{"id":1798,"date":"2026-07-27T10:33:08","date_gmt":"2026-07-27T02:33:08","guid":{"rendered":"https:\/\/jutrion.com\/?page_id=1798"},"modified":"2026-08-07T10:53:43","modified_gmt":"2026-08-07T02:53:43","slug":"pv%e3%82%b9%e3%83%88%e3%83%aa%e3%83%b3%e3%82%b0%e9%9b%bb%e5%9c%a7%e8%a8%88%e7%ae%97%e6%a9%9f","status":"publish","type":"page","link":"https:\/\/jutrion.com\/ja\/tools\/pv-string-voltage-calculator\/","title":{"rendered":"PV\u30b9\u30c8\u30ea\u30f3\u30b0\u96fb\u5727\u8a08\u7b97\u6a5f"},"content":{"rendered":"\n<!-- ===== JUTRION PV String Voltage Calculator \u2014 paste into a WordPress \"Custom HTML\" block ===== -->\n<div class=\"jt-calc\">\n  <p class=\"eyebrow\">Solar &amp; DC<\/p>\n  <h1>PV String Voltage Calculator (Cold V<sub>oc<\/sub> &amp; Max Modules)<\/h1>\n  <p class=\"tool-lede\">Find the worst-case cold open-circuit voltage of a PV string and the maximum number of modules that stays within the inverter&#8217;s DC voltage limit. Cold mornings \u2014 not hot afternoons \u2014 set the highest string voltage, and exceeding the inverter limit can destroy it. Use the module and inverter datasheet values.<\/p>\n\n  <div class=\"jt-card\"><div class=\"jt-grid\">\n    <div class=\"jt-inputs\">\n      <div class=\"jt-two\">\n        <div class=\"jt-field\"><label for=\"jt-voc\">Module V<sub>oc<\/sub> at STC (V)<\/label><input type=\"number\" id=\"jt-voc\" value=\"49.5\" min=\"1\" step=\"0.1\" inputmode=\"decimal\"><\/div>\n        <div class=\"jt-field\"><label for=\"jt-beta\">\u03b2 V<sub>oc<\/sub> (%\/\u00b0C)<\/label><input type=\"number\" id=\"jt-beta\" value=\"-0.27\" max=\"0\" step=\"0.01\" inputmode=\"decimal\"><\/div>\n      <\/div>\n      <div class=\"jt-two\">\n        <div class=\"jt-field\"><label for=\"jt-tmin\">Site min. temperature (\u00b0C)<\/label><input type=\"number\" id=\"jt-tmin\" value=\"-10\" step=\"1\" inputmode=\"numeric\"><\/div>\n        <div class=\"jt-field\"><label for=\"jt-vmax\">Inverter max DC voltage (V)<\/label><input type=\"number\" id=\"jt-vmax\" value=\"1100\" min=\"1\" step=\"10\" inputmode=\"numeric\"><\/div>\n      <\/div>\n      <div class=\"jt-field\"><label for=\"jt-mods\">Modules per string (to check)<\/label><input type=\"number\" id=\"jt-mods\" value=\"20\" min=\"1\" step=\"1\" inputmode=\"numeric\"><\/div>\n      <div class=\"jt-note\"><span>\u24d8<\/span><span>\u03b2 V<sub>oc<\/sub> is the negative temperature coefficient of open-circuit voltage from the module datasheet (typically \u22120.25 to \u22120.35 %\/\u00b0C for crystalline silicon).<\/span><\/div>\n    <\/div>\n    <div class=\"jt-readout\">\n      <div><div class=\"jt-rl\">Cold V<sub>oc<\/sub> per module<\/div><div class=\"jt-big\"><span id=\"jt-cvoc\">\u2014<\/span> <span>V<\/span><\/div><\/div>\n      <div class=\"jt-rec row\"><div class=\"k\">Max modules per string<\/div><div class=\"v\" id=\"jt-max\">\u2014<\/div><\/div>\n      <div class=\"jt-rec row\"><div class=\"k\">String cold V<sub>oc<\/sub> (entered)<\/div><div class=\"v\" id=\"jt-str\">\u2014<\/div><\/div>\n      <div class=\"jt-rec\"><div class=\"k\">Against inverter limit<\/div><div style=\"margin-top:6px\"><span class=\"jt-pill na\" id=\"jt-chk\">\u2014<\/span><\/div><\/div>\n      <button type=\"button\" class=\"jt-copy\" id=\"jt-copy\">Copy result<\/button>\n    <\/div>\n  <\/div><\/div>\n\n  <div class=\"jt-content\">\n    <h2>Why cold weather sets the limit<\/h2>\n    <p>A module&#8217;s open-circuit voltage rises as