss to account for For one-axis trackers, PVWatts ® ® calculates self-shading losses using the Shading analysis tools canĭetermine a loss percentage for shading by nearby objects. ![]() ![]() The default value of 1% represents an array with little or no shading. Trees, or by self-shading for modules arranged in rows when modules in one row cause shadows on those in anĪdjacent row. Shading Reduction in the incident solar radiation from shadows caused by objects near the array such as buildings or The energy output range is based on analysis of 30 years of historical weather data, and is intended to provide an indication of the possible interannual variability in generation for a Fixed (open rack) PV system at this location. IN NO EVENT SHALL DOE/NREL/ALLIANCE BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER, INCLUDING BUT NOT LIMITED TO CLAIMS ASSOCIATED WITH THE LOSS OF DATA OR PROFITS, WHICH MAY RESULT FROM ANY ACTION IN CONTRACT, NEGLIGENCE OR OTHER TORTIOUS CLAIM THAT ARISES OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THE MODEL. THE MODEL IS PROVIDED BY DOE/NREL/ALLIANCE 'AS IS' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING BUT NOT LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE EXPRESSLY DISCLAIMED. YOU AGREE TO INDEMNIFY DOE/NREL/ALLIANCE, AND ITS AFFILIATES, OFFICERS, AGENTS, AND EMPLOYEES AGAINST ANY CLAIM OR DEMAND, INCLUDING REASONABLE ATTORNEYS' FEES, RELATED TO YOUR USE, RELIANCE, OR ADOPTION OF THE MODEL FOR ANY PURPOSE WHATSOEVER. DOE/NREL/ALLIANCE shall not provide any support, consulting, training or assistance of any kind with regard to the use of the Model or any updates, revisions or new versions of the Model. The names DOE/NREL/ALLIANCE shall not be used in any representation, advertising, publicity or other manner whatsoever to endorse or promote any entity that adopts or uses the Model. Department Of Energy ("DOE") and may be used for any purpose whatsoever. For more information, please refer to this NREL report: The Error Report.ĭisclaimer: The PVWatts ® Model ("Model") is provided by the National Renewable Energy Laboratory ("NREL"), which is operated by the Alliance for Sustainable Energy, LLC ("Alliance") for the U.S. The expected range is based on 30 years of actual weather data at the given location and is intended to provide an indication of the variation you might see. Both NREL and private companies provide more sophisticated PV modeling tools (such as the System Advisor Model at ) that allow for more precise and complex modeling of PV systems. For example, PV modules with better performance are not differentiated within PVWatts ® from lesser performing modules. Caution: Photovoltaic system performance predictions calculated by PVWatts ® include many inherent assumptions and uncertainties and do not reflect variations between PV technologies nor site-specific characteristics except as represented by PVWatts ® inputs.
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