Tấm pin quang điệnPhotovoltaic panels · BàiLesson 1/7
Reading Solar Panel Specifications
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Solar Knowledge HubĐọc thông số tấm pinReading panel specifications
Một nhãn tấm pin có hàng chục dòng, nhưng chỉ cần đọc đúng năm con số vàng cùng vài thông số phụ để chọn tấm và dựng chuỗi an toàn.A panel label has dozens of lines, but just five key numbers plus a few extras are enough to select panels and design a safe string.
| Ký hiệuSymbol | TênName | Mô tảDescription | Vai trò khi thiết kếDesign use |
|---|---|---|---|
| PmaxPmax | Công suất tối đaMaximum power | Bằng Vmp × ImpEquals Vmp × Imp | Quy mô hệ, sản lượngSystem sizing, yield |
| VocVoc | Điện áp hở mạchOpen-circuit voltage | Cao nhất, tăng khi lạnhHighest, rises when cold | Số tấm nối tiếp tối đaMax series panels |
| VmpVmp | Điện áp làm việcOperating voltage | Điểm MPPT bám vàoMPPT tracking point | Phải nằm trong dải MPPTMust be within MPPT range |
| IscIsc | Dòng ngắn mạchShort-circuit current | Dòng lớn nhất tấm choMaximum panel current | Chọn cầu chì, tiết diện dâySize fuses and cable |
| ImpImp | Dòng làm việcOperating current | Dòng thực tế chuỗiActual string current | Tính dòng chuỗi thực tếCalculate real string current |
Sai lầm nguy hiểm nhất là để Voc chuỗi vượt áp tối đa biến tần vào buổi sáng lạnh. Datasheet đo Voc ở 25°C nhưng sáng sớm tấm có thể ở 10°C hoặc thấp hơn, Voc thực cao hơn vài phần trăm. Cầu chì chuỗi tối đa phụ thuộc Isc của từng model, đọc trực tiếp trên datasheet, không áp một giá trị chung cho mọi tấm.The most dangerous mistake is letting string Voc exceed the inverter max on a cold morning. The datasheet measures at 25°C, but early-morning panels may be 10°C or colder, raising real Voc by several percent. Max series fuse rating scales with each model’s Isc: read it per datasheet, never assume one value for all panels.
Nắm năm số Pmax, Voc, Vmp, Isc, Imp là nắm 80% việc đọc một tấm pin. Khách chỉ nhìn công suất, nhưng người tư vấn giỏi đọc thêm Voc và Vmp để biết tấm có ghép được với biến tần của khách không.Knowing Pmax, Voc, Vmp, Isc, Imp covers 80% of reading a panel. Customers look at power; good advisors also check Voc and Vmp to know if the panel is compatible with the customer’s inverter.
A panel datasheet contains dozens of lines, but a sales consultant or system designer only needs to read a small group of them correctly to select the right panel and build a safe string. This document teaches how to read the five golden numbers along with a few important secondary parameters, then shows how they are applied when designing strings and advising customers.
For: sales staff reading labels to advise customers, technicians designing strings, beginners starting from the panel.
Quick Summary
The five golden numbers are Pmax, Voc, Vmp, Isc, and Imp. Pmax is the power output, Voc is the highest voltage at open circuit, Vmp is the operating voltage, Isc is the maximum current under short circuit, and Imp is the operating current.
All parameters on the label are measured at Standard Test Conditions (STC): 1000 W/m², 25°C, and AM1.5 spectrum. In the field, output is typically lower; more realistic conditions are described by NMOT.
When designing a string, the two core constraints are: the string Voc must not exceed the inverter’s maximum DC voltage even on a cold morning, and the string Vmp must fall within the MPPT range. Isc and Imp are used to size cables and protection devices.
The Five Golden Numbers
Pmax is the panel’s maximum power output, for example a 590 W panel. It equals the product of Vmp and Imp, so these three values are always consistent with one another.