temperature falls. The coldest expected cell temperature \u2014 a clear, freezing dawn before the array warms \u2014 produces the highest V<sub>oc<\/sub>, and that is the voltage the inverter and all DC components must withstand:<\/p>\n    <div class=\"jt-eq\">V<sub>oc<\/sub>(cold) = V<sub>oc,STC<\/sub> \u00d7 [ 1 + (\u03b2 \/ 100) \u00d7 (T<sub>min<\/sub> \u2212 25) ]\nMax modules = floor( V<sub>dc,max<\/sub> \/ V<sub>oc<\/sub>(cold) )<\/div>\n    <p>\u03b2 is negative, and T<sub>min<\/sub> is below the 25 \u00b0C reference, so the correction raises the voltage above the datasheet figure. Sizing a string on the STC voltage instead of the cold voltage is a common and dangerous error \u2014 it can push the array past the inverter&#8217;s maximum on the first cold morning.<\/p>\n\n    <div class=\"jt-note\"><span>\u26a0<\/span><span><b>Use the lowest credible cell temperature.<\/b> Standards base this on the site&#8217;s record low ambient. The string must stay under the inverter maximum at that temperature with the string as designed, including any future extension.<\/span><\/div>\n\n    <h2>Frequently asked questions<\/h2>\n    <div class=\"jt-faq\">\n      <details><summary>Do I use record low or average low temperature?<\/summary><p>The lowest expected cell temperature, normally derived from the site&#8217;s record low ambient. A milder figure understates the peak voltage and risks exceeding the inverter limit.<\/p><\/details>\n      <details><summary>Which voltage does the inverter limit refer to?<\/summary><p>The absolute maximum DC input voltage \u2014 not the MPPT window. The cold-temperature string V<sub>oc<\/sub> must stay below this absolute maximum; the operating voltage should also sit within the MPPT range for good yield.<\/p><\/details>\n      <details><summary>Does the same voltage size other DC parts?<\/summary><p>Yes. The cold string V<sub>oc<\/sub> sets the minimum voltage rating for the DC isolator, fuses, SPD (U<sub>cpv<\/sub>), and cable \u2014 not just the inverter.<\/p><\/details>\n    <\/div>\n\n    <div class=\"jt-cta\">\n      <h2>Build the DC side<\/h2>\n      <p>With the string voltage fixed, size the combiner, isolator, fuses, and SPD to the same cold V<sub>oc<\/sub>.<\/p>\n      <div class=\"jt-cta-btns\">\n        <a class=\"jt-btn\" href=\"https:\/\/jutrion.com\/pv-combiner-box\/\">Explore PV combiner boxes<\/a>\n        <a class=\"jt-btn ghost\" href=\"https:\/\/jutrion.com\/contact\/\">Get a free quote<\/a>\n      <\/div>\n      <p class=\"jt-related\">Related products: <a href=\"https:\/\/jutrion.com\/pv-combiner-box\/\">PV combiner box<\/a> \u00b7 <a href=\"https:\/\/jutrion.com\/dc-mccb\/\">DC MCCB<\/a> \u00b7 <a href=\"https:\/\/jutrion.com\/spd\/\">SPD<\/a><\/p>\n    <\/div>\n\n    <div class=\"jt-std\"><strong>Standards referenced<\/strong>IEC 60364-7-712 (PV systems) \u00b7 IEC 62548 (PV array design) \u00b7 module &amp; inverter datasheet limits.<\/div>\n    <p class=\"jt-fine\">Estimate for guidance only. Final string sizing must use the module and inverter datasheet values, the site&#8217;s lowest expected temperature, and be verified by a qualified person.<\/p>\n  <\/div>\n<\/div>\n\n<script>\n(function(){\n  var $=function(id){return document.getElementById(id);};\n  var voc=$('jt-voc'),beta=$('jt-beta'),tmin=$('jt-tmin'),vmax=$('jt-vmax'),mods=$('jt-mods'),\n      cvocEl=$('jt-cvoc'),maxEl=$('jt-max'),strEl=$('jt-str'),chk=$('jt-chk');\n  function calc(){\n    var V=parseFloat(voc.value),b=parseFloat(beta.value),T=parseFloat(tmin.value),Vm=parseFloat(vmax.value),n=parseInt(mods.value,10);\n    if(!