{"id":116684,"date":"2015-01-22T08:05:50","date_gmt":"2015-01-22T07:05:50","guid":{"rendered":"https:\/\/www.sma-sunny.com\/?p=116684"},"modified":"2020-12-23T09:27:16","modified_gmt":"2020-12-23T08:27:16","slug":"calculating-max-pv-voltage-is-not-scary","status":"publish","type":"post","link":"https:\/\/www.sma-sunny.com\/us\/calculating-max-pv-voltage-is-not-scary\/","title":{"rendered":"Calculating Max PV Voltage is Not Scary"},"content":{"rendered":"

In 2008, the National Electrical Code (NEC) added a second paragraph to 690.7(A) stating, \u201cWhen open-circuit voltage temperature coefficients are supplied in the instructions for listed PV modules, they shall be used to calculate the maximum PV system voltage as required by 110.3(B) instead of using Table 690.7.\u201d This addition was made because Table 690.7 is very conservative and the temperature coefficient will provide a more accurate voltage increase.<\/p>\n

Listed below is the maximum voltage calculation with open-circuit voltage temperature coefficients. As daunting as it may seem it\u2019s quite easy once you\u2019ve done it a few times. Let\u2019s take a look at how it works:<\/p>\n

Inverter maximum input voltage with the temperature coefficient percentage of the VOC calculation:
\n(STC temp \u2013 low temp) x temp coefficient % VOC x VOC + VOC = VMax
\nInverter max voltage \/ VMax = Maximum modules per series string<\/p>\n

\"Myself<\/a>

Myself on the right installing a Sunny Boy 3000-US with a colleague for GRID Alternatives.<\/p><\/div>\n

For example:
\nRecord-low temperature: -10\u00baC
\nTemperature coefficient of (VOC): – (0.30) %\/\u00baC
\nModule open circuit voltage (VOC): 39.4 V
\nInverter maximum input voltage: 600V<\/p>\n

The STC temperature is 25\u00baC. This temperature needs to be deducted from the array location’s record-low temperature of -10 degrees as follows:<\/p>\n

25 – (-10) = 35\u00ba difference.<\/p>\n

Multiply the 35\u00ba difference by the temperature coefficient of VOC (I\u2019ve used the positive value for an easier calculation, though you get the same result) then multiply by the module\u2019s VOC:<\/p>\n

35 x 0.0030 = 0.105
\n0.105 x 39.4V = 4.137V<\/p>\n

This is how many volts each module will increase due to record-low temperatures. Add the voltage increase to the Module VOC. Then divide the inverter maximum input voltage by that number. This will give you the maximum number of modules that can be wired in a series string per that inverter and specific location.<\/p>\n

4.137 V + 39.4V = 43.537 VMax
\n600V \/ 43.537 = 13.7 (round down to a whole number)<\/p>\n

The maximum number of modules in this series string is 13. A series string of 14 could potentially produce more than 600V during record-low temperatures.<\/p>\n

Lastly, the quantity of modules wired in series multiplied by the VMax equals your maximum system voltage.<\/p>\n

13 x 43.54 V = 566 Maximum System Voltage<\/p>\n

Voil\u00e0, we\u2019ve determined the max PV voltage for our example system and are able to ensure a proper system design without fear of over-voltage for the inverter.<\/p>\n\n\n

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In 2008, the National Electrical Code (NEC) added a second paragraph to 690.7(A) stating, \u201cWhen open-circuit voltage temperature coefficients are…<\/p>\n","protected":false},"author":45,"featured_media":124079,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1715,1324],"tags":[1365,1445,1370,1444,1325,1315],"class_list":["post-116684","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-solutions","category-technology","tag-customer-service","tag-inverter","tag-pv-design","tag-sma","tag-sma-america","tag-solar"],"acf":[],"yoast_head":"\nCalculating Max PV Voltage is Not Scary - Sunny. 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