Voc is the open-circuit voltage, measured when both terminals are left open with no load connected. This is the highest voltage the panel produces, and it rises when the temperature drops, making it the decisive figure for the maximum number of panels in series. Vmp is the voltage at the maximum power point (the actual operating point tracked by the inverter), so the string Vmp must fall within the inverter’s MPPT range.
Isc is the short-circuit current, measured when both terminals are shorted together. It is the maximum current the panel can deliver and is used to select fuses and cable cross-sections. Imp is the current at the maximum power point, i.e., the actual operating current of the string.
| Symbol | Name | Role in Design |
|---|---|---|
| Pmax | Maximum power | System sizing, energy yield |
| Voc | Open-circuit voltage | Maximum panels in series; must not exceed inverter max DC voltage |
| Vmp | Operating voltage | Must fall within the MPPT range |
| Isc | Short-circuit current | Fuse selection, cable sizing |
| Imp | Operating current | Actual string current calculation |
A handy closing point: knowing the five numbers (Pmax, Voc, Vmp, Isc, Imp) covers eighty percent of what it takes to read a solar panel. Customers typically only look at wattage, but a skilled consultant also checks Voc and Vmp to know whether the panel is compatible with the customer’s inverter.
Secondary Parameters Worth Knowing
Beyond the five golden numbers, a few other parameters deserve attention. The maximum system voltage (commonly 1000 or 1500 V DC) is the panel’s own voltage ceiling. Power tolerance, for example 0 to +3%, indicates that the panel always meets or exceeds its rated output; premium panels carry positive-only tolerances. Panel efficiency is the ratio of sunlight converted to electricity, currently in the range of roughly 21% to nearly 25%. Dimensions and weight are relevant to roof load calculations and installation logistics.
Two test conditions must be distinguished. STC is a laboratory standard comprising 1000 W/m², a cell temperature of 25°C, and an AM1.5 light spectrum; it is used for comparing panels against each other. NMOT is a more realistic condition measured at 800 W/m² irradiance and a 20°C ambient temperature, giving results closer to actual outdoor output. Field power is typically 15–25% lower than STC because the panel runs hotter than 25°C, a topic covered in detail in document 02-04.
Using the Parameters for String Design
This is where numbers become engineering decisions. Take a panel with Vmp 43.85 V and Voc 52.20 V, paired with an inverter whose MPPT range is 120–450 V and maximum DC input voltage is 500 V.
Connecting eight panels in series gives a string Vmp of 43.85 × 8 = 350.8 V, which sits comfortably within the MPPT range: acceptable. The string Voc is 52.20 × 8 = 417.6 V, still below 500 V: also acceptable. However, the cold-morning condition must also be checked, because Voc rises as temperature falls. The safety rule is to multiply the string Voc by a factor of approximately 1.1 and compare the result against the inverter’s maximum DC voltage, ensuring the limit is not breached on cold mornings when voltage peaks.
Isc and Imp determine cable sizing and protection. DC cable cross-sections, string fuses, and DC circuit breakers are all selected based on these currents, following the principles set out in Chapter 01.
The most dangerous design mistake is allowing the string Voc to exceed the inverter’s maximum DC voltage on a cold morning. Because datasheets measure Voc at 25°C while panels may be at 10°C or lower at dawn, the actual Voc can be several percent higher than the label value. Ignoring this temperature coefficient is a common cause of damage to the inverter’s input stage.
String Fuses: Don’t Use One Value for Every Panel
A common misconception is assigning a fixed fuse value to all panels. The maximum series fuse rating depends on the panel’s own Isc and is printed on the datasheet. Higher-current panels require larger fuses than lower-current ones. For example, some Jinko series panels list 30 A, higher-current Jinko bifacial models list up to 35 A, and AIKO back-contact panels typically fall in the 25–30 A range. Always read the correct figure from the datasheet of the specific model in use rather than applying a blanket value.