(V>0)||isNaN(b)||isNaN(T)){cvocEl.textContent='\u2014';maxEl.textContent=strEl.textContent='\u2014';chk.className='jt-pill na';chk.textContent='\u2014';return;}\n    var cv=V*(1+(b\/100)*(T-25));\n    cvocEl.textContent=cv.toFixed(1);\n    if(Vm>0){var mx=Math.floor(Vm\/cv);maxEl.textContent=mx+' modules';}else maxEl.textContent='\u2014';\n    if(n>0){var sv=n*cv;strEl.textContent=sv.toFixed(0)+' V';\n      if(Vm>0){var pass=sv<=Vm;chk.className='jt-pill '+(pass?'ok':'no');chk.textContent=pass?('OK \u2014 '+sv.toFixed(0)+' V \u2264 '+Vm+' V'):('EXCEEDS '+Vm+' V \u2014 reduce modules');}\n      else{chk.className='jt-pill na';chk.textContent='enter inverter limit';}}\n    else{strEl.textContent='\u2014';chk.className='jt-pill na';chk.textContent='enter modules';}\n  }\n  [voc,beta,tmin,vmax,mods].forEach(function(el){el.addEventListener('input',calc);el.addEventListener('change',calc);});\n  $('jt-copy').addEventListener('click',function(){var b=$('jt-copy');var txt='Module Voc(STC): '+voc.value+' V, \u03b2 '+beta.value+' %\/\u00b0C, Tmin '+tmin.value+' \u00b0C\\nCold Voc\/module: '+cvocEl.textContent+' V\\nMax modules\/string: '+maxEl.textContent+'\\nString cold Voc: '+strEl.textContent+'\\nCheck: '+chk.textContent;navigator.clipboard.writeText(txt).then(function(){var o=b.textContent;b.textContent='Copied \u2713';setTimeout(function(){b.textContent=o;},1500);}).catch(function(){b.textContent='Press Ctrl+C';});});\n  calc();\n})();\n<\/script>\n<!-- ===== end block ===== -->\n\n","protected":false},"excerpt":{"rendered":"<p>Solar &amp; DC PV String Voltage Calculator (Cold Voc &amp; Max Modules) Find the worst-case cold open-circuit voltage of a PV string and the maximum number of modules that stays within the inverter&#8217;s DC voltage limit. Cold mornings \u2014 not hot afternoons \u2014 set the highest string voltage, and exceeding the inverter limit can destroy it. Use the module and inverter datasheet values. Module Voc at STC (V) \u03b2 Voc (%\/\u00b0C) Site min. temperature (\u00b0C) Inverter max DC voltage (V) Modules per string (to check) \u24d8\u03b2 Voc is the negative temperature coefficient of open-circuit voltage from the module datasheet (typically \u22120.25 to \u22120.35 %\/\u00b0C for crystalline silicon). Cold Voc per [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":1778,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-1798","page","type-page","status-publish","hentry"],"blocksy_meta":[],"_links":{"self":[{"href":"https:\/\/jutrion.com\/ja\/wp-json\/wp\/v2\/pages\/1798","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/jutrion.com\/ja\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/jutrion.com\/ja\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/jutrion.com\/ja\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/jutrion.com\/ja\/wp-json\/wp\/v2\/comments?post=1798"}],"version-history":[{"count":1,"href":"https:\/\/jutrion.com\/ja\/wp-json\/wp\/v2\/pages\/1798\/revisions"}],"predecessor-version":[{"id":1799,"href":"https:\/\/jutrion.com\/ja\/wp-json\/wp\/v2\/pages\/1798\/revisions\/1799"}],"up":[{"embeddable":true,"href":"https:\/\/jutrion.com\/ja\/wp-json\/wp\/v2\/pages\/1778"}],"wp:attachment":[{"href":"https:\/\/jutrion.com\/ja\/wp-json\/wp\/v2\/media?parent=1798"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}